32 files changed, 3008 insertions, 2272 deletions

diff --git a/crates/hir_ty/src/autoderef.rs b/crates/hir_ty/src/autoderef.rs
index dc5fc759a..f8e9db9ae 100644
--- a/crates/hir_ty/src/autoderef.rs
+++ b/crates/hir_ty/src/autoderef.rs
@@ -12,12 +12,8 @@ use hir_expand::name::name;
 use log::{info, warn};
 
 use crate::{
-    db::HirDatabase,
-    to_assoc_type_id, to_chalk_trait_id,
-    traits::{InEnvironment, Solution},
-    utils::generics,
-    AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds, DebruijnIndex, Interner,
-    ProjectionTy, Substitution, TraitRef, Ty, TyKind,
+    db::HirDatabase, AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds, DebruijnIndex,
+    InEnvironment, Interner, ProjectionTyExt, Solution, Ty, TyBuilder, TyKind,
 };
 
 const AUTODEREF_RECURSION_LIMIT: usize = 10;
@@ -39,13 +35,21 @@ pub(crate) fn deref(
     krate: CrateId,
     ty: InEnvironment<&Canonical<Ty>>,
 ) -> Option<Canonical<Ty>> {
-    if let Some(derefed) = ty.goal.value.builtin_deref() {
+    if let Some(derefed) = builtin_deref(&ty.goal.value) {
         Some(Canonical { value: derefed, binders: ty.goal.binders.clone() })
     } else {
         deref_by_trait(db, krate, ty)
     }
 }
 
+fn builtin_deref(ty: &Ty) -> Option<Ty> {
+    match ty.kind(&Interner) {
+        TyKind::Ref(.., ty) => Some(ty.clone()),
+        TyKind::Raw(.., ty) => Some(ty.clone()),
+        _ => None,
+    }
+}
+
 fn deref_by_trait(
     db: &dyn HirDatabase,
     krate: CrateId,
@@ -57,21 +61,20 @@ fn deref_by_trait(
     };
     let target = db.trait_data(deref_trait).associated_type_by_name(&name![Target])?;
 
-    let generic_params = generics(db.upcast(), target.into());
-    if generic_params.len() != 1 {
-        // the Target type + Deref trait should only have one generic parameter,
-        // namely Deref's Self type
-        return None;
-    }
+    let projection = {
+        let b = TyBuilder::assoc_type_projection(db, target);
+        if b.remaining() != 1 {
+            // the Target type + Deref trait should only have one generic parameter,
+            // namely Deref's Self type
+            return None;
+        }
+        b.push(ty.goal.value.clone()).build()
+    };
 
     // FIXME make the Canonical / bound var handling nicer
 
-    let parameters =
-        Substitution::build_for_generics(&generic_params).push(ty.goal.value.clone()).build();
-
     // Check that the type implements Deref at all
-    let trait_ref =
-        TraitRef { trait_id: to_chalk_trait_id(deref_trait), substitution: parameters.clone() };
+    let trait_ref = projection.trait_ref(db);
     let implements_goal = Canonical {
         binders: ty.goal.binders.clone(),
         value: InEnvironment {
@@ -84,11 +87,8 @@ fn deref_by_trait(
     }
 
     // Now do the assoc type projection
-    let projection = AliasEq {
-        alias: AliasTy::Projection(ProjectionTy {
-            associated_ty_id: to_assoc_type_id(target),
-            substitution: parameters,
-        }),
+    let alias_eq = AliasEq {
+        alias: AliasTy::Projection(projection),
         ty: TyKind::BoundVar(BoundVar::new(
             DebruijnIndex::INNERMOST,
             ty.goal.binders.len(&Interner),
@@ -96,9 +96,7 @@ fn deref_by_trait(
         .intern(&Interner),
     };
 
-    let obligation = projection.cast(&Interner);
-
-    let in_env = InEnvironment { goal: obligation, environment: ty.environment };
+    let in_env = InEnvironment { goal: alias_eq.cast(&Interner), environment: ty.environment };
 
     let canonical = Canonical {
         value: in_env,
@@ -130,8 +128,8 @@ fn deref_by_trait(
             // assumptions will be broken. We would need to properly introduce
             // new variables in that case
 
