26 files changed, 1688 insertions, 1330 deletions

diff --git a/crates/hir_ty/Cargo.toml b/crates/hir_ty/Cargo.toml
index b9c93f56f..0ef27cd37 100644
--- a/crates/hir_ty/Cargo.toml
+++ b/crates/hir_ty/Cargo.toml
@@ -10,7 +10,7 @@ edition = "2018"
 doctest = false
 
 [dependencies]
-cov-mark = "1.1"
+cov-mark = { version = "1.1", features = ["thread-local"] }
 itertools = "0.10.0"
 arrayvec = "0.5.1"
 smallvec = "1.2.0"
@@ -31,7 +31,7 @@ profile = { path = "../profile", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
 
 [dev-dependencies]
-test_utils = { path = "../test_utils"  }
+test_utils = { path = "../test_utils" }
 expect-test = "1.1"
 tracing = "0.1"
 tracing-subscriber = { version = "0.2", default-features = false, features = ["env-filter", "registry"] }
diff --git a/crates/hir_ty/src/autoderef.rs b/crates/hir_ty/src/autoderef.rs
index be1fd1f13..56c6b92d4 100644
--- a/crates/hir_ty/src/autoderef.rs
+++ b/crates/hir_ty/src/autoderef.rs
@@ -12,9 +12,10 @@ use log::{info, warn};
 
 use crate::{
     db::HirDatabase,
+    to_assoc_type_id,
     traits::{InEnvironment, Solution},
     utils::generics,
-    BoundVar, Canonical, DebruijnIndex, Obligation, Substs, TraitRef, Ty,
+    BoundVar, Canonical, DebruijnIndex, Interner, Obligation, Substs, TraitRef, Ty, TyKind,
 };
 
 const AUTODEREF_RECURSION_LIMIT: usize = 10;
@@ -81,8 +82,12 @@ fn deref_by_trait(
 
     // Now do the assoc type projection
     let projection = super::traits::ProjectionPredicate {
-        ty: Ty::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, ty.value.kinds.len())),
-        projection_ty: super::ProjectionTy { associated_ty: target, parameters },
+        ty: TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, ty.value.kinds.len()))
+            .intern(&Interner),
+        projection_ty: super::ProjectionTy {
+            associated_ty_id: to_assoc_type_id(target),
+            substitution: parameters,
+        },
     };
 
     let obligation = super::Obligation::Projection(projection);
@@ -114,8 +119,8 @@ fn deref_by_trait(
             // new variables in that case
 
             for i in 1..vars.0.kinds.len() {
-                if vars.0.value[i - 1]
-                    != Ty::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, i - 1))
+                if vars.0.value[i - 1].interned(&Interner)
+                    != &TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, i - 1))
                 {
                     warn!("complex solution for derefing {:?}: {:?}, ignoring", ty.value, solution);
                     return None;
diff --git a/crates/hir_ty/src/db.rs b/crates/hir_ty/src/db.rs
index 06714409f..74a048672 100644
--- a/crates/hir_ty/src/db.rs
+++ b/crates/hir_ty/src/db.rs
@@ -12,7 +12,7 @@ use la_arena::ArenaMap;
 use crate::{
     method_resolution::{InherentImpls, TraitImpls},
     traits::chalk,
-    Binders, CallableDefId, GenericPredicate, InferenceResult, OpaqueTyId, PolyFnSig,
+    Binders, CallableDefId, FnDefId, GenericPredicate, ImplTraitId, InferenceResult, PolyFnSig,
     ReturnTypeImplTraits, TraitRef, Ty, TyDefId, ValueTyDefId,
 };
 use hir_expand::name::Name;
@@ -65,6 +65,9 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::invoke(crate::lower::generic_predicates_query)]
     fn generic_predicates(&self, def: GenericDefId) -> Arc<[Binders<GenericPredicate>]>;
 
+    #[salsa::invoke(crate::lower::trait_environment_query)]
+    fn trait_environment(&self, def: GenericDefId) -> Arc<crate::TraitEnvironment>;
+
     #[salsa::invoke(crate::lower::generic_defaults_query)]
     fn generic_defaults(&self, def: GenericDefId) -> Arc<[Binders<Ty>]>;
 
@@ -81,11 +84,11 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::interned]
     fn intern_callable_def(&self, callable_def: CallableDefId) -> InternedCallableDefId;
     #[salsa::interned]
-    fn intern_type_param_id(&self, param_id: TypeParamId) -> GlobalTypeParamId;
+    fn intern_type_param_id(&self, param_id: TypeParamId) -> InternedTypeParamId;
     #[salsa::interned]
-    fn intern_impl_trait_id(&self, id: OpaqueTyId) -> InternedOpaqueTyId;
+    fn intern_impl_trait_id(&self, id: ImplTraitId) -> InternedOpaqueTyId;
     #[salsa::interned]
-    fn intern_closure(&self, id: (DefWithBodyId, ExprId)) -> ClosureId;
+    fn intern_closure(&self, id: (DefWithBodyId, ExprId)) -> InternedClosureId;
 
     #[salsa::invoke(chalk::associated_ty_data_query)]
     fn associated_ty_data(&self, id: chalk::AssocTypeId) -> Arc<chalk::AssociatedTyDatum>;
@@ -100,10 +103,10 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     fn impl_datum(&self, krate: CrateId, impl_id: chalk::ImplId) -> Arc<chalk::ImplDatum>;
 
     #[salsa::invoke(crate::traits::chalk::fn_def_datum_query)]
-    fn fn_def_datum(&self, krate: CrateId, fn_def_id: chalk::FnDefId) -> Arc<chalk::FnDefDatum>;
+    fn fn_def_datum(&self, krate: CrateId, fn_def_id: FnDefId) -> Arc<chalk::FnDefDatum>;
 
     #[salsa::invoke(crate::traits::chalk::fn_def_variance_query)]
-    fn fn_def_variance(&self, krate: CrateId, fn_def_id: chalk::FnDefId) -> chalk::Variances;
+    fn fn_def_variance(&self, krate: CrateId, fn_def_id: FnDefId) -> chalk::Variances;
 
     #[salsa::invoke(crate::traits::chalk::adt_variance_query)]
     fn adt_variance(&self, krate: CrateId, adt_id: chalk::AdtId) -> chalk::Variances;
@@ -149,16 +152,16 @@ fn hir_database_is_object_safe() {
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct GlobalTypeParamId(salsa::InternId);
-impl_intern_key!(GlobalTypeParamId);
+pub struct InternedTypeParamId(salsa::InternId);
+impl_intern_key!(InternedTypeParamId);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct InternedOpaqueTyId(salsa::InternId);
 impl_intern_key!(InternedOpaqueTyId);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct ClosureId(salsa::InternId);
-impl_intern_key!(ClosureId);
+pub struct InternedClosureId(salsa::InternId);
+impl_intern_key!(InternedClosureId);
 
 /// This exists just for Chalk, because Chalk just has a single `FnDefId` where
 /// we have different IDs for struct and enum variant constructors.
diff --git a/crates/hir_ty/src/diagnostics/decl_check.rs b/crates/hir_ty/src/diagnostics/decl_check.rs
index 3605ca581..982ad5b9e 100644
--- a/crates/hir_ty/src/diagnostics/decl_check.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check.rs
@@ -91,7 +91,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
     fn validate_func(&mut self, func: FunctionId) {
         let data = self.db.function_data(func);
-        if data.is_extern {
+        if data.is_in_extern_block {
             cov_mark::hit!(extern_func_incorrect_case_ignored);
             return;
         }
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index 2751cd304..b2bfd68d4 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -15,7 +15,7 @@ use crate::{
         MissingPatFields, RemoveThisSemicolon,
     },
     utils::variant_data,
-    AdtId, InferenceResult, Ty,
+    AdtId, InferenceResult, Interner, Ty, TyKind,
 };
 
 pub(crate) use hir_def::{
@@ -289,11 +289,10 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
         let (body, source_map): (Arc<Body>, Arc<BodySourceMap>) =
             db.body_with_source_map(self.owner.into());
 
-        let match_expr_ty = match infer.type_of_expr.get(match_expr) {
-            // If we can't resolve the type of the match expression
-            // we cannot perform exhaustiveness checks.
-            None | Some(Ty::Unknown) => return,
-            Some(ty) => ty,
+        let match_expr_ty = if infer.type_of_expr[match_expr].is_unknown() {
+            return;
+        } else {
+            &infer.type_of_expr[match_expr]
         };
 
         let cx = MatchCheckCtx { match_expr, body, infer: infer.clone(), db };
@@ -379,14 +378,14 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             _ => return,
         };
 
-        let (params, required) = match mismatch.expected {
-            Ty::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref parameters)
-                if enum_id == core_result_enum =>
+        let (params, required) = match mismatch.expected.interned(&Interner) {
+            TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref parameters)
+                if *enum_id == core_result_enum =>
             {
                 (parameters, "Ok".to_string())
             }
-            Ty::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref parameters)
-                if enum_id == core_option_enum =>
+            TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref parameters)
+                if *enum_id == core_option_enum =>
             {
                 (parameters, "Some".to_string())
             }
diff --git a/crates/hir_ty/src/diagnostics/match_check.rs b/crates/hir_ty/src/diagnostics/match_check.rs
index 04d39c571..5a5cdcbf3 100644
--- a/crates/hir_ty/src/diagnostics/match_check.rs
+++ b/crates/hir_ty/src/diagnostics/match_check.rs
@@ -227,7 +227,7 @@ use hir_def::{
 use la_arena::Idx;
 use smallvec::{smallvec, SmallVec};
 
-use crate::{db::HirDatabase, AdtId, InferenceResult, Ty};
+use crate::{db::HirDatabase, AdtId, InferenceResult, Interner, TyKind};
 
 #[derive(Debug, Clone, Copy)]
 /// Either a pattern from the source code being analyzed, represented as
@@ -626,13 +626,13 @@ pub(super) fn is_useful(
     // - enum with no variants
     // - `!` type
     // In those cases, no match arm is useful.
-    match cx.infer[cx.match_expr].strip_references() {
-        Ty::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ..) => {
+    match cx.infer[cx.match_expr].strip_references().interned(&Interner) {
+        TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ..) => {
             if cx.db.enum_data(*enum_id).variants.is_empty() {
                 return Ok(Usefulness::NotUseful);
             }
         }
-        Ty::Never => return Ok(Usefulness::NotUseful),
+        TyKind::Never => return Ok(Usefulness::NotUseful),
         _ => (),
     }
 
diff --git a/crates/hir_ty/src/diagnostics/unsafe_check.rs b/crates/hir_ty/src/diagnostics/unsafe_check.rs
index e77a20fea..44a7e5506 100644
--- a/crates/hir_ty/src/diagnostics/unsafe_check.rs
+++ b/crates/hir_ty/src/diagnostics/unsafe_check.rs
@@ -11,7 +11,7 @@ use hir_def::{
 };
 use hir_expand::diagnostics::DiagnosticSink;
 
-use crate::{db::HirDatabase, diagnostics::MissingUnsafe, InferenceResult, Ty};
+use crate::{db::HirDatabase, diagnostics::MissingUnsafe, InferenceResult, Interner, TyKind};
 
 pub(super) struct UnsafeValidator<'a, 'b: 'a> {
     owner: DefWithBodyId,
@@ -32,7 +32,7 @@ impl<'a, 'b> UnsafeValidator<'a, 'b> {
         let def = self.owner.into();
         let unsafe_expressions = unsafe_expressions(db, self.infer.as_ref(), def);
         let is_unsafe = match self.owner {
-            DefWithBodyId::FunctionId(it) => db.function_data(it).is_unsafe,
+            DefWithBodyId::FunctionId(it) => db.function_data(it).qualifier.is_unsafe,
             DefWithBodyId::StaticId(_) | DefWithBodyId::ConstId(_) => false,
         };
         if is_unsafe
@@ -85,8 +85,8 @@ fn walk_unsafe(
     let expr = &body.exprs[current];
     match expr {
         &Expr::Call { callee, .. } => {
-            if let Some(func) = infer[callee].as_fn_def() {
-                if db.function_data(func).is_unsafe {
+            if let Some(func) = infer[callee].as_fn_def(db) {
+                if db.function_data(func).qualifier.is_unsafe {
                     unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
                 }
             }
@@ -103,14 +103,14 @@ fn walk_unsafe(
         Expr::MethodCall { .. } => {
             if infer
                 .method_resolution(current)
-                .map(|func| db.function_data(func).is_unsafe)
+                .map(|func| db.function_data(func).qualifier.is_unsafe)
                 .unwrap_or(false)
             {
                 unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
             }
         }
         Expr::UnaryOp { expr, op: UnaryOp::Deref } => {
-            if let Ty::Raw(..) = &infer[*expr] {
+            if let TyKind::Raw(..) = &infer[*expr].interned(&Interner) {
                 unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
             }
         }
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index ab51cb0a6..c572bb114 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -5,15 +5,22 @@ use std::{borrow::Cow, fmt};
 use arrayvec::ArrayVec;
 use chalk_ir::Mutability;
 use hir_def::{
-    db::DefDatabase, find_path, generics::TypeParamProvenance, item_scope::ItemInNs,
+    db::DefDatabase,
+    find_path,
+    generics::TypeParamProvenance,
+    item_scope::ItemInNs,
+    path::{GenericArg, Path, PathKind},
+    type_ref::{TypeBound, TypeRef},
+    visibility::Visibility,
     AssocContainerId, Lookup, ModuleId, TraitId,
 };
 use hir_expand::name::Name;
 
 use crate::{
-    db::HirDatabase, primitive, utils::generics, AdtId, AliasTy, CallableDefId, CallableSig,
-    GenericPredicate, Lifetime, Obligation, OpaqueTy, OpaqueTyId, ProjectionTy, Scalar, Substs,
-    TraitRef, Ty,
+    db::HirDatabase, from_assoc_type_id, from_foreign_def_id, from_placeholder_idx, primitive,
+    to_assoc_type_id, traits::chalk::from_chalk, utils::generics, AdtId, AliasTy, CallableDefId,
+    CallableSig, GenericPredicate, ImplTraitId, Interner, Lifetime, Obligation, OpaqueTy,
+    ProjectionTy, Scalar, Substs, TraitRef, Ty, TyKind,
 };
 
 pub struct HirFormatter<'a> {
@@ -231,7 +238,7 @@ where
 
 const TYPE_HINT_TRUNCATION: &str = "…";
 
-impl HirDisplay for &Ty {
+impl<T: HirDisplay> HirDisplay for &'_ T {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         HirDisplay::hir_fmt(*self, f)
     }
@@ -244,19 +251,19 @@ impl HirDisplay for ProjectionTy {
         }
 
         let trait_ = f.db.trait_data(self.trait_(f.db));
-        let first_parameter = self.parameters[0].into_displayable(
+        let first_parameter = self.substitution[0].into_displayable(
             f.db,
             f.max_size,
             f.omit_verbose_types,
             f.display_target,
         );
         write!(f, "<{} as {}", first_parameter, trait_.name)?;
-        if self.parameters.len() > 1 {
+        if self.substitution.len() > 1 {
             write!(f, "<")?;
-            f.write_joined(&self.parameters[1..], ", ")?;
+            f.write_joined(&self.substitution[1..], ", ")?;
             write!(f, ">")?;
         }
-        write!(f, ">::{}", f.db.type_alias_data(self.associated_ty).name)?;
+        write!(f, ">::{}", f.db.type_alias_data(from_assoc_type_id(self.associated_ty_id)).name)?;
         Ok(())
     }
 }
@@ -267,32 +274,29 @@ impl HirDisplay for Ty {
             return write!(f, "{}", TYPE_HINT_TRUNCATION);
         }
 
-        match self {
-            Ty::Never => write!(f, "!")?,
-            Ty::Str => write!(f, "str")?,
-            Ty::Scalar(Scalar::Bool) => write!(f, "bool")?,
-            Ty::Scalar(Scalar::Char) => write!(f, "char")?,
-            &Ty::Scalar(Scalar::Float(t)) => write!(f, "{}", primitive::float_ty_to_string(t))?,
-            &Ty::Scalar(Scalar::Int(t)) => write!(f, "{}", primitive::int_ty_to_string(t))?,
-            &Ty::Scalar(Scalar::Uint(t)) => write!(f, "{}", primitive::uint_ty_to_string(t))?,
-            Ty::Slice(parameters) => {
-                let t = parameters.as_single();
+        match self.interned(&Interner) {
+            TyKind::Never => write!(f, "!")?,
+            TyKind::Str => write!(f, "str")?,
+            TyKind::Scalar(Scalar::Bool) => write!(f, "bool")?,
+            TyKind::Scalar(Scalar::Char) => write!(f, "char")?,
+            &TyKind::Scalar(Scalar::Float(t)) => write!(f, "{}", primitive::float_ty_to_string(t))?,
+            &TyKind::Scalar(Scalar::Int(t)) => write!(f, "{}", primitive::int_ty_to_string(t))?,
+            &TyKind::Scalar(Scalar::Uint(t)) => write!(f, "{}", primitive::uint_ty_to_string(t))?,
+            TyKind::Slice(t) => {
                 write!(f, "[")?;
                 t.hir_fmt(f)?;
                 write!(f, "]")?;
             }
-            Ty::Array(parameters) => {
-                let t = parameters.as_single();
+            TyKind::Array(t) => {
                 write!(f, "[")?;
                 t.hir_fmt(f)?;
                 write!(f, "; _]")?;
             }
-            Ty::Raw(m, parameters) | Ty::Ref(m, parameters) => {
-                let t = parameters.as_single();
+            TyKind::Raw(m, t) | TyKind::Ref(m, t) => {
                 let ty_display =
                     t.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
 
-                if matches!(self, Ty::Raw(..)) {
+                if matches!(self.interned(&Interner), TyKind::Raw(..)) {
                     write!(
                         f,
                         "*{}",
@@ -312,22 +316,29 @@ impl HirDisplay for Ty {
                     )?;
                 }
 
+                // FIXME: all this just to decide whether to use parentheses...
                 let datas;
-                let predicates = match t {
-                    Ty::Dyn(predicates) if predicates.len() > 1 => {
+                let predicates = match t.interned(&Interner) {
+                    TyKind::Dyn(predicates) if predicates.len() > 1 => {
                         Cow::Borrowed(predicates.as_ref())
                     }
-                    &Ty::Alias(AliasTy::Opaque(OpaqueTy {
-                        opaque_ty_id: OpaqueTyId::ReturnTypeImplTrait(func, idx),
-                        ref parameters,
+                    &TyKind::Alias(AliasTy::Opaque(OpaqueTy {
+                        opaque_ty_id,
+                        substitution: ref parameters,
                     })) => {
-                        datas =
-                            f.db.return_type_impl_traits(func).expect("impl trait id without data");
-                        let data = (*datas)
-                            .as_ref()
-                            .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
-                        let bounds = data.subst(parameters);
-                        Cow::Owned(bounds.value)
+                        let impl_trait_id = f.db.lookup_intern_impl_trait_id(opaque_ty_id.into());
+                        if let ImplTraitId::ReturnTypeImplTrait(func, idx) = impl_trait_id {
+                            datas =
+                                f.db.return_type_impl_traits(func)
+                                    .expect("impl trait id without data");
+                            let data = (*datas)
+                                .as_ref()
+                                .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
+                            let bounds = data.subst(parameters);
+                            Cow::Owned(bounds.value)
+                        } else {
+                            Cow::Borrowed(&[][..])
+                        }
                     }
                     _ => Cow::Borrowed(&[][..]),
                 };
@@ -347,7 +358,7 @@ impl HirDisplay for Ty {
                     write!(f, "{}", ty_display)?;
                 }
             }
-            Ty::Tuple(_, substs) => {
+            TyKind::Tuple(_, substs) => {
                 if substs.len() == 1 {
                     write!(f, "(")?;
                     substs[0].hir_fmt(f)?;
@@ -358,12 +369,12 @@ impl HirDisplay for Ty {
                     write!(f, ")")?;
                 }
             }
-            Ty::Function(fn_ptr) => {
+            TyKind::Function(fn_ptr) => {
                 let sig = CallableSig::from_fn_ptr(fn_ptr);
                 sig.hir_fmt(f)?;
             }
-            Ty::FnDef(def, parameters) => {
-                let def = *def;
+            TyKind::FnDef(def, parameters) => {
+                let def = from_chalk(f.db, *def);
                 let sig = f.db.callable_item_signature(def).subst(parameters);
                 match def {
                     CallableDefId::FunctionId(ff) => {
@@ -401,7 +412,7 @@ impl HirDisplay for Ty {
                     write!(f, " -> {}", ret_display)?;
                 }
             }
-            Ty::Adt(AdtId(def_id), parameters) => {
+            TyKind::Adt(AdtId(def_id), parameters) => {
                 match f.display_target {
                     DisplayTarget::Diagnostics | DisplayTarget::Test => {
                         let name = match *def_id {
@@ -427,37 +438,39 @@ impl HirDisplay for Ty {
                 }
 
                 if parameters.len() > 0 {
-                    let parameters_to_write =
-                        if f.display_target.is_source_code() || f.omit_verbose_types() {
-                            match self
-                                .as_generic_def()
-                                .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
-                                .filter(|defaults| !defaults.is_empty())
-                            {
-                                None => parameters.0.as_ref(),
-                                Some(default_parameters) => {
-                                    let mut default_from = 0;
-                                    for (i, parameter) in parameters.iter().enumerate() {
-                                        match (parameter, default_parameters.get(i)) {
-                                            (&Ty::Unknown, _) | (_, None) => {
+                    let parameters_to_write = if f.display_target.is_source_code()
+                        || f.omit_verbose_types()
+                    {
+                        match self
+                            .as_generic_def(f.db)
+                            .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
+                            .filter(|defaults| !defaults.is_empty())
+                        {
+                            None => parameters.0.as_ref(),
+                            Some(default_parameters) => {
+                                let mut default_from = 0;
+                                for (i, parameter) in parameters.iter().enumerate() {
+                                    match (parameter.interned(&Interner), default_parameters.get(i))
+                                    {
+                                        (&TyKind::Unknown, _) | (_, None) => {
+                                            default_from = i + 1;
+                                        }
+                                        (_, Some(default_parameter)) => {
+                                            let actual_default = default_parameter
+                                                .clone()
+                                                .subst(&parameters.prefix(i));
+                                            if parameter != &actual_default {
                                                 default_from = i + 1;
                                             }
-                                            (_, Some(default_parameter)) => {
-                                                let actual_default = default_parameter
-                                                    .clone()
-                                                    .subst(&parameters.prefix(i));
-                                                if parameter != &actual_default {
-                                                    default_from = i + 1;
-                                                }
-                                            }
                                         }
                                     }
-                                    &parameters.0[0..default_from]
                                 }
+                                &parameters.0[0..default_from]
                             }
-                        } else {
-                            parameters.0.as_ref()
-                        };
+                        }
+                    } else {
+                        parameters.0.as_ref()
+                    };
                     if !parameters_to_write.is_empty() {
                         write!(f, "<")?;
                         f.write_joined(parameters_to_write, ", ")?;
@@ -465,13 +478,14 @@ impl HirDisplay for Ty {
                     }
                 }
             }
-            Ty::AssociatedType(type_alias, parameters) => {
+            TyKind::AssociatedType(assoc_type_id, parameters) => {
+                let type_alias = from_assoc_type_id(*assoc_type_id);
                 let trait_ = match type_alias.lookup(f.db.upcast()).container {
                     AssocContainerId::TraitId(it) => it,
                     _ => panic!("not an associated type"),
                 };
                 let trait_ = f.db.trait_data(trait_);
-                let type_alias_data = f.db.type_alias_data(*type_alias);
+                let type_alias_data = f.db.type_alias_data(type_alias);
 
                 // Use placeholder associated types when the target is test (https://rust-lang.github.io/chalk/book/clauses/type_equality.html#placeholder-associated-types)
                 if f.display_target.is_test() {
@@ -482,19 +496,22 @@ impl HirDisplay for Ty {
                         write!(f, ">")?;
                     }
                 } else {
-                    let projection_ty =
-                        ProjectionTy { associated_ty: *type_alias, parameters: parameters.clone() };
+                    let projection_ty = ProjectionTy {
+                        associated_ty_id: to_assoc_type_id(type_alias),
+                        substitution: parameters.clone(),
+                    };
 
                     projection_ty.hir_fmt(f)?;
                 }
             }
-            Ty::ForeignType(type_alias) => {
-                let type_alias = f.db.type_alias_data(*type_alias);
+            TyKind::ForeignType(type_alias) => {
+                let type_alias = f.db.type_alias_data(from_foreign_def_id(*type_alias));
                 write!(f, "{}", type_alias.name)?;
             }
-            Ty::OpaqueType(opaque_ty_id, parameters) => {
-                match opaque_ty_id {
-                    &OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+            TyKind::OpaqueType(opaque_ty_id, parameters) => {
+                let impl_trait_id = f.db.lookup_intern_impl_trait_id((*opaque_ty_id).into());
+                match impl_trait_id {
+                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                         let datas =
                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
                         let data = (*datas)
@@ -504,14 +521,14 @@ impl HirDisplay for Ty {
                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
                         // FIXME: it would maybe be good to distinguish this from the alias type (when debug printing), and to show the substitution
                     }
-                    OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
+                    ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                         write!(f, "impl Future<Output = ")?;
                         parameters[0].hir_fmt(f)?;
                         write!(f, ">")?;
                     }
                 }
             }
-            Ty::Closure(.., substs) => {
+            TyKind::Closure(.., substs) => {
                 let sig = substs[0].callable_sig(f.db);
                 if let Some(sig) = sig {
                     if sig.params().is_empty() {
@@ -535,7 +552,8 @@ impl HirDisplay for Ty {
                     write!(f, "{{closure}}")?;
                 }
             }
-            Ty::Placeholder(id) => {
+            TyKind::Placeholder(idx) => {
+                let id = from_placeholder_idx(f.db, *idx);
                 let generics = generics(f.db.upcast(), id.parent);
                 let param_data = &generics.params.types[id.local_id];
                 match param_data.provenance {
@@ -543,8 +561,8 @@ impl HirDisplay for Ty {
                         write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
                     }
                     TypeParamProvenance::ArgumentImplTrait => {
-                        let bounds = f.db.generic_predicates_for_param(*id);
-                        let substs = Substs::type_params_for_generics(&generics);
+                        let bounds = f.db.generic_predicates_for_param(id);
+                        let substs = Substs::type_params_for_generics(f.db, &generics);
                         write_bounds_like_dyn_trait_with_prefix(
                             "impl",
                             &bounds.iter().map(|b| b.clone().subst(&substs)).collect::<Vec<_>>(),
@@ -553,28 +571,29 @@ impl HirDisplay for Ty {
                     }
                 }
             }
-            Ty::BoundVar(idx) => write!(f, "?{}.{}", idx.debruijn.depth(), idx.index)?,
-            Ty::Dyn(predicates) => {
+            TyKind::BoundVar(idx) => write!(f, "?{}.{}", idx.debruijn.depth(), idx.index)?,
+            TyKind::Dyn(predicates) => {
                 write_bounds_like_dyn_trait_with_prefix("dyn", predicates, f)?;
             }
-            Ty::Alias(AliasTy::Projection(p_ty)) => p_ty.hir_fmt(f)?,
-            Ty::Alias(AliasTy::Opaque(opaque_ty)) => {
-                match opaque_ty.opaque_ty_id {
-                    OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+            TyKind::Alias(AliasTy::Projection(p_ty)) => p_ty.hir_fmt(f)?,
+            TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
+                let impl_trait_id = f.db.lookup_intern_impl_trait_id(opaque_ty.opaque_ty_id.into());
+                match impl_trait_id {
+                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                         let datas =
                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
                         let data = (*datas)
                             .as_ref()
                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
-                        let bounds = data.subst(&opaque_ty.parameters);
+                        let bounds = data.subst(&opaque_ty.substitution);
                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
                     }
-                    OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
+                    ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                         write!(f, "{{async block}}")?;
                     }
                 };
             }
-            Ty::Unknown => {
+            TyKind::Unknown => {
                 if f.display_target.is_source_code() {
                     return Err(HirDisplayError::DisplaySourceCodeError(
                         DisplaySourceCodeError::UnknownType,
@@ -582,7 +601,7 @@ impl HirDisplay for Ty {
                 }
                 write!(f, "{{unknown}}")?;
             }
-            Ty::InferenceVar(..) => write!(f, "_")?,
+            TyKind::InferenceVar(..) => write!(f, "_")?,
         }
         Ok(())
     }
@@ -695,7 +714,9 @@ fn write_bounds_like_dyn_trait(
                     write!(f, "<")?;
                     angle_open = true;
                 }
-                let type_alias = f.db.type_alias_data(projection_pred.projection_ty.associated_ty);
+                let type_alias = f.db.type_alias_data(from_assoc_type_id(
+                    projection_pred.projection_ty.associated_ty_id,
+                ));
                 write!(f, "{} = ", type_alias.name)?;
                 projection_pred.ty.hir_fmt(f)?;
             }
@@ -746,12 +767,6 @@ impl HirDisplay for TraitRef {
     }
 }
 