-            for i in 1..vars.0.binders.len(&Interner) {
-                if vars.0.value[i - 1].interned(&Interner)
+            for i in 1..vars.binders.len(&Interner) {
+                if vars.value.subst.at(&Interner, i - 1).assert_ty_ref(&Interner).kind(&Interner)
                     != &TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, i - 1))
                 {
                     warn!("complex solution for derefing {:?}: {:?}, ignoring", ty.goal, solution);
@@ -139,8 +137,13 @@ fn deref_by_trait(
                 }
             }
             Some(Canonical {
-                value: vars.0.value[vars.0.value.len() - 1].clone(),
-                binders: vars.0.binders.clone(),
+                value: vars
+                    .value
+                    .subst
+                    .at(&Interner, vars.value.subst.len(&Interner) - 1)
+                    .assert_ty_ref(&Interner)
+                    .clone(),
+                binders: vars.binders.clone(),
             })
         }
         Solution::Ambig(_) => {
diff --git a/crates/hir_ty/src/builder.rs b/crates/hir_ty/src/builder.rs
new file mode 100644
index 000000000..09512d1ce
--- /dev/null
+++ b/crates/hir_ty/src/builder.rs
@@ -0,0 +1,223 @@
+//! `TyBuilder`, a helper for building instances of `Ty` and related types.
+
+use std::iter;
+
+use chalk_ir::{
+    cast::{Cast, CastTo, Caster},
+    interner::HasInterner,
+    AdtId, BoundVar, DebruijnIndex, Safety, Scalar,
+};
+use hir_def::{builtin_type::BuiltinType, GenericDefId, TraitId, TypeAliasId};
+use smallvec::SmallVec;
+
+use crate::{
+    db::HirDatabase, primitive, to_assoc_type_id, to_chalk_trait_id, utils::generics, Binders,
+    CallableSig, FnPointer, FnSig, FnSubst, GenericArg, Interner, ProjectionTy, Substitution,
+    TraitRef, Ty, TyDefId, TyExt, TyKind, TypeWalk, ValueTyDefId,
+};
+
+/// This is a builder for `Ty` or anything that needs a `Substitution`.
+pub struct TyBuilder<D> {
+    /// The `data` field is used to keep track of what we're building (e.g. an
+    /// ADT, a `TraitRef`, ...).
+    data: D,
+    vec: SmallVec<[GenericArg; 2]>,
+    param_count: usize,
+}
+
+impl<D> TyBuilder<D> {
+    fn new(data: D, param_count: usize) -> TyBuilder<D> {
+        TyBuilder { data, param_count, vec: SmallVec::with_capacity(param_count) }
+    }
+
+    fn build_internal(self) -> (D, Substitution) {
+        assert_eq!(self.vec.len(), self.param_count);
+        // FIXME: would be good to have a way to construct a chalk_ir::Substitution from the interned form
+        let subst = Substitution::intern(self.vec);
+        (self.data, subst)
+    }
+
+    pub fn push(mut self, arg: impl CastTo<GenericArg>) -> Self {
+        self.vec.push(arg.cast(&Interner));
+        self
+    }
+
+    pub fn remaining(&self) -> usize {
+        self.param_count - self.vec.len()
+    }
+
+    pub fn fill_with_bound_vars(self, debruijn: DebruijnIndex, starting_from: usize) -> Self {
+        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(TyKind::Error.intern(&Interner)))
+    }
+
+    pub fn fill(mut self, filler: impl Iterator<Item = impl CastTo<GenericArg>>) -> Self {
+        self.vec.extend(filler.take(self.remaining()).casted(&Interner));
+        assert_eq!(self.remaining(), 0);
+        self
+    }
+
+    pub fn use_parent_substs(mut self, parent_substs: &Substitution) -> Self {
+        assert!(self.vec.is_empty());
+        assert!(parent_substs.len(&Interner) <= self.param_count);
+        self.vec.extend(parent_substs.iter(&Interner).cloned());
+        self
+    }
+}
+
+impl TyBuilder<()> {
+    pub fn unit() -> Ty {
+        TyKind::Tuple(0, Substitution::empty(&Interner)).intern(&Interner)
+    }
+
+    pub fn fn_ptr(sig: CallableSig) -> Ty {
+        TyKind::Function(FnPointer {
+            num_binders: 0,
+            sig: FnSig { abi: (), safety: Safety::Safe, variadic: sig.is_varargs },
+            substitution: FnSubst(Substitution::from_iter(
+                &Interner,
+                sig.params_and_return.iter().cloned(),
+            )),
+        })
+        .intern(&Interner)
+    }
+
+    pub fn builtin(builtin: BuiltinType) -> Ty {
+        match builtin {
+            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 type_params_subst(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> Substitution {
+        let params = generics(db.upcast(), def.into());
+        params.type_params_subst(db)
+    }
+
+    pub fn subst_for_def(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> TyBuilder<()> {
+        let def = def.into();
+        let params = generics(db.upcast(), def);
+        let param_count = params.len();
+        TyBuilder::new((), param_count)
+    }
+
+    pub fn build(self) -> Substitution {
+        let ((), subst) = self.build_internal();
+        subst
+    }
+}
+
+impl TyBuilder<hir_def::AdtId> {
+    pub fn adt(db: &dyn HirDatabase, adt: hir_def::AdtId) -> TyBuilder<hir_def::AdtId> {
+        let generics = generics(db.upcast(), adt.into());
+        let param_count = generics.len();
+        TyBuilder::new(adt, param_count)
+    }
+
+    pub fn fill_with_defaults(
+        mut self,
+        db: &dyn HirDatabase,
+        mut fallback: impl FnMut() -> Ty,
+    ) -> Self {
+        let defaults = db.generic_defaults(self.data.into());
+        for default_ty in defaults.iter().skip(self.vec.len()) {
+            if default_ty.skip_binders().is_unknown() {
+                self.vec.push(fallback().cast(&Interner));
+            } else {
+                // each default can depend on the previous parameters
+                let subst_so_far = Substitution::intern(self.vec.clone());
+                self.vec
+                    .push(default_ty.clone().substitute(&Interner, &subst_so_far).cast(&Interner));
+            }
+        }
+        self
+    }
+
+    pub fn build(self) -> Ty {
+        let (adt, subst) = self.build_internal();
+        TyKind::Adt(AdtId(adt), subst).intern(&Interner)
+    }
+}
+
+pub struct Tuple(usize);
+impl TyBuilder<Tuple> {
+    pub fn tuple(size: usize) -> TyBuilder<Tuple> {
+        TyBuilder::new(Tuple(size), size)
+    }
+
+    pub fn build(self) -> Ty {
+        let (Tuple(size), subst) = self.build_internal();
+        TyKind::Tuple(size, subst).intern(&Interner)
+    }
+}
+
+impl TyBuilder<TraitId> {
+    pub fn trait_ref(db: &dyn HirDatabase, trait_id: TraitId) -> TyBuilder<TraitId> {
+        let generics = generics(db.upcast(), trait_id.into());
+        let param_count = generics.len();
+        TyBuilder::new(trait_id, param_count)
+    }
+
+    pub fn build(self) -> TraitRef {
+        let (trait_id, substitution) = self.build_internal();
+        TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution }
+    }
+}
+
+impl TyBuilder<TypeAliasId> {
+    pub fn assoc_type_projection(
+        db: &dyn HirDatabase,
+        type_alias: TypeAliasId,
+    ) -> TyBuilder<TypeAliasId> {
+        let generics = generics(db.upcast(), type_alias.into());
+        let param_count = generics.len();
+        TyBuilder::new(type_alias, param_count)
+    }
+
+    pub fn build(self) -> ProjectionTy {
+        let (type_alias, substitution) = self.build_internal();
+        ProjectionTy { associated_ty_id: to_assoc_type_id(type_alias), substitution }
+    }
+}
+
+impl<T: TypeWalk + HasInterner<Interner = Interner>> TyBuilder<Binders<T>> {
+    fn subst_binders(b: Binders<T>) -> Self {
+        let param_count = b.binders.len(&Interner);
+        TyBuilder::new(b, param_count)
+    }
+
+    pub fn build(self) -> T {
+        let (b, subst) = self.build_internal();
+        b.substitute(&Interner, &subst)
+    }
+}
+
+impl TyBuilder<Binders<Ty>> {
+    pub fn def_ty(db: &dyn HirDatabase, def: TyDefId) -> TyBuilder<Binders<Ty>> {
+        TyBuilder::subst_binders(db.ty(def.into()))
+    }
+
+    pub fn impl_self_ty(db: &dyn HirDatabase, def: hir_def::ImplId) -> TyBuilder<Binders<Ty>> {
+        TyBuilder::subst_binders(db.impl_self_ty(def))
+    }
+
+    pub fn value_ty(db: &dyn HirDatabase, def: ValueTyDefId) -> TyBuilder<Binders<Ty>> {
+        TyBuilder::subst_binders(db.value_ty(def))
+    }
+}
diff --git a/crates/hir_ty/src/chalk_cast.rs b/crates/hir_ty/src/chalk_cast.rs
index bf884ae15..df6492113 100644
--- a/crates/hir_ty/src/chalk_cast.rs
+++ b/crates/hir_ty/src/chalk_cast.rs
@@ -5,7 +5,7 @@ use chalk_ir::{
     interner::HasInterner,
 };
 
-use crate::{AliasEq, DomainGoal, Interner, TraitRef, WhereClause};
+use crate::{AliasEq, DomainGoal, GenericArg, GenericArgData, Interner, TraitRef, Ty, WhereClause};
 
 macro_rules! has_interner {
     ($t:ty) => {
@@ -17,6 +17,8 @@ macro_rules! has_interner {
 
 has_interner!(WhereClause);
 has_interner!(DomainGoal);
+has_interner!(GenericArg);
+has_interner!(Ty);
 
 impl CastTo<WhereClause> for TraitRef {
     fn cast_to(self, _interner: &Interner) -> WhereClause {
@@ -36,6 +38,12 @@ impl CastTo<DomainGoal> for WhereClause {
     }
 }
 
+impl CastTo<GenericArg> for Ty {
+    fn cast_to(self, interner: &Interner) -> GenericArg {
+        GenericArg::new(interner, GenericArgData::Ty(self))
+    }
+}
+
 macro_rules! transitive_impl {
     ($a:ty, $b:ty, $c:ty) => {
         impl CastTo<$c> for $a {
@@ -51,3 +59,15 @@ macro_rules! transitive_impl {
 
 transitive_impl!(TraitRef, WhereClause, DomainGoal);
 transitive_impl!(AliasEq, WhereClause, DomainGoal);
+
+macro_rules! reflexive_impl {
+    ($a:ty) => {
+        impl CastTo<$a> for $a {
+            fn cast_to(self, _interner: &Interner) -> $a {
+                self
+            }
+        }
+    };
+}
+
+reflexive_impl!(GenericArg);
diff --git a/crates/hir_ty/src/chalk_ext.rs b/crates/hir_ty/src/chalk_ext.rs
new file mode 100644
index 000000000..28ed3aac6
--- /dev/null
+++ b/crates/hir_ty/src/chalk_ext.rs
@@ -0,0 +1,305 @@
+//! Various extensions traits for Chalk types.
+
+use chalk_ir::Mutability;
+use hir_def::{
+    type_ref::Rawness, AssocContainerId, FunctionId, GenericDefId, HasModule, Lookup, TraitId,
+};
+
+use crate::{
+    db::HirDatabase, from_assoc_type_id, from_chalk_trait_id, from_foreign_def_id,
+    from_placeholder_idx, to_chalk_trait_id, AdtId, AliasEq, AliasTy, Binders, CallableDefId,
+    CallableSig, FnPointer, ImplTraitId, Interner, Lifetime, ProjectionTy, QuantifiedWhereClause,
+    Substitution, TraitRef, Ty, TyBuilder, TyKind, WhereClause,
+};
+
+pub trait TyExt {
+    fn is_unit(&self) -> bool;
+    fn is_never(&self) -> bool;
+    fn is_unknown(&self) -> bool;
+
+    fn as_adt(&self) -> Option<(hir_def::AdtId, &Substitution)>;
+    fn as_tuple(&self) -> Option<&Substitution>;
+    fn as_fn_def(&self, db: &dyn HirDatabase) -> Option<FunctionId>;
+    fn as_reference(&self) -> Option<(&Ty, Lifetime, Mutability)>;
+    fn as_reference_or_ptr(&self) -> Option<(&Ty, Rawness, Mutability)>;
+    fn as_generic_def(&self, db: &dyn HirDatabase) -> Option<GenericDefId>;
+
+    fn callable_def(&self, db: &dyn HirDatabase) -> Option<CallableDefId>;
+    fn callable_sig(&self, db: &dyn HirDatabase) -> Option<CallableSig>;
+
+    fn strip_references(&self) -> &Ty;
+
+    /// If this is a `dyn Trait`, returns that trait.
+    fn dyn_trait(&self) -> Option<TraitId>;
+
+    fn impl_trait_bounds(&self, db: &dyn HirDatabase) -> Option<Vec<QuantifiedWhereClause>>;
+    fn associated_type_parent_trait(&self, db: &dyn HirDatabase) -> Option<TraitId>;
+
+    /// FIXME: Get rid of this, it's not a good abstraction
+    fn equals_ctor(&self, other: &Ty) -> bool;
+}
+
+impl TyExt for Ty {
+    fn is_unit(&self) -> bool {
+        matches!(self.kind(&Interner), TyKind::Tuple(0, _))
+    }
+
+    fn is_never(&self) -> bool {
+        matches!(self.kind(&Interner), TyKind::Never)
+    }
+
+    fn is_unknown(&self) -> bool {
+        matches!(self.kind(&Interner), TyKind::Error)
+    }
+
+    fn as_adt(&self) -> Option<(hir_def::AdtId, &Substitution)> {
+        match self.kind(&Interner) {
+            TyKind::Adt(AdtId(adt), parameters) => Some((*adt, parameters)),
+            _ => None,
+        }
+    }
+
+    fn as_tuple(&self) -> Option<&Substitution> {
+        match self.kind(&Interner) {
+            TyKind::Tuple(_, substs) => Some(substs),
+            _ => None,
+        }
+    }
+
+    fn as_fn_def(&self, db: &dyn HirDatabase) -> Option<FunctionId> {
+        if let Some(CallableDefId::FunctionId(func)) = self.callable_def(db) {
+            Some(func)
+        } else {
+            None
+        }
+    }
+    fn as_reference(&self) -> Option<(&Ty, Lifetime, Mutability)> {
+        match self.kind(&Interner) {
+            TyKind::Ref(mutability, lifetime, ty) => Some((ty, *lifetime, *mutability)),
+            _ => None,
+        }
+    }
+
+    fn as_reference_or_ptr(&self) -> Option<(&Ty, Rawness, Mutability)> {
+        match self.kind(&Interner) {
+            TyKind::Ref(mutability, _, ty) => Some((ty, Rawness::Ref, *mutability)),
+            TyKind::Raw(mutability, ty) => Some((ty, Rawness::RawPtr, *mutability)),
+            _ => None,
+        }
+    }
+
+    fn as_generic_def(&self, db: &dyn HirDatabase) -> Option<GenericDefId> {
+        match *self.kind(&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::Foreign(type_alias, ..) => Some(from_foreign_def_id(type_alias).into()),
+            _ => None,
+        }
+    }
+
+    fn callable_def(&self, db: &dyn HirDatabase) -> Option<CallableDefId> {
+        match self.kind(&Interner) {
+            &TyKind::FnDef(def, ..) => Some(db.lookup_intern_callable_def(def.into())),
+            _ => None,
+        }
+    }
+
+    fn callable_sig(&self, db: &dyn HirDatabase) -> Option<CallableSig> {
+        match self.kind(&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.substitute(&Interner, &parameters))
+            }
+            TyKind::Closure(.., substs) => {
+                let sig_param = substs.at(&Interner, 0).assert_ty_ref(&Interner);
+                sig_param.callable_sig(db)
+            }
+            _ => None,
+        }
+    }
+
+    fn dyn_trait(&self) -> Option<TraitId> {
+        let trait_ref = match self.kind(&Interner) {
+            TyKind::Dyn(dyn_ty) => dyn_ty.bounds.skip_binders().interned().get(0).and_then(|b| {
+                match b.skip_binders() {
+                    WhereClause::Implemented(trait_ref) => Some(trait_ref),
+                    _ => None,
+                }
+            }),
+            _ => None,
+        }?;
+        Some(from_chalk_trait_id(trait_ref.trait_id))
+    }
+
+    fn strip_references(&self) -> &Ty {
+        let mut t: &Ty = self;
+        while let TyKind::Ref(_mutability, _lifetime, ty) = t.kind(&Interner) {
+            t = ty;
+        }
+        t
+    }
+
+    fn impl_trait_bounds(&self, db: &dyn HirDatabase) -> Option<Vec<QuantifiedWhereClause>> {
+        match self.kind(&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())
+                            .and_then(|item| item.as_trait())
+                        {
+                            // This is only used by type walking.
+                            // Parameters will be walked outside, and projection predicate is not used.
+                            // So just provide the Future trait.
+                            let impl_bound = Binders::empty(
+                                &Interner,
+                                WhereClause::Implemented(TraitRef {
+                                    trait_id: to_chalk_trait_id(future_trait),
+                                    substitution: Substitution::empty(&Interner),
+                                }),
+                            );
+                            Some(vec![impl_bound])
+                        } else {
+                            None
+                        }
+                    }
+                    ImplTraitId::ReturnTypeImplTrait(..) => None,
+                }
+            }
+            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.substitute(&Interner, &opaque_ty.substitution)
+                        })
+                    }
+                    // It always has an parameter for Future::Output type.
+                    ImplTraitId::AsyncBlockTypeImplTrait(..) => unreachable!(),
+                };
+
+                predicates.map(|it| it.into_value_and_skipped_binders().0)
+            }
+            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 substs = TyBuilder::type_params_subst(db, id.parent);
+                        let predicates = db
+                            .generic_predicates(id.parent)
+                            .into_iter()
+                            .map(|pred| pred.clone().substitute(&Interner, &substs))
+                            .filter(|wc| match &wc.skip_binders() {
+                                WhereClause::Implemented(tr) => {
+                                    &tr.self_type_parameter(&Interner) == self
+                                }
+                                WhereClause::AliasEq(AliasEq {
+                                    alias: AliasTy::Projection(proj),
+                                    ty: _,
+                                }) => &proj.self_type_parameter(&Interner) == self,
+                                _ => false,
+                            })
+                            .collect::<Vec<_>>();
+
+                        Some(predicates)
+                    }
+                    _ => None,
+                }
+            }
+            _ => None,
+        }
+    }
+
+    fn associated_type_parent_trait(&self, db: &dyn HirDatabase) -> Option<TraitId> {
+        match self.kind(&Interner) {
+            TyKind::AssociatedType(id, ..) => {
+                match from_assoc_type_id(*id).lookup(db.upcast()).container {
+                    AssocContainerId::TraitId(trait_id) => Some(trait_id),
+                    _ => None,
+                }
+            }
+            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,
+                }
+            }
+            _ => None,
+        }
+    }
+
+    fn equals_ctor(&self, other: &Ty) -> bool {
+        match (self.kind(&Interner), other.kind(&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::Foreign(ty_id, ..), TyKind::Foreign(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
+            }
+            (
+                TyKind::Function(FnPointer { num_binders, sig, .. }),
+                TyKind::Function(FnPointer { num_binders: num_binders2, sig: sig2, .. }),
+            ) => num_binders == num_binders2 && sig == sig2,
+            (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,
+        }
+    }
+}
+
+pub trait ProjectionTyExt {
+    fn trait_ref(&self, db: &dyn HirDatabase) -> TraitRef;
+    fn trait_(&self, db: &dyn HirDatabase) -> TraitId;
+}
+
+impl ProjectionTyExt for ProjectionTy {
+    fn trait_ref(&self, db: &dyn HirDatabase) -> TraitRef {
+        TraitRef {
+            trait_id: to_chalk_trait_id(self.trait_(db)),
+            substitution: self.substitution.clone(),
+        }
+    }
+
+    fn trait_(&self, db: &dyn HirDatabase) -> TraitId {
+        match from_assoc_type_id(self.associated_ty_id).lookup(db.upcast()).container {
+            AssocContainerId::TraitId(it) => it,
+            _ => panic!("projection ty without parent trait"),
+        }
+    }
+}
+
+pub trait TraitRefExt {
+    fn hir_trait_id(&self) -> TraitId;
+}
+
+impl TraitRefExt for TraitRef {
+    fn hir_trait_id(&self) -> TraitId {
+        from_chalk_trait_id(self.trait_id)
+    }
+}
diff --git a/crates/hir_ty/src/db.rs b/crates/hir_ty/src/db.rs
index 58e4247c6..326c20240 100644
--- a/crates/hir_ty/src/db.rs
+++ b/crates/hir_ty/src/db.rs
@@ -5,7 +5,7 @@ use std::sync::Arc;
 use base_db::{impl_intern_key, salsa, CrateId, Upcast};
 use hir_def::{
     db::DefDatabase, expr::ExprId, ConstParamId, DefWithBodyId, FunctionId, GenericDefId, ImplId,
-    LocalFieldId, TypeParamId, VariantId,
+    LifetimeParamId, LocalFieldId, TypeParamId, VariantId,
 };
 use la_arena::ArenaMap;
 