-impl HirDisplay for &GenericPredicate {
-    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
-        HirDisplay::hir_fmt(*self, f)
-    }
-}
-
 impl HirDisplay for GenericPredicate {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         if f.should_truncate() {
@@ -766,7 +781,10 @@ impl HirDisplay for GenericPredicate {
                 write!(
                     f,
                     ">::{} = ",
-                    f.db.type_alias_data(projection_pred.projection_ty.associated_ty).name,
+                    f.db.type_alias_data(from_assoc_type_id(
+                        projection_pred.projection_ty.associated_ty_id
+                    ))
+                    .name,
                 )?;
                 projection_pred.ty.hir_fmt(f)?;
             }
@@ -807,3 +825,190 @@ impl HirDisplay for Obligation {
         }
     }
 }
+
+pub fn write_visibility(
+    module_id: ModuleId,
+    vis: Visibility,
+    f: &mut HirFormatter,
+) -> Result<(), HirDisplayError> {
+    match vis {
+        Visibility::Public => write!(f, "pub "),
+        Visibility::Module(vis_id) => {
+            let def_map = module_id.def_map(f.db.upcast());
+            let root_module_id = def_map.module_id(def_map.root());
+            if vis_id == module_id {
+                // pub(self) or omitted
+                Ok(())
+            } else if root_module_id == vis_id {
+                write!(f, "pub(crate) ")
+            } else if module_id.containing_module(f.db.upcast()) == Some(vis_id) {
+                write!(f, "pub(super) ")
+            } else {
+                write!(f, "pub(in ...) ")
+            }
+        }
+    }
+}
+
+impl HirDisplay for TypeRef {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match self {
+            TypeRef::Never => write!(f, "!")?,
+            TypeRef::Placeholder => write!(f, "_")?,
+            TypeRef::Tuple(elems) => {
+                write!(f, "(")?;
+                f.write_joined(elems, ", ")?;
+                if elems.len() == 1 {
+                    write!(f, ",")?;
+                }
+                write!(f, ")")?;
+            }
+            TypeRef::Path(path) => path.hir_fmt(f)?,
+            TypeRef::RawPtr(inner, mutability) => {
+                let mutability = match mutability {
+                    hir_def::type_ref::Mutability::Shared => "*const ",
+                    hir_def::type_ref::Mutability::Mut => "*mut ",
+                };
+                write!(f, "{}", mutability)?;
+                inner.hir_fmt(f)?;
+            }
+            TypeRef::Reference(inner, lifetime, mutability) => {
+                let mutability = match mutability {
+                    hir_def::type_ref::Mutability::Shared => "",
+                    hir_def::type_ref::Mutability::Mut => "mut ",
+                };
+                write!(f, "&")?;
+                if let Some(lifetime) = lifetime {
+                    write!(f, "{} ", lifetime.name)?;
+                }
+                write!(f, "{}", mutability)?;
+                inner.hir_fmt(f)?;
+            }
+            TypeRef::Array(inner) => {
+                write!(f, "[")?;
+                inner.hir_fmt(f)?;
+                // FIXME: Array length?
+                write!(f, "; _]")?;
+            }
+            TypeRef::Slice(inner) => {
+                write!(f, "[")?;
+                inner.hir_fmt(f)?;
+                write!(f, "]")?;
+            }
+            TypeRef::Fn(tys, is_varargs) => {
+                // FIXME: Function pointer qualifiers.
+                write!(f, "fn(")?;
+                f.write_joined(&tys[..tys.len() - 1], ", ")?;
+                if *is_varargs {
+                    write!(f, "{}...", if tys.len() == 1 { "" } else { ", " })?;
+                }
+                write!(f, ")")?;
+                let ret_ty = tys.last().unwrap();
+                match ret_ty {
+                    TypeRef::Tuple(tup) if tup.is_empty() => {}
+                    _ => {
+                        write!(f, " -> ")?;
+                        ret_ty.hir_fmt(f)?;
+                    }
+                }
+            }
+            TypeRef::ImplTrait(bounds) => {
+                write!(f, "impl ")?;
+                f.write_joined(bounds, " + ")?;
+            }
+            TypeRef::DynTrait(bounds) => {
+                write!(f, "dyn ")?;
+                f.write_joined(bounds, " + ")?;
+            }
+            TypeRef::Error => write!(f, "{{error}}")?,
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for TypeBound {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match self {
+            TypeBound::Path(path) => path.hir_fmt(f),
+            TypeBound::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
+            TypeBound::Error => write!(f, "{{error}}"),
+        }
+    }
+}
+
+impl HirDisplay for Path {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match (self.type_anchor(), self.kind()) {
+            (Some(anchor), _) => {
+                write!(f, "<")?;
+                anchor.hir_fmt(f)?;
+                write!(f, ">")?;
+            }
+            (_, PathKind::Plain) => {}
+            (_, PathKind::Abs) => write!(f, "::")?,
+            (_, PathKind::Crate) => write!(f, "crate")?,
+            (_, PathKind::Super(0)) => write!(f, "self")?,
+            (_, PathKind::Super(n)) => {
+                write!(f, "super")?;
+                for _ in 0..*n {
+                    write!(f, "::super")?;
+                }
+            }
+            (_, PathKind::DollarCrate(_)) => write!(f, "{{extern_crate}}")?,
+        }
+
+        for (seg_idx, segment) in self.segments().iter().enumerate() {
+            if seg_idx != 0 {
+                write!(f, "::")?;
+            }
+            write!(f, "{}", segment.name)?;
+            if let Some(generic_args) = segment.args_and_bindings {
+                // We should be in type context, so format as `Foo<Bar>` instead of `Foo::<Bar>`.
+                // Do we actually format expressions?
+                write!(f, "<")?;
+                let mut first = true;
+                for arg in &generic_args.args {
+                    if first {
+                        first = false;
+                        if generic_args.has_self_type {
+                            // FIXME: Convert to `<Ty as Trait>` form.
+                            write!(f, "Self = ")?;
+                        }
+                    } else {
+                        write!(f, ", ")?;
+                    }
+                    arg.hir_fmt(f)?;
+                }
+                for binding in &generic_args.bindings {
+                    if first {
+                        first = false;
+                    } else {
+                        write!(f, ", ")?;
+                    }
+                    write!(f, "{}", binding.name)?;
+                    match &binding.type_ref {
+                        Some(ty) => {
+                            write!(f, " = ")?;
+                            ty.hir_fmt(f)?
+                        }
+                        None => {
+                            write!(f, ": ")?;
+                            f.write_joined(&binding.bounds, " + ")?;
+                        }
+                    }
+                }
+                write!(f, ">")?;
+            }
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for GenericArg {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match self {
+            GenericArg::Type(ty) => ty.hir_fmt(f),
+            GenericArg::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
+        }
+    }
+}
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 4d771a91e..9c385b845 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -41,7 +41,8 @@ use super::{
     InEnvironment, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TypeWalk,
 };
 use crate::{
-    db::HirDatabase, infer::diagnostics::InferenceDiagnostic, lower::ImplTraitLoweringMode, AliasTy,
+    db::HirDatabase, infer::diagnostics::InferenceDiagnostic, lower::ImplTraitLoweringMode,
+    to_assoc_type_id, AliasTy, Interner, TyKind,
 };
 
 pub(crate) use unify::unify;
@@ -107,6 +108,17 @@ pub struct TypeMismatch {
     pub actual: Ty,
 }
 
+#[derive(Clone, PartialEq, Eq, Debug)]
+struct InternedStandardTypes {
+    unknown: Ty,
+}
+
+impl Default for InternedStandardTypes {
+    fn default() -> Self {
+        InternedStandardTypes { unknown: TyKind::Unknown.intern(&Interner) }
+    }
+}
+
 /// The result of type inference: A mapping from expressions and patterns to types.
 #[derive(Clone, PartialEq, Eq, Debug, Default)]
 pub struct InferenceResult {
@@ -125,6 +137,8 @@ pub struct InferenceResult {
     pub type_of_expr: ArenaMap<ExprId, Ty>,
     pub type_of_pat: ArenaMap<PatId, Ty>,
     pub(super) type_mismatches: ArenaMap<ExprId, TypeMismatch>,
+    /// Interned Unknown to return references to.
+    standard_types: InternedStandardTypes,
 }
 
 impl InferenceResult {
@@ -169,7 +183,7 @@ impl Index<ExprId> for InferenceResult {
     type Output = Ty;
 
     fn index(&self, expr: ExprId) -> &Ty {
-        self.type_of_expr.get(expr).unwrap_or(&Ty::Unknown)
+        self.type_of_expr.get(expr).unwrap_or(&self.standard_types.unknown)
     }
 }
 
@@ -177,7 +191,7 @@ impl Index<PatId> for InferenceResult {
     type Output = Ty;
 
     fn index(&self, pat: PatId) -> &Ty {
-        self.type_of_pat.get(pat).unwrap_or(&Ty::Unknown)
+        self.type_of_pat.get(pat).unwrap_or(&self.standard_types.unknown)
     }
 }
 
@@ -226,8 +240,10 @@ impl<'a> InferenceContext<'a> {
             result: InferenceResult::default(),
             table: unify::InferenceTable::new(),
             obligations: Vec::default(),
-            return_ty: Ty::Unknown, // set in collect_fn_signature
-            trait_env: TraitEnvironment::lower(db, &resolver),
+            return_ty: TyKind::Unknown.intern(&Interner), // set in collect_fn_signature
+            trait_env: owner
+                .as_generic_def_id()
+                .map_or_else(Default::default, |d| db.trait_environment(d)),
             db,
             owner,
             body: db.body(owner),
@@ -237,15 +253,19 @@ impl<'a> InferenceContext<'a> {
         }
     }
 
+    fn err_ty(&self) -> Ty {
+        TyKind::Unknown.intern(&Interner)
+    }
+
     fn resolve_all(mut self) -> InferenceResult {
         // FIXME resolve obligations as well (use Guidance if necessary)
         let mut result = std::mem::take(&mut self.result);
         for ty in result.type_of_expr.values_mut() {
-            let resolved = self.table.resolve_ty_completely(mem::replace(ty, Ty::Unknown));
+            let resolved = self.table.resolve_ty_completely(ty.clone());
             *ty = resolved;
         }
         for ty in result.type_of_pat.values_mut() {
-            let resolved = self.table.resolve_ty_completely(mem::replace(ty, Ty::Unknown));
+            let resolved = self.table.resolve_ty_completely(ty.clone());
             *ty = resolved;
         }
         result
@@ -287,7 +307,7 @@ impl<'a> InferenceContext<'a> {
         // FIXME use right resolver for block
         let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
             .with_impl_trait_mode(impl_trait_mode);
-        let ty = Ty::from_hir(&ctx, type_ref);
+        let ty = ctx.lower_ty(type_ref);
         let ty = self.insert_type_vars(ty);
         self.normalize_associated_types_in(ty)
     }
@@ -298,8 +318,8 @@ impl<'a> InferenceContext<'a> {
 
     /// Replaces Ty::Unknown by a new type var, so we can maybe still infer it.
     fn insert_type_vars_shallow(&mut self, ty: Ty) -> Ty {
-        match ty {
-            Ty::Unknown => self.table.new_type_var(),
+        match ty.interned(&Interner) {
+            TyKind::Unknown => self.table.new_type_var(),
             _ => ty,
         }
     }
@@ -377,13 +397,16 @@ impl<'a> InferenceContext<'a> {
                 let trait_ref = TraitRef { trait_, substs: substs.clone() };
                 let projection = ProjectionPredicate {
                     ty: ty.clone(),
-                    projection_ty: ProjectionTy { associated_ty: res_assoc_ty, parameters: substs },
+                    projection_ty: ProjectionTy {
+                        associated_ty_id: to_assoc_type_id(res_assoc_ty),
+                        substitution: substs,
+                    },
                 };
                 self.obligations.push(Obligation::Trait(trait_ref));
                 self.obligations.push(Obligation::Projection(projection));
                 self.resolve_ty_as_possible(ty)
             }
-            None => Ty::Unknown,
+            None => self.err_ty(),
         }
     }
 
@@ -395,8 +418,10 @@ impl<'a> InferenceContext<'a> {
     /// to do it as well.
     fn normalize_associated_types_in(&mut self, ty: Ty) -> Ty {
         let ty = self.resolve_ty_as_possible(ty);
-        ty.fold(&mut |ty| match ty {
-            Ty::Alias(AliasTy::Projection(proj_ty)) => self.normalize_projection_ty(proj_ty),
+        ty.fold(&mut |ty| match ty.interned(&Interner) {
+            TyKind::Alias(AliasTy::Projection(proj_ty)) => {
+                self.normalize_projection_ty(proj_ty.clone())
+            }
             _ => ty,
         })
     }
@@ -412,7 +437,7 @@ impl<'a> InferenceContext<'a> {
     fn resolve_variant(&mut self, path: Option<&Path>) -> (Ty, Option<VariantId>) {
         let path = match path {
             Some(path) => path,
-            None => return (Ty::Unknown, None),
+            None => return (self.err_ty(), None),
         };
         let resolver = &self.resolver;
         let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
@@ -421,30 +446,30 @@ impl<'a> InferenceContext<'a> {
         let (resolution, unresolved) =
             match resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
                 Some(it) => it,
-                None => return (Ty::Unknown, None),
+                None => return (self.err_ty(), None),
             };
         return match resolution {
             TypeNs::AdtId(AdtId::StructId(strukt)) => {
-                let substs = Ty::substs_from_path(&ctx, path, strukt.into(), true);
+                let substs = ctx.substs_from_path(path, strukt.into(), true);
                 let ty = self.db.ty(strukt.into());
                 let ty = self.insert_type_vars(ty.subst(&substs));
                 forbid_unresolved_segments((ty, Some(strukt.into())), unresolved)
             }
             TypeNs::AdtId(AdtId::UnionId(u)) => {
-                let substs = Ty::substs_from_path(&ctx, path, u.into(), true);
+                let substs = ctx.substs_from_path(path, u.into(), true);
                 let ty = self.db.ty(u.into());
                 let ty = self.insert_type_vars(ty.subst(&substs));
                 forbid_unresolved_segments((ty, Some(u.into())), unresolved)
             }
             TypeNs::EnumVariantId(var) => {
-                let substs = Ty::substs_from_path(&ctx, path, var.into(), true);
+                let substs = ctx.substs_from_path(path, var.into(), true);
                 let ty = self.db.ty(var.parent.into());
                 let ty = self.insert_type_vars(ty.subst(&substs));
                 forbid_unresolved_segments((ty, Some(var.into())), unresolved)
             }
             TypeNs::SelfType(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
-                let substs = Substs::type_params_for_generics(&generics);
+                let substs = Substs::type_params_for_generics(self.db, &generics);
                 let ty = self.db.impl_self_ty(impl_id).subst(&substs);
                 match unresolved {
                     None => {
@@ -462,11 +487,11 @@ impl<'a> InferenceContext<'a> {
                             }
                         }
                         // FIXME potentially resolve assoc type
-                        (Ty::Unknown, None)
+                        (self.err_ty(), None)
                     }
                     Some(_) => {
                         // FIXME diagnostic
-                        (Ty::Unknown, None)
+                        (self.err_ty(), None)
                     }
                 }
             }
@@ -480,15 +505,15 @@ impl<'a> InferenceContext<'a> {
             }
             TypeNs::AdtSelfType(_) => {
                 // FIXME this could happen in array size expressions, once we're checking them
-                (Ty::Unknown, None)
+                (self.err_ty(), None)
             }
             TypeNs::GenericParam(_) => {
                 // FIXME potentially resolve assoc type
-                (Ty::Unknown, None)
+                (self.err_ty(), None)
             }
             TypeNs::AdtId(AdtId::EnumId(_)) | TypeNs::BuiltinType(_) | TypeNs::TraitId(_) => {
                 // FIXME diagnostic
-                (Ty::Unknown, None)
+                (self.err_ty(), None)
             }
         };
 
@@ -500,7 +525,7 @@ impl<'a> InferenceContext<'a> {
                 result
             } else {
                 // FIXME diagnostic
-                (Ty::Unknown, None)
+                (TyKind::Unknown.intern(&Interner), None)
             }
         }
 
@@ -529,7 +554,7 @@ impl<'a> InferenceContext<'a> {
         let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
             .with_impl_trait_mode(ImplTraitLoweringMode::Param);
         let param_tys =
-            data.params.iter().map(|type_ref| Ty::from_hir(&ctx, type_ref)).collect::<Vec<_>>();
+            data.params.iter().map(|type_ref| ctx.lower_ty(type_ref)).collect::<Vec<_>>();
         for (ty, pat) in param_tys.into_iter().zip(body.params.iter()) {
             let ty = self.insert_type_vars(ty);
             let ty = self.normalize_associated_types_in(ty);
@@ -711,14 +736,19 @@ impl Expectation {
 
     /// This expresses no expectation on the type.
     fn none() -> Self {
-        Expectation { ty: Ty::Unknown, rvalue_hint: false }
+        Expectation {
+            // FIXME
+            ty: TyKind::Unknown.intern(&Interner),
+            rvalue_hint: false,
+        }
     }
 
-    fn coercion_target(&self) -> &Ty {
+    fn coercion_target(&self) -> Ty {
         if self.rvalue_hint {
-            &Ty::Unknown
+            // FIXME
+            TyKind::Unknown.intern(&Interner)
         } else {
-            &self.ty
+            self.ty.clone()
         }
     }
 }
@@ -772,7 +802,7 @@ mod diagnostics {
 
     #[derive(Debug, PartialEq, Eq, Clone)]
     pub(super) enum InferenceDiagnostic {
-        NoSuchField { expr: ExprId, field: usize },
+        NoSuchField { expr: ExprId },
         BreakOutsideOfLoop { expr: ExprId },
     }
 
@@ -784,9 +814,9 @@ mod diagnostics {
             sink: &mut DiagnosticSink,
         ) {
             match self {
-                InferenceDiagnostic::NoSuchField { expr, field } => {
+                InferenceDiagnostic::NoSuchField { expr } => {
                     let (_, source_map) = db.body_with_source_map(owner);
-                    let field = source_map.field_syntax(*expr, *field);
+                    let field = source_map.field_syntax(*expr);
                     sink.push(NoSuchField { file: field.file_id, field: field.value })
                 }
                 InferenceDiagnostic::BreakOutsideOfLoop { expr } => {
diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs
index 7e8846f27..137419264 100644
--- a/crates/hir_ty/src/infer/coerce.rs
+++ b/crates/hir_ty/src/infer/coerce.rs
@@ -7,7 +7,7 @@
 use chalk_ir::{Mutability, TyVariableKind};
 use hir_def::lang_item::LangItemTarget;
 
-use crate::{autoderef, traits::Solution, Obligation, Substs, TraitRef, Ty};
+use crate::{autoderef, traits::Solution, Interner, Obligation, Substs, TraitRef, Ty, TyKind};
 
 use super::{InEnvironment, InferenceContext};
 
@@ -33,7 +33,9 @@ impl<'a> InferenceContext<'a> {
         } else if self.coerce(ty2, ty1) {
             ty1.clone()
         } else {
-            if let (Ty::FnDef(..), Ty::FnDef(..)) = (ty1, ty2) {
+            if let (TyKind::FnDef(..), TyKind::FnDef(..)) =
+                (ty1.interned(&Interner), ty2.interned(&Interner))
+            {
                 cov_mark::hit!(coerce_fn_reification);
                 // Special case: two function types. Try to coerce both to
                 // pointers to have a chance at getting a match. See
@@ -51,13 +53,13 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn coerce_inner(&mut self, mut from_ty: Ty, to_ty: &Ty) -> bool {
-        match (&from_ty, to_ty) {
+        match (from_ty.interned(&Interner), to_ty.interned(&Interner)) {
             // Never type will make type variable to fallback to Never Type instead of Unknown.
-            (Ty::Never, Ty::InferenceVar(tv, TyVariableKind::General)) => {
+            (TyKind::Never, TyKind::InferenceVar(tv, TyVariableKind::General)) => {
                 self.table.type_variable_table.set_diverging(*tv, true);
                 return true;
             }
-            (Ty::Never, _) => return true,
+            (TyKind::Never, _) => return true,
 
             // Trivial cases, this should go after `never` check to
             // avoid infer result type to be never
@@ -69,33 +71,33 @@ impl<'a> InferenceContext<'a> {
         }
 
         // Pointer weakening and function to pointer
-        match (&mut from_ty, to_ty) {
+        match (from_ty.interned_mut(), to_ty.interned(&Interner)) {
             // `*mut T` -> `*const T`
             // `&mut T` -> `&T`
-            (Ty::Raw(m1, ..), Ty::Raw(m2 @ Mutability::Not, ..))
-            | (Ty::Ref(m1, ..), Ty::Ref(m2 @ Mutability::Not, ..)) => {
+            (TyKind::Raw(m1, ..), TyKind::Raw(m2 @ Mutability::Not, ..))
+            | (TyKind::Ref(m1, ..), TyKind::Ref(m2 @ Mutability::Not, ..)) => {
                 *m1 = *m2;
             }
             // `&T` -> `*const T`
             // `&mut T` -> `*mut T`/`*const T`
-            (Ty::Ref(.., substs), &Ty::Raw(m2 @ Mutability::Not, ..))
-            | (Ty::Ref(Mutability::Mut, substs), &Ty::Raw(m2, ..)) => {
-                from_ty = Ty::Raw(m2, substs.clone());
+            (TyKind::Ref(.., substs), &TyKind::Raw(m2 @ Mutability::Not, ..))
+            | (TyKind::Ref(Mutability::Mut, substs), &TyKind::Raw(m2, ..)) => {
+                from_ty = TyKind::Raw(m2, substs.clone()).intern(&Interner);
             }
 
             // Illegal mutability conversion
-            (Ty::Raw(Mutability::Not, ..), Ty::Raw(Mutability::Mut, ..))
-            | (Ty::Ref(Mutability::Not, ..), Ty::Ref(Mutability::Mut, ..)) => return false,
+            (TyKind::Raw(Mutability::Not, ..), TyKind::Raw(Mutability::Mut, ..))
+            | (TyKind::Ref(Mutability::Not, ..), TyKind::Ref(Mutability::Mut, ..)) => return false,
 
             // `{function_type}` -> `fn()`
-            (Ty::FnDef(..), Ty::Function { .. }) => match from_ty.callable_sig(self.db) {
+            (TyKind::FnDef(..), TyKind::Function { .. }) => match from_ty.callable_sig(self.db) {
                 None => return false,
                 Some(sig) => {
                     from_ty = Ty::fn_ptr(sig);
                 }
             },
 
-            (Ty::Closure(.., substs), Ty::Function { .. }) => {
+            (TyKind::Closure(.., substs), TyKind::Function { .. }) => {
                 from_ty = substs[0].clone();
             }
 
@@ -107,9 +109,9 @@ impl<'a> InferenceContext<'a> {
         }
 
         // Auto Deref if cannot coerce
-        match (&from_ty, to_ty) {
+        match (from_ty.interned(&Interner), to_ty.interned(&Interner)) {
             // FIXME: DerefMut
-            (Ty::Ref(_, st1), Ty::Ref(_, st2)) => self.unify_autoderef_behind_ref(&st1[0], &st2[0]),
+            (TyKind::Ref(_, st1), TyKind::Ref(_, st2)) => self.unify_autoderef_behind_ref(st1, st2),
 
             // Otherwise, normal unify
             _ => self.unify(&from_ty, to_ty),
@@ -174,11 +176,7 @@ impl<'a> InferenceContext<'a> {
             // Stop when constructor matches.
             if from_ty.equals_ctor(&to_ty) {
                 // It will not recurse to `coerce`.
-                return match (from_ty.substs(), to_ty.substs()) {
-                    (Some(st1), Some(st2)) => self.table.unify_substs(st1, st2, 0),
-                    (None, None) => true,
-                    _ => false,
-                };
+                return self.table.unify(&from_ty, &to_ty);
             } else if self.table.unify_inner_trivial(&derefed_ty, &to_ty, 0) {
                 return true;
             }
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 262177ffb..f40dec17f 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -18,10 +18,11 @@ use crate::{
     lower::lower_to_chalk_mutability,
     method_resolution, op,
     primitive::{self, UintTy},
-    traits::{FnTrait, InEnvironment},
+    to_assoc_type_id,
+    traits::{chalk::from_chalk, FnTrait, InEnvironment},
     utils::{generics, variant_data, Generics},
-    AdtId, Binders, CallableDefId, FnPointer, FnSig, Obligation, OpaqueTyId, Rawness, Scalar,
-    Substs, TraitRef, Ty,
+    AdtId, Binders, CallableDefId, FnPointer, FnSig, Interner, Obligation, Rawness, Scalar, Substs,
+    TraitRef, Ty, TyKind,
 };
 
 use super::{
@@ -57,7 +58,7 @@ impl<'a> InferenceContext<'a> {
             // Return actual type when type mismatch.
             // This is needed for diagnostic when return type mismatch.
             ty
-        } else if expected.coercion_target() == &Ty::Unknown {
+        } else if expected.coercion_target().is_unknown() {
             ty
         } else {
             expected.ty.clone()
@@ -84,7 +85,7 @@ impl<'a> InferenceContext<'a> {
             arg_tys.push(arg);
         }
         let parameters = param_builder.build();
-        let arg_ty = Ty::Tuple(num_args, parameters);
+        let arg_ty = TyKind::Tuple(num_args, parameters).intern(&Interner);
         let substs =
             Substs::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
 
@@ -97,8 +98,10 @@ impl<'a> InferenceContext<'a> {
         });
         if self.db.trait_solve(krate, goal.value).is_some() {
             self.obligations.push(implements_fn_trait);
-            let output_proj_ty =
-                crate::ProjectionTy { associated_ty: output_assoc_type, parameters: substs };
+            let output_proj_ty = crate::ProjectionTy {
+                associated_ty_id: to_assoc_type_id(output_assoc_type),
+                substitution: substs,
+            };
             let return_ty = self.normalize_projection_ty(output_proj_ty);
             Some((arg_tys, return_ty))
         } else {
@@ -116,10 +119,13 @@ impl<'a> InferenceContext<'a> {
     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
         let ty = match &body[tgt_expr] {
-            Expr::Missing => Ty::Unknown,
+            Expr::Missing => self.err_ty(),
             Expr::If { condition, then_branch, else_branch } => {
                 // if let is desugared to match, so this is always simple if
-                self.infer_expr(*condition, &Expectation::has_type(Ty::Scalar(Scalar::Bool)));
+                self.infer_expr(
+                    *condition,
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
+                );
 
                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
                 let mut both_arms_diverge = Diverges::Always;
@@ -167,14 +173,15 @@ impl<'a> InferenceContext<'a> {
             Expr::TryBlock { body } => {
                 let _inner = self.infer_expr(*body, expected);
                 // FIXME should be std::result::Result<{inner}, _>
-                Ty::Unknown
+                self.err_ty()
             }
             Expr::Async { body } => {
                 // Use the first type parameter as the output type of future.
                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
                 let inner_ty = self.infer_expr(*body, &Expectation::none());
-                let opaque_ty_id = OpaqueTyId::AsyncBlockTypeImplTrait(self.owner, *body);
-                Ty::OpaqueType(opaque_ty_id, Substs::single(inner_ty))
+                let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
+                let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
+                TyKind::OpaqueType(opaque_ty_id, Substs::single(inner_ty)).intern(&Interner)
             }
             Expr::Loop { body, label } => {
                 self.breakables.push(BreakableContext {
@@ -192,17 +199,20 @@ impl<'a> InferenceContext<'a> {
                 if ctxt.may_break {
                     ctxt.break_ty
                 } else {
-                    Ty::Never
+                    TyKind::Never.intern(&Interner)
                 }
             }
             Expr::While { condition, body, label } => {
                 self.breakables.push(BreakableContext {
                     may_break: false,
-                    break_ty: Ty::Unknown,
+                    break_ty: self.err_ty(),
                     label: label.map(|label| self.body[label].name.clone()),
                 });
                 // while let is desugared to a match loop, so this is always simple while
-                self.infer_expr(*condition, &Expectation::has_type(Ty::Scalar(Scalar::Bool)));
+                self.infer_expr(
+                    *condition,
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
+                );
                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
                 // the body may not run, so it diverging doesn't mean we diverge
@@ -214,7 +224,7 @@ impl<'a> InferenceContext<'a> {
 
                 self.breakables.push(BreakableContext {
                     may_break: false,
-                    break_ty: Ty::Unknown,
+                    break_ty: self.err_ty(),
                     label: label.map(|label| self.body[label].name.clone()),
                 });
                 let pat_ty =
@@ -249,12 +259,15 @@ impl<'a> InferenceContext<'a> {
                     None => self.table.new_type_var(),
                 };
                 sig_tys.push(ret_ty.clone());
-                let sig_ty = Ty::Function(FnPointer {
+                let sig_ty = TyKind::Function(FnPointer {
                     num_args: sig_tys.len() - 1,
-                    sig: FnSig { variadic: false },
+                    sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
                     substs: Substs(sig_tys.clone().into()),
-                });
-                let closure_ty = Ty::Closure(self.owner, tgt_expr, Substs::single(sig_ty));
+                })
+                .intern(&Interner);
+                let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
+                let closure_ty =
+                    TyKind::Closure(closure_id, Substs::single(sig_ty)).intern(&Interner);
 
                 // Eagerly try to relate the closure type with the expected
                 // type, otherwise we often won't have enough information to
@@ -295,7 +308,7 @@ impl<'a> InferenceContext<'a> {
                             args.len(),
                         )
                     })
-                    .unwrap_or((Vec::new(), Ty::Unknown));
+                    .unwrap_or((Vec::new(), self.err_ty()));
                 self.register_obligations_for_call(&callee_ty);
                 self.check_call_arguments(args, &param_tys);
                 self.normalize_associated_types_in(ret_ty)
@@ -305,8 +318,11 @@ impl<'a> InferenceContext<'a> {
             Expr::Match { expr, arms } => {
                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 
-                let mut result_ty =
-                    if arms.is_empty() { Ty::Never } else { self.table.new_type_var() };
+                let mut result_ty = if arms.is_empty() {
+                    TyKind::Never.intern(&Interner)
+                } else {
+                    self.table.new_type_var()
+                };
 
                 let matchee_diverges = self.diverges;
                 let mut all_arms_diverge = Diverges::Always;
@@ -317,7 +333,7 @@ impl<'a> InferenceContext<'a> {
                     if let Some(guard_expr) = arm.guard {
                         self.infer_expr(
                             guard_expr,
-                            &Expectation::has_type(Ty::Scalar(Scalar::Bool)),
+                            &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
                         );
                     }
 