@@ -86,6 +86,10 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::interned]
     fn intern_type_param_id(&self, param_id: TypeParamId) -> InternedTypeParamId;
     #[salsa::interned]
+    fn intern_lifetime_param_id(&self, param_id: LifetimeParamId) -> InternedLifetimeParamId;
+    #[salsa::interned]
+    fn intern_const_param_id(&self, param_id: ConstParamId) -> InternedConstParamId;
+    #[salsa::interned]
     fn intern_impl_trait_id(&self, id: ImplTraitId) -> InternedOpaqueTyId;
     #[salsa::interned]
     fn intern_closure(&self, id: (DefWithBodyId, ExprId)) -> InternedClosureId;
@@ -123,7 +127,7 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
         &self,
         krate: CrateId,
         goal: crate::Canonical<crate::InEnvironment<crate::DomainGoal>>,
-    ) -> Option<crate::traits::Solution>;
+    ) -> Option<crate::Solution>;
 
     #[salsa::invoke(crate::traits::chalk::program_clauses_for_chalk_env_query)]
     fn program_clauses_for_chalk_env(
@@ -156,6 +160,14 @@ pub struct InternedTypeParamId(salsa::InternId);
 impl_intern_key!(InternedTypeParamId);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct InternedLifetimeParamId(salsa::InternId);
+impl_intern_key!(InternedLifetimeParamId);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct InternedConstParamId(salsa::InternId);
+impl_intern_key!(InternedConstParamId);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct InternedOpaqueTyId(salsa::InternId);
 impl_intern_key!(InternedOpaqueTyId);
 
diff --git a/crates/hir_ty/src/diagnostics/decl_check.rs b/crates/hir_ty/src/diagnostics/decl_check.rs
index 33a0f4d7d..1c9f9ede7 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_in_extern_block {
+        if data.is_in_extern_block() {
             cov_mark::hit!(extern_func_incorrect_case_ignored);
             return;
         }
@@ -99,8 +99,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
         let body = self.db.body(func.into());
 
         // Recursively validate inner scope items, such as static variables and constants.
-        let db = self.db;
-        for block_def_map in body.block_scopes.iter().filter_map(|block| db.block_def_map(*block)) {
+        for (_, block_def_map) in body.blocks(self.db.upcast()) {
             for (_, module) in block_def_map.modules() {
                 for def_id in module.scope.declarations() {
                     let mut validator = DeclValidator::new(self.db, self.krate, self.sink);
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index 3909ad354..79602c3dd 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -14,8 +14,7 @@ use crate::{
         MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkOrSomeInTailExpr,
         MissingPatFields, RemoveThisSemicolon,
     },
-    utils::variant_data,
-    AdtId, InferenceResult, Interner, Ty, TyKind,
+    AdtId, InferenceResult, Interner, TyExt, TyKind,
 };
 
 pub(crate) use hir_def::{
@@ -104,7 +103,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             let root = source_ptr.file_syntax(db.upcast());
             if let ast::Expr::RecordExpr(record_expr) = &source_ptr.value.to_node(&root) {
                 if let Some(_) = record_expr.record_expr_field_list() {
-                    let variant_data = variant_data(db.upcast(), variant_def);
+                    let variant_data = variant_def.variant_data(db.upcast());
                     let missed_fields = missed_fields
                         .into_iter()
                         .map(|idx| variant_data.fields()[idx].name.clone())
@@ -135,7 +134,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
                 let root = source_ptr.file_syntax(db.upcast());
                 if let ast::Pat::RecordPat(record_pat) = expr.to_node(&root) {
                     if let Some(_) = record_pat.record_pat_field_list() {
-                        let variant_data = variant_data(db.upcast(), variant_def);
+                        let variant_data = variant_def.variant_data(db.upcast());
                         let missed_fields = missed_fields
                             .into_iter()
                             .map(|idx| variant_data.fields()[idx].name.clone())
@@ -245,7 +244,8 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
                     Some(callee) => callee,
                     None => return,
                 };
-                let sig = db.callable_item_signature(callee.into()).value;
+                let sig =
+                    db.callable_item_signature(callee.into()).into_value_and_skipped_binders().0;
 
                 (sig, args)
             }
@@ -314,7 +314,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
                 if pat_ty == match_expr_ty
                     || match_expr_ty
                         .as_reference()
-                        .map(|(match_expr_ty, _)| match_expr_ty == pat_ty)
+                        .map(|(match_expr_ty, ..)| match_expr_ty == pat_ty)
                         .unwrap_or(false)
                 {
                     // If we had a NotUsefulMatchArm diagnostic, we could
@@ -378,7 +378,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             _ => return,
         };
 
-        let (params, required) = match mismatch.expected.interned(&Interner) {
+        let (params, required) = match mismatch.expected.kind(&Interner) {
             TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref parameters)
                 if *enum_id == core_result_enum =>
             {
@@ -392,7 +392,9 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             _ => return,
         };
 
-        if params.len() > 0 && params[0] == mismatch.actual {
+        if params.len(&Interner) > 0
+            && params.at(&Interner, 0).ty(&Interner) == Some(&mismatch.actual)
+        {
             let (_, source_map) = db.body_with_source_map(self.owner);
 
             if let Ok(source_ptr) = source_map.expr_syntax(id) {
@@ -421,7 +423,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             None => return,
         };
 
-        if mismatch.actual != Ty::unit() || mismatch.expected != *possible_tail_ty {
+        if !mismatch.actual.is_unit() || mismatch.expected != *possible_tail_ty {
             return;
         }
 
@@ -450,7 +452,7 @@ pub fn record_literal_missing_fields(
         return None;
     }
 
-    let variant_data = variant_data(db.upcast(), variant_def);
+    let variant_data = variant_def.variant_data(db.upcast());
 
     let specified_fields: FxHashSet<_> = fields.iter().map(|f| &f.name).collect();
     let missed_fields: Vec<LocalFieldId> = variant_data
@@ -480,7 +482,7 @@ pub fn record_pattern_missing_fields(
         return None;
     }
 
-    let variant_data = variant_data(db.upcast(), variant_def);
+    let variant_data = variant_def.variant_data(db.upcast());
 
     let specified_fields: FxHashSet<_> = fields.iter().map(|f| &f.name).collect();
     let missed_fields: Vec<LocalFieldId> = variant_data
diff --git a/crates/hir_ty/src/diagnostics/match_check.rs b/crates/hir_ty/src/diagnostics/match_check.rs
index 5a5cdcbf3..e9762622f 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, Interner, TyKind};
+use crate::{db::HirDatabase, AdtId, InferenceResult, Interner, TyExt, TyKind};
 