@@ -333,9 +349,9 @@ impl<'a> InferenceContext<'a> {
             Expr::Path(p) => {
                 // FIXME this could be more efficient...
                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
-                self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(Ty::Unknown)
+                self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(self.err_ty())
             }
-            Expr::Continue { .. } => Ty::Never,
+            Expr::Continue { .. } => TyKind::Never.intern(&Interner),
             Expr::Break { expr, label } => {
                 let val_ty = if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none())
@@ -347,7 +363,7 @@ impl<'a> InferenceContext<'a> {
                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
                         ctxt.break_ty.clone()
                     } else {
-                        Ty::Unknown
+                        self.err_ty()
                     };
 
                 let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
@@ -360,7 +376,7 @@ impl<'a> InferenceContext<'a> {
                         expr: tgt_expr,
                     });
                 }
-                Ty::Never
+                TyKind::Never.intern(&Interner)
             }
             Expr::Return { expr } => {
                 if let Some(expr) = expr {
@@ -369,14 +385,14 @@ impl<'a> InferenceContext<'a> {
                     let unit = Ty::unit();
                     self.coerce(&unit, &self.return_ty.clone());
                 }
-                Ty::Never
+                TyKind::Never.intern(&Interner)
             }
             Expr::Yield { expr } => {
                 // FIXME: track yield type for coercion
                 if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none());
                 }
-                Ty::Never
+                TyKind::Never.intern(&Interner)
             }
             Expr::RecordLit { path, fields, spread } => {
                 let (ty, def_id) = self.resolve_variant(path.as_ref());
@@ -389,14 +405,13 @@ impl<'a> InferenceContext<'a> {
                 let substs = ty.substs().cloned().unwrap_or_else(Substs::empty);
                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
                 let variant_data = def_id.map(|it| variant_data(self.db.upcast(), it));
-                for (field_idx, field) in fields.iter().enumerate() {
+                for field in fields.iter() {
                     let field_def =
                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
                             None => {
                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
-                                    expr: tgt_expr,
-                                    field: field_idx,
+                                    expr: field.expr,
                                 });
                                 None
                             }
@@ -404,8 +419,9 @@ impl<'a> InferenceContext<'a> {
                     if let Some(field_def) = field_def {
                         self.result.record_field_resolutions.insert(field.expr, field_def);
                     }
-                    let field_ty = field_def
-                        .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
+                    let field_ty = field_def.map_or(self.err_ty(), |it| {
+                        field_types[it.local_id].clone().subst(&substs)
+                    });
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
                 if let Some(expr) = spread {
@@ -424,27 +440,33 @@ impl<'a> InferenceContext<'a> {
                         environment: self.trait_env.clone(),
                     },
                 )
-                .find_map(|derefed_ty| match canonicalized.decanonicalize_ty(derefed_ty.value) {
-                    Ty::Tuple(_, substs) => {
-                        name.as_tuple_index().and_then(|idx| substs.0.get(idx).cloned())
-                    }
-                    Ty::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
-                        self.db.struct_data(s).variant_data.field(name).map(|local_id| {
-                            let field = FieldId { parent: s.into(), local_id };
-                            self.write_field_resolution(tgt_expr, field);
-                            self.db.field_types(s.into())[field.local_id].clone().subst(&parameters)
-                        })
-                    }
-                    Ty::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
-                        self.db.union_data(u).variant_data.field(name).map(|local_id| {
-                            let field = FieldId { parent: u.into(), local_id };
-                            self.write_field_resolution(tgt_expr, field);
-                            self.db.field_types(u.into())[field.local_id].clone().subst(&parameters)
-                        })
+                .find_map(|derefed_ty| {
+                    match canonicalized.decanonicalize_ty(derefed_ty.value).interned(&Interner) {
+                        TyKind::Tuple(_, substs) => {
+                            name.as_tuple_index().and_then(|idx| substs.0.get(idx).cloned())
+                        }
+                        TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
+                            self.db.struct_data(*s).variant_data.field(name).map(|local_id| {
+                                let field = FieldId { parent: (*s).into(), local_id };
+                                self.write_field_resolution(tgt_expr, field);
+                                self.db.field_types((*s).into())[field.local_id]
+                                    .clone()
+                                    .subst(&parameters)
+                            })
+                        }
+                        TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
+                            self.db.union_data(*u).variant_data.field(name).map(|local_id| {
+                                let field = FieldId { parent: (*u).into(), local_id };
+                                self.write_field_resolution(tgt_expr, field);
+                                self.db.field_types((*u).into())[field.local_id]
+                                    .clone()
+                                    .subst(&parameters)
+                            })
+                        }
+                        _ => None,
                     }
-                    _ => None,
                 })
-                .unwrap_or(Ty::Unknown);
+                .unwrap_or(self.err_ty());
                 let ty = self.insert_type_vars(ty);
                 self.normalize_associated_types_in(ty)
             }
@@ -481,9 +503,10 @@ impl<'a> InferenceContext<'a> {
                 };
                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
                 match rawness {
-                    Rawness::RawPtr => Ty::Raw(mutability, Substs::single(inner_ty)),
-                    Rawness::Ref => Ty::Ref(mutability, Substs::single(inner_ty)),
+                    Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
+                    Rawness::Ref => TyKind::Ref(mutability, inner_ty),
                 }
+                .intern(&Interner)
             }
             Expr::Box { expr } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
@@ -499,7 +522,7 @@ impl<'a> InferenceContext<'a> {
                     sb = sb.fill(repeat_with(|| self.table.new_type_var()));
                     Ty::adt_ty(box_, sb.build())
                 } else {
-                    Ty::Unknown
+                    self.err_ty()
                 }
             }
             Expr::UnaryOp { expr, op } => {
@@ -519,31 +542,31 @@ impl<'a> InferenceContext<'a> {
                                 Some(derefed_ty) => {
                                     canonicalized.decanonicalize_ty(derefed_ty.value)
                                 }
-                                None => Ty::Unknown,
+                                None => self.err_ty(),
                             }
                         }
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     UnaryOp::Neg => {
-                        match &inner_ty {
+                        match inner_ty.interned(&Interner) {
                             // Fast path for builtins
-                            Ty::Scalar(Scalar::Int(_))
-                            | Ty::Scalar(Scalar::Uint(_))
-                            | Ty::Scalar(Scalar::Float(_))
-                            | Ty::InferenceVar(_, TyVariableKind::Integer)
-                            | Ty::InferenceVar(_, TyVariableKind::Float) => inner_ty,
+                            TyKind::Scalar(Scalar::Int(_))
+                            | TyKind::Scalar(Scalar::Uint(_))
+                            | TyKind::Scalar(Scalar::Float(_))
+                            | TyKind::InferenceVar(_, TyVariableKind::Integer)
+                            | TyKind::InferenceVar(_, TyVariableKind::Float) => inner_ty,
                             // Otherwise we resolve via the std::ops::Neg trait
                             _ => self
                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
                         }
                     }
                     UnaryOp::Not => {
-                        match &inner_ty {
+                        match inner_ty.interned(&Interner) {
                             // Fast path for builtins
-                            Ty::Scalar(Scalar::Bool)
-                            | Ty::Scalar(Scalar::Int(_))
-                            | Ty::Scalar(Scalar::Uint(_))
-                            | Ty::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
+                            TyKind::Scalar(Scalar::Bool)
+                            | TyKind::Scalar(Scalar::Int(_))
+                            | TyKind::Scalar(Scalar::Uint(_))
+                            | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
                             // Otherwise we resolve via the std::ops::Not trait
                             _ => self
                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
@@ -554,7 +577,9 @@ impl<'a> InferenceContext<'a> {
             Expr::BinaryOp { lhs, rhs, op } => match op {
                 Some(op) => {
                     let lhs_expectation = match op {
-                        BinaryOp::LogicOp(..) => Expectation::has_type(Ty::Scalar(Scalar::Bool)),
+                        BinaryOp::LogicOp(..) => {
+                            Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
+                        }
                         _ => Expectation::none(),
                     };
                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
@@ -563,7 +588,7 @@ impl<'a> InferenceContext<'a> {
 
                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 
-                    if ret == Ty::Unknown {
+                    if ret.is_unknown() {
                         cov_mark::hit!(infer_expr_inner_binary_operator_overload);
 
                         self.resolve_associated_type_with_params(
@@ -575,7 +600,7 @@ impl<'a> InferenceContext<'a> {
                         ret
                     }
                 }
-                _ => Ty::Unknown,
+                _ => self.err_ty(),
             },
             Expr::Range { lhs, rhs, range_type } => {
                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
@@ -586,33 +611,33 @@ impl<'a> InferenceContext<'a> {
                 match (range_type, lhs_ty, rhs_ty) {
                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
                         Some(adt) => Ty::adt_ty(adt, Substs::empty()),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
                         Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     (RangeOp::Inclusive, None, Some(ty)) => {
                         match self.resolve_range_to_inclusive() {
                             Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                            None => Ty::Unknown,
+                            None => self.err_ty(),
                         }
                     }
                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
                         Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
                         match self.resolve_range_inclusive() {
                             Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                            None => Ty::Unknown,
+                            None => self.err_ty(),
                         }
                     }
                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
                         Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
-                    (RangeOp::Inclusive, _, None) => Ty::Unknown,
+                    (RangeOp::Inclusive, _, None) => self.err_ty(),
                 }
             }
             Expr::Index { base, index } => {
@@ -631,19 +656,19 @@ impl<'a> InferenceContext<'a> {
                         index_trait,
                     );
                     let self_ty =
-                        self_ty.map_or(Ty::Unknown, |t| canonicalized.decanonicalize_ty(t.value));
+                        self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
                     self.resolve_associated_type_with_params(
                         self_ty,
                         self.resolve_ops_index_output(),
                         &[index_ty],
                     )
                 } else {
-                    Ty::Unknown
+                    self.err_ty()
                 }
             }
             Expr::Tuple { exprs } => {
-                let mut tys = match &expected.ty {
-                    Ty::Tuple(_, substs) => substs
+                let mut tys = match expected.ty.interned(&Interner) {
+                    TyKind::Tuple(_, substs) => substs
                         .iter()
                         .cloned()
                         .chain(repeat_with(|| self.table.new_type_var()))
@@ -656,11 +681,11 @@ impl<'a> InferenceContext<'a> {
                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
                 }
 
-                Ty::Tuple(tys.len(), Substs(tys.into()))
+                TyKind::Tuple(tys.len(), Substs(tys.into())).intern(&Interner)
             }
             Expr::Array(array) => {
-                let elem_ty = match &expected.ty {
-                    Ty::Array(st) | Ty::Slice(st) => st.as_single().clone(),
+                let elem_ty = match expected.ty.interned(&Interner) {
+                    TyKind::Array(st) | TyKind::Slice(st) => st.clone(),
                     _ => self.table.new_type_var(),
                 };
 
@@ -677,43 +702,50 @@ impl<'a> InferenceContext<'a> {
                         );
                         self.infer_expr(
                             *repeat,
-                            &Expectation::has_type(Ty::Scalar(Scalar::Uint(UintTy::Usize))),
+                            &Expectation::has_type(
+                                TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
+                            ),
                         );
                     }
                 }
 
-                Ty::Array(Substs::single(elem_ty))
+                TyKind::Array(elem_ty).intern(&Interner)
             }
             Expr::Literal(lit) => match lit {
-                Literal::Bool(..) => Ty::Scalar(Scalar::Bool),
-                Literal::String(..) => Ty::Ref(Mutability::Not, Substs::single(Ty::Str)),
+                Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
+                Literal::String(..) => {
+                    TyKind::Ref(Mutability::Not, TyKind::Str.intern(&Interner)).intern(&Interner)
+                }
                 Literal::ByteString(..) => {
-                    let byte_type = Ty::Scalar(Scalar::Uint(UintTy::U8));
-                    let array_type = Ty::Array(Substs::single(byte_type));
-                    Ty::Ref(Mutability::Not, Substs::single(array_type))
+                    let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
+                    let array_type = TyKind::Array(byte_type).intern(&Interner);
+                    TyKind::Ref(Mutability::Not, array_type).intern(&Interner)
                 }
-                Literal::Char(..) => Ty::Scalar(Scalar::Char),
+                Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
                 Literal::Int(_v, ty) => match ty {
                     Some(int_ty) => {
-                        Ty::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
+                        TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
+                            .intern(&Interner)
                     }
                     None => self.table.new_integer_var(),
                 },
                 Literal::Uint(_v, ty) => match ty {
                     Some(int_ty) => {
-                        Ty::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
+                        TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
+                            .intern(&Interner)
                     }
                     None => self.table.new_integer_var(),
                 },
                 Literal::Float(_v, ty) => match ty {
                     Some(float_ty) => {
-                        Ty::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
+                        TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
+                            .intern(&Interner)
                     }
                     None => self.table.new_float_var(),
                 },
             },
         };
-        // use a new type variable if we got Ty::Unknown here
+        // use a new type variable if we got unknown here
         let ty = self.insert_type_vars_shallow(ty);
         let ty = self.resolve_ty_as_possible(ty);
         self.write_expr_ty(tgt_expr, ty.clone());
@@ -730,7 +762,7 @@ impl<'a> InferenceContext<'a> {
             match stmt {
                 Statement::Let { pat, type_ref, initializer } => {
                     let decl_ty =
-                        type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(Ty::Unknown);
+                        type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(self.err_ty());
 
                     // Always use the declared type when specified
                     let mut ty = decl_ty.clone();
@@ -738,7 +770,7 @@ impl<'a> InferenceContext<'a> {
                     if let Some(expr) = initializer {
                         let actual_ty =
                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
-                        if decl_ty == Ty::Unknown {
+                        if decl_ty.is_unknown() {
                             ty = actual_ty;
                         }
                     }
@@ -766,7 +798,7 @@ impl<'a> InferenceContext<'a> {
                 // we don't even make an attempt at coercion
                 self.table.new_maybe_never_var()
             } else {
-                self.coerce(&Ty::unit(), expected.coercion_target());
+                self.coerce(&Ty::unit(), &expected.coercion_target());
                 Ty::unit()
             }
         };
@@ -802,7 +834,7 @@ impl<'a> InferenceContext<'a> {
                 self.write_method_resolution(tgt_expr, func);
                 (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
             }
-            None => (receiver_ty, Binders::new(0, Ty::Unknown), None),
+            None => (receiver_ty, Binders::new(0, self.err_ty()), None),
         };
         let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
         let method_ty = method_ty.subst(&substs);
@@ -813,15 +845,15 @@ impl<'a> InferenceContext<'a> {
                 if !sig.params().is_empty() {
                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
                 } else {
-                    (Ty::Unknown, Vec::new(), sig.ret().clone())
+                    (self.err_ty(), Vec::new(), sig.ret().clone())
                 }
             }
-            None => (Ty::Unknown, Vec::new(), Ty::Unknown),
+            None => (self.err_ty(), Vec::new(), self.err_ty()),
         };
         // Apply autoref so the below unification works correctly
         // FIXME: return correct autorefs from lookup_method
         let actual_receiver_ty = match expected_receiver_ty.as_reference() {
-            Some((_, mutability)) => Ty::Ref(mutability, Substs::single(derefed_receiver_ty)),
+            Some((_, mutability)) => TyKind::Ref(mutability, derefed_receiver_ty).intern(&Interner),
             _ => derefed_receiver_ty,
         };
         self.unify(&expected_receiver_ty, &actual_receiver_ty);
@@ -837,7 +869,7 @@ impl<'a> InferenceContext<'a> {
         // that we have more information about the types of arguments when we
         // type-check the functions. This isn't really the right way to do this.
         for &check_closures in &[false, true] {
-            let param_iter = param_tys.iter().cloned().chain(repeat(Ty::Unknown));
+            let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
             for (&arg, param_ty) in args.iter().zip(param_iter) {
                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
                 if is_closure != check_closures {
@@ -867,7 +899,7 @@ impl<'a> InferenceContext<'a> {
                 if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
                     substs.push(receiver_ty.clone());
                 } else {
-                    substs.push(Ty::Unknown);
+                    substs.push(self.err_ty());
                 }
             }
         }
@@ -891,14 +923,15 @@ impl<'a> InferenceContext<'a> {
         };
         let supplied_params = substs.len();
         for _ in supplied_params..total_len {
-            substs.push(Ty::Unknown);
+            substs.push(self.err_ty());
         }
         assert_eq!(substs.len(), total_len);
         Substs(substs.into())
     }
 
     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
-        if let &Ty::FnDef(def, ref parameters) = callable_ty {
+        if let TyKind::FnDef(fn_def, parameters) = callable_ty.interned(&Interner) {
+            let def: CallableDefId = from_chalk(self.db, *fn_def);
             let generic_predicates = self.db.generic_predicates(def.into());
             for predicate in generic_predicates.iter() {
                 let predicate = predicate.clone().subst(parameters);
diff --git a/crates/hir_ty/src/infer/pat.rs b/crates/hir_ty/src/infer/pat.rs
index a0ac8d80f..9e8ca18ef 100644
--- a/crates/hir_ty/src/infer/pat.rs
+++ b/crates/hir_ty/src/infer/pat.rs
@@ -12,7 +12,7 @@ use hir_def::{
 use hir_expand::name::Name;
 
 use super::{BindingMode, Expectation, InferenceContext};
-use crate::{lower::lower_to_chalk_mutability, utils::variant_data, Substs, Ty};
+use crate::{lower::lower_to_chalk_mutability, utils::variant_data, Interner, Substs, Ty, TyKind};
 
 impl<'a> InferenceContext<'a> {
     fn infer_tuple_struct_pat(
@@ -46,7 +46,7 @@ impl<'a> InferenceContext<'a> {
             let expected_ty = var_data
                 .as_ref()
                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
-                .map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
+                .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat, &expected_ty, default_bm);
         }
@@ -80,8 +80,8 @@ impl<'a> InferenceContext<'a> {
                 self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
             }
 
-            let expected_ty =
-                matching_field.map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
+            let expected_ty = matching_field
+                .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat.pat, &expected_ty, default_bm);
         }
@@ -129,7 +129,8 @@ impl<'a> InferenceContext<'a> {
                     None => (&args[..], &[][..]),
                 };
                 let n_uncovered_patterns = expectations.len().saturating_sub(args.len());
-                let mut expectations_iter = expectations.iter().chain(repeat(&Ty::Unknown));
+                let err_ty = self.err_ty();
+                let mut expectations_iter = expectations.iter().chain(repeat(&err_ty));
                 let mut infer_pat = |(&pat, ty)| self.infer_pat(pat, ty, default_bm);
 
                 let mut inner_tys = Vec::with_capacity(n_uncovered_patterns + args.len());
@@ -137,7 +138,7 @@ impl<'a> InferenceContext<'a> {
                 inner_tys.extend(expectations_iter.by_ref().take(n_uncovered_patterns).cloned());
                 inner_tys.extend(post.iter().zip(expectations_iter).map(infer_pat));
 
-                Ty::Tuple(inner_tys.len(), Substs(inner_tys.into()))
+                TyKind::Tuple(inner_tys.len(), Substs(inner_tys.into())).intern(&Interner)
             }
             Pat::Or(ref pats) => {
                 if let Some((first_pat, rest)) = pats.split_first() {
@@ -147,7 +148,7 @@ impl<'a> InferenceContext<'a> {
                     }
                     ty
                 } else {
-                    Ty::Unknown
+                    self.err_ty()
                 }
             }
             Pat::Ref { pat, mutability } => {
@@ -157,12 +158,12 @@ impl<'a> InferenceContext<'a> {
                         if mutability != exp_mut {
                             // FIXME: emit type error?
                         }
-                        inner_ty
+                        inner_ty.clone()
                     }
-                    _ => &Ty::Unknown,
+                    _ => self.result.standard_types.unknown.clone(),
                 };
-                let subty = self.infer_pat(*pat, expectation, default_bm);
-                Ty::Ref(mutability, Substs::single(subty))
+                let subty = self.infer_pat(*pat, &expectation, default_bm);
+                TyKind::Ref(mutability, subty).intern(&Interner)
             }
             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
                 p.as_ref(),
@@ -178,7 +179,7 @@ impl<'a> InferenceContext<'a> {
             Pat::Path(path) => {
                 // FIXME use correct resolver for the surrounding expression
                 let resolver = self.resolver.clone();
-                self.infer_path(&resolver, &path, pat.into()).unwrap_or(Ty::Unknown)
+                self.infer_path(&resolver, &path, pat.into()).unwrap_or(self.err_ty())
             }
             Pat::Bind { mode, name: _, subpat } => {
                 let mode = if mode == &BindingAnnotation::Unannotated {
@@ -195,7 +196,7 @@ impl<'a> InferenceContext<'a> {
 
                 let bound_ty = match mode {
                     BindingMode::Ref(mutability) => {
-                        Ty::Ref(mutability, Substs::single(inner_ty.clone()))
+                        TyKind::Ref(mutability, inner_ty.clone()).intern(&Interner)
                     }
                     BindingMode::Move => inner_ty.clone(),
                 };
@@ -204,17 +205,17 @@ impl<'a> InferenceContext<'a> {
                 return inner_ty;
             }
             Pat::Slice { prefix, slice, suffix } => {
-                let (container_ty, elem_ty): (fn(_) -> _, _) = match &expected {
-                    Ty::Array(st) => (Ty::Array, st.as_single().clone()),
-                    Ty::Slice(st) => (Ty::Slice, st.as_single().clone()),
-                    _ => (Ty::Slice, Ty::Unknown),
+                let (container_ty, elem_ty): (fn(_) -> _, _) = match expected.interned(&Interner) {
+                    TyKind::Array(st) => (TyKind::Array, st.clone()),
+                    TyKind::Slice(st) => (TyKind::Slice, st.clone()),
+                    _ => (TyKind::Slice, self.err_ty()),
                 };
 
                 for pat_id in prefix.iter().chain(suffix) {
                     self.infer_pat(*pat_id, &elem_ty, default_bm);
                 }
 
-                let pat_ty = container_ty(Substs::single(elem_ty));
+                let pat_ty = container_ty(elem_ty).intern(&Interner);
                 if let Some(slice_pat_id) = slice {
                     self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
                 }
@@ -231,21 +232,21 @@ impl<'a> InferenceContext<'a> {
             Pat::Box { inner } => match self.resolve_boxed_box() {
                 Some(box_adt) => {
                     let inner_expected = match expected.as_adt() {
-                        Some((adt, substs)) if adt == box_adt => substs.as_single(),
-                        _ => &Ty::Unknown,
+                        Some((adt, substs)) if adt == box_adt => substs.as_single().clone(),
+                        _ => self.result.standard_types.unknown.clone(),
                     };
 
-                    let inner_ty = self.infer_pat(*inner, inner_expected, default_bm);
+                    let inner_ty = self.infer_pat(*inner, &inner_expected, default_bm);
                     Ty::adt_ty(box_adt, Substs::single(inner_ty))
                 }
-                None => Ty::Unknown,
+                None => self.err_ty(),
             },
             Pat::ConstBlock(expr) => {
                 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
             }
-            Pat::Missing => Ty::Unknown,
+            Pat::Missing => self.err_ty(),
         };
-        // use a new type variable if we got Ty::Unknown here
+        // use a new type variable if we got error type here
         let ty = self.insert_type_vars_shallow(ty);
         if !self.unify(&ty, expected) {
             // FIXME record mismatch, we need to change the type of self.type_mismatches for that
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index ae3554bac..af108fb6c 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -9,7 +9,7 @@ use hir_def::{
 };
 use hir_expand::name::Name;
 
-use crate::{method_resolution, Substs, Ty, ValueTyDefId};
+use crate::{method_resolution, Interner, Substs, Ty, TyKind, ValueTyDefId};
 
 use super::{ExprOrPatId, InferenceContext, TraitRef};
 
@@ -40,7 +40,7 @@ impl<'a> InferenceContext<'a> {
             let ty = self.make_ty(type_ref);
             let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
             let ctx = crate::lower::TyLoweringContext::new(self.db, &resolver);
-            let (ty, _) = Ty::from_type_relative_path(&ctx, ty, None, remaining_segments_for_ty);
+            let (ty, _) = ctx.lower_ty_relative_path(ty, None, remaining_segments_for_ty);
             self.resolve_ty_assoc_item(
                 ty,
                 &path.segments().last().expect("path had at least one segment").name,
@@ -79,7 +79,7 @@ impl<'a> InferenceContext<'a> {
             }
             ValueNs::ImplSelf(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
-                let substs = Substs::type_params_for_generics(&generics);
+                let substs = Substs::type_params_for_generics(self.db, &generics);
                 let ty = self.db.impl_self_ty(impl_id).subst(&substs);
                 if let Some((AdtId::StructId(struct_id), substs)) = ty.as_adt() {
                     let ty = self.db.value_ty(struct_id.into()).subst(&substs);
@@ -96,7 +96,7 @@ impl<'a> InferenceContext<'a> {
         // self_subst is just for the parent
         let parent_substs = self_subst.unwrap_or_else(Substs::empty);
         let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
-        let substs = Ty::substs_from_path(&ctx, path, typable, true);
+        let substs = ctx.substs_from_path(path, typable, true);
         let full_substs = Substs::builder(substs.len())
             .use_parent_substs(&parent_substs)
             .fill(substs.0[parent_substs.len()..].iter().cloned())
@@ -126,7 +126,8 @@ impl<'a> InferenceContext<'a> {
                 let segment =
                     remaining_segments.last().expect("there should be at least one segment here");
                 let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
-                let trait_ref = TraitRef::from_resolved_path(&ctx, trait_, resolved_segment, None);
+                let trait_ref =
+                    ctx.lower_trait_ref_from_resolved_path(trait_, resolved_segment, None);
                 self.resolve_trait_assoc_item(trait_ref, segment, id)
             }
             (def, _) => {
@@ -137,14 +138,13 @@ impl<'a> InferenceContext<'a> {
                 let remaining_segments_for_ty =
                     remaining_segments.take(remaining_segments.len() - 1);
                 let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
-                let (ty, _) = Ty::from_partly_resolved_hir_path(
-                    &ctx,
+                let (ty, _) = ctx.lower_partly_resolved_path(
                     def,
                     resolved_segment,
                     remaining_segments_for_ty,
                     true,
                 );
-                if let Ty::Unknown = ty {
+                if let TyKind::Unknown = ty.interned(&Interner) {
                     return None;
                 }
 
@@ -209,7 +209,7 @@ impl<'a> InferenceContext<'a> {
         name: &Name,
         id: ExprOrPatId,
     ) -> Option<(ValueNs, Option<Substs>)> {
-        if let Ty::Unknown = ty {
+        if let TyKind::Unknown = ty.interned(&Interner) {
             return None;
         }
 
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index 54fcfed10..7795f446f 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -7,8 +7,8 @@ use ena::unify::{InPlaceUnificationTable, NoError, UnifyKey, UnifyValue};
 
 use super::{InferenceContext, Obligation};
 use crate::{
-    BoundVar, Canonical, DebruijnIndex, GenericPredicate, InEnvironment, InferenceVar, Scalar,
-    Substs, Ty, TypeWalk,
+    BoundVar, Canonical, DebruijnIndex, FnPointer, GenericPredicate, InEnvironment, InferenceVar,
+    Interner, Scalar, Substs, Ty, TyKind, TypeWalk,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -49,8 +49,8 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
 
     fn do_canonicalize<T: TypeWalk>(&mut self, t: T, binders: DebruijnIndex) -> T {
         t.fold_binders(
-            &mut |ty, binders| match ty {
-                Ty::InferenceVar(var, kind) => {
+            &mut |ty, binders| match ty.interned(&Interner) {
+                &TyKind::InferenceVar(var, kind) => {
                     let inner = var.to_inner();
                     if self.var_stack.contains(&inner) {
                         // recursive type
@@ -66,7 +66,7 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
                     } else {
                         let root = self.ctx.table.var_unification_table.find(inner);
                         let position = self.add(InferenceVar::from_inner(root), kind);
-                        Ty::BoundVar(BoundVar::new(binders, position))
+                        TyKind::BoundVar(BoundVar::new(binders, position)).intern(&Interner)
                     }
                 }
                 _ => ty,
@@ -108,10 +108,10 @@ impl<T> Canonicalized<T> {
     pub(super) fn decanonicalize_ty(&self, mut ty: Ty) -> Ty {
         ty.walk_mut_binders(
             &mut |ty, binders| {
-                if let &mut Ty::BoundVar(bound) = ty {
+                if let &mut TyKind::BoundVar(bound) = ty.interned_mut() {
                     if bound.debruijn >= binders {
                         let (v, k) = self.free_vars[bound.index];
-                        *ty = Ty::InferenceVar(v, k);
+                        *ty = TyKind::InferenceVar(v, k).intern(&Interner);
                     }
                 }
             },
@@ -142,7 +142,7 @@ impl<T> Canonicalized<T> {
             // eagerly replace projections in the type; we may be getting types
             // e.g. from where clauses where this hasn't happened yet
             let ty = ctx.normalize_associated_types_in(ty.clone().subst_bound_vars(&new_vars));
-            ctx.table.unify(&Ty::InferenceVar(v, k), &ty);
+            ctx.table.unify(&TyKind::InferenceVar(v, k).intern(&Interner), &ty);
         }
     }
 }
@@ -166,7 +166,10 @@ pub(crate) fn unify(tys: &Canonical<(Ty, Ty)>) -> Option<Substs> {
     // (kind of hacky)
     for (i, var) in vars.iter().enumerate() {
         if &*table.resolve_ty_shallow(var) == var {
-            table.unify(var, &Ty::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, i)));
+            table.unify(
+                var,
+                &TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, i)).intern(&Interner),
+            );
         }
     }
     Some(
@@ -196,11 +199,12 @@ impl TypeVariableTable {
 
     fn fallback_value(&self, iv: InferenceVar, kind: TyVariableKind) -> Ty {
         match kind {
-            _ if self.inner[iv.to_inner().0 as usize].diverging => Ty::Never,
-            TyVariableKind::General => Ty::Unknown,
-            TyVariableKind::Integer => Ty::Scalar(Scalar::Int(IntTy::I32)),
-            TyVariableKind::Float => Ty::Scalar(Scalar::Float(FloatTy::F64)),
+            _ if self.inner[iv.to_inner().0 as usize].diverging => TyKind::Never,
+            TyVariableKind::General => TyKind::Unknown,
+            TyVariableKind::Integer => TyKind::Scalar(Scalar::Int(IntTy::I32)),
+            TyVariableKind::Float => TyKind::Scalar(Scalar::Float(FloatTy::F64)),
         }
+        .intern(&Interner)
     }
 }
 
@@ -227,7 +231,7 @@ impl InferenceTable {
         self.type_variable_table.push(TypeVariableData { diverging });
         let key = self.var_unification_table.new_key(TypeVarValue::Unknown);
         assert_eq!(key.0 as usize, self.type_variable_table.inner.len() - 1);
-        Ty::InferenceVar(InferenceVar::from_inner(key), kind)
+        TyKind::InferenceVar(InferenceVar::from_inner(key), kind).intern(&Interner)
     }
 
     pub(crate) fn new_type_var(&mut self) -> Ty {
@@ -279,10 +283,24 @@ impl InferenceTable {
         let ty1 = self.resolve_ty_shallow(ty1);
         let ty2 = self.resolve_ty_shallow(ty2);
         if ty1.equals_ctor(&ty2) {
-            match (ty1.substs(), ty2.substs()) {
-                (Some(st1), Some(st2)) => self.unify_substs(st1, st2, depth + 1),
-                (None, None) => true,
-                _ => false,
+            match (ty1.interned(&Interner), ty2.interned(&Interner)) {
+                (TyKind::Adt(_, substs1), TyKind::Adt(_, substs2))
+                | (TyKind::FnDef(_, substs1), TyKind::FnDef(_, substs2))
+                | (
+                    TyKind::Function(FnPointer { substs: substs1, .. }),
+                    TyKind::Function(FnPointer { substs: substs2, .. }),
+                )
+                | (TyKind::Tuple(_, substs1), TyKind::Tuple(_, substs2))
+                | (TyKind::OpaqueType(_, substs1), TyKind::OpaqueType(_, substs2))
+                | (TyKind::AssociatedType(_, substs1), TyKind::AssociatedType(_, substs2))
+                | (TyKind::Closure(.., substs1), TyKind::Closure(.., substs2)) => {
+                    self.unify_substs(substs1, substs2, depth + 1)
+                }
+                (TyKind::Ref(_, ty1), TyKind::Ref(_, ty2))
+                | (TyKind::Raw(_, ty1), TyKind::Raw(_, ty2))
+                | (TyKind::Array(ty1), TyKind::Array(ty2))
+                | (TyKind::Slice(ty1), TyKind::Slice(ty2)) => self.unify_inner(ty1, ty2, depth + 1),
+                _ => true, /* we checked equals_ctor already */
             }
         } else {
             self.unify_inner_trivial(&ty1, &ty2, depth)
@@ -290,12 +308,12 @@ impl InferenceTable {
     }
 
     pub(super) fn unify_inner_trivial(&mut self, ty1: &Ty, ty2: &Ty, depth: usize) -> bool {
-        match (ty1, ty2) {
-            (Ty::Unknown, _) | (_, Ty::Unknown) => true,
+        match (ty1.interned(&Interner), ty2.interned(&Interner)) {
+            (TyKind::Unknown, _) | (_, TyKind::Unknown) => true,
 
-            (Ty::Placeholder(p1), Ty::Placeholder(p2)) if *p1 == *p2 => true,
+            (TyKind::Placeholder(p1), TyKind::Placeholder(p2)) if *p1 == *p2 => true,
 
-            (Ty::Dyn(dyn1), Ty::Dyn(dyn2)) if dyn1.len() == dyn2.len() => {
+            (TyKind::Dyn(dyn1), TyKind::Dyn(dyn2)) if dyn1.len() == dyn2.len() => {
                 for (pred1, pred2) in dyn1.iter().zip(dyn2.iter()) {
                     if !self.unify_preds(pred1, pred2, depth + 1) {
                         return false;
@@ -305,16 +323,16 @@ impl InferenceTable {
             }
 