 #[derive(Debug, Clone, Copy)]
 /// Either a pattern from the source code being analyzed, represented as
@@ -539,7 +539,7 @@ impl Matrix {
         if let Some(Pat::Or(pat_ids)) = row.get_head().map(|pat_id| pat_id.as_pat(cx)) {
             // Or patterns are expanded here
             for pat_id in pat_ids {
-                self.0.push(PatStack::from_pattern(pat_id));
+                self.0.push(row.replace_head_with([pat_id].iter()));
             }
         } else {
             self.0.push(row);
@@ -626,7 +626,7 @@ 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().interned(&Interner) {
+    match cx.infer[cx.match_expr].strip_references().kind(&Interner) {
         TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ..) => {
             if cx.db.enum_data(*enum_id).variants.is_empty() {
                 return Ok(Usefulness::NotUseful);
@@ -792,7 +792,10 @@ fn pat_constructor(cx: &MatchCheckCtx, pat: PatIdOrWild) -> MatchCheckResult<Opt
         Pat::Tuple { .. } => {
             let pat_id = pat.as_id().expect("we already know this pattern is not a wild");
             Some(Constructor::Tuple {
-                arity: cx.infer.type_of_pat[pat_id].as_tuple().ok_or(MatchCheckErr::Unknown)?.len(),
+                arity: cx.infer.type_of_pat[pat_id]
+                    .as_tuple()
+                    .ok_or(MatchCheckErr::Unknown)?
+                    .len(&Interner),
             })
         }
         Pat::Lit(lit_expr) => match cx.body.exprs[lit_expr] {
@@ -1085,6 +1088,20 @@ fn main() {
     }
 
     #[test]
+    fn or_pattern_no_diagnostic() {
+        check_diagnostics(
+            r#"
+enum Either {A, B}
+
+fn main() {
+    match (Either::A, Either::B) {
+        (Either::A | Either::B, _) => (),
+    }
+}"#,
+        )
+    }
+
+    #[test]
     fn mismatched_types() {
         // Match statements with arms that don't match the
         // expression pattern do not fire this diagnostic.
@@ -1336,30 +1353,6 @@ fn bang(never: !) {
     }
 
     #[test]
-    fn or_pattern_panic() {
-        check_diagnostics(
-            r#"
-pub enum Category { Infinity, Zero }
-
-fn panic(a: Category, b: Category) {
-    match (a, b) {
-        (Category::Zero | Category::Infinity, _) => (),
-        (_, Category::Zero | Category::Infinity) => (),
-    }
-
-    // FIXME: This is a false positive, but the code used to cause a panic in the match checker,
-    // so this acts as a regression test for that.
-    match (a, b) {
-        //^^^^^^ Missing match arm
-        (Category::Infinity, Category::Infinity) | (Category::Zero, Category::Zero) => (),
-        (Category::Infinity | Category::Zero, _) => (),
-    }
-}
-"#,
-        );
-    }
-
-    #[test]
     fn unknown_type() {
         check_diagnostics(
             r#"
diff --git a/crates/hir_ty/src/diagnostics/unsafe_check.rs b/crates/hir_ty/src/diagnostics/unsafe_check.rs
index 1f49a4909..ed97dc0e3 100644
--- a/crates/hir_ty/src/diagnostics/unsafe_check.rs
+++ b/crates/hir_ty/src/diagnostics/unsafe_check.rs
@@ -11,7 +11,9 @@ use hir_def::{
 };
 use hir_expand::diagnostics::DiagnosticSink;
 
-use crate::{db::HirDatabase, diagnostics::MissingUnsafe, InferenceResult, Interner, TyKind};
+use crate::{
+    db::HirDatabase, diagnostics::MissingUnsafe, InferenceResult, Interner, TyExt, TyKind,
+};
 
 pub(super) struct UnsafeValidator<'a, 'b: 'a> {
     owner: DefWithBodyId,
@@ -32,7 +34,7 @@ impl<'a, 'b> UnsafeValidator<'a, 'b> {
         let def = self.owner;
         let unsafe_expressions = unsafe_expressions(db, self.infer.as_ref(), def);
         let is_unsafe = match self.owner {
-            DefWithBodyId::FunctionId(it) => db.function_data(it).qualifier.is_unsafe,
+            DefWithBodyId::FunctionId(it) => db.function_data(it).is_unsafe(),
             DefWithBodyId::StaticId(_) | DefWithBodyId::ConstId(_) => false,
         };
         if is_unsafe
@@ -86,7 +88,7 @@ fn walk_unsafe(
     match expr {
         &Expr::Call { callee, .. } => {
             if let Some(func) = infer[callee].as_fn_def(db) {
-                if db.function_data(func).qualifier.is_unsafe {
+                if db.function_data(func).is_unsafe() {
                     unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
                 }
             }
@@ -103,14 +105,14 @@ fn walk_unsafe(
         Expr::MethodCall { .. } => {
             if infer
                 .method_resolution(current)
-                .map(|func| db.function_data(func).qualifier.is_unsafe)
+                .map(|func| db.function_data(func).is_unsafe())
                 .unwrap_or(false)
             {
                 unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
             }
         }
         Expr::UnaryOp { expr, op: UnaryOp::Deref } => {
-            if let TyKind::Raw(..) = &infer[*expr].interned(&Interner) {
+            if let TyKind::Raw(..) = &infer[*expr].kind(&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 51480304b..e0ca96c6d 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -1,14 +1,17 @@
 //! FIXME: write short doc here
 
-use std::{array, fmt};
+use std::{
+    array,
+    fmt::{self, Debug},
+};
 
-use chalk_ir::Mutability;
+use chalk_ir::BoundVar;
 use hir_def::{
     db::DefDatabase,
     find_path,
     generics::TypeParamProvenance,
     item_scope::ItemInNs,
-    path::{GenericArg, Path, PathKind},
+    path::{Path, PathKind},
     type_ref::{TypeBound, TypeRef},
     visibility::Visibility,
     AssocContainerId, Lookup, ModuleId, TraitId,
@@ -16,10 +19,12 @@ use hir_def::{
 use hir_expand::name::Name;
 
 use crate::{
-    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, AliasEq, AliasTy,
-    CallableDefId, CallableSig, DomainGoal, ImplTraitId, Interner, Lifetime, OpaqueTy,
-    ProjectionTy, QuantifiedWhereClause, Scalar, Substitution, TraitRef, Ty, TyKind, WhereClause,
+    const_from_placeholder_idx, db::HirDatabase, from_assoc_type_id, from_foreign_def_id,
+    from_placeholder_idx, lt_from_placeholder_idx, primitive, subst_prefix, to_assoc_type_id,
+    traits::chalk::from_chalk, utils::generics, AdtId, AliasEq, AliasTy, CallableDefId,
+    CallableSig, Const, ConstValue, DomainGoal, GenericArg, ImplTraitId, Interner, Lifetime,
+    LifetimeData, LifetimeOutlives, Mutability, OpaqueTy, ProjectionTy, ProjectionTyExt,
+    QuantifiedWhereClause, Scalar, TraitRef, TraitRefExt, Ty, TyExt, TyKind, WhereClause,
 };
 
 pub struct HirFormatter<'a> {
@@ -46,6 +51,10 @@ pub trait HirDisplay {
     where
         Self: Sized,
     {
+        assert!(
+            !matches!(display_target, DisplayTarget::SourceCode { .. }),
+            "HirDisplayWrapper cannot fail with DisplaySourceCodeError, use HirDisplay::hir_fmt directly instead"
+        );
         HirDisplayWrapper { db, t: self, max_size, omit_verbose_types, display_target }
     }
 
@@ -230,7 +239,7 @@ where
             Err(HirDisplayError::FmtError) => Err(fmt::Error),
             Err(HirDisplayError::DisplaySourceCodeError(_)) => {
                 // This should never happen
-                panic!("HirDisplay failed when calling Display::fmt!")
+                panic!("HirDisplay::hir_fmt failed with DisplaySourceCodeError when calling Display::fmt!")
             }
         }
     }
@@ -251,16 +260,12 @@ impl HirDisplay for ProjectionTy {
         }
 
         let trait_ = f.db.trait_data(self.trait_(f.db));
-        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.substitution.len() > 1 {
+        write!(f, "<")?;
+        self.self_type_parameter(&Interner).hir_fmt(f)?;
+        write!(f, " as {}", trait_.name)?;
+        if self.substitution.len(&Interner) > 1 {
             write!(f, "<")?;
-            f.write_joined(&self.substitution[1..], ", ")?;
+            f.write_joined(&self.substitution.interned()[1..], ", ")?;
             write!(f, ">")?;
         }
         write!(f, ">::{}", f.db.type_alias_data(from_assoc_type_id(self.associated_ty_id)).name)?;
@@ -274,7 +279,38 @@ impl HirDisplay for OpaqueTy {
             return write!(f, "{}", TYPE_HINT_TRUNCATION);
         }
 