             (
-                Ty::InferenceVar(tv1, TyVariableKind::General),
-                Ty::InferenceVar(tv2, TyVariableKind::General),
+                TyKind::InferenceVar(tv1, TyVariableKind::General),
+                TyKind::InferenceVar(tv2, TyVariableKind::General),
             )
             | (
-                Ty::InferenceVar(tv1, TyVariableKind::Integer),
-                Ty::InferenceVar(tv2, TyVariableKind::Integer),
+                TyKind::InferenceVar(tv1, TyVariableKind::Integer),
+                TyKind::InferenceVar(tv2, TyVariableKind::Integer),
             )
             | (
-                Ty::InferenceVar(tv1, TyVariableKind::Float),
-                Ty::InferenceVar(tv2, TyVariableKind::Float),
+                TyKind::InferenceVar(tv1, TyVariableKind::Float),
+                TyKind::InferenceVar(tv2, TyVariableKind::Float),
             ) if self.type_variable_table.is_diverging(*tv1)
                 == self.type_variable_table.is_diverging(*tv2) =>
             {
@@ -326,24 +344,37 @@ impl InferenceTable {
             // The order of MaybeNeverTypeVar matters here.
             // Unifying MaybeNeverTypeVar and TypeVar will let the latter become MaybeNeverTypeVar.
             // Unifying MaybeNeverTypeVar and other concrete type will let the former become it.
-            (Ty::InferenceVar(tv, TyVariableKind::General), other)
-            | (other, Ty::InferenceVar(tv, TyVariableKind::General))
-            | (Ty::InferenceVar(tv, TyVariableKind::Integer), other @ Ty::Scalar(Scalar::Int(_)))
-            | (other @ Ty::Scalar(Scalar::Int(_)), Ty::InferenceVar(tv, TyVariableKind::Integer))
+            (TyKind::InferenceVar(tv, TyVariableKind::General), other)
+            | (other, TyKind::InferenceVar(tv, TyVariableKind::General))
             | (
-                Ty::InferenceVar(tv, TyVariableKind::Integer),
-                other @ Ty::Scalar(Scalar::Uint(_)),
+                TyKind::InferenceVar(tv, TyVariableKind::Integer),
+                other @ TyKind::Scalar(Scalar::Int(_)),
             )
             | (
-                other @ Ty::Scalar(Scalar::Uint(_)),
-                Ty::InferenceVar(tv, TyVariableKind::Integer),
+                other @ TyKind::Scalar(Scalar::Int(_)),
+                TyKind::InferenceVar(tv, TyVariableKind::Integer),
             )
-            | (Ty::InferenceVar(tv, TyVariableKind::Float), other @ Ty::Scalar(Scalar::Float(_)))
-            | (other @ Ty::Scalar(Scalar::Float(_)), Ty::InferenceVar(tv, TyVariableKind::Float)) =>
-            {
+            | (
+                TyKind::InferenceVar(tv, TyVariableKind::Integer),
+                other @ TyKind::Scalar(Scalar::Uint(_)),
+            )
+            | (
+                other @ TyKind::Scalar(Scalar::Uint(_)),
+                TyKind::InferenceVar(tv, TyVariableKind::Integer),
+            )
+            | (
+                TyKind::InferenceVar(tv, TyVariableKind::Float),
+                other @ TyKind::Scalar(Scalar::Float(_)),
+            )
+            | (
+                other @ TyKind::Scalar(Scalar::Float(_)),
+                TyKind::InferenceVar(tv, TyVariableKind::Float),
+            ) => {
                 // the type var is unknown since we tried to resolve it
-                self.var_unification_table
-                    .union_value(tv.to_inner(), TypeVarValue::Known(other.clone()));
+                self.var_unification_table.union_value(
+                    tv.to_inner(),
+                    TypeVarValue::Known(other.clone().intern(&Interner)),
+                );
                 true
             }
 
@@ -364,11 +395,11 @@ impl InferenceTable {
                 self.unify_substs(&tr1.substs, &tr2.substs, depth + 1)
             }
             (GenericPredicate::Projection(proj1), GenericPredicate::Projection(proj2))
-                if proj1.projection_ty.associated_ty == proj2.projection_ty.associated_ty =>
+                if proj1.projection_ty.associated_ty_id == proj2.projection_ty.associated_ty_id =>
             {
                 self.unify_substs(
-                    &proj1.projection_ty.parameters,
-                    &proj2.projection_ty.parameters,
+                    &proj1.projection_ty.substitution,
+                    &proj2.projection_ty.substitution,
                     depth + 1,
                 ) && self.unify_inner(&proj1.ty, &proj2.ty, depth + 1)
             }
@@ -387,8 +418,8 @@ impl InferenceTable {
             if i > 0 {
                 cov_mark::hit!(type_var_resolves_to_int_var);
             }
-            match &*ty {
-                Ty::InferenceVar(tv, _) => {
+            match ty.interned(&Interner) {
+                TyKind::InferenceVar(tv, _) => {
                     let inner = tv.to_inner();
                     match self.var_unification_table.inlined_probe_value(inner).known() {
                         Some(known_ty) => {
@@ -410,8 +441,8 @@ impl InferenceTable {
     /// be resolved as far as possible, i.e. contain no type variables with
     /// known type.
     fn resolve_ty_as_possible_inner(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
-        ty.fold(&mut |ty| match ty {
-            Ty::InferenceVar(tv, kind) => {
+        ty.fold(&mut |ty| match ty.interned(&Interner) {
+            &TyKind::InferenceVar(tv, kind) => {
                 let inner = tv.to_inner();
                 if tv_stack.contains(&inner) {
                     cov_mark::hit!(type_var_cycles_resolve_as_possible);
@@ -435,10 +466,10 @@ impl InferenceTable {
     }
 
     /// Resolves the type completely; type variables without known type are
-    /// replaced by Ty::Unknown.
+    /// replaced by TyKind::Unknown.
     fn resolve_ty_completely_inner(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
-        ty.fold(&mut |ty| match ty {
-            Ty::InferenceVar(tv, kind) => {
+        ty.fold(&mut |ty| match ty.interned(&Interner) {
+            &TyKind::InferenceVar(tv, kind) => {
                 let inner = tv.to_inner();
                 if tv_stack.contains(&inner) {
                     cov_mark::hit!(type_var_cycles_resolve_completely);
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index e77f24e4e..850385280 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -27,11 +27,11 @@ use std::{iter, mem, ops::Deref, sync::Arc};
 
 use base_db::salsa;
 use hir_def::{
-    builtin_type::BuiltinType, expr::ExprId, type_ref::Rawness, AssocContainerId, DefWithBodyId,
-    FunctionId, GenericDefId, HasModule, LifetimeParamId, Lookup, TraitId, TypeAliasId,
-    TypeParamId,
+    builtin_type::BuiltinType, expr::ExprId, type_ref::Rawness, AssocContainerId, FunctionId,
+    GenericDefId, HasModule, LifetimeParamId, Lookup, TraitId, TypeAliasId, TypeParamId,
 };
 use itertools::Itertools;
+use smallvec::SmallVec;
 
 use crate::{
     db::HirDatabase,
@@ -47,9 +47,16 @@ pub use lower::{
 };
 pub use traits::{InEnvironment, Obligation, ProjectionPredicate, TraitEnvironment};
 
-pub use chalk_ir::{AdtId, BoundVar, DebruijnIndex, Mutability, Scalar, TyVariableKind};
+pub use chalk_ir::{AdtId, BoundVar, DebruijnIndex, Mutability, Safety, Scalar, TyVariableKind};
 
-pub(crate) use crate::traits::chalk::Interner;
+pub use crate::traits::chalk::Interner;
+
+pub type ForeignDefId = chalk_ir::ForeignDefId<Interner>;
+pub type AssocTypeId = chalk_ir::AssocTypeId<Interner>;
+pub type FnDefId = chalk_ir::FnDefId<Interner>;
+pub type ClosureId = chalk_ir::ClosureId<Interner>;
+pub type OpaqueTyId = chalk_ir::OpaqueTyId<Interner>;
+pub type PlaceholderIndex = chalk_ir::PlaceholderIndex;
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum Lifetime {
@@ -60,7 +67,7 @@ pub enum Lifetime {
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct OpaqueTy {
     pub opaque_ty_id: OpaqueTyId,
-    pub parameters: Substs,
+    pub substitution: Substs,
 }
 
 /// A "projection" type corresponds to an (unnormalized)
@@ -68,17 +75,17 @@ pub struct OpaqueTy {
 /// trait and all its parameters are fully known.
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct ProjectionTy {
-    pub associated_ty: TypeAliasId,
-    pub parameters: Substs,
+    pub associated_ty_id: AssocTypeId,
+    pub substitution: Substs,
 }
 
 impl ProjectionTy {
     pub fn trait_ref(&self, db: &dyn HirDatabase) -> TraitRef {
-        TraitRef { trait_: self.trait_(db), substs: self.parameters.clone() }
+        TraitRef { trait_: self.trait_(db), substs: self.substitution.clone() }
     }
 
     fn trait_(&self, db: &dyn HirDatabase) -> TraitId {
-        match self.associated_ty.lookup(db.upcast()).container {
+        match from_assoc_type_id(self.associated_ty_id).lookup(db.upcast()).container {
             AssocContainerId::TraitId(it) => it,
             _ => panic!("projection ty without parent trait"),
         }
@@ -87,7 +94,7 @@ impl ProjectionTy {
 
 impl TypeWalk for ProjectionTy {
     fn walk(&self, f: &mut impl FnMut(&Ty)) {
-        self.parameters.walk(f);
+        self.substitution.walk(f);
     }
 
     fn walk_mut_binders(
@@ -95,14 +102,11 @@ impl TypeWalk for ProjectionTy {
         f: &mut impl FnMut(&mut Ty, DebruijnIndex),
         binders: DebruijnIndex,
     ) {
-        self.parameters.walk_mut_binders(f, binders);
+        self.substitution.walk_mut_binders(f, binders);
     }
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
-pub struct FnSig {
-    pub variadic: bool,
-}
+pub type FnSig = chalk_ir::FnSig<Interner>;
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct FnPointer {
@@ -131,7 +135,7 @@ pub enum AliasTy {
 ///
 /// This should be cheap to clone.
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
-pub enum Ty {
+pub enum TyKind {
     /// Structures, enumerations and unions.
     Adt(AdtId<Interner>, Substs),
 
@@ -139,7 +143,7 @@ pub enum Ty {
     /// when we have tried to normalize a projection like `T::Item` but
     /// couldn't find a better representation.  In that case, we generate
     /// an **application type** like `(Iterator::Item)<T>`.
-    AssociatedType(TypeAliasId, Substs),
+    AssociatedType(AssocTypeId, Substs),
 
     /// a scalar type like `bool` or `u32`
     Scalar(Scalar),
@@ -148,17 +152,17 @@ pub enum Ty {
     Tuple(usize, Substs),
 
     /// An array with the given length. Written as `[T; n]`.
-    Array(Substs),
+    Array(Ty),
 
     /// The pointee of an array slice.  Written as `[T]`.
-    Slice(Substs),
+    Slice(Ty),
 
     /// A raw pointer. Written as `*mut T` or `*const T`
-    Raw(Mutability, Substs),
+    Raw(Mutability, Ty),
 
     /// A reference; a pointer with an associated lifetime. Written as
     /// `&'a mut T` or `&'a T`.
-    Ref(Mutability, Substs),
+    Ref(Mutability, Ty),
 
     /// This represents a placeholder for an opaque type in situations where we
     /// don't know the hidden type (i.e. currently almost always). This is
@@ -179,7 +183,7 @@ pub enum Ty {
     /// fn foo() -> i32 { 1 }
     /// let bar = foo; // bar: fn() -> i32 {foo}
     /// ```
-    FnDef(CallableDefId, Substs),
+    FnDef(FnDefId, Substs),
 
     /// The pointee of a string slice. Written as `str`.
     Str,
@@ -191,10 +195,10 @@ pub enum Ty {
     ///
     /// The closure signature is stored in a `FnPtr` type in the first type
     /// parameter.
-    Closure(DefWithBodyId, ExprId, Substs),
+    Closure(ClosureId, Substs),
 
     /// Represents a foreign type declared in external blocks.
-    ForeignType(TypeAliasId),
+    ForeignType(ForeignDefId),
 
     /// A pointer to a function.  Written as `fn() -> i32`.
     ///
@@ -216,7 +220,7 @@ pub enum Ty {
     /// {}` when we're type-checking the body of that function. In this
     /// situation, we know this stands for *some* type, but don't know the exact
     /// type.
-    Placeholder(TypeParamId),
+    Placeholder(PlaceholderIndex),
 
     /// A bound type variable. This is used in various places: when representing
     /// some polymorphic type like the type of function `fn f<T>`, the type
@@ -244,9 +248,32 @@ pub enum Ty {
     Unknown,
 }
 
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
+pub struct Ty(Arc<TyKind>);
+
+impl TyKind {
+    pub fn intern(self, _interner: &Interner) -> Ty {
+        Ty(Arc::new(self))
+    }
+}
+
+impl Ty {
+    pub fn interned(&self, _interner: &Interner) -> &TyKind {
+        &self.0
+    }
+
+    pub fn interned_mut(&mut self) -> &mut TyKind {
+        Arc::make_mut(&mut self.0)
+    }
+
+    pub fn into_inner(self) -> TyKind {
+        Arc::try_unwrap(self.0).unwrap_or_else(|a| (*a).clone())
+    }
+}
+
 /// A list of substitutions for generic parameters.
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
-pub struct Substs(Arc<[Ty]>);
+pub struct Substs(SmallVec<[Ty; 2]>);
 
 impl TypeWalk for Substs {
     fn walk(&self, f: &mut impl FnMut(&Ty)) {
@@ -260,19 +287,27 @@ impl TypeWalk for Substs {
         f: &mut impl FnMut(&mut Ty, DebruijnIndex),
         binders: DebruijnIndex,
     ) {
-        for t in make_mut_slice(&mut self.0) {
+        for t in &mut self.0 {
             t.walk_mut_binders(f, binders);
         }
     }
 }
 
 impl Substs {
+    pub fn interned(&self, _: &Interner) -> &[Ty] {
+        &self.0
+    }
+
     pub fn empty() -> Substs {
-        Substs(Arc::new([]))
+        Substs(SmallVec::new())
     }
 
     pub fn single(ty: Ty) -> Substs {
-        Substs(Arc::new([ty]))
+        Substs({
+            let mut v = SmallVec::new();
+            v.push(ty);
+            v
+        })
     }
 
     pub fn prefix(&self, n: usize) -> Substs {
@@ -290,15 +325,27 @@ impl Substs {
         &self.0[0]
     }
 
+    pub fn from_iter(_interner: &Interner, elements: impl IntoIterator<Item = Ty>) -> Self {
+        Substs(elements.into_iter().collect())
+    }
+
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub(crate) fn type_params_for_generics(generic_params: &Generics) -> Substs {
-        Substs(generic_params.iter().map(|(id, _)| Ty::Placeholder(id)).collect())
+    pub(crate) fn type_params_for_generics(
+        db: &dyn HirDatabase,
+        generic_params: &Generics,
+    ) -> Substs {
+        Substs(
+            generic_params
+                .iter()
+                .map(|(id, _)| TyKind::Placeholder(to_placeholder_idx(db, id)).intern(&Interner))
+                .collect(),
+        )
     }
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
     pub fn type_params(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> Substs {
         let params = generics(db.upcast(), def.into());
-        Substs::type_params_for_generics(&params)
+        Substs::type_params_for_generics(db, &params)
     }
 
     /// Return Substs that replace each parameter by a bound variable.
@@ -307,7 +354,7 @@ impl Substs {
             generic_params
                 .iter()
                 .enumerate()
-                .map(|(idx, _)| Ty::BoundVar(BoundVar::new(debruijn, idx)))
+                .map(|(idx, _)| TyKind::BoundVar(BoundVar::new(debruijn, idx)).intern(&Interner))
                 .collect(),
         )
     }
@@ -355,11 +402,14 @@ impl SubstsBuilder {
     }
 
     pub fn fill_with_bound_vars(self, debruijn: DebruijnIndex, starting_from: usize) -> Self {
-        self.fill((starting_from..).map(|idx| Ty::BoundVar(BoundVar::new(debruijn, idx))))
+        self.fill(
+            (starting_from..)
+                .map(|idx| TyKind::BoundVar(BoundVar::new(debruijn, idx)).intern(&Interner)),
+        )
     }
 
     pub fn fill_with_unknown(self) -> Self {
-        self.fill(iter::repeat(Ty::Unknown))
+        self.fill(iter::repeat(TyKind::Unknown.intern(&Interner)))
     }
 
     pub fn fill(mut self, filler: impl Iterator<Item = Ty>) -> Self {
@@ -563,13 +613,13 @@ impl CallableSig {
 
     pub fn from_fn_ptr(fn_ptr: &FnPointer) -> CallableSig {
         CallableSig {
-            params_and_return: Arc::clone(&fn_ptr.substs.0),
+            params_and_return: fn_ptr.substs.interned(&Interner).iter().cloned().collect(),
             is_varargs: fn_ptr.sig.variadic,
         }
     }
 
     pub fn from_substs(substs: &Substs) -> CallableSig {
-        CallableSig { params_and_return: Arc::clone(&substs.0), is_varargs: false }
+        CallableSig { params_and_return: substs.iter().cloned().collect(), is_varargs: false }
     }
 
     pub fn params(&self) -> &[Ty] {
@@ -601,47 +651,50 @@ impl TypeWalk for CallableSig {
 
 impl Ty {
     pub fn unit() -> Self {
-        Ty::Tuple(0, Substs::empty())
+        TyKind::Tuple(0, Substs::empty()).intern(&Interner)
     }
 
     pub fn adt_ty(adt: hir_def::AdtId, substs: Substs) -> Ty {
-        Ty::Adt(AdtId(adt), substs)
+        TyKind::Adt(AdtId(adt), substs).intern(&Interner)
     }
 
     pub fn fn_ptr(sig: CallableSig) -> Self {
-        Ty::Function(FnPointer {
+        TyKind::Function(FnPointer {
             num_args: sig.params().len(),
-            sig: FnSig { variadic: sig.is_varargs },
-            substs: Substs(sig.params_and_return),
+            sig: FnSig { abi: (), safety: Safety::Safe, variadic: sig.is_varargs },
+            substs: Substs::from_iter(&Interner, sig.params_and_return.iter().cloned()),
         })
+        .intern(&Interner)
     }
 
     pub fn builtin(builtin: BuiltinType) -> Self {
         match builtin {
-            BuiltinType::Char => Ty::Scalar(Scalar::Char),
-            BuiltinType::Bool => Ty::Scalar(Scalar::Bool),
-            BuiltinType::Str => Ty::Str,
-            BuiltinType::Int(t) => Ty::Scalar(Scalar::Int(primitive::int_ty_from_builtin(t))),
-            BuiltinType::Uint(t) => Ty::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(t))),
-            BuiltinType::Float(t) => Ty::Scalar(Scalar::Float(primitive::float_ty_from_builtin(t))),
+            BuiltinType::Char => TyKind::Scalar(Scalar::Char).intern(&Interner),
+            BuiltinType::Bool => TyKind::Scalar(Scalar::Bool).intern(&Interner),
+            BuiltinType::Str => TyKind::Str.intern(&Interner),
+            BuiltinType::Int(t) => {
+                TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(t))).intern(&Interner)
+            }
+            BuiltinType::Uint(t) => {
+                TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(t))).intern(&Interner)
+            }
+            BuiltinType::Float(t) => {
+                TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(t))).intern(&Interner)
+            }
         }
     }
 
     pub fn as_reference(&self) -> Option<(&Ty, Mutability)> {
-        match self {
-            Ty::Ref(mutability, parameters) => Some((parameters.as_single(), *mutability)),
+        match self.interned(&Interner) {
+            TyKind::Ref(mutability, ty) => Some((ty, *mutability)),
             _ => None,
         }
     }
 
     pub fn as_reference_or_ptr(&self) -> Option<(&Ty, Rawness, Mutability)> {
-        match self {
-            Ty::Ref(mutability, parameters) => {
-                Some((parameters.as_single(), Rawness::Ref, *mutability))
-            }
-            Ty::Raw(mutability, parameters) => {
-                Some((parameters.as_single(), Rawness::RawPtr, *mutability))
-            }
+        match self.interned(&Interner) {
+            TyKind::Ref(mutability, ty) => Some((ty, Rawness::Ref, *mutability)),
+            TyKind::Raw(mutability, ty) => Some((ty, Rawness::RawPtr, *mutability)),
             _ => None,
         }
     }
@@ -649,73 +702,79 @@ impl Ty {
     pub fn strip_references(&self) -> &Ty {
         let mut t: &Ty = self;
 
-        while let Ty::Ref(_mutability, parameters) = t {
-            t = parameters.as_single();
+        while let TyKind::Ref(_mutability, ty) = t.interned(&Interner) {
+            t = ty;
         }
 
         t
     }
 
     pub fn as_adt(&self) -> Option<(hir_def::AdtId, &Substs)> {
-        match self {
-            Ty::Adt(AdtId(adt), parameters) => Some((*adt, parameters)),
+        match self.interned(&Interner) {
+            TyKind::Adt(AdtId(adt), parameters) => Some((*adt, parameters)),
             _ => None,
         }
     }
 
     pub fn as_tuple(&self) -> Option<&Substs> {
-        match self {
-            Ty::Tuple(_, substs) => Some(substs),
+        match self.interned(&Interner) {
+            TyKind::Tuple(_, substs) => Some(substs),
             _ => None,
         }
     }
 
-    pub fn as_generic_def(&self) -> Option<GenericDefId> {
-        match *self {
-            Ty::Adt(AdtId(adt), ..) => Some(adt.into()),
-            Ty::FnDef(callable, ..) => Some(callable.into()),
-            Ty::AssociatedType(type_alias, ..) => Some(type_alias.into()),
-            Ty::ForeignType(type_alias, ..) => Some(type_alias.into()),
+    pub fn as_generic_def(&self, db: &dyn HirDatabase) -> Option<GenericDefId> {
+        match *self.interned(&Interner) {
+            TyKind::Adt(AdtId(adt), ..) => Some(adt.into()),
+            TyKind::FnDef(callable, ..) => {
+                Some(db.lookup_intern_callable_def(callable.into()).into())
+            }
+            TyKind::AssociatedType(type_alias, ..) => Some(from_assoc_type_id(type_alias).into()),
+            TyKind::ForeignType(type_alias, ..) => Some(from_foreign_def_id(type_alias).into()),
             _ => None,
         }
     }
 
     pub fn is_never(&self) -> bool {
-        matches!(self, Ty::Never)
+        matches!(self.interned(&Interner), TyKind::Never)
     }
 
     pub fn is_unknown(&self) -> bool {
-        matches!(self, Ty::Unknown)
+        matches!(self.interned(&Interner), TyKind::Unknown)
     }
 
     pub fn equals_ctor(&self, other: &Ty) -> bool {
-        match (self, other) {
-            (Ty::Adt(adt, ..), Ty::Adt(adt2, ..)) => adt == adt2,
-            (Ty::Slice(_), Ty::Slice(_)) | (Ty::Array(_), Ty::Array(_)) => true,
-            (Ty::FnDef(def_id, ..), Ty::FnDef(def_id2, ..)) => def_id == def_id2,
-            (Ty::OpaqueType(ty_id, ..), Ty::OpaqueType(ty_id2, ..)) => ty_id == ty_id2,
-            (Ty::AssociatedType(ty_id, ..), Ty::AssociatedType(ty_id2, ..))
-            | (Ty::ForeignType(ty_id, ..), Ty::ForeignType(ty_id2, ..)) => ty_id == ty_id2,
-            (Ty::Closure(def, expr, _), Ty::Closure(def2, expr2, _)) => {
-                expr == expr2 && def == def2
+        match (self.interned(&Interner), other.interned(&Interner)) {
+            (TyKind::Adt(adt, ..), TyKind::Adt(adt2, ..)) => adt == adt2,
+            (TyKind::Slice(_), TyKind::Slice(_)) | (TyKind::Array(_), TyKind::Array(_)) => true,
+            (TyKind::FnDef(def_id, ..), TyKind::FnDef(def_id2, ..)) => def_id == def_id2,
+            (TyKind::OpaqueType(ty_id, ..), TyKind::OpaqueType(ty_id2, ..)) => ty_id == ty_id2,
+            (TyKind::AssociatedType(ty_id, ..), TyKind::AssociatedType(ty_id2, ..)) => {
+                ty_id == ty_id2
+            }
+            (TyKind::ForeignType(ty_id, ..), TyKind::ForeignType(ty_id2, ..)) => ty_id == ty_id2,
+            (TyKind::Closure(id1, _), TyKind::Closure(id2, _)) => id1 == id2,
+            (TyKind::Ref(mutability, ..), TyKind::Ref(mutability2, ..))
+            | (TyKind::Raw(mutability, ..), TyKind::Raw(mutability2, ..)) => {
+                mutability == mutability2
             }
-            (Ty::Ref(mutability, ..), Ty::Ref(mutability2, ..))
-            | (Ty::Raw(mutability, ..), Ty::Raw(mutability2, ..)) => mutability == mutability2,
             (
-                Ty::Function(FnPointer { num_args, sig, .. }),
-                Ty::Function(FnPointer { num_args: num_args2, sig: sig2, .. }),
+                TyKind::Function(FnPointer { num_args, sig, .. }),
+                TyKind::Function(FnPointer { num_args: num_args2, sig: sig2, .. }),
             ) => num_args == num_args2 && sig == sig2,
-            (Ty::Tuple(cardinality, _), Ty::Tuple(cardinality2, _)) => cardinality == cardinality2,
-            (Ty::Str, Ty::Str) | (Ty::Never, Ty::Never) => true,
-            (Ty::Scalar(scalar), Ty::Scalar(scalar2)) => scalar == scalar2,
+            (TyKind::Tuple(cardinality, _), TyKind::Tuple(cardinality2, _)) => {
+                cardinality == cardinality2
+            }
+            (TyKind::Str, TyKind::Str) | (TyKind::Never, TyKind::Never) => true,
+            (TyKind::Scalar(scalar), TyKind::Scalar(scalar2)) => scalar == scalar2,
             _ => false,
         }
     }
 
     /// If this is a `dyn Trait` type, this returns the `Trait` part.
     pub fn dyn_trait_ref(&self) -> Option<&TraitRef> {
-        match self {
-            Ty::Dyn(bounds) => bounds.get(0).and_then(|b| match b {
+        match self.interned(&Interner) {
+            TyKind::Dyn(bounds) => bounds.get(0).and_then(|b| match b {
                 GenericPredicate::Implemented(trait_ref) => Some(trait_ref),
                 _ => None,
             }),
@@ -729,28 +788,37 @@ impl Ty {
     }
 
     fn builtin_deref(&self) -> Option<Ty> {
-        match self {
-            Ty::Ref(.., parameters) => Some(Ty::clone(parameters.as_single())),
-            Ty::Raw(.., parameters) => Some(Ty::clone(parameters.as_single())),
+        match self.interned(&Interner) {
+            TyKind::Ref(.., ty) => Some(ty.clone()),
+            TyKind::Raw(.., ty) => Some(ty.clone()),
             _ => None,
         }
     }
 
-    pub fn as_fn_def(&self) -> Option<FunctionId> {
-        match self {
-            &Ty::FnDef(CallableDefId::FunctionId(func), ..) => Some(func),
+    pub fn callable_def(&self, db: &dyn HirDatabase) -> Option<CallableDefId> {
+        match self.interned(&Interner) {
+            &TyKind::FnDef(def, ..) => Some(db.lookup_intern_callable_def(def.into())),
             _ => None,
         }
     }
 
+    pub fn as_fn_def(&self, db: &dyn HirDatabase) -> Option<FunctionId> {
+        if let Some(CallableDefId::FunctionId(func)) = self.callable_def(db) {
+            Some(func)
+        } else {
+            None
+        }
+    }
+
     pub fn callable_sig(&self, db: &dyn HirDatabase) -> Option<CallableSig> {
-        match self {
-            Ty::Function(fn_ptr) => Some(CallableSig::from_fn_ptr(fn_ptr)),
-            Ty::FnDef(def, parameters) => {
-                let sig = db.callable_item_signature(*def);
+        match self.interned(&Interner) {
+            TyKind::Function(fn_ptr) => Some(CallableSig::from_fn_ptr(fn_ptr)),
+            TyKind::FnDef(def, parameters) => {
+                let callable_def = db.lookup_intern_callable_def((*def).into());
+                let sig = db.callable_item_signature(callable_def);
                 Some(sig.subst(&parameters))
             }
-            Ty::Closure(.., substs) => {
+            TyKind::Closure(.., substs) => {
                 let sig_param = &substs[0];
                 sig_param.callable_sig(db)
             }
@@ -758,72 +826,39 @@ impl Ty {
         }
     }
 
-    /// If this is a type with type parameters (an ADT or function), replaces
-    /// the `Substs` for these type parameters with the given ones. (So e.g. if
-    /// `self` is `Option<_>` and the substs contain `u32`, we'll have
-    /// `Option<u32>` afterwards.)
-    pub fn apply_substs(mut self, new_substs: Substs) -> Ty {
-        match &mut self {
-            Ty::Adt(_, substs)
-            | Ty::Slice(substs)
-            | Ty::Array(substs)
-            | Ty::Raw(_, substs)
-            | Ty::Ref(_, substs)
-            | Ty::FnDef(_, substs)
-            | Ty::Function(FnPointer { substs, .. })
-            | Ty::Tuple(_, substs)
-            | Ty::OpaqueType(_, substs)
-            | Ty::AssociatedType(_, substs)
-            | Ty::Closure(.., substs) => {
-                assert_eq!(substs.len(), new_substs.len());
-                *substs = new_substs;
-            }
-            _ => (),
-        }
-        self
-    }
-
     /// Returns the type parameters of this type if it has some (i.e. is an ADT
     /// or function); so if `self` is `Option<u32>`, this returns the `u32`.
     pub fn substs(&self) -> Option<&Substs> {
-        match self {
-            Ty::Adt(_, substs)
-            | Ty::Slice(substs)
-            | Ty::Array(substs)
-            | Ty::Raw(_, substs)
-            | Ty::Ref(_, substs)
-            | Ty::FnDef(_, substs)
-            | Ty::Function(FnPointer { substs, .. })
-            | Ty::Tuple(_, substs)
-            | Ty::OpaqueType(_, substs)
-            | Ty::AssociatedType(_, substs)
-            | Ty::Closure(.., substs) => Some(substs),
+        match self.interned(&Interner) {
+            TyKind::Adt(_, substs)
+            | TyKind::FnDef(_, substs)
+            | TyKind::Function(FnPointer { substs, .. })
+            | TyKind::Tuple(_, substs)
+            | TyKind::OpaqueType(_, substs)
+            | TyKind::AssociatedType(_, substs)
+            | TyKind::Closure(.., substs) => Some(substs),
             _ => None,
         }
     }
 