-        self.substitution[0].hir_fmt(f)
+        self.substitution.at(&Interner, 0).hir_fmt(f)
+    }
+}
+
+impl HirDisplay for GenericArg {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match self.interned() {
+            crate::GenericArgData::Ty(ty) => ty.hir_fmt(f),
+        }
+    }
+}
+
+impl HirDisplay for Const {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        let data = self.interned();
+        match data.value {
+            ConstValue::BoundVar(idx) => idx.hir_fmt(f),
+            ConstValue::InferenceVar(..) => write!(f, "_"),
+            ConstValue::Placeholder(idx) => {
+                let id = const_from_placeholder_idx(f.db, idx);
+                let generics = generics(f.db.upcast(), id.parent);
+                let param_data = &generics.params.consts[id.local_id];
+                write!(f, "{}", param_data.name)
+            }
+            ConstValue::Concrete(_) => write!(f, "_"),
+        }
+    }
+}
+
+impl HirDisplay for BoundVar {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write!(f, "?{}.{}", self.debruijn.depth(), self.index)
     }
 }
 
@@ -284,7 +320,7 @@ impl HirDisplay for Ty {
             return write!(f, "{}", TYPE_HINT_TRUNCATION);
         }
 
-        match self.interned(&Interner) {
+        match self.kind(&Interner) {
             TyKind::Never => write!(f, "!")?,
             TyKind::Str => write!(f, "str")?,
             TyKind::Scalar(Scalar::Bool) => write!(f, "bool")?,
@@ -297,16 +333,15 @@ impl HirDisplay for Ty {
                 t.hir_fmt(f)?;
                 write!(f, "]")?;
             }
-            TyKind::Array(t) => {
+            TyKind::Array(t, c) => {
                 write!(f, "[")?;
                 t.hir_fmt(f)?;
-                write!(f, "; _]")?;
+                write!(f, "; ")?;
+                c.hir_fmt(f)?;
+                write!(f, "]")?;
             }
-            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.interned(&Interner), TyKind::Raw(..)) {
+            TyKind::Raw(m, t) | TyKind::Ref(m, _, t) => {
+                if matches!(self.kind(&Interner), TyKind::Raw(..)) {
                     write!(
                         f,
                         "*{}",
@@ -328,7 +363,7 @@ impl HirDisplay for Ty {
 
                 // FIXME: all this just to decide whether to use parentheses...
                 let datas;
-                let predicates: Vec<_> = match t.interned(&Interner) {
+                let predicates: Vec<_> = match t.kind(&Interner) {
                     TyKind::Dyn(dyn_ty) if dyn_ty.bounds.skip_binders().interned().len() > 1 => {
                         dyn_ty.bounds.skip_binders().interned().iter().cloned().collect()
                     }
@@ -344,8 +379,8 @@ impl HirDisplay for Ty {
                             let data = (*datas)
                                 .as_ref()
                                 .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
-                            let bounds = data.subst(parameters);
-                            bounds.value
+                            let bounds = data.substitute(&Interner, parameters);
+                            bounds.into_value_and_skipped_binders().0
                         } else {
                             Vec::new()
                         }
@@ -360,26 +395,26 @@ impl HirDisplay for Ty {
                     if fn_traits(f.db.upcast(), trait_).any(|it| it == trait_)
                         && predicates.len() <= 2
                     {
-                        return write!(f, "{}", ty_display);
+                        return t.hir_fmt(f);
                     }
                 }
 
                 if predicates.len() > 1 {
                     write!(f, "(")?;
-                    write!(f, "{}", ty_display)?;
+                    t.hir_fmt(f)?;
                     write!(f, ")")?;
                 } else {
-                    write!(f, "{}", ty_display)?;
+                    t.hir_fmt(f)?;
                 }
             }
             TyKind::Tuple(_, substs) => {
-                if substs.len() == 1 {
+                if substs.len(&Interner) == 1 {
                     write!(f, "(")?;
-                    substs[0].hir_fmt(f)?;
+                    substs.at(&Interner, 0).hir_fmt(f)?;
                     write!(f, ",)")?;
                 } else {
                     write!(f, "(")?;
-                    f.write_joined(&*substs.0, ", ")?;
+                    f.write_joined(&*substs.interned(), ", ")?;
                     write!(f, ")")?;
                 }
             }
@@ -389,7 +424,7 @@ impl HirDisplay for Ty {
             }
             TyKind::FnDef(def, parameters) => {
                 let def = from_chalk(f.db, *def);
-                let sig = f.db.callable_item_signature(def).subst(parameters);
+                let sig = f.db.callable_item_signature(def).substitute(&Interner, parameters);
                 match def {
                     CallableDefId::FunctionId(ff) => {
                         write!(f, "fn {}", f.db.function_data(ff).name)?
@@ -399,7 +434,7 @@ impl HirDisplay for Ty {
                         write!(f, "{}", f.db.enum_data(e.parent).variants[e.local_id].name)?
                     }
                 };
-                if parameters.len() > 0 {
+                if parameters.len(&Interner) > 0 {
                     let generics = generics(f.db.upcast(), def.into());
                     let (parent_params, self_param, type_params, _impl_trait_params) =
                         generics.provenance_split();
@@ -407,7 +442,7 @@ impl HirDisplay for Ty {
                     // We print all params except implicit impl Trait params. Still a bit weird; should we leave out parent and self?
                     if total_len > 0 {
                         write!(f, "<")?;
-                        f.write_joined(&parameters.0[..total_len], ", ")?;
+                        f.write_joined(&parameters.interned()[..total_len], ", ")?;
                         write!(f, ">")?;
                     }
                 }
@@ -415,15 +450,9 @@ impl HirDisplay for Ty {
                 f.write_joined(sig.params(), ", ")?;
                 write!(f, ")")?;
                 let ret = sig.ret();
-                if *ret != Ty::unit() {
-                    let ret_display = ret.into_displayable(
-                        f.db,
-                        f.max_size,
-                        f.omit_verbose_types,
-                        f.display_target,
-                    );
-
-                    write!(f, " -> {}", ret_display)?;
+                if !ret.is_unit() {
+                    write!(f, " -> ")?;
+                    ret.hir_fmt(f)?;
                 }
             }
             TyKind::Adt(AdtId(def_id), parameters) => {
@@ -451,7 +480,7 @@ impl HirDisplay for Ty {
                     }
                 }
 