-    pub fn substs_mut(&mut self) -> Option<&mut Substs> {
-        match self {
-            Ty::Adt(_, substs)
-            | Ty::Slice(substs)
-            | Ty::Array(substs)
-            | Ty::Raw(_, substs)
-            | Ty::Ref(_, substs)
-            | Ty::FnDef(_, substs)
-            | Ty::Function(FnPointer { substs, .. })
-            | Ty::Tuple(_, substs)
-            | Ty::OpaqueType(_, substs)
-            | Ty::AssociatedType(_, substs)
-            | Ty::Closure(.., substs) => Some(substs),
+    fn substs_mut(&mut self) -> Option<&mut Substs> {
+        match self.interned_mut() {
+            TyKind::Adt(_, substs)
+            | TyKind::FnDef(_, substs)
+            | TyKind::Function(FnPointer { substs, .. })
+            | TyKind::Tuple(_, substs)
+            | TyKind::OpaqueType(_, substs)
+            | TyKind::AssociatedType(_, substs)
+            | TyKind::Closure(.., substs) => Some(substs),
             _ => None,
         }
     }
 
     pub fn impl_trait_bounds(&self, db: &dyn HirDatabase) -> Option<Vec<GenericPredicate>> {
-        match self {
-            Ty::OpaqueType(opaque_ty_id, ..) => {
-                match opaque_ty_id {
-                    OpaqueTyId::AsyncBlockTypeImplTrait(def, _expr) => {
+        match self.interned(&Interner) {
+            TyKind::OpaqueType(opaque_ty_id, ..) => {
+                match db.lookup_intern_impl_trait_id((*opaque_ty_id).into()) {
+                    ImplTraitId::AsyncBlockTypeImplTrait(def, _expr) => {
                         let krate = def.module(db.upcast()).krate();
                         if let Some(future_trait) = db
                             .lang_item(krate, "future_trait".into())
@@ -841,32 +876,34 @@ impl Ty {
                             None
                         }
                     }
-                    OpaqueTyId::ReturnTypeImplTrait(..) => None,
+                    ImplTraitId::ReturnTypeImplTrait(..) => None,
                 }
             }
-            Ty::Alias(AliasTy::Opaque(opaque_ty)) => {
-                let predicates = match opaque_ty.opaque_ty_id {
-                    OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+            TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
+                let predicates = match db.lookup_intern_impl_trait_id(opaque_ty.opaque_ty_id.into())
+                {
+                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                         db.return_type_impl_traits(func).map(|it| {
                             let data = (*it)
                                 .as_ref()
                                 .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
-                            data.subst(&opaque_ty.parameters)
+                            data.subst(&opaque_ty.substitution)
                         })
                     }
                     // It always has an parameter for Future::Output type.
-                    OpaqueTyId::AsyncBlockTypeImplTrait(..) => unreachable!(),
+                    ImplTraitId::AsyncBlockTypeImplTrait(..) => unreachable!(),
                 };
 
                 predicates.map(|it| it.value)
             }
-            Ty::Placeholder(id) => {
+            TyKind::Placeholder(idx) => {
+                let id = from_placeholder_idx(db, *idx);
                 let generic_params = db.generic_params(id.parent);
                 let param_data = &generic_params.types[id.local_id];
                 match param_data.provenance {
                     hir_def::generics::TypeParamProvenance::ArgumentImplTrait => {
                         let predicates = db
-                            .generic_predicates_for_param(*id)
+                            .generic_predicates_for_param(id)
                             .into_iter()
                             .map(|pred| pred.value.clone())
                             .collect_vec();
@@ -881,15 +918,18 @@ impl Ty {
     }
 
     pub fn associated_type_parent_trait(&self, db: &dyn HirDatabase) -> Option<TraitId> {
-        match self {
-            Ty::AssociatedType(type_alias_id, ..) => {
-                match type_alias_id.lookup(db.upcast()).container {
+        match self.interned(&Interner) {
+            TyKind::AssociatedType(id, ..) => {
+                match from_assoc_type_id(*id).lookup(db.upcast()).container {
                     AssocContainerId::TraitId(trait_id) => Some(trait_id),
                     _ => None,
                 }
             }
-            Ty::Alias(AliasTy::Projection(projection_ty)) => {
-                match projection_ty.associated_ty.lookup(db.upcast()).container {
+            TyKind::Alias(AliasTy::Projection(projection_ty)) => {
+                match from_assoc_type_id(projection_ty.associated_ty_id)
+                    .lookup(db.upcast())
+                    .container
+                {
                     AssocContainerId::TraitId(trait_id) => Some(trait_id),
                     _ => None,
                 }
@@ -908,13 +948,13 @@ pub trait TypeWalk {
     }
     /// Walk the type, counting entered binders.
     ///
-    /// `Ty::Bound` variables use DeBruijn indexing, which means that 0 refers
+    /// `TyKind::Bound` variables use DeBruijn indexing, which means that 0 refers
     /// to the innermost binder, 1 to the next, etc.. So when we want to
     /// substitute a certain bound variable, we can't just walk the whole type
     /// and blindly replace each instance of a certain index; when we 'enter'
     /// things that introduce new bound variables, we have to keep track of
     /// that. Currently, the only thing that introduces bound variables on our
-    /// side are `Ty::Dyn` and `Ty::Opaque`, which each introduce a bound
+    /// side are `TyKind::Dyn` and `TyKind::Opaque`, which each introduce a bound
     /// variable for the self type.
     fn walk_mut_binders(
         &mut self,
@@ -932,7 +972,7 @@ pub trait TypeWalk {
     {
         self.walk_mut_binders(
             &mut |ty_mut, binders| {
-                let ty = mem::replace(ty_mut, Ty::Unknown);
+                let ty = mem::replace(ty_mut, TyKind::Unknown.intern(&Interner));
                 *ty_mut = f(ty, binders);
             },
             binders,
@@ -945,13 +985,13 @@ pub trait TypeWalk {
         Self: Sized,
     {
         self.walk_mut(&mut |ty_mut| {
-            let ty = mem::replace(ty_mut, Ty::Unknown);
+            let ty = mem::replace(ty_mut, TyKind::Unknown.intern(&Interner));
             *ty_mut = f(ty);
         });
         self
     }
 
-    /// Substitutes `Ty::Bound` vars with the given substitution.
+    /// Substitutes `TyKind::Bound` vars with the given substitution.
     fn subst_bound_vars(self, substs: &Substs) -> Self
     where
         Self: Sized,
@@ -959,14 +999,14 @@ pub trait TypeWalk {
         self.subst_bound_vars_at_depth(substs, DebruijnIndex::INNERMOST)
     }
 
-    /// Substitutes `Ty::Bound` vars with the given substitution.
+    /// Substitutes `TyKind::Bound` vars with the given substitution.
     fn subst_bound_vars_at_depth(mut self, substs: &Substs, depth: DebruijnIndex) -> Self
     where
         Self: Sized,
     {
         self.walk_mut_binders(
             &mut |ty, binders| {
-                if let &mut Ty::BoundVar(bound) = ty {
+                if let &mut TyKind::BoundVar(bound) = ty.interned_mut() {
                     if bound.debruijn >= binders {
                         *ty = substs.0[bound.index].clone().shift_bound_vars(binders);
                     }
@@ -977,17 +1017,17 @@ pub trait TypeWalk {
         self
     }
 
-    /// Shifts up debruijn indices of `Ty::Bound` vars by `n`.
+    /// Shifts up debruijn indices of `TyKind::Bound` vars by `n`.
     fn shift_bound_vars(self, n: DebruijnIndex) -> Self
     where
         Self: Sized,
     {
         self.fold_binders(
-            &mut |ty, binders| match ty {
-                Ty::BoundVar(bound) if bound.debruijn >= binders => {
-                    Ty::BoundVar(bound.shifted_in_from(n))
+            &mut |ty, binders| match ty.interned(&Interner) {
+                TyKind::BoundVar(bound) if bound.debruijn >= binders => {
+                    TyKind::BoundVar(bound.shifted_in_from(n)).intern(&Interner)
                 }
-                ty => ty,
+                _ => ty,
             },
             DebruijnIndex::INNERMOST,
         )
@@ -996,22 +1036,25 @@ pub trait TypeWalk {
 
 impl TypeWalk for Ty {
     fn walk(&self, f: &mut impl FnMut(&Ty)) {
-        match self {
-            Ty::Alias(AliasTy::Projection(p_ty)) => {
-                for t in p_ty.parameters.iter() {
+        match self.interned(&Interner) {
+            TyKind::Alias(AliasTy::Projection(p_ty)) => {
+                for t in p_ty.substitution.iter() {
                     t.walk(f);
                 }
             }
-            Ty::Alias(AliasTy::Opaque(o_ty)) => {
-                for t in o_ty.parameters.iter() {
+            TyKind::Alias(AliasTy::Opaque(o_ty)) => {
+                for t in o_ty.substitution.iter() {
                     t.walk(f);
                 }
             }
-            Ty::Dyn(predicates) => {
+            TyKind::Dyn(predicates) => {
                 for p in predicates.iter() {
                     p.walk(f);
                 }
             }
+            TyKind::Slice(ty) | TyKind::Array(ty) | TyKind::Ref(_, ty) | TyKind::Raw(_, ty) => {
+                ty.walk(f);
+            }
             _ => {
                 if let Some(substs) = self.substs() {
                     for t in substs.iter() {
@@ -1028,17 +1071,20 @@ impl TypeWalk for Ty {
         f: &mut impl FnMut(&mut Ty, DebruijnIndex),
         binders: DebruijnIndex,
     ) {
-        match self {
-            Ty::Alias(AliasTy::Projection(p_ty)) => {
-                p_ty.parameters.walk_mut_binders(f, binders);
+        match self.interned_mut() {
+            TyKind::Alias(AliasTy::Projection(p_ty)) => {
+                p_ty.substitution.walk_mut_binders(f, binders);
             }
-            Ty::Dyn(predicates) => {
+            TyKind::Dyn(predicates) => {
                 for p in make_mut_slice(predicates) {
                     p.walk_mut_binders(f, binders.shifted_in());
                 }
             }
-            Ty::Alias(AliasTy::Opaque(o_ty)) => {
-                o_ty.parameters.walk_mut_binders(f, binders);
+            TyKind::Alias(AliasTy::Opaque(o_ty)) => {
+                o_ty.substitution.walk_mut_binders(f, binders);
+            }
+            TyKind::Slice(ty) | TyKind::Array(ty) | TyKind::Ref(_, ty) | TyKind::Raw(_, ty) => {
+                ty.walk_mut_binders(f, binders);
             }
             _ => {
                 if let Some(substs) = self.substs_mut() {
@@ -1068,7 +1114,7 @@ impl<T: TypeWalk> TypeWalk for Vec<T> {
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
-pub enum OpaqueTyId {
+pub enum ImplTraitId {
     ReturnTypeImplTrait(hir_def::FunctionId, u16),
     AsyncBlockTypeImplTrait(hir_def::DefWithBodyId, ExprId),
 }
@@ -1082,3 +1128,33 @@ pub struct ReturnTypeImplTraits {
 pub(crate) struct ReturnTypeImplTrait {
     pub(crate) bounds: Binders<Vec<GenericPredicate>>,
 }
+
+pub fn to_foreign_def_id(id: TypeAliasId) -> ForeignDefId {
+    chalk_ir::ForeignDefId(salsa::InternKey::as_intern_id(&id))
+}
+
+pub fn from_foreign_def_id(id: ForeignDefId) -> TypeAliasId {
+    salsa::InternKey::from_intern_id(id.0)
+}
+
+pub fn to_assoc_type_id(id: TypeAliasId) -> AssocTypeId {
+    chalk_ir::AssocTypeId(salsa::InternKey::as_intern_id(&id))
+}
+
+pub fn from_assoc_type_id(id: AssocTypeId) -> TypeAliasId {
+    salsa::InternKey::from_intern_id(id.0)
+}
+
+pub fn from_placeholder_idx(db: &dyn HirDatabase, idx: PlaceholderIndex) -> TypeParamId {
+    assert_eq!(idx.ui, chalk_ir::UniverseIndex::ROOT);
+    let interned_id = salsa::InternKey::from_intern_id(salsa::InternId::from(idx.idx));
+    db.lookup_intern_type_param_id(interned_id)
+}
+
+pub fn to_placeholder_idx(db: &dyn HirDatabase, id: TypeParamId) -> PlaceholderIndex {
+    let interned_id = db.intern_type_param_id(id);
+    PlaceholderIndex {
+        ui: chalk_ir::UniverseIndex::ROOT,
+        idx: salsa::InternKey::as_intern_id(&interned_id).as_usize(),
+    }
+}
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index d84ec9b7a..6ab757bfc 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -8,7 +8,7 @@
 use std::{iter, sync::Arc};
 
 use base_db::CrateId;
-use chalk_ir::{cast::Cast, Mutability};
+use chalk_ir::{cast::Cast, Mutability, Safety};
 use hir_def::{
     adt::StructKind,
     builtin_type::BuiltinType,
@@ -27,14 +27,15 @@ use stdx::impl_from;
 
 use crate::{
     db::HirDatabase,
+    to_assoc_type_id, to_placeholder_idx,
     traits::chalk::{Interner, ToChalk},
     utils::{
         all_super_trait_refs, associated_type_by_name_including_super_traits, generics,
-        make_mut_slice, variant_data,
+        variant_data,
     },
     AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, FnPointer, FnSig, GenericPredicate,
-    OpaqueTy, OpaqueTyId, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
-    ReturnTypeImplTraits, Substs, TraitEnvironment, TraitRef, Ty, TypeWalk,
+    ImplTraitId, OpaqueTy, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
+    ReturnTypeImplTraits, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeWalk,
 };
 
 #[derive(Debug)]
@@ -139,69 +140,70 @@ pub enum TypeParamLoweringMode {
     Variable,
 }
 
-impl Ty {
-    pub fn from_hir(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Self {
-        Ty::from_hir_ext(ctx, type_ref).0
+impl<'a> TyLoweringContext<'a> {
+    pub fn lower_ty(&self, type_ref: &TypeRef) -> Ty {
+        self.lower_ty_ext(type_ref).0
     }
-    pub fn from_hir_ext(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> (Self, Option<TypeNs>) {
+
+    fn lower_ty_ext(&self, type_ref: &TypeRef) -> (Ty, Option<TypeNs>) {
         let mut res = None;
         let ty = match type_ref {
-            TypeRef::Never => Ty::Never,
+            TypeRef::Never => TyKind::Never.intern(&Interner),
             TypeRef::Tuple(inner) => {
-                let inner_tys: Arc<[Ty]> = inner.iter().map(|tr| Ty::from_hir(ctx, tr)).collect();
-                Ty::Tuple(inner_tys.len(), Substs(inner_tys))
+                let inner_tys = inner.iter().map(|tr| self.lower_ty(tr));
+                TyKind::Tuple(inner_tys.len(), Substs::from_iter(&Interner, inner_tys))
+                    .intern(&Interner)
             }
             TypeRef::Path(path) => {
-                let (ty, res_) = Ty::from_hir_path(ctx, path);
+                let (ty, res_) = self.lower_path(path);
                 res = res_;
                 ty
             }
             TypeRef::RawPtr(inner, mutability) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                Ty::Raw(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Raw(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
             }
             TypeRef::Array(inner) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                Ty::Array(Substs::single(inner_ty))
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Array(inner_ty).intern(&Interner)
             }
             TypeRef::Slice(inner) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                Ty::Slice(Substs::single(inner_ty))
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Slice(inner_ty).intern(&Interner)
             }
             TypeRef::Reference(inner, _, mutability) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                Ty::Ref(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Ref(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
             }
-            TypeRef::Placeholder => Ty::Unknown,
+            TypeRef::Placeholder => TyKind::Unknown.intern(&Interner),
             TypeRef::Fn(params, is_varargs) => {
-                let substs = Substs(params.iter().map(|tr| Ty::from_hir(ctx, tr)).collect());
-                Ty::Function(FnPointer {
+                let substs = Substs(params.iter().map(|tr| self.lower_ty(tr)).collect());
+                TyKind::Function(FnPointer {
                     num_args: substs.len() - 1,
-                    sig: FnSig { variadic: *is_varargs },
+                    sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
                     substs,
                 })
+                .intern(&Interner)
             }
             TypeRef::DynTrait(bounds) => {
-                let self_ty = Ty::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0));
-                let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
-                    bounds
-                        .iter()
-                        .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
-                        .collect()
+                let self_ty =
+                    TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
+                let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
+                    bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone())).collect()
                 });
-                Ty::Dyn(predicates)
+                TyKind::Dyn(predicates).intern(&Interner)
             }
             TypeRef::ImplTrait(bounds) => {
-                match ctx.impl_trait_mode {
+                match self.impl_trait_mode {
                     ImplTraitLoweringMode::Opaque => {
-                        let idx = ctx.impl_trait_counter.get();
-                        ctx.impl_trait_counter.set(idx + 1);
+                        let idx = self.impl_trait_counter.get();
+                        self.impl_trait_counter.set(idx + 1);
 
-                        assert!(idx as usize == ctx.opaque_type_data.borrow().len());
+                        assert!(idx as usize == self.opaque_type_data.borrow().len());
                         // this dance is to make sure the data is in the right
                         // place even if we encounter more opaque types while
                         // lowering the bounds
-                        ctx.opaque_type_data
+                        self.opaque_type_data
                             .borrow_mut()
                             .push(ReturnTypeImplTrait { bounds: Binders::new(1, Vec::new()) });
                         // We don't want to lower the bounds inside the binders
@@ -213,65 +215,70 @@ impl Ty {
                         // other, but separately. So if the `T` refers to a type
                         // parameter of the outer function, it's just one binder
                         // away instead of two.
-                        let actual_opaque_type_data = ctx
+                        let actual_opaque_type_data = self
                             .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
-                                ReturnTypeImplTrait::from_hir(ctx, &bounds)
+                                ctx.lower_impl_trait(&bounds)
                             });
-                        ctx.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
+                        self.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
 
-                        let func = match ctx.resolver.generic_def() {
+                        let func = match self.resolver.generic_def() {
                             Some(GenericDefId::FunctionId(f)) => f,
                             _ => panic!("opaque impl trait lowering in non-function"),
                         };
-                        let impl_trait_id = OpaqueTyId::ReturnTypeImplTrait(func, idx);
-                        let generics = generics(ctx.db.upcast(), func.into());
-                        let parameters = Substs::bound_vars(&generics, ctx.in_binders);
-                        Ty::Alias(AliasTy::Opaque(OpaqueTy {
-                            opaque_ty_id: impl_trait_id,
-                            parameters,
+                        let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
+                        let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
+                        let generics = generics(self.db.upcast(), func.into());
+                        let parameters = Substs::bound_vars(&generics, self.in_binders);
+                        TyKind::Alias(AliasTy::Opaque(OpaqueTy {
+                            opaque_ty_id,
+                            substitution: parameters,
                         }))
+                        .intern(&Interner)
                     }
                     ImplTraitLoweringMode::Param => {
-                        let idx = ctx.impl_trait_counter.get();
+                        let idx = self.impl_trait_counter.get();
                         // FIXME we're probably doing something wrong here
-                        ctx.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
-                        if let Some(def) = ctx.resolver.generic_def() {
-                            let generics = generics(ctx.db.upcast(), def);
+                        self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
+                        if let Some(def) = self.resolver.generic_def() {
+                            let generics = generics(self.db.upcast(), def);
                             let param = generics
                                 .iter()
                                 .filter(|(_, data)| {
                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
                                 })
                                 .nth(idx as usize)
-                                .map_or(Ty::Unknown, |(id, _)| Ty::Placeholder(id));
-                            param
+                                .map_or(TyKind::Unknown, |(id, _)| {
+                                    TyKind::Placeholder(to_placeholder_idx(self.db, id))
+                                });
+                            param.intern(&Interner)
                         } else {
-                            Ty::Unknown
+                            TyKind::Unknown.intern(&Interner)
                         }
                     }
                     ImplTraitLoweringMode::Variable => {
-                        let idx = ctx.impl_trait_counter.get();
+                        let idx = self.impl_trait_counter.get();
                         // FIXME we're probably doing something wrong here
-                        ctx.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
+                        self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
                         let (parent_params, self_params, list_params, _impl_trait_params) =
-                            if let Some(def) = ctx.resolver.generic_def() {
-                                let generics = generics(ctx.db.upcast(), def);
+                            if let Some(def) = self.resolver.generic_def() {
+                                let generics = generics(self.db.upcast(), def);
                                 generics.provenance_split()
                             } else {
                                 (0, 0, 0, 0)
                             };
-                        Ty::BoundVar(BoundVar::new(
-                            ctx.in_binders,
+                        TyKind::BoundVar(BoundVar::new(
+                            self.in_binders,
                             idx as usize + parent_params + self_params + list_params,
                         ))
+                        .intern(&Interner)
                     }
                     ImplTraitLoweringMode::Disallowed => {
                         // FIXME: report error
-                        Ty::Unknown
+                        TyKind::Unknown.intern(&Interner)
                     }
                 }
             }
-            TypeRef::Error => Ty::Unknown,
+            TypeRef::Error => TyKind::Unknown.intern(&Interner),
         };
         (ty, res)
     }
@@ -279,7 +286,7 @@ impl Ty {
     /// This is only for `generic_predicates_for_param`, where we can't just
     /// lower the self types of the predicates since that could lead to cycles.
     /// So we just check here if the `type_ref` resolves to a generic param, and which.
-    fn from_hir_only_param(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Option<TypeParamId> {
+    fn lower_ty_only_param(&self, type_ref: &TypeRef) -> Option<TypeParamId> {
         let path = match type_ref {
             TypeRef::Path(path) => path,
             _ => return None,
@@ -291,7 +298,7 @@ impl Ty {
             return None;
         }
         let resolution =
-            match ctx.resolver.resolve_path_in_type_ns(ctx.db.upcast(), path.mod_path()) {
+            match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
                 Some((it, None)) => it,
                 _ => return None,
             };
@@ -302,8 +309,8 @@ impl Ty {
         }
     }
 
-    pub(crate) fn from_type_relative_path(
-        ctx: &TyLoweringContext<'_>,
+    pub(crate) fn lower_ty_relative_path(
+        &self,
         ty: Ty,
         // We need the original resolution to lower `Self::AssocTy` correctly
         res: Option<TypeNs>,
@@ -312,17 +319,17 @@ impl Ty {
         if remaining_segments.len() == 1 {
             // resolve unselected assoc types
             let segment = remaining_segments.first().unwrap();
-            (Ty::select_associated_type(ctx, res, segment), None)
+            (self.select_associated_type(res, segment), None)
         } else if remaining_segments.len() > 1 {
             // FIXME report error (ambiguous associated type)
-            (Ty::Unknown, None)
+            (TyKind::Unknown.intern(&Interner), None)
         } else {
             (ty, res)
         }
     }
 
-    pub(crate) fn from_partly_resolved_hir_path(
-        ctx: &TyLoweringContext<'_>,
+    pub(crate) fn lower_partly_resolved_path(
+        &self,
         resolution: TypeNs,
         resolved_segment: PathSegment<'_>,
         remaining_segments: PathSegments<'_>,
@@ -332,103 +339,109 @@ impl Ty {
             TypeNs::TraitId(trait_) => {
                 // if this is a bare dyn Trait, we'll directly put the required ^0 for the self type in there
                 let self_ty = if remaining_segments.len() == 0 {
-                    Some(Ty::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)))
+                    Some(
+                        TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
+                            .intern(&Interner),
+                    )
                 } else {
                     None
                 };
                 let trait_ref =
-                    TraitRef::from_resolved_path(ctx, trait_, resolved_segment, self_ty);
+                    self.lower_trait_ref_from_resolved_path(trait_, resolved_segment, self_ty);
                 let ty = if remaining_segments.len() == 1 {
                     let segment = remaining_segments.first().unwrap();
                     let found = associated_type_by_name_including_super_traits(
-                        ctx.db,
+                        self.db,
                         trait_ref,
                         &segment.name,
                     );
                     match found {
                         Some((super_trait_ref, associated_ty)) => {
                             // FIXME handle type parameters on the segment
-                            Ty::Alias(AliasTy::Projection(ProjectionTy {
-                                associated_ty,
-                                parameters: super_trait_ref.substs,
+                            TyKind::Alias(AliasTy::Projection(ProjectionTy {
+                                associated_ty_id: to_assoc_type_id(associated_ty),
+                                substitution: super_trait_ref.substs,
                             }))
+                            .intern(&Interner)
                         }
                         None => {
                             // FIXME: report error (associated type not found)
-                            Ty::Unknown
+                            TyKind::Unknown.intern(&Interner)
                         }
                     }
                 } else if remaining_segments.len() > 1 {
                     // FIXME report error (ambiguous associated type)
-                    Ty::Unknown
+                    TyKind::Unknown.intern(&Interner)
                 } else {
-                    Ty::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
+                    TyKind::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
+                        .intern(&Interner)
                 };
                 return (ty, None);
             }
             TypeNs::GenericParam(param_id) => {
                 let generics = generics(
-                    ctx.db.upcast(),
-                    ctx.resolver.generic_def().expect("generics in scope"),
+                    self.db.upcast(),
+                    self.resolver.generic_def().expect("generics in scope"),
                 );
-                match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => Ty::Placeholder(param_id),
+                match self.type_param_mode {
+                    TypeParamLoweringMode::Placeholder => {
+                        TyKind::Placeholder(to_placeholder_idx(self.db, param_id))
+                    }
                     TypeParamLoweringMode::Variable => {
                         let idx = generics.param_idx(param_id).expect("matching generics");
-                        Ty::BoundVar(BoundVar::new(ctx.in_binders, idx))
+                        TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
                     }
                 }
+                .intern(&Interner)
             }
             TypeNs::SelfType(impl_id) => {
-                let generics = generics(ctx.db.upcast(), impl_id.into());
-                let substs = match ctx.type_param_mode {
+                let generics = generics(self.db.upcast(), impl_id.into());
+                let substs = match self.type_param_mode {
                     TypeParamLoweringMode::Placeholder => {
-                        Substs::type_params_for_generics(&generics)
+                        Substs::type_params_for_generics(self.db, &generics)
                     }
                     TypeParamLoweringMode::Variable => {
-                        Substs::bound_vars(&generics, ctx.in_binders)
+                        Substs::bound_vars(&generics, self.in_binders)
                     }
                 };
-                ctx.db.impl_self_ty(impl_id).subst(&substs)
+                self.db.impl_self_ty(impl_id).subst(&substs)
             }
             TypeNs::AdtSelfType(adt) => {
-                let generics = generics(ctx.db.upcast(), adt.into());
-                let substs = match ctx.type_param_mode {
+                let generics = generics(self.db.upcast(), adt.into());
+                let substs = match self.type_param_mode {
                     TypeParamLoweringMode::Placeholder => {
-                        Substs::type_params_for_generics(&generics)
+                        Substs::type_params_for_generics(self.db, &generics)
                     }
                     TypeParamLoweringMode::Variable => {
-                        Substs::bound_vars(&generics, ctx.in_binders)
+                        Substs::bound_vars(&generics, self.in_binders)
                     }
                 };
-                ctx.db.ty(adt.into()).subst(&substs)
+                self.db.ty(adt.into()).subst(&substs)
             }
 
-            TypeNs::AdtId(it) => {
-                Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
-            }
+            TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
             TypeNs::BuiltinType(it) => {
-                Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
+                self.lower_path_inner(resolved_segment, it.into(), infer_args)
             }
             TypeNs::TypeAliasId(it) => {
-                Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
+                self.lower_path_inner(resolved_segment, it.into(), infer_args)
             }
             // FIXME: report error
-            TypeNs::EnumVariantId(_) => return (Ty::Unknown, None),
+            TypeNs::EnumVariantId(_) => return (TyKind::Unknown.intern(&Interner), None),
         };
-        Ty::from_type_relative_path(ctx, ty, Some(resolution), remaining_segments)
+        self.lower_ty_relative_path(ty, Some(resolution), remaining_segments)
     }
 
-    pub(crate) fn from_hir_path(ctx: &TyLoweringContext<'_>, path: &Path) -> (Ty, Option<TypeNs>) {
+    pub(crate) fn lower_path(&self, path: &Path) -> (Ty, Option<TypeNs>) {
         // Resolve the path (in type namespace)
         if let Some(type_ref) = path.type_anchor() {
-            let (ty, res) = Ty::from_hir_ext(ctx, &type_ref);
-            return Ty::from_type_relative_path(ctx, ty, res, path.segments());
+            let (ty, res) = self.lower_ty_ext(&type_ref);
+            return self.lower_ty_relative_path(ty, res, path.segments());
         }
         let (resolution, remaining_index) =
-            match ctx.resolver.resolve_path_in_type_ns(ctx.db.upcast(), path.mod_path()) {
+            match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
                 Some(it) => it,
-                None => return (Ty::Unknown, None),
+                None => return (TyKind::Unknown.intern(&Interner), None),
             };
         let (resolved_segment, remaining_segments) = match remaining_index {
             None => (
@@ -437,31 +450,23 @@ impl Ty {
             ),
             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
         };
-        Ty::from_partly_resolved_hir_path(
-            ctx,
-            resolution,
-            resolved_segment,
-            remaining_segments,
-            false,
-        )
+        self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
     }
 
-    fn select_associated_type(
-        ctx: &TyLoweringContext<'_>,
-        res: Option<TypeNs>,
-        segment: PathSegment<'_>,
-    ) -> Ty {
+    fn select_associated_type(&self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
         if let Some(res) = res {
-            let ty =
-                associated_type_shorthand_candidates(ctx.db, res, move |name, t, associated_ty| {
+            let ty = associated_type_shorthand_candidates(
+                self.db,
+                res,
+                move |name, t, associated_ty| {
                     if name == segment.name {
-                        let substs = match ctx.type_param_mode {
+                        let substs = match self.type_param_mode {
                             TypeParamLoweringMode::Placeholder => {
                                 // if we're lowering to placeholders, we have to put
                                 // them in now
                                 let s = Substs::type_params(
-                                    ctx.db,
-                                    ctx.resolver.generic_def().expect(
+                                    self.db,
+                                    self.resolver.generic_def().expect(
                                         "there should be generics if there's a generic param",
                                     ),
                                 );
@@ -471,25 +476,29 @@ impl Ty {
                         };
                         // We need to shift in the bound vars, since
                         // associated_type_shorthand_candidates does not do that
-                        let substs = substs.shift_bound_vars(ctx.in_binders);
+                        let substs = substs.shift_bound_vars(self.in_binders);
                         // FIXME handle type parameters on the segment
-                        return Some(Ty::Alias(AliasTy::Projection(ProjectionTy {
-                            associated_ty,
-                            parameters: substs,
-                        })));
+                        return Some(
+                            TyKind::Alias(AliasTy::Projection(ProjectionTy {
+                                associated_ty_id: to_assoc_type_id(associated_ty),
+                                substitution: substs,
+                            }))
+                            .intern(&Interner),
+                        );
                     }
 
                     None
-                });
+                },
+            );
 
-            ty.unwrap_or(Ty::Unknown)
+            ty.unwrap_or(TyKind::Unknown.intern(&Interner))
         } else {
-            Ty::Unknown
+            TyKind::Unknown.intern(&Interner)
         }
     }
 
-    fn from_hir_path_inner(
-        ctx: &TyLoweringContext<'_>,
+    fn lower_path_inner(
+        &self,
         segment: PathSegment<'_>,
         typeable: TyDefId,
         infer_args: bool,
@@ -499,14 +508,14 @@ impl Ty {
             TyDefId::AdtId(it) => Some(it.into()),
             TyDefId::TypeAliasId(it) => Some(it.into()),
         };
-        let substs = substs_from_path_segment(ctx, segment, generic_def, infer_args);
-        ctx.db.ty(typeable).subst(&substs)
+        let substs = self.substs_from_path_segment(segment, generic_def, infer_args);
+        self.db.ty(typeable).subst(&substs)
     }
 
     /// Collect generic arguments from a path into a `Substs`. See also
     /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
     pub(super) fn substs_from_path(
-        ctx: &TyLoweringContext<'_>,
+        &self,
         path: &Path,
         // Note that we don't call `db.value_type(resolved)` here,
         // `ValueTyDefId` is just a convenient way to pass generics and
@@ -536,169 +545,161 @@ impl Ty {
                 (segment, Some(var.parent.into()))
             }
         };
-        substs_from_path_segment(ctx, segment, generic_def, infer_args)
+        self.substs_from_path_segment(segment, generic_def, infer_args)
     }
-}
 
-fn substs_from_path_segment(
-    ctx: &TyLoweringContext<'_>,
-    segment: PathSegment<'_>,
-    def_generic: Option<GenericDefId>,
-    infer_args: bool,
-) -> Substs {
-    let mut substs = Vec::new();
-    let def_generics = def_generic.map(|def| generics(ctx.db.upcast(), def));
+    fn substs_from_path_segment(
+        &self,
+        segment: PathSegment<'_>,
+        def_generic: Option<GenericDefId>,
+        infer_args: bool,
+    ) -> Substs {
+        let mut substs = Vec::new();
+        let def_generics = def_generic.map(|def| generics(self.db.upcast(), def));
 
-    let (parent_params, self_params, type_params, impl_trait_params) =
-        def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
-    let total_len = parent_params + self_params + type_params + impl_trait_params;
+        let (parent_params, self_params, type_params, impl_trait_params) =
+            def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
+        let total_len = parent_params + self_params + type_params + impl_trait_params;
 
-    substs.extend(iter::repeat(Ty::Unknown).take(parent_params));
+        substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(parent_params));
 
-    let mut had_explicit_type_args = false;
+        let mut had_explicit_type_args = false;
 
-    if let Some(generic_args) = &segment.args_and_bindings {
-        if !generic_args.has_self_type {
-            substs.extend(iter::repeat(Ty::Unknown).take(self_params));
-        }
-        let expected_num =
-            if generic_args.has_self_type { self_params + type_params } else { type_params };
-        let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
-        // if args are provided, it should be all of them, but we can't rely on that
-        for arg in generic_args
-            .args
-            .iter()
-            .filter(|arg| matches!(arg, GenericArg::Type(_)))
-            .skip(skip)
-            .take(expected_num)
-        {
-            match arg {
-                GenericArg::Type(type_ref) => {
-                    had_explicit_type_args = true;
-                    let ty = Ty::from_hir(ctx, type_ref);
-                    substs.push(ty);
+        if let Some(generic_args) = &segment.args_and_bindings {
+            if !generic_args.has_self_type {
+                substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(self_params));
+            }
+            let expected_num =
+                if generic_args.has_self_type { self_params + type_params } else { type_params };
+            let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
+            // if args are provided, it should be all of them, but we can't rely on that
+            for arg in generic_args
+                .args
+                .iter()
+                .filter(|arg| matches!(arg, GenericArg::Type(_)))
+                .skip(skip)
+                .take(expected_num)
+            {
+                match arg {
+                    GenericArg::Type(type_ref) => {
+                        had_explicit_type_args = true;
+                        let ty = self.lower_ty(type_ref);
+                        substs.push(ty);
+                    }
+                    GenericArg::Lifetime(_) => {}
                 }
-                GenericArg::Lifetime(_) => {}
             }
         }
-    }
 
-    // handle defaults. In expression or pattern path segments without
-    // explicitly specified type arguments, missing type arguments are inferred
-    // (i.e. defaults aren't used).
-    if !infer_args || had_explicit_type_args {
-        if let Some(def_generic) = def_generic {
-            let defaults = ctx.db.generic_defaults(def_generic);
-            assert_eq!(total_len, defaults.len());
-
-            for default_ty in defaults.iter().skip(substs.len()) {
-                // each default can depend on the previous parameters
-                let substs_so_far = Substs(substs.clone().into());
-                substs.push(default_ty.clone().subst(&substs_so_far));
+        // handle defaults. In expression or pattern path segments without
+        // explicitly specified type arguments, missing type arguments are inferred
+        // (i.e. defaults aren't used).
+        if !infer_args || had_explicit_type_args {
+            if let Some(def_generic) = def_generic {
+                let defaults = self.db.generic_defaults(def_generic);
+                assert_eq!(total_len, defaults.len());
+
+                for default_ty in defaults.iter().skip(substs.len()) {
+                    // each default can depend on the previous parameters
+                    let substs_so_far = Substs(substs.clone().into());
+                    substs.push(default_ty.clone().subst(&substs_so_far));
+                }
             }
         }
-    }
 
-    // add placeholders for args that were not provided
-    // FIXME: emit diagnostics in contexts where this is not allowed
-    for _ in substs.len()..total_len {
-        substs.push(Ty::Unknown);
-    }
-    assert_eq!(substs.len(), total_len);
+        // add placeholders for args that were not provided
+        // FIXME: emit diagnostics in contexts where this is not allowed
+        for _ in substs.len()..total_len {
+            substs.push(TyKind::Unknown.intern(&Interner));
+        }
+        assert_eq!(substs.len(), total_len);
 
-    Substs(substs.into())
-}
+        Substs(substs.into())
+    }
 
-impl TraitRef {
-    fn from_path(
-        ctx: &TyLoweringContext<'_>,
+    fn lower_trait_ref_from_path(
+        &self,
         path: &Path,
         explicit_self_ty: Option<Ty>,
-    ) -> Option<Self> {
+    ) -> Option<TraitRef> {
         let resolved =
-            match ctx.resolver.resolve_path_in_type_ns_fully(ctx.db.upcast(), path.mod_path())? {
+            match self.resolver.resolve_path_in_type_ns_fully(self.db.upcast(), path.mod_path())? {
                 TypeNs::TraitId(tr) => tr,
                 _ => return None,
             };
         let segment = path.segments().last().expect("path should have at least one segment");
-        Some(TraitRef::from_resolved_path(ctx, resolved, segment, explicit_self_ty))
+        Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
     }
 
-    pub(crate) fn from_resolved_path(
-        ctx: &TyLoweringContext<'_>,
+    pub(crate) fn lower_trait_ref_from_resolved_path(
+        &self,
         resolved: TraitId,
         segment: PathSegment<'_>,
         explicit_self_ty: Option<Ty>,
-    ) -> Self {
-        let mut substs = TraitRef::substs_from_path(ctx, segment, resolved);
+    ) -> TraitRef {
+        let mut substs = self.trait_ref_substs_from_path(segment, resolved);
         if let Some(self_ty) = explicit_self_ty {
-            make_mut_slice(&mut substs.0)[0] = self_ty;
+            substs.0[0] = self_ty;
         }
         TraitRef { trait_: resolved, substs }
     }
 
-    fn from_hir(
-        ctx: &TyLoweringContext<'_>,
+    fn lower_trait_ref(
+        &self,
         type_ref: &TypeRef,
         explicit_self_ty: Option<Ty>,
-    ) -> Option<Self> {
+    ) -> Option<TraitRef> {
         let path = match type_ref {
             TypeRef::Path(path) => path,
             _ => return None,
         };
-        TraitRef::from_path(ctx, path, explicit_self_ty)
+        self.lower_trait_ref_from_path(path, explicit_self_ty)
     }
 
-    fn substs_from_path(
-        ctx: &TyLoweringContext<'_>,
-        segment: PathSegment<'_>,
-        resolved: TraitId,
-    ) -> Substs {
-        substs_from_path_segment(ctx, segment, Some(resolved.into()), false)
+    fn trait_ref_substs_from_path(&self, segment: PathSegment<'_>, resolved: TraitId) -> Substs {
+        self.substs_from_path_segment(segment, Some(resolved.into()), false)
     }
-}
 
-impl GenericPredicate {
-    pub(crate) fn from_where_predicate<'a>(
-        ctx: &'a TyLoweringContext<'a>,
+    pub(crate) fn lower_where_predicate(
+        &'a self,
         where_predicate: &'a WherePredicate,
     ) -> impl Iterator<Item = GenericPredicate> + 'a {
         match where_predicate {
             WherePredicate::ForLifetime { target, bound, .. }
             | WherePredicate::TypeBound { target, bound } => {
                 let self_ty = match target {
-                    WherePredicateTypeTarget::TypeRef(type_ref) => Ty::from_hir(ctx, type_ref),
+                    WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
                     WherePredicateTypeTarget::TypeParam(param_id) => {
-                        let generic_def = ctx.resolver.generic_def().expect("generics in scope");
-                        let generics = generics(ctx.db.upcast(), generic_def);
+                        let generic_def = self.resolver.generic_def().expect("generics in scope");
+                        let generics = generics(self.db.upcast(), generic_def);
                         let param_id =
                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
-                        match ctx.type_param_mode {
-                            TypeParamLoweringMode::Placeholder => Ty::Placeholder(param_id),
+                        let placeholder = to_placeholder_idx(self.db, param_id);
+                        match self.type_param_mode {
+                            TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
                             TypeParamLoweringMode::Variable => {
                                 let idx = generics.param_idx(param_id).expect("matching generics");
-                                Ty::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
+                                TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
                             }
                         }
+                        .intern(&Interner)
                     }
                 };
-                GenericPredicate::from_type_bound(ctx, bound, self_ty)
-                    .collect::<Vec<_>>()
-                    .into_iter()
+                self.lower_type_bound(bound, self_ty).collect::<Vec<_>>().into_iter()
             }
             WherePredicate::Lifetime { .. } => vec![].into_iter(),
         }
     }
 
-    pub(crate) fn from_type_bound<'a>(
-        ctx: &'a TyLoweringContext<'a>,
+    pub(crate) fn lower_type_bound(
+        &'a self,
         bound: &'a TypeBound,
         self_ty: Ty,
     ) -> impl Iterator<Item = GenericPredicate> + 'a {
         let mut bindings = None;
         let trait_ref = match bound {
             TypeBound::Path(path) => {
-                bindings = TraitRef::from_path(ctx, path, Some(self_ty));
+                bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
                 Some(
                     bindings.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented),
                 )
@@ -709,64 +710,62 @@ impl GenericPredicate {
         trait_ref.into_iter().chain(
             bindings
                 .into_iter()
-                .flat_map(move |tr| assoc_type_bindings_from_type_bound(ctx, bound, tr)),
+                .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
         )
     }
-}
 
-fn assoc_type_bindings_from_type_bound<'a>(
-    ctx: &'a TyLoweringContext<'a>,
-    bound: &'a TypeBound,
-    trait_ref: TraitRef,
-) -> impl Iterator<Item = GenericPredicate> + 'a {
-    let last_segment = match bound {
-        TypeBound::Path(path) => path.segments().last(),
-        TypeBound::Error | TypeBound::Lifetime(_) => None,
-    };
-    last_segment
-        .into_iter()
-        .flat_map(|segment| segment.args_and_bindings.into_iter())
-        .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
-        .flat_map(move |binding| {
-            let found = associated_type_by_name_including_super_traits(
-                ctx.db,
-                trait_ref.clone(),
-                &binding.name,
-            );
-            let (super_trait_ref, associated_ty) = match found {
-                None => return SmallVec::<[GenericPredicate; 1]>::new(),
-                Some(t) => t,
-            };
-            let projection_ty = ProjectionTy { associated_ty, parameters: super_trait_ref.substs };
-            let mut preds = SmallVec::with_capacity(
-                binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
-            );
-            if let Some(type_ref) = &binding.type_ref {
-                let ty = Ty::from_hir(ctx, type_ref);
-                let projection_predicate =
-                    ProjectionPredicate { projection_ty: projection_ty.clone(), ty };
-                preds.push(GenericPredicate::Projection(projection_predicate));
-            }
-            for bound in &binding.bounds {
-                preds.extend(GenericPredicate::from_type_bound(
-                    ctx,
-                    bound,
-                    Ty::Alias(AliasTy::Projection(projection_ty.clone())),
-                ));
-            }
-            preds
-        })
-}
+    fn assoc_type_bindings_from_type_bound(
+        &'a self,
+        bound: &'a TypeBound,
+        trait_ref: TraitRef,
+    ) -> impl Iterator<Item = GenericPredicate> + 'a {
+        let last_segment = match bound {
+            TypeBound::Path(path) => path.segments().last(),
+            TypeBound::Error | TypeBound::Lifetime(_) => None,
+        };
+        last_segment
+            .into_iter()
+            .flat_map(|segment| segment.args_and_bindings.into_iter())
+            .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
+            .flat_map(move |binding| {
+                let found = associated_type_by_name_including_super_traits(
+                    self.db,
+                    trait_ref.clone(),
+                    &binding.name,
+                );
+                let (super_trait_ref, associated_ty) = match found {
+                    None => return SmallVec::<[GenericPredicate; 1]>::new(),
+                    Some(t) => t,
+                };
+                let projection_ty = ProjectionTy {
+                    associated_ty_id: to_assoc_type_id(associated_ty),
+                    substitution: super_trait_ref.substs,
+                };
+                let mut preds = SmallVec::with_capacity(
+                    binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
+                );
+                if let Some(type_ref) = &binding.type_ref {
+                    let ty = self.lower_ty(type_ref);
+                    let projection_predicate =
+                        ProjectionPredicate { projection_ty: projection_ty.clone(), ty };
+                    preds.push(GenericPredicate::Projection(projection_predicate));
+                }
+                for bound in &binding.bounds {
+                    preds.extend(self.lower_type_bound(
+                        bound,
+                        TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
+                    ));
+                }
+                preds
+            })
+    }
 
-impl ReturnTypeImplTrait {
-    fn from_hir(ctx: &TyLoweringContext, bounds: &[TypeBound]) -> Self {
+    fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
         cov_mark::hit!(lower_rpit);
-        let self_ty = Ty::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0));
-        let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
-            bounds
-                .iter()
-                .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
-                .collect()
+        let self_ty =
+            TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
+        let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
+            bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone())).collect()
         });
         ReturnTypeImplTrait { bounds: Binders::new(1, predicates) }
     }
@@ -862,7 +861,7 @@ pub(crate) fn field_types_query(
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     for (field_id, field_data) in var_data.fields().iter() {
-        res.insert(field_id, Binders::new(generics.len(), Ty::from_hir(&ctx, &field_data.type_ref)))
+        res.insert(field_id, Binders::new(generics.len(), ctx.lower_ty(&field_data.type_ref)))
     }
     Arc::new(res)
 }
@@ -890,16 +889,13 @@ pub(crate) fn generic_predicates_for_param_query(
             WherePredicate::ForLifetime { target, .. }
             | WherePredicate::TypeBound { target, .. } => match target {
                 WherePredicateTypeTarget::TypeRef(type_ref) => {
-                    Ty::from_hir_only_param(&ctx, type_ref) == Some(param_id)
+                    ctx.lower_ty_only_param(type_ref) == Some(param_id)
                 }
                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
             },
             WherePredicate::Lifetime { .. } => false,
         })
-        .flat_map(|pred| {
-            GenericPredicate::from_where_predicate(&ctx, pred)
-                .map(|p| Binders::new(generics.len(), p))
-        })
+        .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
         .collect()
 }
 
@@ -911,55 +907,55 @@ pub(crate) fn generic_predicates_for_param_recover(
     Arc::new([])
 }
 
-impl TraitEnvironment {
-    pub fn lower(db: &dyn HirDatabase, resolver: &Resolver) -> Arc<TraitEnvironment> {
-        let ctx = TyLoweringContext::new(db, &resolver)
-            .with_type_param_mode(TypeParamLoweringMode::Placeholder);
-        let mut traits_in_scope = Vec::new();
-        let mut clauses = Vec::new();
-        for pred in resolver.where_predicates_in_scope() {
-            for pred in GenericPredicate::from_where_predicate(&ctx, pred) {
-                if pred.is_error() {
-                    continue;
-                }
-                if let GenericPredicate::Implemented(tr) = &pred {
-                    traits_in_scope.push((tr.self_ty().clone(), tr.trait_));
-                }
-                let program_clause: chalk_ir::ProgramClause<Interner> =
-                    pred.clone().to_chalk(db).cast(&Interner);
-                clauses.push(program_clause.into_from_env_clause(&Interner));
+pub(crate) fn trait_environment_query(
+    db: &dyn HirDatabase,
+    def: GenericDefId,
+) -> Arc<TraitEnvironment> {
+    let resolver = def.resolver(db.upcast());
+    let ctx = TyLoweringContext::new(db, &resolver)
+        .with_type_param_mode(TypeParamLoweringMode::Placeholder);
+    let mut traits_in_scope = Vec::new();
+    let mut clauses = Vec::new();
+    for pred in resolver.where_predicates_in_scope() {
+        for pred in ctx.lower_where_predicate(pred) {
+            if pred.is_error() {
+                continue;
             }
-        }
-
-        if let Some(def) = resolver.generic_def() {
-            let container: Option<AssocContainerId> = match def {
-                // FIXME: is there a function for this?
-                GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
-                GenericDefId::AdtId(_) => None,
-                GenericDefId::TraitId(_) => None,
-                GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
-                GenericDefId::ImplId(_) => None,
-                GenericDefId::EnumVariantId(_) => None,
-                GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
-            };
-            if let Some(AssocContainerId::TraitId(trait_id)) = container {
-                // add `Self: Trait<T1, T2, ...>` to the environment in trait
-                // function default implementations (and hypothetical code
-                // inside consts or type aliases)
-                cov_mark::hit!(trait_self_implements_self);
-                let substs = Substs::type_params(db, trait_id);
-                let trait_ref = TraitRef { trait_: trait_id, substs };
-                let pred = GenericPredicate::Implemented(trait_ref);
-                let program_clause: chalk_ir::ProgramClause<Interner> =
-                    pred.clone().to_chalk(db).cast(&Interner);
-                clauses.push(program_clause.into_from_env_clause(&Interner));
+            if let GenericPredicate::Implemented(tr) = &pred {
+                traits_in_scope.push((tr.self_ty().clone(), tr.trait_));
             }
+            let program_clause: chalk_ir::ProgramClause<Interner> =
+                pred.clone().to_chalk(db).cast(&Interner);
+            clauses.push(program_clause.into_from_env_clause(&Interner));
         }
+    }
 
-        let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
-
-        Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
+    let container: Option<AssocContainerId> = match def {
+        // FIXME: is there a function for this?
+        GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
+        GenericDefId::AdtId(_) => None,
+        GenericDefId::TraitId(_) => None,
+        GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
+        GenericDefId::ImplId(_) => None,
+        GenericDefId::EnumVariantId(_) => None,
+        GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
+    };
+    if let Some(AssocContainerId::TraitId(trait_id)) = container {
+        // add `Self: Trait<T1, T2, ...>` to the environment in trait
+        // function default implementations (and hypothetical code
+        // inside consts or type aliases)
+        cov_mark::hit!(trait_self_implements_self);
+        let substs = Substs::type_params(db, trait_id);
+        let trait_ref = TraitRef { trait_: trait_id, substs };
+        let pred = GenericPredicate::Implemented(trait_ref);
+        let program_clause: chalk_ir::ProgramClause<Interner> =
+            pred.clone().to_chalk(db).cast(&Interner);
+        clauses.push(program_clause.into_from_env_clause(&Interner));
     }
+
+    let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
+
+    Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 }
 
 /// Resolve the where clause(s) of an item with generics.
@@ -973,10 +969,7 @@ pub(crate) fn generic_predicates_query(
     let generics = generics(db.upcast(), def);
     resolver
         .where_predicates_in_scope()
-        .flat_map(|pred| {
-            GenericPredicate::from_where_predicate(&ctx, pred)
-                .map(|p| Binders::new(generics.len(), p))
-        })
+        .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
         .collect()
 }
 
@@ -994,17 +987,18 @@ pub(crate) fn generic_defaults_query(
         .iter()
         .enumerate()
         .map(|(idx, (_, p))| {
-            let mut ty = p.default.as_ref().map_or(Ty::Unknown, |t| Ty::from_hir(&ctx, t));
+            let mut ty =
+                p.default.as_ref().map_or(TyKind::Unknown.intern(&Interner), |t| ctx.lower_ty(t));
 
             // Each default can only refer to previous parameters.
             ty.walk_mut_binders(
-                &mut |ty, binders| match ty {
-                    Ty::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
+                &mut |ty, binders| match ty.interned_mut() {
+                    TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
                         if *index >= idx {
                             // type variable default referring to parameter coming
                             // after it. This is forbidden (FIXME: report
                             // diagnostic)
-                            *ty = Ty::Unknown;
+                            *ty = TyKind::Unknown.intern(&Interner);
                         }
                     }
                     _ => {}
@@ -1025,11 +1019,11 @@ fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
     let ctx_params = TyLoweringContext::new(db, &resolver)
         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
         .with_type_param_mode(TypeParamLoweringMode::Variable);
-    let params = data.params.iter().map(|tr| Ty::from_hir(&ctx_params, tr)).collect::<Vec<_>>();
+    let params = data.params.iter().map(|tr| (&ctx_params).lower_ty(tr)).collect::<Vec<_>>();
     let ctx_ret = TyLoweringContext::new(db, &resolver)
         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
         .with_type_param_mode(TypeParamLoweringMode::Variable);
-    let ret = Ty::from_hir(&ctx_ret, &data.ret_type);
+    let ret = (&ctx_ret).lower_ty(&data.ret_type);
     let generics = generics(db.upcast(), def.into());
     let num_binders = generics.len();
     Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs))
@@ -1040,7 +1034,10 @@ fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
     let generics = generics(db.upcast(), def.into());
     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
-    Binders::new(substs.len(), Ty::FnDef(def.into(), substs))
+    Binders::new(
+        substs.len(),
+        TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
+    )
 }
 
 /// Build the declared type of a const.
@@ -1051,7 +1048,7 @@ fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 
-    Binders::new(generics.len(), Ty::from_hir(&ctx, &data.type_ref))
+    Binders::new(generics.len(), ctx.lower_ty(&data.type_ref))
 }
 
 /// Build the declared type of a static.
@@ -1060,7 +1057,7 @@ fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
     let resolver = def.resolver(db.upcast());
     let ctx = TyLoweringContext::new(db, &resolver);
 
-    Binders::new(0, Ty::from_hir(&ctx, &data.type_ref))
+    Binders::new(0, ctx.lower_ty(&data.type_ref))
 }
 
 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
@@ -1069,8 +1066,7 @@ fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnS
     let resolver = def.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-    let params =
-        fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
+    let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
     let ret = type_for_adt(db, def.into());
     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
 }
@@ -1083,7 +1079,10 @@ fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<T
     }
     let generics = generics(db.upcast(), def.into());
     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
-    Binders::new(substs.len(), Ty::FnDef(def.into(), substs))
+    Binders::new(
+        substs.len(),
+        TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
+    )
 }
 
 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
@@ -1093,8 +1092,7 @@ fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId)
     let resolver = def.parent.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-    let params =
-        fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
+    let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
     let ret = type_for_adt(db, def.parent.into());
     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
 }
@@ -1108,7 +1106,10 @@ fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -
     }
     let generics = generics(db.upcast(), def.parent.into());
     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
-    Binders::new(substs.len(), Ty::FnDef(def.into(), substs))
+    Binders::new(
+        substs.len(),
+        TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
+    )
 }
 
 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
@@ -1123,11 +1124,11 @@ fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     if db.type_alias_data(t).is_extern {
-        Binders::new(0, Ty::ForeignType(t))
+        Binders::new(0, TyKind::ForeignType(crate::to_foreign_def_id(t)).intern(&Interner))
     } else {
         let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
         let type_ref = &db.type_alias_data(t).type_ref;
-        let inner = Ty::from_hir(&ctx, type_ref.as_ref().unwrap_or(&TypeRef::Error));
+        let inner = ctx.lower_ty(type_ref.as_ref().unwrap_or(&TypeRef::Error));
         Binders::new(substs.len(), inner)
     }
 }
@@ -1199,7 +1200,7 @@ pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId)
         TyDefId::AdtId(it) => generics(db.upcast(), it.into()).len(),
         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()).len(),
     };
-    Binders::new(num_binders, Ty::Unknown)
+    Binders::new(num_binders, TyKind::Unknown.intern(&Interner))
 }
 
 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
@@ -1219,7 +1220,7 @@ pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binde
     let generics = generics(db.upcast(), impl_id.into());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-    Binders::new(generics.len(), Ty::from_hir(&ctx, &impl_data.target_type))
+    Binders::new(generics.len(), ctx.lower_ty(&impl_data.target_type))
 }
 
 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
@@ -1228,7 +1229,7 @@ pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> T
     let resolver = def.parent.resolver(db.upcast());
     let ctx = TyLoweringContext::new(db, &resolver);
 
-    Ty::from_hir(&ctx, &data.ty)
+    ctx.lower_ty(&data.ty)
 }
 
 pub(crate) fn impl_self_ty_recover(
@@ -1237,7 +1238,7 @@ pub(crate) fn impl_self_ty_recover(
     impl_id: &ImplId,
 ) -> Binders<Ty> {
     let generics = generics(db.upcast(), (*impl_id).into());
-    Binders::new(generics.len(), Ty::Unknown)
+    Binders::new(generics.len(), TyKind::Unknown.intern(&Interner))
 }
 
 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
@@ -1247,10 +1248,7 @@ pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     let self_ty = db.impl_self_ty(impl_id);
     let target_trait = impl_data.target_trait.as_ref()?;
-    Some(Binders::new(
-        self_ty.num_binders,
-        TraitRef::from_hir(&ctx, target_trait, Some(self_ty.value))?,
-    ))
+    Some(Binders::new(self_ty.num_binders, ctx.lower_trait_ref(target_trait, Some(self_ty.value))?))
 }
 
 pub(crate) fn return_type_impl_traits(
@@ -1263,7 +1261,7 @@ pub(crate) fn return_type_impl_traits(
     let ctx_ret = TyLoweringContext::new(db, &resolver)
         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
         .with_type_param_mode(TypeParamLoweringMode::Variable);
-    let _ret = Ty::from_hir(&ctx_ret, &data.ret_type);
+    let _ret = (&ctx_ret).lower_ty(&data.ret_type);
     let generics = generics(db.upcast(), def.into());
     let num_binders = generics.len();
     let return_type_impl_traits =
diff --git a/crates/hir_ty/src/method_resolution.rs b/crates/hir_ty/src/method_resolution.rs
index d57c6de70..be72c4a1c 100644
--- a/crates/hir_ty/src/method_resolution.rs
+++ b/crates/hir_ty/src/method_resolution.rs
@@ -9,7 +9,7 @@ use base_db::CrateId;
 use chalk_ir::Mutability;
 use hir_def::{
     lang_item::LangItemTarget, AssocContainerId, AssocItemId, FunctionId, GenericDefId, HasModule,
-    ImplId, Lookup, ModuleId, TraitId, TypeAliasId,
+    ImplId, Lookup, ModuleId, TraitId,
 };
 use hir_expand::name::Name;
 use rustc_hash::{FxHashMap, FxHashSet};
@@ -17,10 +17,11 @@ use rustc_hash::{FxHashMap, FxHashSet};
 use crate::{
     autoderef,
     db::HirDatabase,
+    from_foreign_def_id,
     primitive::{self, FloatTy, IntTy, UintTy},
     utils::all_super_traits,
-    AdtId, Canonical, DebruijnIndex, FnPointer, FnSig, InEnvironment, Scalar, Substs,
-    TraitEnvironment, TraitRef, Ty, TypeWalk,
+    AdtId, Canonical, DebruijnIndex, FnPointer, FnSig, ForeignDefId, InEnvironment, Interner,
+    Scalar, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeWalk,
 };
 
 /// This is used as a key for indexing impls.
@@ -35,7 +36,7 @@ pub enum TyFingerprint {
     Adt(hir_def::AdtId),
     Dyn(TraitId),
     Tuple(usize),
-    ForeignType(TypeAliasId),
+    ForeignType(ForeignDefId),
     FnPtr(usize, FnSig),
 }
 
@@ -43,19 +44,21 @@ impl TyFingerprint {
     /// Creates a TyFingerprint for looking up an impl. Only certain types can
     /// have impls: if we have some `struct S`, we can have an `impl S`, but not
     /// `impl &S`. Hence, this will return `None` for reference types and such.
-    pub(crate) fn for_impl(ty: &Ty) -> Option<TyFingerprint> {
-        let fp = match ty {
-            &Ty::Str => TyFingerprint::Str,
-            &Ty::Never => TyFingerprint::Never,
-            &Ty::Slice(..) => TyFingerprint::Slice,
-            &Ty::Array(..) => TyFingerprint::Array,
-            &Ty::Scalar(scalar) => TyFingerprint::Scalar(scalar),
-            &Ty::Adt(AdtId(adt), _) => TyFingerprint::Adt(adt),
-            &Ty::Tuple(cardinality, _) => TyFingerprint::Tuple(cardinality),
-            &Ty::Raw(mutability, ..) => TyFingerprint::RawPtr(mutability),
-            &Ty::ForeignType(alias_id, ..) => TyFingerprint::ForeignType(alias_id),
-            &Ty::Function(FnPointer { num_args, sig, .. }) => TyFingerprint::FnPtr(num_args, sig),
-            Ty::Dyn(_) => ty.dyn_trait().map(|trait_| TyFingerprint::Dyn(trait_))?,
+    pub fn for_impl(ty: &Ty) -> Option<TyFingerprint> {
+        let fp = match *ty.interned(&Interner) {
+            TyKind::Str => TyFingerprint::Str,
+            TyKind::Never => TyFingerprint::Never,
+            TyKind::Slice(..) => TyFingerprint::Slice,
+            TyKind::Array(..) => TyFingerprint::Array,
+            TyKind::Scalar(scalar) => TyFingerprint::Scalar(scalar),
+            TyKind::Adt(AdtId(adt), _) => TyFingerprint::Adt(adt),
+            TyKind::Tuple(cardinality, _) => TyFingerprint::Tuple(cardinality),
+            TyKind::Raw(mutability, ..) => TyFingerprint::RawPtr(mutability),
+            TyKind::ForeignType(alias_id, ..) => TyFingerprint::ForeignType(alias_id),
+            TyKind::Function(FnPointer { num_args, sig, .. }) => {
+                TyFingerprint::FnPtr(num_args, sig)
+            }
+            TyKind::Dyn(_) => ty.dyn_trait().map(|trait_| TyFingerprint::Dyn(trait_))?,
             _ => return None,
         };
         Some(fp)
@@ -138,6 +141,14 @@ impl TraitImpls {
         }
     }
 
+    /// Queries all trait impls for the given type.
+    pub fn for_self_ty(&self, fp: TyFingerprint) -> impl Iterator<Item = ImplId> + '_ {
+        self.map
+            .values()
+            .flat_map(move |impls| impls.get(&None).into_iter().chain(impls.get(&Some(fp))))
+            .flat_map(|it| it.iter().copied())
+    }
+
     /// Queries all impls of the given trait.
     pub fn for_trait(&self, trait_: TraitId) -> impl Iterator<Item = ImplId> + '_ {
         self.map
@@ -230,31 +241,33 @@ impl Ty {
 
         let mod_to_crate_ids = |module: ModuleId| Some(std::iter::once(module.krate()).collect());
 