-                if parameters.len() > 0 {
+                if parameters.len(&Interner) > 0 {
                     let parameters_to_write = if f.display_target.is_source_code()
                         || f.omit_verbose_types()
                     {
@@ -460,30 +489,35 @@ impl HirDisplay for Ty {
                             .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
                             .filter(|defaults| !defaults.is_empty())
                         {
-                            None => parameters.0.as_ref(),
+                            None => parameters.interned().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) => {
+                                for (i, parameter) in parameters.iter(&Interner).enumerate() {
+                                    match (
+                                        parameter.assert_ty_ref(&Interner).kind(&Interner),
+                                        default_parameters.get(i),
+                                    ) {
+                                        (&TyKind::Error, _) | (_, None) => {
                                             default_from = i + 1;
                                         }
                                         (_, Some(default_parameter)) => {
-                                            let actual_default = default_parameter
-                                                .clone()
-                                                .subst(&parameters.prefix(i));
-                                            if parameter != &actual_default {
+                                            let actual_default =
+                                                default_parameter.clone().substitute(
+                                                    &Interner,
+                                                    &subst_prefix(parameters, i),
+                                                );
+                                            if parameter.assert_ty_ref(&Interner) != &actual_default
+                                            {
                                                 default_from = i + 1;
                                             }
                                         }
                                     }
                                 }
-                                &parameters.0[0..default_from]
+                                &parameters.interned()[0..default_from]
                             }
                         }
                     } else {
-                        parameters.0.as_ref()
+                        parameters.interned().as_ref()
                     };
                     if !parameters_to_write.is_empty() {
                         write!(f, "<")?;
@@ -504,9 +538,9 @@ impl HirDisplay for Ty {
                 // 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() {
                     write!(f, "{}::{}", trait_.name, type_alias_data.name)?;
-                    if parameters.len() > 0 {
+                    if parameters.len(&Interner) > 0 {
                         write!(f, "<")?;
-                        f.write_joined(&*parameters.0, ", ")?;
+                        f.write_joined(&*parameters.interned(), ", ")?;
                         write!(f, ">")?;
                     }
                 } else {
@@ -518,7 +552,7 @@ impl HirDisplay for Ty {
                     projection_ty.hir_fmt(f)?;
                 }
             }
-            TyKind::ForeignType(type_alias) => {
+            TyKind::Foreign(type_alias) => {
                 let type_alias = f.db.type_alias_data(from_foreign_def_id(*type_alias));
                 write!(f, "{}", type_alias.name)?;
             }
@@ -531,13 +565,13 @@ impl HirDisplay for Ty {
                         let data = (*datas)
                             .as_ref()
                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
-                        let bounds = data.subst(&parameters);
-                        write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
+                        let bounds = data.substitute(&Interner, &parameters);
+                        write_bounds_like_dyn_trait_with_prefix("impl", bounds.skip_binders(), f)?;
                         // FIXME: it would maybe be good to distinguish this from the alias type (when debug printing), and to show the substitution
                     }
                     ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                         write!(f, "impl Future<Output = ")?;
-                        parameters[0].hir_fmt(f)?;
+                        parameters.at(&Interner, 0).hir_fmt(f)?;
                         write!(f, ">")?;
                     }
                 }
@@ -548,7 +582,7 @@ impl HirDisplay for Ty {
                         DisplaySourceCodeError::Closure,
                     ));
                 }
-                let sig = substs[0].callable_sig(f.db);
+                let sig = substs.at(&Interner, 0).assert_ty_ref(&Interner).callable_sig(f.db);
                 if let Some(sig) = sig {
                     if sig.params().is_empty() {
                         write!(f, "||")?;
@@ -560,13 +594,8 @@ impl HirDisplay for Ty {
                         write!(f, "|")?;
                     };
 
-                    let ret_display = sig.ret().into_displayable(
-                        f.db,
-                        f.max_size,
-                        f.omit_verbose_types,
-                        f.display_target,
-                    );
-                    write!(f, " -> {}", ret_display)?;
+                    write!(f, " -> ")?;
+                    sig.ret().hir_fmt(f)?;
                 } else {
                     write!(f, "{{closure}}")?;
                 }
@@ -580,26 +609,27 @@ impl HirDisplay for Ty {
                         write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
                     }
                     TypeParamProvenance::ArgumentImplTrait => {
-                        let substs = Substitution::type_params_for_generics(f.db, &generics);
-                        let bounds = f
-                            .db
-                            .generic_predicates(id.parent)
-                            .into_iter()
-                            .map(|pred| pred.clone().subst(&substs))
-                            .filter(|wc| match &wc.skip_binders() {
-                                WhereClause::Implemented(tr) => tr.self_type_parameter() == self,
-                                WhereClause::AliasEq(AliasEq {
-                                    alias: AliasTy::Projection(proj),
-                                    ty: _,
-                                }) => proj.self_type_parameter() == self,
-                                _ => false,
-                            })
-                            .collect::<Vec<_>>();
+                        let substs = generics.type_params_subst(f.db);
+                        let bounds =
+                            f.db.generic_predicates(id.parent)
+                                .into_iter()
+                                .map(|pred| pred.clone().substitute(&Interner, &substs))
+                                .filter(|wc| match &wc.skip_binders() {
+                                    WhereClause::Implemented(tr) => {
+                                        &tr.self_type_parameter(&Interner) == self
+                                    }
+                                    WhereClause::AliasEq(AliasEq {
+                                        alias: AliasTy::Projection(proj),
+                                        ty: _,
+                                    }) => &proj.self_type_parameter(&Interner) == self,
+                                    _ => false,
+                                })
+                                .collect::<Vec<_>>();
                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds, f)?;
                     }
                 }
             }
-            TyKind::BoundVar(idx) => write!(f, "?{}.{}", idx.debruijn.depth(), idx.index)?,
+            TyKind::BoundVar(idx) => idx.hir_fmt(f)?,
             TyKind::Dyn(dyn_ty) => {
                 write_bounds_like_dyn_trait_with_prefix(
                     "dyn",
@@ -617,15 +647,15 @@ impl HirDisplay for Ty {
                         let data = (*datas)
                             .as_ref()
                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
-                        let bounds = data.subst(&opaque_ty.substitution);
-                        write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
+                        let bounds = data.substitute(&Interner, &opaque_ty.substitution);
+                        write_bounds_like_dyn_trait_with_prefix("impl", bounds.skip_binders(), f)?;
                     }
                     ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                         write!(f, "{{async block}}")?;
                     }
                 };
             }
-            TyKind::Unknown => {
+            TyKind::Error => {
                 if f.display_target.is_source_code() {
                     return Err(HirDisplayError::DisplaySourceCodeError(
                         DisplaySourceCodeError::UnknownType,
@@ -652,10 +682,9 @@ impl HirDisplay for CallableSig {
         }
         write!(f, ")")?;
         let ret = self.ret();
-        if *ret != Ty::unit() {
-            let ret_display =
-                ret.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
-            write!(f, " -> {}", ret_display)?;
+        if !ret.is_unit() {
+            write!(f, " -> ")?;
+            ret.hir_fmt(f)?;
         }
         Ok(())
     }
@@ -716,11 +745,13 @@ fn write_bounds_like_dyn_trait(
                 // existential) here, which is the only thing that's
                 // possible in actual Rust, and hence don't print it
                 write!(f, "{}", f.db.trait_data(trait_).name)?;
-                if let [_, params @ ..] = &*trait_ref.substitution.0 {
+                if let [_, params @ ..] = &*trait_ref.substitution.interned().as_slice() {
                     if is_fn_trait {
-                        if let Some(args) = params.first().and_then(|it| it.as_tuple()) {
+                        if let Some(args) =
+                            params.first().and_then(|it| it.assert_ty_ref(&Interner).as_tuple())
+                        {
                             write!(f, "(")?;
-                            f.write_joined(&*args.0, ", ")?;
+                            f.write_joined(&*args.interned(), ", ")?;
                             write!(f, ")")?;
                         }
                     } else if !params.is_empty() {
@@ -761,31 +792,29 @@ fn write_bounds_like_dyn_trait(
     Ok(())
 }
 
-impl TraitRef {
-    fn hir_fmt_ext(&self, f: &mut HirFormatter, use_as: bool) -> Result<(), HirDisplayError> {
-        if f.should_truncate() {
-            return write!(f, "{}", TYPE_HINT_TRUNCATION);
-        }
+fn fmt_trait_ref(tr: &TraitRef, f: &mut HirFormatter, use_as: bool) -> Result<(), HirDisplayError> {
+    if f.should_truncate() {
+        return write!(f, "{}", TYPE_HINT_TRUNCATION);
+    }
 
-        self.substitution[0].hir_fmt(f)?;
-        if use_as {
-            write!(f, " as ")?;
-        } else {
-            write!(f, ": ")?;
-        }
-        write!(f, "{}", f.db.trait_data(self.hir_trait_id()).name)?;
-        if self.substitution.len() > 1 {
-            write!(f, "<")?;
-            f.write_joined(&self.substitution[1..], ", ")?;
-            write!(f, ">")?;
-        }
-        Ok(())
+    tr.self_type_parameter(&Interner).hir_fmt(f)?;
+    if use_as {
+        write!(f, " as ")?;
+    } else {
+        write!(f, ": ")?;
     }
+    write!(f, "{}", f.db.trait_data(tr.hir_trait_id()).name)?;
+    if tr.substitution.len(&Interner) > 1 {
+        write!(f, "<")?;
+        f.write_joined(&tr.substitution.interned()[1..], ", ")?;
+        write!(f, ">")?;
+    }
+    Ok(())
 }
 
 impl HirDisplay for TraitRef {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
-        self.hir_fmt_ext(f, false)
+        fmt_trait_ref(self, f, false)
     }
 }
 