-        let lang_item_targets = match self {
-            Ty::Adt(AdtId(def_id), _) => {
+        let lang_item_targets = match self.interned(&Interner) {
+            TyKind::Adt(AdtId(def_id), _) => {
                 return mod_to_crate_ids(def_id.module(db.upcast()));
             }
-            Ty::ForeignType(type_alias_id) => {
-                return mod_to_crate_ids(type_alias_id.lookup(db.upcast()).module(db.upcast()));
+            TyKind::ForeignType(id) => {
+                return mod_to_crate_ids(
+                    from_foreign_def_id(*id).lookup(db.upcast()).module(db.upcast()),
+                );
             }
-            Ty::Scalar(Scalar::Bool) => lang_item_crate!("bool"),
-            Ty::Scalar(Scalar::Char) => lang_item_crate!("char"),
-            Ty::Scalar(Scalar::Float(f)) => match f {
+            TyKind::Scalar(Scalar::Bool) => lang_item_crate!("bool"),
+            TyKind::Scalar(Scalar::Char) => lang_item_crate!("char"),
+            TyKind::Scalar(Scalar::Float(f)) => match f {
                 // There are two lang items: one in libcore (fXX) and one in libstd (fXX_runtime)
                 FloatTy::F32 => lang_item_crate!("f32", "f32_runtime"),
                 FloatTy::F64 => lang_item_crate!("f64", "f64_runtime"),
             },
-            &Ty::Scalar(Scalar::Int(t)) => {
+            &TyKind::Scalar(Scalar::Int(t)) => {
                 lang_item_crate!(primitive::int_ty_to_string(t))
             }
-            &Ty::Scalar(Scalar::Uint(t)) => {
+            &TyKind::Scalar(Scalar::Uint(t)) => {
                 lang_item_crate!(primitive::uint_ty_to_string(t))
             }
-            Ty::Str => lang_item_crate!("str_alloc", "str"),
-            Ty::Slice(_) => lang_item_crate!("slice_alloc", "slice"),
-            Ty::Raw(Mutability::Not, _) => lang_item_crate!("const_ptr"),
-            Ty::Raw(Mutability::Mut, _) => lang_item_crate!("mut_ptr"),
-            Ty::Dyn(_) => {
+            TyKind::Str => lang_item_crate!("str_alloc", "str"),
+            TyKind::Slice(_) => lang_item_crate!("slice_alloc", "slice"),
+            TyKind::Raw(Mutability::Not, _) => lang_item_crate!("const_ptr"),
+            TyKind::Raw(Mutability::Mut, _) => lang_item_crate!("mut_ptr"),
+            TyKind::Dyn(_) => {
                 return self.dyn_trait().and_then(|trait_| {
                     mod_to_crate_ids(GenericDefId::TraitId(trait_).module(db.upcast()))
                 });
@@ -430,7 +443,7 @@ fn iterate_method_candidates_with_autoref(
     }
     let refed = Canonical {
         kinds: deref_chain[0].kinds.clone(),
-        value: Ty::Ref(Mutability::Not, Substs::single(deref_chain[0].value.clone())),
+        value: TyKind::Ref(Mutability::Not, deref_chain[0].value.clone()).intern(&Interner),
     };
     if iterate_method_candidates_by_receiver(
         &refed,
@@ -446,7 +459,7 @@ fn iterate_method_candidates_with_autoref(
     }
     let ref_muted = Canonical {
         kinds: deref_chain[0].kinds.clone(),
-        value: Ty::Ref(Mutability::Mut, Substs::single(deref_chain[0].value.clone())),
+        value: TyKind::Ref(Mutability::Mut, deref_chain[0].value.clone()).intern(&Interner),
     };
     if iterate_method_candidates_by_receiver(
         &ref_muted,
@@ -526,7 +539,7 @@ fn iterate_trait_method_candidates(
     // if ty is `dyn Trait`, the trait doesn't need to be in scope
     let inherent_trait =
         self_ty.value.dyn_trait().into_iter().flat_map(|t| all_super_traits(db.upcast(), t));
-    let env_traits = if let Ty::Placeholder(_) = self_ty.value {
+    let env_traits = if let TyKind::Placeholder(_) = self_ty.value.interned(&Interner) {
         // if we have `T: Trait` in the param env, the trait doesn't need to be in scope
         env.traits_in_scope_from_clauses(&self_ty.value)
             .flat_map(|t| all_super_traits(db.upcast(), t))
@@ -679,13 +692,13 @@ pub(crate) fn inherent_impl_substs(
 }
 
 /// This replaces any 'free' Bound vars in `s` (i.e. those with indices past
-/// num_vars_to_keep) by `Ty::Unknown`.
+/// num_vars_to_keep) by `TyKind::Unknown`.
 fn fallback_bound_vars(s: Substs, num_vars_to_keep: usize) -> Substs {
     s.fold_binders(
         &mut |ty, binders| {
-            if let Ty::BoundVar(bound) = &ty {
+            if let TyKind::BoundVar(bound) = ty.interned(&Interner) {
                 if bound.index >= num_vars_to_keep && bound.debruijn >= binders {
-                    Ty::Unknown
+                    TyKind::Unknown.intern(&Interner)
                 } else {
                     ty
                 }
@@ -772,9 +785,11 @@ fn autoderef_method_receiver(
 ) -> Vec<Canonical<Ty>> {
     let mut deref_chain: Vec<_> = autoderef::autoderef(db, Some(krate), ty).collect();
     // As a last step, we can do array unsizing (that's the only unsizing that rustc does for method receivers!)
-    if let Some(Ty::Array(parameters)) = deref_chain.last().map(|ty| &ty.value) {
+    if let Some(TyKind::Array(parameters)) =
+        deref_chain.last().map(|ty| ty.value.interned(&Interner))
+    {
         let kinds = deref_chain.last().unwrap().kinds.clone();
-        let unsized_ty = Ty::Slice(parameters.clone());
+        let unsized_ty = TyKind::Slice(parameters.clone()).intern(&Interner);
         deref_chain.push(Canonical { value: unsized_ty, kinds })
     }
     deref_chain
diff --git a/crates/hir_ty/src/op.rs b/crates/hir_ty/src/op.rs
index bb9b8bbfc..527c5cbbd 100644
--- a/crates/hir_ty/src/op.rs
+++ b/crates/hir_ty/src/op.rs
@@ -2,51 +2,55 @@
 use chalk_ir::TyVariableKind;
 use hir_def::expr::{ArithOp, BinaryOp, CmpOp};
 
-use crate::{Scalar, Ty};
+use crate::{Interner, Scalar, Ty, TyKind};
 
 pub(super) fn binary_op_return_ty(op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Ty {
     match op {
-        BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => Ty::Scalar(Scalar::Bool),
+        BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
         BinaryOp::Assignment { .. } => Ty::unit(),
-        BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => match lhs_ty {
-            Ty::Scalar(Scalar::Int(_))
-            | Ty::Scalar(Scalar::Uint(_))
-            | Ty::Scalar(Scalar::Float(_)) => lhs_ty,
-            Ty::InferenceVar(_, TyVariableKind::Integer)
-            | Ty::InferenceVar(_, TyVariableKind::Float) => lhs_ty,
-            _ => Ty::Unknown,
-        },
-        BinaryOp::ArithOp(_) => match rhs_ty {
-            Ty::Scalar(Scalar::Int(_))
-            | Ty::Scalar(Scalar::Uint(_))
-            | Ty::Scalar(Scalar::Float(_)) => rhs_ty,
-            Ty::InferenceVar(_, TyVariableKind::Integer)
-            | Ty::InferenceVar(_, TyVariableKind::Float) => rhs_ty,
-            _ => Ty::Unknown,
+        BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => {
+            match lhs_ty.interned(&Interner) {
+                TyKind::Scalar(Scalar::Int(_))
+                | TyKind::Scalar(Scalar::Uint(_))
+                | TyKind::Scalar(Scalar::Float(_)) => lhs_ty,
+                TyKind::InferenceVar(_, TyVariableKind::Integer)
+                | TyKind::InferenceVar(_, TyVariableKind::Float) => lhs_ty,
+                _ => TyKind::Unknown.intern(&Interner),
+            }
+        }
+        BinaryOp::ArithOp(_) => match rhs_ty.interned(&Interner) {
+            TyKind::Scalar(Scalar::Int(_))
+            | TyKind::Scalar(Scalar::Uint(_))
+            | TyKind::Scalar(Scalar::Float(_)) => rhs_ty,
+            TyKind::InferenceVar(_, TyVariableKind::Integer)
+            | TyKind::InferenceVar(_, TyVariableKind::Float) => rhs_ty,
+            _ => TyKind::Unknown.intern(&Interner),
         },
     }
 }
 
 pub(super) fn binary_op_rhs_expectation(op: BinaryOp, lhs_ty: Ty) -> Ty {
     match op {
-        BinaryOp::LogicOp(..) => Ty::Scalar(Scalar::Bool),
+        BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
         BinaryOp::Assignment { op: None } => lhs_ty,
-        BinaryOp::CmpOp(CmpOp::Eq { .. }) => match lhs_ty {
-            Ty::Scalar(_) | Ty::Str => lhs_ty,
-            Ty::InferenceVar(_, TyVariableKind::Integer)
-            | Ty::InferenceVar(_, TyVariableKind::Float) => lhs_ty,
-            _ => Ty::Unknown,
+        BinaryOp::CmpOp(CmpOp::Eq { .. }) => match lhs_ty.interned(&Interner) {
+            TyKind::Scalar(_) | TyKind::Str => lhs_ty,
+            TyKind::InferenceVar(_, TyVariableKind::Integer)
+            | TyKind::InferenceVar(_, TyVariableKind::Float) => lhs_ty,
+            _ => TyKind::Unknown.intern(&Interner),
         },
-        BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => Ty::Unknown,
+        BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => {
+            TyKind::Unknown.intern(&Interner)
+        }
         BinaryOp::CmpOp(CmpOp::Ord { .. })
         | BinaryOp::Assignment { op: Some(_) }
-        | BinaryOp::ArithOp(_) => match lhs_ty {
-            Ty::Scalar(Scalar::Int(_))
-            | Ty::Scalar(Scalar::Uint(_))
-            | Ty::Scalar(Scalar::Float(_)) => lhs_ty,
-            Ty::InferenceVar(_, TyVariableKind::Integer)
-            | Ty::InferenceVar(_, TyVariableKind::Float) => lhs_ty,
-            _ => Ty::Unknown,
+        | BinaryOp::ArithOp(_) => match lhs_ty.interned(&Interner) {
+            TyKind::Scalar(Scalar::Int(_))
+            | TyKind::Scalar(Scalar::Uint(_))
+            | TyKind::Scalar(Scalar::Float(_)) => lhs_ty,
+            TyKind::InferenceVar(_, TyVariableKind::Integer)
+            | TyKind::InferenceVar(_, TyVariableKind::Float) => lhs_ty,
+            _ => TyKind::Unknown.intern(&Interner),
         },
     }
 }
diff --git a/crates/hir_ty/src/tests.rs b/crates/hir_ty/src/tests.rs
index fc770ea60..0a4141e69 100644
--- a/crates/hir_ty/src/tests.rs
+++ b/crates/hir_ty/src/tests.rs
@@ -19,6 +19,7 @@ use hir_def::{
     item_scope::ItemScope,
     keys,
     nameres::DefMap,
+    src::HasSource,
     AssocItemId, DefWithBodyId, LocalModuleId, Lookup, ModuleDefId,
 };
 use hir_expand::{db::AstDatabase, InFile};
@@ -195,18 +196,15 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
     defs.sort_by_key(|def| match def {
         DefWithBodyId::FunctionId(it) => {
             let loc = it.lookup(&db);
-            let tree = db.item_tree(loc.id.file_id);
-            tree.source(&db, loc.id).syntax().text_range().start()
+            loc.source(&db).value.syntax().text_range().start()
         }
         DefWithBodyId::ConstId(it) => {
             let loc = it.lookup(&db);
-            let tree = db.item_tree(loc.id.file_id);
-            tree.source(&db, loc.id).syntax().text_range().start()
+            loc.source(&db).value.syntax().text_range().start()
         }
         DefWithBodyId::StaticId(it) => {
             let loc = it.lookup(&db);
-            let tree = db.item_tree(loc.id.file_id);
-            tree.source(&db, loc.id).syntax().text_range().start()
+            loc.source(&db).value.syntax().text_range().start()
         }
     });
     for def in defs {
diff --git a/crates/hir_ty/src/tests/macros.rs b/crates/hir_ty/src/tests/macros.rs
index fb3afaedc..af4f8bb11 100644
--- a/crates/hir_ty/src/tests/macros.rs
+++ b/crates/hir_ty/src/tests/macros.rs
@@ -216,6 +216,22 @@ fn expr_macro_expanded_in_various_places() {
 }
 
 #[test]
+fn expr_macro_expanded_in_stmts() {
+    check_infer(
+        r#"
+        macro_rules! id { ($($es:tt)*) => { $($es)* } }
+        fn foo() {
+            id! { let a = (); }
+        }
+        "#,
+        expect![[r#"
+            !0..8 'leta=();': ()
+            57..84 '{     ...); } }': ()
+        "#]],
+    );
+}
+
+#[test]
 fn infer_type_value_macro_having_same_name() {
     check_infer(
         r#"
diff --git a/crates/hir_ty/src/tests/traits.rs b/crates/hir_ty/src/tests/traits.rs
index e185b1c0a..93d3ad020 100644
--- a/crates/hir_ty/src/tests/traits.rs
+++ b/crates/hir_ty/src/tests/traits.rs
@@ -1699,7 +1699,7 @@ fn super_trait_assoc_type_bounds() {
 
 #[test]
 fn fn_trait() {
-    check_infer(
+    check_infer_with_mismatches(
         r#"
         trait FnOnce<Args> {
             type Output;
@@ -1727,7 +1727,7 @@ fn fn_trait() {
 
 #[test]
 fn fn_ptr_and_item() {
-    check_infer(
+    check_infer_with_mismatches(
         r#"
         #[lang="fn_once"]
         trait FnOnce<Args> {
@@ -1743,12 +1743,12 @@ fn fn_ptr_and_item() {
         struct Bar<T>(T);
 
         impl<A1, R, F: FnOnce(A1) -> R> Foo<(A1, R)> for Bar<F> {
-            fn foo(&self) -> (A1, R) {}
+            fn foo(&self) -> (A1, R) { loop {} }
         }
 
         enum Opt<T> { None, Some(T) }
         impl<T> Opt<T> {
-            fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Opt<U> {}
+            fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Opt<U> { loop {} }
         }
 
         fn test() {
@@ -1765,19 +1765,23 @@ fn fn_ptr_and_item() {
             80..84 'args': Args
             139..143 'self': &Self
             243..247 'self': &Bar<F>
-            260..262 '{}': ()
-            346..350 'self': Opt<T>
-            352..353 'f': F
-            368..370 '{}': ()
-            384..500 '{     ...(f); }': ()
-            394..397 'bar': Bar<fn(u8) -> u32>
-            423..426 'bar': Bar<fn(u8) -> u32>
-            423..432 'bar.foo()': (u8, u32)
-            443..446 'opt': Opt<u8>
-            465..466 'f': fn(u8) -> u32
-            487..490 'opt': Opt<u8>
-            487..497 'opt.map(f)': Opt<u32>
-            495..496 'f': fn(u8) -> u32
+            260..271 '{ loop {} }': (A1, R)
+            262..269 'loop {}': !
+            267..269 '{}': ()
+            355..359 'self': Opt<T>
+            361..362 'f': F
+            377..388 '{ loop {} }': Opt<U>
+            379..386 'loop {}': !
+            384..386 '{}': ()
+            402..518 '{     ...(f); }': ()
+            412..415 'bar': Bar<fn(u8) -> u32>
+            441..444 'bar': Bar<fn(u8) -> u32>
+            441..450 'bar.foo()': (u8, u32)
+            461..464 'opt': Opt<u8>
+            483..484 'f': fn(u8) -> u32
+            505..508 'opt': Opt<u8>
+            505..515 'opt.map(f)': Opt<u32>
+            513..514 'f': fn(u8) -> u32
         "#]],
     );
 }
@@ -1859,7 +1863,7 @@ fn fn_trait_deref_with_ty_default() {
 
 #[test]
 fn closure_1() {
-    check_infer(
+    check_infer_with_mismatches(
         r#"
         #[lang = "fn_once"]
         trait FnOnce<Args> {
@@ -1868,7 +1872,7 @@ fn closure_1() {
 
         enum Option<T> { Some(T), None }
         impl<T> Option<T> {
-            fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Option<U> {}
+            fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Option<U> { loop {} }
         }
 
         fn test() {
@@ -1881,37 +1885,39 @@ fn closure_1() {
         expect![[r#"
             147..151 'self': Option<T>
             153..154 'f': F
-            172..174 '{}': ()
-            188..307 '{     ... 1); }': ()
-            198..199 'x': Option<u32>
-            202..214 'Option::Some': Some<u32>(u32) -> Option<u32>
-            202..220 'Option...(1u32)': Option<u32>
-            215..219 '1u32': u32
-            226..227 'x': Option<u32>
-            226..242 'x.map(...v + 1)': Option<u32>
-            232..241 '|v| v + 1': |u32| -> u32
-            233..234 'v': u32
-            236..237 'v': u32
-            236..241 'v + 1': u32
-            240..241 '1': u32
-            248..249 'x': Option<u32>
-            248..264 'x.map(... 1u64)': Option<u64>
-            254..263 '|_v| 1u64': |u32| -> u64
-            255..257 '_v': u32
-            259..263 '1u64': u64
-            274..275 'y': Option<i64>
-            291..292 'x': Option<u32>
-            291..304 'x.map(|_v| 1)': Option<i64>
-            297..303 '|_v| 1': |u32| -> i64
-            298..300 '_v': u32
-            302..303 '1': i64
+            172..183 '{ loop {} }': Option<U>
+            174..181 'loop {}': !
+            179..181 '{}': ()
+            197..316 '{     ... 1); }': ()
+            207..208 'x': Option<u32>
+            211..223 'Option::Some': Some<u32>(u32) -> Option<u32>
+            211..229 'Option...(1u32)': Option<u32>
+            224..228 '1u32': u32
+            235..236 'x': Option<u32>
+            235..251 'x.map(...v + 1)': Option<u32>
+            241..250 '|v| v + 1': |u32| -> u32
+            242..243 'v': u32
+            245..246 'v': u32
+            245..250 'v + 1': u32
+            249..250 '1': u32
+            257..258 'x': Option<u32>
+            257..273 'x.map(... 1u64)': Option<u64>
+            263..272 '|_v| 1u64': |u32| -> u64
+            264..266 '_v': u32
+            268..272 '1u64': u64
+            283..284 'y': Option<i64>
+            300..301 'x': Option<u32>
+            300..313 'x.map(|_v| 1)': Option<i64>
+            306..312 '|_v| 1': |u32| -> i64
+            307..309 '_v': u32
+            311..312 '1': i64
         "#]],
     );
 }
 
 #[test]
 fn closure_2() {
-    check_infer(
+    check_infer_with_mismatches(
         r#"
         trait FnOnce<Args> {
             type Output;
@@ -1951,22 +1957,22 @@ fn closure_2() {
 
 #[test]
 fn closure_as_argument_inference_order() {
-    check_infer(
+    check_infer_with_mismatches(
         r#"
         #[lang = "fn_once"]
         trait FnOnce<Args> {
             type Output;
         }
 
-        fn foo1<T, U, F: FnOnce(T) -> U>(x: T, f: F) -> U {}
-        fn foo2<T, U, F: FnOnce(T) -> U>(f: F, x: T) -> U {}
+        fn foo1<T, U, F: FnOnce(T) -> U>(x: T, f: F) -> U { loop {} }
+        fn foo2<T, U, F: FnOnce(T) -> U>(f: F, x: T) -> U { loop {} }
 
         struct S;
         impl S {
             fn method(self) -> u64;
 
-            fn foo1<T, U, F: FnOnce(T) -> U>(self, x: T, f: F) -> U {}
-            fn foo2<T, U, F: FnOnce(T) -> U>(self, f: F, x: T) -> U {}
+            fn foo1<T, U, F: FnOnce(T) -> U>(self, x: T, f: F) -> U { loop {} }
+            fn foo2<T, U, F: FnOnce(T) -> U>(self, f: F, x: T) -> U { loop {} }
         }
 
         fn test() {
@@ -1979,52 +1985,60 @@ fn closure_as_argument_inference_order() {
         expect![[r#"
             94..95 'x': T
             100..101 'f': F
-            111..113 '{}': ()
-            147..148 'f': F
-            153..154 'x': T
-            164..166 '{}': ()
-            201..205 'self': S
-            253..257 'self': S
-            259..260 'x': T
-            265..266 'f': F
-            276..278 '{}': ()
-            316..320 'self': S
-            322..323 'f': F
-            328..329 'x': T
-            339..341 '{}': ()
-            355..514 '{     ... S); }': ()
-            365..367 'x1': u64
-            370..374 'foo1': fn foo1<S, u64, |S| -> u64>(S, |S| -> u64) -> u64
-            370..393 'foo1(S...hod())': u64
-            375..376 'S': S
-            378..392 '|s| s.method()': |S| -> u64
-            379..380 's': S
-            382..383 's': S
-            382..392 's.method()': u64
-            403..405 'x2': u64
-            408..412 'foo2': fn foo2<S, u64, |S| -> u64>(|S| -> u64, S) -> u64
-            408..431 'foo2(|...(), S)': u64
-            413..427 '|s| s.method()': |S| -> u64
-            414..415 's': S
-            417..418 's': S
-            417..427 's.method()': u64
-            429..430 'S': S
-            441..443 'x3': u64
-            446..447 'S': S
-            446..471 'S.foo1...hod())': u64
-            453..454 'S': S
-            456..470 '|s| s.method()': |S| -> u64
-            457..458 's': S
-            460..461 's': S
-            460..470 's.method()': u64
-            481..483 'x4': u64
-            486..487 'S': S
-            486..511 'S.foo2...(), S)': u64
-            493..507 '|s| s.method()': |S| -> u64
-            494..495 's': S
-            497..498 's': S
-            497..507 's.method()': u64
-            509..510 'S': S
+            111..122 '{ loop {} }': U
+            113..120 'loop {}': !
+            118..120 '{}': ()
+            156..157 'f': F
+            162..163 'x': T
+            173..184 '{ loop {} }': U
+            175..182 'loop {}': !
+            180..182 '{}': ()
+            219..223 'self': S
+            271..275 'self': S
+            277..278 'x': T
+            283..284 'f': F
+            294..305 '{ loop {} }': U
+            296..303 'loop {}': !
+            301..303 '{}': ()
+            343..347 'self': S
+            349..350 'f': F
+            355..356 'x': T
+            366..377 '{ loop {} }': U
+            368..375 'loop {}': !
+            373..375 '{}': ()
+            391..550 '{     ... S); }': ()
+            401..403 'x1': u64
+            406..410 'foo1': fn foo1<S, u64, |S| -> u64>(S, |S| -> u64) -> u64
+            406..429 'foo1(S...hod())': u64
+            411..412 'S': S
+            414..428 '|s| s.method()': |S| -> u64
+            415..416 's': S
+            418..419 's': S
+            418..428 's.method()': u64
+            439..441 'x2': u64
+            444..448 'foo2': fn foo2<S, u64, |S| -> u64>(|S| -> u64, S) -> u64
+            444..467 'foo2(|...(), S)': u64
+            449..463 '|s| s.method()': |S| -> u64
+            450..451 's': S
+            453..454 's': S
+            453..463 's.method()': u64
+            465..466 'S': S
+            477..479 'x3': u64
+            482..483 'S': S
+            482..507 'S.foo1...hod())': u64
+            489..490 'S': S
+            492..506 '|s| s.method()': |S| -> u64
+            493..494 's': S
+            496..497 's': S
+            496..506 's.method()': u64
+            517..519 'x4': u64
+            522..523 'S': S
+            522..547 'S.foo2...(), S)': u64
+            529..543 '|s| s.method()': |S| -> u64
+            530..531 's': S
+            533..534 's': S
+            533..543 's.method()': u64
+            545..546 'S': S
         "#]],
     );
 }
@@ -2536,7 +2550,7 @@ fn test() {
 
 #[test]
 fn iterator_chain() {
-    check_infer(
+    check_infer_with_mismatches(
         r#"
         //- /main.rs
         #[lang = "fn_once"]
@@ -2939,7 +2953,7 @@ fn infer_closure_arg() {
 
 #[test]
 fn infer_fn_trait_arg() {
-    check_infer(
+    check_infer_with_mismatches(
         r#"
         //- /lib.rs deps:std
 
@@ -2986,7 +3000,8 @@ fn infer_fn_trait_arg() {
 
 #[test]
 fn infer_box_fn_arg() {
-    check_infer(
+    // The type mismatch is a bug
+    check_infer_with_mismatches(
         r#"
         //- /lib.rs deps:std
 
@@ -3025,7 +3040,7 @@ fn infer_box_fn_arg() {
         fn foo() {
             let s = Option::None;
             let f: Box<dyn FnOnce(&Option<i32>)> = box (|ps| {});
-            f(&s)
+            f(&s);
         }
         "#,
         expect![[r#"
@@ -3037,7 +3052,7 @@ fn infer_box_fn_arg() {
             406..417 '&self.inner': &*mut T
             407..411 'self': &Box<T>
             407..417 'self.inner': *mut T
-            478..575 '{     ...(&s) }': FnOnce::Output<dyn FnOnce(&Option<i32>), (&Option<i32>,)>
+            478..576 '{     ...&s); }': ()
             488..489 's': Option<i32>
             492..504 'Option::None': Option<i32>
             514..515 'f': Box<dyn FnOnce(&Option<i32>)>
@@ -3049,6 +3064,7 @@ fn infer_box_fn_arg() {
             568..573 'f(&s)': FnOnce::Output<dyn FnOnce(&Option<i32>), (&Option<i32>,)>
             570..572 '&s': &Option<i32>
             571..572 's': Option<i32>
+            549..562: expected Box<dyn FnOnce(&Option<i32>)>, got Box<|_| -> ()>
         "#]],
     );
 }
diff --git a/crates/hir_ty/src/traits.rs b/crates/hir_ty/src/traits.rs
index 27f350f70..a6a63c673 100644
--- a/crates/hir_ty/src/traits.rs
+++ b/crates/hir_ty/src/traits.rs
@@ -10,7 +10,9 @@ use stdx::panic_context;
 
 use crate::{db::HirDatabase, DebruijnIndex, Substs};
 
-use super::{Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty, TypeWalk};
+use super::{
+    Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty, TyKind, TypeWalk,
+};
 
 use self::chalk::{from_chalk, Interner, ToChalk};
 
@@ -61,6 +63,15 @@ impl TraitEnvironment {
     }
 }
 
+impl Default for TraitEnvironment {
+    fn default() -> Self {
+        TraitEnvironment {
+            traits_from_clauses: Vec::new(),
+            env: chalk_ir::Environment::new(&Interner),
+        }
+    }
+}
+
 /// Something (usually a goal), along with an environment.
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct InEnvironment<T> {
@@ -132,7 +143,7 @@ pub(crate) fn trait_solve_query(
     log::info!("trait_solve_query({})", goal.value.value.display(db));
 
     if let Obligation::Projection(pred) = &goal.value.value {
-        if let Ty::BoundVar(_) = &pred.projection_ty.parameters[0] {
+        if let TyKind::BoundVar(_) = &pred.projection_ty.substitution[0].interned(&Interner) {
             // Hack: don't ask Chalk to normalize with an unknown self type, it'll say that's impossible
             return Some(Solution::Ambig(Guidance::Unknown));
         }
diff --git a/crates/hir_ty/src/traits/chalk.rs b/crates/hir_ty/src/traits/chalk.rs
index 1a2a3a8c7..4bd8ba303 100644
--- a/crates/hir_ty/src/traits/chalk.rs
+++ b/crates/hir_ty/src/traits/chalk.rs
@@ -17,16 +17,18 @@ use super::ChalkContext;
 use crate::{
     db::HirDatabase,
     display::HirDisplay,
+    from_assoc_type_id,
     method_resolution::{TyFingerprint, ALL_FLOAT_FPS, ALL_INT_FPS},
+    to_assoc_type_id,
     utils::generics,
-    BoundVar, CallableDefId, CallableSig, DebruijnIndex, GenericPredicate, ProjectionPredicate,
-    ProjectionTy, Substs, TraitRef, Ty,
+    BoundVar, CallableDefId, CallableSig, DebruijnIndex, FnDefId, GenericPredicate,
+    ProjectionPredicate, ProjectionTy, Substs, TraitRef, Ty, TyKind,
 };
 use mapping::{
-    convert_where_clauses, generic_predicate_to_inline_bound, make_binders, TypeAliasAsAssocType,
-    TypeAliasAsValue,
+    convert_where_clauses, generic_predicate_to_inline_bound, make_binders, TypeAliasAsValue,
 };
 
+pub use self::interner::Interner;
 pub(crate) use self::interner::*;
 
 pub(super) mod tls;
@@ -90,7 +92,7 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
             ty: &Ty,
             binders: &CanonicalVarKinds<Interner>,
         ) -> Option<chalk_ir::TyVariableKind> {
-            if let Ty::BoundVar(bv) = ty {
+            if let TyKind::BoundVar(bv) = ty.interned(&Interner) {
                 let binders = binders.as_slice(&Interner);
                 if bv.debruijn == DebruijnIndex::INNERMOST {
                     if let chalk_ir::VariableKind::Ty(tk) = binders[bv.index].kind {
@@ -175,10 +177,9 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
     }
 
     fn opaque_ty_data(&self, id: chalk_ir::OpaqueTyId<Interner>) -> Arc<OpaqueTyDatum> {
-        let interned_id = crate::db::InternedOpaqueTyId::from(id);
-        let full_id = self.db.lookup_intern_impl_trait_id(interned_id);
+        let full_id = self.db.lookup_intern_impl_trait_id(id.into());
         let bound = match full_id {
-            crate::OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+            crate::ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                 let datas = self
                     .db
                     .return_type_impl_traits(func)
@@ -200,7 +201,7 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
                 let num_vars = datas.num_binders;
                 make_binders(bound, num_vars)
             }
-            crate::OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
+            crate::ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                 if let Some((future_trait, future_output)) = self
                     .db
                     .lang_item(self.krate, "future_trait".into())
@@ -220,21 +221,25 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
                     let impl_bound = GenericPredicate::Implemented(TraitRef {
                         trait_: future_trait,
                         // Self type as the first parameter.
-                        substs: Substs::single(Ty::BoundVar(BoundVar {
-                            debruijn: DebruijnIndex::INNERMOST,
-                            index: 0,
-                        })),
+                        substs: Substs::single(
+                            TyKind::BoundVar(BoundVar {
+                                debruijn: DebruijnIndex::INNERMOST,
+                                index: 0,
+                            })
+                            .intern(&Interner),
+                        ),
                     });
                     let proj_bound = GenericPredicate::Projection(ProjectionPredicate {
                         // The parameter of the opaque type.
-                        ty: Ty::BoundVar(BoundVar { debruijn: DebruijnIndex::ONE, index: 0 }),
+                        ty: TyKind::BoundVar(BoundVar { debruijn: DebruijnIndex::ONE, index: 0 })
+                            .intern(&Interner),
                         projection_ty: ProjectionTy {
-                            associated_ty: future_output,
+                            associated_ty_id: to_assoc_type_id(future_output),
                             // Self type as the first parameter.
-                            parameters: Substs::single(Ty::BoundVar(BoundVar::new(
-                                DebruijnIndex::INNERMOST,
-                                0,
-                            ))),
+                            substitution: Substs::single(
+                                TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
+                                    .intern(&Interner),
+                            ),
                         },
                     });
                     let bound = OpaqueTyDatumBound {
@@ -263,7 +268,7 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
 
     fn hidden_opaque_type(&self, _id: chalk_ir::OpaqueTyId<Interner>) -> chalk_ir::Ty<Interner> {
         // FIXME: actually provide the hidden type; it is relevant for auto traits
-        Ty::Unknown.to_chalk(self.db)
+        TyKind::Unknown.intern(&Interner).to_chalk(self.db)
     }
 
     fn is_object_safe(&self, _trait_id: chalk_ir::TraitId<Interner>) -> bool {
@@ -378,7 +383,7 @@ pub(crate) fn associated_ty_data_query(
     id: AssocTypeId,
 ) -> Arc<AssociatedTyDatum> {
     debug!("associated_ty_data {:?}", id);
-    let type_alias: TypeAliasId = from_chalk::<TypeAliasAsAssocType, _>(db, id).0;
+    let type_alias: TypeAliasId = from_assoc_type_id(id);
     let trait_ = match type_alias.lookup(db.upcast()).container {
         AssocContainerId::TraitId(t) => t,
         _ => panic!("associated type not in trait"),
@@ -391,11 +396,12 @@ pub(crate) fn associated_ty_data_query(
     let resolver = hir_def::resolver::HasResolver::resolver(type_alias, db.upcast());
     let ctx = crate::TyLoweringContext::new(db, &resolver)
         .with_type_param_mode(crate::lower::TypeParamLoweringMode::Variable);
-    let self_ty = Ty::BoundVar(crate::BoundVar::new(crate::DebruijnIndex::INNERMOST, 0));
+    let self_ty =
+        TyKind::BoundVar(BoundVar::new(crate::DebruijnIndex::INNERMOST, 0)).intern(&Interner);
     let bounds = type_alias_data
         .bounds
         .iter()
-        .flat_map(|bound| GenericPredicate::from_type_bound(&ctx, bound, self_ty.clone()))
+        .flat_map(|bound| ctx.lower_type_bound(bound, self_ty.clone()))
         .filter_map(|pred| generic_predicate_to_inline_bound(db, &pred, &self_ty))
         .map(|bound| make_binders(bound.shifted_in(&Interner), 0))
         .collect();
@@ -423,7 +429,7 @@ pub(crate) fn trait_datum_query(
     let generic_params = generics(db.upcast(), trait_.into());
     let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
     let flags = rust_ir::TraitFlags {
-        auto: trait_data.auto,
+        auto: trait_data.is_auto,
         upstream: trait_.lookup(db.upcast()).container.krate() != krate,
         non_enumerable: true,
         coinductive: false, // only relevant for Chalk testing
@@ -432,10 +438,8 @@ pub(crate) fn trait_datum_query(
         fundamental: false,
     };
     let where_clauses = convert_where_clauses(db, trait_.into(), &bound_vars);
-    let associated_ty_ids = trait_data
-        .associated_types()
-        .map(|type_alias| TypeAliasAsAssocType(type_alias).to_chalk(db))
-        .collect();
+    let associated_ty_ids =
+        trait_data.associated_types().map(|type_alias| to_assoc_type_id(type_alias)).collect();
     let trait_datum_bound = rust_ir::TraitDatumBound { where_clauses };
     let well_known =
         lang_attr(db.upcast(), trait_).and_then(|name| well_known_trait_from_lang_attr(&name));
@@ -617,7 +621,7 @@ fn type_alias_associated_ty_value(
     let value_bound = rust_ir::AssociatedTyValueBound { ty: ty.value.to_chalk(db) };
     let value = rust_ir::AssociatedTyValue {
         impl_id: impl_id.to_chalk(db),
-        associated_ty_id: TypeAliasAsAssocType(assoc_ty).to_chalk(db),
+        associated_ty_id: to_assoc_type_id(assoc_ty),
         value: make_binders(value_bound, ty.num_binders),
     };
     Arc::new(value)
@@ -711,14 +715,14 @@ impl From<crate::db::InternedOpaqueTyId> for OpaqueTyId {
     }
 }
 
-impl From<chalk_ir::ClosureId<Interner>> for crate::db::ClosureId {
+impl From<chalk_ir::ClosureId<Interner>> for crate::db::InternedClosureId {
     fn from(id: chalk_ir::ClosureId<Interner>) -> Self {
         Self::from_intern_id(id.0)
     }
 }
 
-impl From<crate::db::ClosureId> for chalk_ir::ClosureId<Interner> {
-    fn from(id: crate::db::ClosureId) -> Self {
+impl From<crate::db::InternedClosureId> for chalk_ir::ClosureId<Interner> {
+    fn from(id: crate::db::InternedClosureId) -> Self {
         chalk_ir::ClosureId(id.as_intern_id())
     }
 }
diff --git a/crates/hir_ty/src/traits/chalk/interner.rs b/crates/hir_ty/src/traits/chalk/interner.rs
index 54bd1c724..94e94a26d 100644
--- a/crates/hir_ty/src/traits/chalk/interner.rs
+++ b/crates/hir_ty/src/traits/chalk/interner.rs
@@ -5,6 +5,7 @@ use super::tls;
 use base_db::salsa::InternId;
 use chalk_ir::{GenericArg, Goal, GoalData};
 use hir_def::TypeAliasId;
+use smallvec::SmallVec;
 use std::{fmt, sync::Arc};
 
 #[derive(Debug, Copy, Clone, Hash, PartialOrd, Ord, PartialEq, Eq)]
@@ -12,7 +13,6 @@ pub struct Interner;
 
 pub(crate) type AssocTypeId = chalk_ir::AssocTypeId<Interner>;
 pub(crate) type AssociatedTyDatum = chalk_solve::rust_ir::AssociatedTyDatum<Interner>;
-pub(crate) type ForeignDefId = chalk_ir::ForeignDefId<Interner>;
 pub(crate) type TraitId = chalk_ir::TraitId<Interner>;
 pub(crate) type TraitDatum = chalk_solve::rust_ir::TraitDatum<Interner>;
 pub(crate) type AdtId = chalk_ir::AdtId<Interner>;
@@ -21,7 +21,6 @@ pub(crate) type ImplId = chalk_ir::ImplId<Interner>;
 pub(crate) type ImplDatum = chalk_solve::rust_ir::ImplDatum<Interner>;
 pub(crate) type AssociatedTyValueId = chalk_solve::rust_ir::AssociatedTyValueId<Interner>;
 pub(crate) type AssociatedTyValue = chalk_solve::rust_ir::AssociatedTyValue<Interner>;
-pub(crate) type FnDefId = chalk_ir::FnDefId<Interner>;
 pub(crate) type FnDefDatum = chalk_solve::rust_ir::FnDefDatum<Interner>;
 pub(crate) type OpaqueTyId = chalk_ir::OpaqueTyId<Interner>;
 pub(crate) type OpaqueTyDatum = chalk_solve::rust_ir::OpaqueTyDatum<Interner>;
@@ -35,7 +34,7 @@ impl chalk_ir::interner::Interner for Interner {
     type InternedGenericArg = chalk_ir::GenericArgData<Self>;
     type InternedGoal = Arc<GoalData<Self>>;
     type InternedGoals = Vec<Goal<Self>>;
-    type InternedSubstitution = Vec<GenericArg<Self>>;
+    type InternedSubstitution = SmallVec<[GenericArg<Self>; 2]>;
     type InternedProgramClause = Arc<chalk_ir::ProgramClauseData<Self>>;
     type InternedProgramClauses = Arc<[chalk_ir::ProgramClause<Self>]>;
     type InternedQuantifiedWhereClauses = Vec<chalk_ir::QuantifiedWhereClause<Self>>;
@@ -267,13 +266,13 @@ impl chalk_ir::interner::Interner for Interner {
     fn intern_substitution<E>(
         &self,
         data: impl IntoIterator<Item = Result<GenericArg<Self>, E>>,
-    ) -> Result<Vec<GenericArg<Self>>, E> {
+    ) -> Result<Self::InternedSubstitution, E> {
         data.into_iter().collect()
     }
 
     fn substitution_data<'a>(
         &self,
-        substitution: &'a Vec<GenericArg<Self>>,
+        substitution: &'a Self::InternedSubstitution,
     ) -> &'a [GenericArg<Self>] {
         substitution
     }
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index b0415e8b0..6a8b6752e 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -3,10 +3,7 @@
 //! Chalk (in both directions); plus some helper functions for more specialized
 //! conversions.
 
-use chalk_ir::{
-    cast::Cast, fold::shift::Shift, interner::HasInterner, LifetimeData, PlaceholderIndex,
-    UniverseIndex,
-};
+use chalk_ir::{cast::Cast, fold::shift::Shift, interner::HasInterner, LifetimeData};
 use chalk_solve::rust_ir;
 
 use base_db::salsa::InternKey;
@@ -14,10 +11,11 @@ use hir_def::{AssocContainerId, GenericDefId, Lookup, TypeAliasId};
 
 use crate::{
     db::HirDatabase,
+    from_assoc_type_id,
     primitive::UintTy,
     traits::{Canonical, Obligation},
-    AliasTy, CallableDefId, FnPointer, FnSig, GenericPredicate, InEnvironment, OpaqueTy,
-    OpaqueTyId, ProjectionPredicate, ProjectionTy, Scalar, Substs, TraitRef, Ty,
+    AliasTy, CallableDefId, FnPointer, GenericPredicate, InEnvironment, OpaqueTy,
+    ProjectionPredicate, ProjectionTy, Scalar, Substs, TraitRef, Ty,
 };
 
 use super::interner::*;
@@ -26,71 +24,60 @@ use super::*;
 impl ToChalk for Ty {
     type Chalk = chalk_ir::Ty<Interner>;
     fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Ty<Interner> {
-        match self {
-            Ty::Ref(m, parameters) => ref_to_chalk(db, m, parameters),
-            Ty::Array(parameters) => array_to_chalk(db, parameters),
-            Ty::Function(FnPointer { sig: FnSig { variadic }, substs, .. }) => {
+        match self.into_inner() {
+            TyKind::Ref(m, ty) => ref_to_chalk(db, m, ty),
+            TyKind::Array(ty) => array_to_chalk(db, ty),
+            TyKind::Function(FnPointer { sig, substs, .. }) => {
                 let substitution = chalk_ir::FnSubst(substs.to_chalk(db).shifted_in(&Interner));
                 chalk_ir::TyKind::Function(chalk_ir::FnPointer {
                     num_binders: 0,
-                    sig: chalk_ir::FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic },
+                    sig,
                     substitution,
                 })
                 .intern(&Interner)
             }
-            Ty::AssociatedType(type_alias, substs) => {
-                let assoc_type = TypeAliasAsAssocType(type_alias);
-                let assoc_type_id = assoc_type.to_chalk(db);
+            TyKind::AssociatedType(assoc_type_id, substs) => {
                 let substitution = substs.to_chalk(db);
                 chalk_ir::TyKind::AssociatedType(assoc_type_id, substitution).intern(&Interner)
             }
 
-            Ty::OpaqueType(impl_trait_id, substs) => {
-                let id = impl_trait_id.to_chalk(db);
+            TyKind::OpaqueType(id, substs) => {
                 let substitution = substs.to_chalk(db);
                 chalk_ir::TyKind::OpaqueType(id, substitution).intern(&Interner)
             }
 
-            Ty::ForeignType(type_alias) => {
-                let foreign_type = TypeAliasAsForeignType(type_alias);
-                let foreign_type_id = foreign_type.to_chalk(db);
-                chalk_ir::TyKind::Foreign(foreign_type_id).intern(&Interner)
-            }
+            TyKind::ForeignType(id) => chalk_ir::TyKind::Foreign(id).intern(&Interner),
 
-            Ty::Scalar(scalar) => chalk_ir::TyKind::Scalar(scalar).intern(&Interner),
+            TyKind::Scalar(scalar) => chalk_ir::TyKind::Scalar(scalar).intern(&Interner),
 
-            Ty::Tuple(cardinality, substs) => {
+            TyKind::Tuple(cardinality, substs) => {
                 let substitution = substs.to_chalk(db);
                 chalk_ir::TyKind::Tuple(cardinality.into(), substitution).intern(&Interner)
             }
-            Ty::Raw(mutability, substs) => {
-                let ty = substs[0].clone().to_chalk(db);
+            TyKind::Raw(mutability, ty) => {
+                let ty = ty.to_chalk(db);
                 chalk_ir::TyKind::Raw(mutability, ty).intern(&Interner)
             }
-            Ty::Slice(substs) => {
-                chalk_ir::TyKind::Slice(substs[0].clone().to_chalk(db)).intern(&Interner)
-            }
-            Ty::Str => chalk_ir::TyKind::Str.intern(&Interner),
-            Ty::FnDef(callable_def, substs) => {
-                let id = callable_def.to_chalk(db);
+            TyKind::Slice(ty) => chalk_ir::TyKind::Slice(ty.to_chalk(db)).intern(&Interner),
+            TyKind::Str => chalk_ir::TyKind::Str.intern(&Interner),
+            TyKind::FnDef(id, substs) => {
                 let substitution = substs.to_chalk(db);
                 chalk_ir::TyKind::FnDef(id, substitution).intern(&Interner)
             }
-            Ty::Never => chalk_ir::TyKind::Never.intern(&Interner),
+            TyKind::Never => chalk_ir::TyKind::Never.intern(&Interner),
 
-            Ty::Closure(def, expr, substs) => {
-                let closure_id = db.intern_closure((def, expr));
+            TyKind::Closure(closure_id, substs) => {
                 let substitution = substs.to_chalk(db);
-                chalk_ir::TyKind::Closure(closure_id.into(), substitution).intern(&Interner)
+                chalk_ir::TyKind::Closure(closure_id, substitution).intern(&Interner)
             }
 
-            Ty::Adt(adt_id, substs) => {
+            TyKind::Adt(adt_id, substs) => {
                 let substitution = substs.to_chalk(db);
                 chalk_ir::TyKind::Adt(adt_id, substitution).intern(&Interner)
             }
-            Ty::Alias(AliasTy::Projection(proj_ty)) => {
-                let associated_ty_id = TypeAliasAsAssocType(proj_ty.associated_ty).to_chalk(db);
-                let substitution = proj_ty.parameters.to_chalk(db);
+            TyKind::Alias(AliasTy::Projection(proj_ty)) => {
+                let associated_ty_id = proj_ty.associated_ty_id;
+                let substitution = proj_ty.substitution.to_chalk(db);
                 chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
                     associated_ty_id,
                     substitution,
@@ -98,17 +85,17 @@ impl ToChalk for Ty {
                 .cast(&Interner)
                 .intern(&Interner)
             }
-            Ty::Placeholder(id) => {
-                let interned_id = db.intern_type_param_id(id);
-                PlaceholderIndex {
-                    ui: UniverseIndex::ROOT,
-                    idx: interned_id.as_intern_id().as_usize(),
-                }
-                .to_ty::<Interner>(&Interner)
-            }
-            Ty::BoundVar(idx) => chalk_ir::TyKind::BoundVar(idx).intern(&Interner),
-            Ty::InferenceVar(..) => panic!("uncanonicalized infer ty"),
-            Ty::Dyn(predicates) => {
+            TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
+                let opaque_ty_id = opaque_ty.opaque_ty_id;
+                let substitution = opaque_ty.substitution.to_chalk(db);
+                chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy { opaque_ty_id, substitution })
+                    .cast(&Interner)
+                    .intern(&Interner)
+            }
+            TyKind::Placeholder(idx) => idx.to_ty::<Interner>(&Interner),
+            TyKind::BoundVar(idx) => chalk_ir::TyKind::BoundVar(idx).intern(&Interner),
+            TyKind::InferenceVar(..) => panic!("uncanonicalized infer ty"),
+            TyKind::Dyn(predicates) => {
                 let where_clauses = chalk_ir::QuantifiedWhereClauses::from_iter(
                     &Interner,
                     predicates.iter().filter(|p| !p.is_error()).cloned().map(|p| p.to_chalk(db)),
@@ -119,43 +106,30 @@ impl ToChalk for Ty {
                 };
                 chalk_ir::TyKind::Dyn(bounded_ty).intern(&Interner)
             }
-            Ty::Alias(AliasTy::Opaque(opaque_ty)) => {
-                let opaque_ty_id = opaque_ty.opaque_ty_id.to_chalk(db);
-                let substitution = opaque_ty.parameters.to_chalk(db);
-                chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
-                    opaque_ty_id,
-                    substitution,
-                }))
-                .intern(&Interner)
-            }
-            Ty::Unknown => chalk_ir::TyKind::Error.intern(&Interner),
+            TyKind::Unknown => chalk_ir::TyKind::Error.intern(&Interner),
         }
     }
     fn from_chalk(db: &dyn HirDatabase, chalk: chalk_ir::Ty<Interner>) -> Self {
         match chalk.data(&Interner).kind.clone() {
-            chalk_ir::TyKind::Error => Ty::Unknown,
-            chalk_ir::TyKind::Array(ty, _size) => Ty::Array(Substs::single(from_chalk(db, ty))),
-            chalk_ir::TyKind::Placeholder(idx) => {
-                assert_eq!(idx.ui, UniverseIndex::ROOT);
-                let interned_id = crate::db::GlobalTypeParamId::from_intern_id(
-                    crate::salsa::InternId::from(idx.idx),
-                );
-                Ty::Placeholder(db.lookup_intern_type_param_id(interned_id))
-            }
+            chalk_ir::TyKind::Error => TyKind::Unknown,
+            chalk_ir::TyKind::Array(ty, _size) => TyKind::Array(from_chalk(db, ty)),
+            chalk_ir::TyKind::Placeholder(idx) => TyKind::Placeholder(idx),
             chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Projection(proj)) => {
-                let associated_ty =
-                    from_chalk::<TypeAliasAsAssocType, _>(db, proj.associated_ty_id).0;
+                let associated_ty = proj.associated_ty_id;
                 let parameters = from_chalk(db, proj.substitution);
-                Ty::Alias(AliasTy::Projection(ProjectionTy { associated_ty, parameters }))
+                TyKind::Alias(AliasTy::Projection(ProjectionTy {
+                    associated_ty_id: associated_ty,
+                    substitution: parameters,
+                }))
             }
             chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(opaque_ty)) => {
-                let impl_trait_id = from_chalk(db, opaque_ty.opaque_ty_id);
+                let opaque_ty_id = opaque_ty.opaque_ty_id;
                 let parameters = from_chalk(db, opaque_ty.substitution);
-                Ty::Alias(AliasTy::Opaque(OpaqueTy { opaque_ty_id: impl_trait_id, parameters }))
+                TyKind::Alias(AliasTy::Opaque(OpaqueTy { opaque_ty_id, substitution: parameters }))
             }
             chalk_ir::TyKind::Function(chalk_ir::FnPointer {
                 num_binders,
-                sig: chalk_ir::FnSig { variadic, .. },
+                sig,
                 substitution,
                 ..
             }) => {
@@ -164,14 +138,10 @@ impl ToChalk for Ty {
                     db,
                     substitution.0.shifted_out(&Interner).expect("fn ptr should have no binders"),
                 );
-                Ty::Function(FnPointer {
-                    num_args: (substs.len() - 1),
-                    sig: FnSig { variadic },
-                    substs,
-                })
+                TyKind::Function(FnPointer { num_args: (substs.len() - 1), sig, substs })
             }
-            chalk_ir::TyKind::BoundVar(idx) => Ty::BoundVar(idx),
-            chalk_ir::TyKind::InferenceVar(_iv, _kind) => Ty::Unknown,
+            chalk_ir::TyKind::BoundVar(idx) => TyKind::BoundVar(idx),
+            chalk_ir::TyKind::InferenceVar(_iv, _kind) => TyKind::Unknown,
             chalk_ir::TyKind::Dyn(where_clauses) => {
                 assert_eq!(where_clauses.bounds.binders.len(&Interner), 1);
                 let predicates = where_clauses
@@ -180,49 +150,41 @@ impl ToChalk for Ty {
                     .iter(&Interner)
                     .map(|c| from_chalk(db, c.clone()))
                     .collect();
-                Ty::Dyn(predicates)
+                TyKind::Dyn(predicates)
             }
 
-            chalk_ir::TyKind::Adt(adt_id, subst) => Ty::Adt(adt_id, from_chalk(db, subst)),
-            chalk_ir::TyKind::AssociatedType(type_id, subst) => Ty::AssociatedType(
-                from_chalk::<TypeAliasAsAssocType, _>(db, type_id).0,
-                from_chalk(db, subst),
-            ),
+            chalk_ir::TyKind::Adt(adt_id, subst) => TyKind::Adt(adt_id, from_chalk(db, subst)),
+            chalk_ir::TyKind::AssociatedType(type_id, subst) => {
+                TyKind::AssociatedType(type_id, from_chalk(db, subst))
+            }
 
             chalk_ir::TyKind::OpaqueType(opaque_type_id, subst) => {
-                Ty::OpaqueType(from_chalk(db, opaque_type_id), from_chalk(db, subst))
+                TyKind::OpaqueType(opaque_type_id, from_chalk(db, subst))
             }
 
-            chalk_ir::TyKind::Scalar(scalar) => Ty::Scalar(scalar),
+            chalk_ir::TyKind::Scalar(scalar) => TyKind::Scalar(scalar),
             chalk_ir::TyKind::Tuple(cardinality, subst) => {
-                Ty::Tuple(cardinality, from_chalk(db, subst))
-            }
-            chalk_ir::TyKind::Raw(mutability, ty) => {
-                Ty::Raw(mutability, Substs::single(from_chalk(db, ty)))
+                TyKind::Tuple(cardinality, from_chalk(db, subst))
             }
-            chalk_ir::TyKind::Slice(ty) => Ty::Slice(Substs::single(from_chalk(db, ty))),
+            chalk_ir::TyKind::Raw(mutability, ty) => TyKind::Raw(mutability, from_chalk(db, ty)),
+            chalk_ir::TyKind::Slice(ty) => TyKind::Slice(from_chalk(db, ty)),
             chalk_ir::TyKind::Ref(mutability, _lifetime, ty) => {
-                Ty::Ref(mutability, Substs::single(from_chalk(db, ty)))
+                TyKind::Ref(mutability, from_chalk(db, ty))
             }
-            chalk_ir::TyKind::Str => Ty::Str,
-            chalk_ir::TyKind::Never => Ty::Never,
+            chalk_ir::TyKind::Str => TyKind::Str,
+            chalk_ir::TyKind::Never => TyKind::Never,
 
             chalk_ir::TyKind::FnDef(fn_def_id, subst) => {
-                Ty::FnDef(from_chalk(db, fn_def_id), from_chalk(db, subst))
+                TyKind::FnDef(fn_def_id, from_chalk(db, subst))
             }
 
-            chalk_ir::TyKind::Closure(id, subst) => {
-                let id: crate::db::ClosureId = id.into();
-                let (def, expr) = db.lookup_intern_closure(id);
-                Ty::Closure(def, expr, from_chalk(db, subst))
-            }
+            chalk_ir::TyKind::Closure(id, subst) => TyKind::Closure(id, from_chalk(db, subst)),
 
-            chalk_ir::TyKind::Foreign(foreign_def_id) => {
-                Ty::ForeignType(from_chalk::<TypeAliasAsForeignType, _>(db, foreign_def_id).0)
-            }
+            chalk_ir::TyKind::Foreign(foreign_def_id) => TyKind::ForeignType(foreign_def_id),
             chalk_ir::TyKind::Generator(_, _) => unimplemented!(), // FIXME
             chalk_ir::TyKind::GeneratorWitness(_, _) => unimplemented!(), // FIXME
         }
+        .intern(&Interner)
     }
 }
 
@@ -231,17 +193,17 @@ impl ToChalk for Ty {
 fn ref_to_chalk(
     db: &dyn HirDatabase,
     mutability: chalk_ir::Mutability,
-    subst: Substs,
+    ty: Ty,
 ) -> chalk_ir::Ty<Interner> {
-    let arg = subst[0].clone().to_chalk(db);
+    let arg = ty.to_chalk(db);
     let lifetime = LifetimeData::Static.intern(&Interner);
     chalk_ir::TyKind::Ref(mutability, lifetime, arg).intern(&Interner)
 }
 
 /// We currently don't model constants, but Chalk does. So, we have to insert a
 /// fake constant here, because Chalks built-in logic may expect it to be there.
-fn array_to_chalk(db: &dyn HirDatabase, subst: Substs) -> chalk_ir::Ty<Interner> {
-    let arg = subst[0].clone().to_chalk(db);
+fn array_to_chalk(db: &dyn HirDatabase, ty: Ty) -> chalk_ir::Ty<Interner> {
+    let arg = ty.to_chalk(db);
     let usize_ty = chalk_ir::TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner);
     let const_ = chalk_ir::ConstData {
         ty: usize_ty,
@@ -298,21 +260,6 @@ impl ToChalk for hir_def::TraitId {
     }
 }
 
-impl ToChalk for OpaqueTyId {
-    type Chalk = chalk_ir::OpaqueTyId<Interner>;
-
-    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::OpaqueTyId<Interner> {
-        db.intern_impl_trait_id(self).into()
-    }
-
-    fn from_chalk(
-        db: &dyn HirDatabase,
-        opaque_ty_id: chalk_ir::OpaqueTyId<Interner>,
-    ) -> OpaqueTyId {
-        db.lookup_intern_impl_trait_id(opaque_ty_id.into())
-    }
-}
-
 impl ToChalk for hir_def::ImplId {
     type Chalk = ImplId;
 
@@ -337,34 +284,6 @@ impl ToChalk for CallableDefId {
     }
 }
 
-pub(crate) struct TypeAliasAsAssocType(pub(crate) TypeAliasId);
-
-impl ToChalk for TypeAliasAsAssocType {
-    type Chalk = AssocTypeId;
-
-    fn to_chalk(self, _db: &dyn HirDatabase) -> AssocTypeId {
-        chalk_ir::AssocTypeId(self.0.as_intern_id())
-    }
-
-    fn from_chalk(_db: &dyn HirDatabase, assoc_type_id: AssocTypeId) -> TypeAliasAsAssocType {
-        TypeAliasAsAssocType(InternKey::from_intern_id(assoc_type_id.0))
-    }
-}
-
-pub(crate) struct TypeAliasAsForeignType(pub(crate) TypeAliasId);
-
-impl ToChalk for TypeAliasAsForeignType {
-    type Chalk = ForeignDefId;
-
-    fn to_chalk(self, _db: &dyn HirDatabase) -> ForeignDefId {
-        chalk_ir::ForeignDefId(self.0.as_intern_id())
-    }
-
-    fn from_chalk(_db: &dyn HirDatabase, foreign_def_id: ForeignDefId) -> TypeAliasAsForeignType {
-        TypeAliasAsForeignType(InternKey::from_intern_id(foreign_def_id.0))
-    }
-}
-
 pub(crate) struct TypeAliasAsValue(pub(crate) TypeAliasId);
 
 impl ToChalk for TypeAliasAsValue {
@@ -446,8 +365,8 @@ impl ToChalk for ProjectionTy {
 
     fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::ProjectionTy<Interner> {
         chalk_ir::ProjectionTy {
-            associated_ty_id: TypeAliasAsAssocType(self.associated_ty).to_chalk(db),
-            substitution: self.parameters.to_chalk(db),
+            associated_ty_id: self.associated_ty_id,
+            substitution: self.substitution.to_chalk(db),
         }
     }
 
@@ -456,12 +375,8 @@ impl ToChalk for ProjectionTy {
         projection_ty: chalk_ir::ProjectionTy<Interner>,
     ) -> ProjectionTy {
         ProjectionTy {
-            associated_ty: from_chalk::<TypeAliasAsAssocType, _>(
-                db,
-                projection_ty.associated_ty_id,
-            )
-            .0,
-            parameters: from_chalk(db, projection_ty.substitution),
+            associated_ty_id: projection_ty.associated_ty_id,
+            substitution: from_chalk(db, projection_ty.substitution),
         }
     }
 }
@@ -611,22 +526,24 @@ pub(super) fn generic_predicate_to_inline_bound(
             Some(rust_ir::InlineBound::TraitBound(trait_bound))
         }
         GenericPredicate::Projection(proj) => {
-            if &proj.projection_ty.parameters[0] != self_ty {
+            if &proj.projection_ty.substitution[0] != self_ty {
                 return None;
             }
-            let trait_ = match proj.projection_ty.associated_ty.lookup(db.upcast()).container {
+            let trait_ = match from_assoc_type_id(proj.projection_ty.associated_ty_id)
+                .lookup(db.upcast())
+                .container
+            {
                 AssocContainerId::TraitId(t) => t,
                 _ => panic!("associated type not in trait"),
             };
-            let args_no_self = proj.projection_ty.parameters[1..]
+            let args_no_self = proj.projection_ty.substitution[1..]
                 .iter()
                 .map(|ty| ty.clone().to_chalk(db).cast(&Interner))
                 .collect();
             let alias_eq_bound = rust_ir::AliasEqBound {
                 value: proj.ty.clone().to_chalk(db),
                 trait_bound: rust_ir::TraitBound { trait_id: trait_.to_chalk(db), args_no_self },
-                associated_ty_id: TypeAliasAsAssocType(proj.projection_ty.associated_ty)
-                    .to_chalk(db),
+                associated_ty_id: proj.projection_ty.associated_ty_id,
                 parameters: Vec::new(), // FIXME we don't support generic associated types yet
             };
             Some(rust_ir::InlineBound::AliasEqBound(alias_eq_bound))
diff --git a/crates/hir_ty/src/traits/chalk/tls.rs b/crates/hir_ty/src/traits/chalk/tls.rs
index 75b16172e..8892a63a9 100644
--- a/crates/hir_ty/src/traits/chalk/tls.rs
+++ b/crates/hir_ty/src/traits/chalk/tls.rs
@@ -4,8 +4,8 @@ use std::fmt;
 use chalk_ir::{AliasTy, GenericArg, Goal, Goals, Lifetime, ProgramClauseImplication};
 use itertools::Itertools;
 
-use super::{from_chalk, Interner, TypeAliasAsAssocType};
-use crate::{db::HirDatabase, CallableDefId};
+use super::{from_chalk, Interner};
+use crate::{db::HirDatabase, from_assoc_type_id, CallableDefId};
 use hir_def::{AdtId, AssocContainerId, Lookup, TypeAliasId};
 
 pub(crate) use unsafe_tls::{set_current_program, with_current_program};
@@ -41,7 +41,7 @@ impl DebugContext<'_> {
         id: super::AssocTypeId,
         fmt: &mut fmt::Formatter<'_>,
     ) -> Result<(), fmt::Error> {
-        let type_alias: TypeAliasId = from_chalk::<TypeAliasAsAssocType, _>(self.0, id).0;
+        let type_alias: TypeAliasId = from_assoc_type_id(id);
         let type_alias_data = self.0.type_alias_data(type_alias);
         let trait_ = match type_alias.lookup(self.0.upcast()).container {
             AssocContainerId::TraitId(t) => t,
@@ -75,8 +75,7 @@ impl DebugContext<'_> {
         projection_ty: &chalk_ir::ProjectionTy<Interner>,
         fmt: &mut fmt::Formatter<'_>,
     ) -> Result<(), fmt::Error> {
-        let type_alias: TypeAliasId =
-            from_chalk::<TypeAliasAsAssocType, _>(self.0, projection_ty.associated_ty_id).0;
+        let type_alias = from_assoc_type_id(projection_ty.associated_ty_id);
         let type_alias_data = self.0.type_alias_data(type_alias);
         let trait_ = match type_alias.lookup(self.0.upcast()).container {
             AssocContainerId::TraitId(t) => t,