@@ -799,7 +828,7 @@ impl HirDisplay for WhereClause {
             WhereClause::Implemented(trait_ref) => trait_ref.hir_fmt(f)?,
             WhereClause::AliasEq(AliasEq { alias: AliasTy::Projection(projection_ty), ty }) => {
                 write!(f, "<")?;
-                projection_ty.trait_ref(f.db).hir_fmt_ext(f, true)?;
+                fmt_trait_ref(&projection_ty.trait_ref(f.db), f, true)?;
                 write!(
                     f,
                     ">::{} = ",
@@ -813,15 +842,35 @@ impl HirDisplay for WhereClause {
     }
 }
 
+impl HirDisplay for LifetimeOutlives {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        self.a.hir_fmt(f)?;
+        write!(f, ": ")?;
+        self.b.hir_fmt(f)
+    }
+}
+
 impl HirDisplay for Lifetime {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        self.interned().hir_fmt(f)
+    }
+}
+
+impl HirDisplay for LifetimeData {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         match self {
-            Lifetime::Parameter(id) => {
+            LifetimeData::BoundVar(idx) => idx.hir_fmt(f),
+            LifetimeData::InferenceVar(_) => write!(f, "_"),
+            LifetimeData::Placeholder(idx) => {
+                let id = lt_from_placeholder_idx(f.db, *idx);
                 let generics = generics(f.db.upcast(), id.parent);
                 let param_data = &generics.params.lifetimes[id.local_id];
-                write!(f, "{}", &param_data.name)
+                write!(f, "{}", param_data.name)
             }
-            Lifetime::Static => write!(f, "'static"),
+            LifetimeData::Static => write!(f, "'static"),
+            LifetimeData::Empty(_) => Ok(()),
+            LifetimeData::Erased => Ok(()),
+            LifetimeData::Phantom(_, _) => Ok(()),
         }
     }
 }
@@ -1016,11 +1065,11 @@ impl HirDisplay for Path {
     }
 }
 
-impl HirDisplay for GenericArg {
+impl HirDisplay for hir_def::path::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),
+            hir_def::path::GenericArg::Type(ty) => ty.hir_fmt(f),
+            hir_def::path::GenericArg::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
         }
     }
 }
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 8f9cf7480..531159e54 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -37,14 +37,19 @@ use stdx::impl_from;
 use syntax::SmolStr;
 
 use super::{
-    traits::{DomainGoal, Guidance, Solution},
-    InEnvironment, ProjectionTy, Substitution, TraitEnvironment, TraitRef, Ty, TypeWalk,
+    DomainGoal, Guidance, InEnvironment, ProjectionTy, Solution, TraitEnvironment, TraitRef, Ty,
+    TypeWalk,
 };
 use crate::{
     db::HirDatabase, infer::diagnostics::InferenceDiagnostic, lower::ImplTraitLoweringMode,
-    to_assoc_type_id, to_chalk_trait_id, AliasEq, AliasTy, Interner, TyKind,
+    to_assoc_type_id, AliasEq, AliasTy, Canonical, Interner, TyBuilder, TyExt, TyKind,
 };
 
+// This lint has a false positive here. See the link below for details.
+//
+// https://github.com/rust-lang/rust/issues/57411
+#[allow(unreachable_pub)]
+pub use unify::could_unify;
 pub(crate) use unify::unify;
 
 mod unify;
@@ -115,7 +120,7 @@ struct InternedStandardTypes {
 
 impl Default for InternedStandardTypes {
     fn default() -> Self {
-        InternedStandardTypes { unknown: TyKind::Unknown.intern(&Interner) }
+        InternedStandardTypes { unknown: TyKind::Error.intern(&Interner) }
     }
 }
 
@@ -126,10 +131,7 @@ pub struct InferenceResult {
     method_resolutions: FxHashMap<ExprId, FunctionId>,
     /// For each field access expr, records the field it resolves to.
     field_resolutions: FxHashMap<ExprId, FieldId>,
-    /// For each field in record literal, records the field it resolves to.
-    record_field_resolutions: FxHashMap<ExprId, FieldId>,
-    record_pat_field_resolutions: FxHashMap<PatId, FieldId>,
-    /// For each struct literal, records the variant it resolves to.
+    /// For each struct literal or pattern, records the variant it resolves to.
     variant_resolutions: FxHashMap<ExprOrPatId, VariantId>,
     /// For each associated item record what it resolves to
     assoc_resolutions: FxHashMap<ExprOrPatId, AssocItemId>,
@@ -148,12 +150,6 @@ impl InferenceResult {
     pub fn field_resolution(&self, expr: ExprId) -> Option<FieldId> {
         self.field_resolutions.get(&expr).copied()
     }
-    pub fn record_field_resolution(&self, expr: ExprId) -> Option<FieldId> {
-        self.record_field_resolutions.get(&expr).copied()
-    }
-    pub fn record_pat_field_resolution(&self, pat: PatId) -> Option<FieldId> {
-        self.record_pat_field_resolutions.get(&pat).copied()
-    }
     pub fn variant_resolution_for_expr(&self, id: ExprId) -> Option<VariantId> {
         self.variant_resolutions.get(&id.into()).copied()
     }
@@ -205,6 +201,7 @@ struct InferenceContext<'a> {
     table: unify::InferenceTable,
     trait_env: Arc<TraitEnvironment>,
     obligations: Vec<DomainGoal>,
+    last_obligations_check: Option<u32>,
     result: InferenceResult,
     /// The return type of the function being inferred, or the closure if we're
     /// currently within one.
@@ -240,7 +237,8 @@ impl<'a> InferenceContext<'a> {
             result: InferenceResult::default(),
             table: unify::InferenceTable::new(),
             obligations: Vec::default(),
-            return_ty: TyKind::Unknown.intern(&Interner), // set in collect_fn_signature
+            last_obligations_check: None,
+            return_ty: TyKind::Error.intern(&Interner), // set in collect_fn_signature
             trait_env: owner
                 .as_generic_def_id()
                 .map_or_else(Default::default, |d| db.trait_environment(d)),
@@ -254,7 +252,7 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn err_ty(&self) -> Ty {
-        TyKind::Unknown.intern(&Interner)
+        TyKind::Error.intern(&Interner)
     }
 
     fn resolve_all(mut self) -> InferenceResult {
@@ -318,8 +316,8 @@ 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.interned(&Interner) {
-            TyKind::Unknown => self.table.new_type_var(),
+        match ty.kind(&Interner) {
+            TyKind::Error => self.table.new_type_var(),
             _ => ty,
         }
     }
@@ -329,19 +327,33 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn resolve_obligations_as_possible(&mut self) {
+        if self.last_obligations_check == Some(self.table.revision) {
+            // no change
+            return;
+        }
+        let _span = profile::span("resolve_obligations_as_possible");
+
+        self.last_obligations_check = Some(self.table.revision);
         let obligations = mem::replace(&mut self.obligations, Vec::new());
         for obligation in obligations {
-            let in_env = InEnvironment::new(self.trait_env.env.clone(), obligation.clone());
+            let in_env = InEnvironment::new(&self.trait_env.env, obligation.clone());
             let canonicalized = self.canonicalizer().canonicalize_obligation(in_env);
             let solution =
                 self.db.trait_solve(self.resolver.krate().unwrap(), canonicalized.value.clone());
 
             match solution {
-                Some(Solution::Unique(substs)) => {
-                    canonicalized.apply_solution(self, substs.0);
+                Some(Solution::Unique(canonical_subst)) => {
+                    canonicalized.apply_solution(
+                        self,
+                        Canonical {
+                            binders: canonical_subst.binders,
+                            // FIXME: handle constraints
+                            value: canonical_subst.value.subst,
+                        },
+                    );
                 }
                 Some(Solution::Ambig(Guidance::Definite(substs))) => {
-                    canonicalized.apply_solution(self, substs.0);
+                    canonicalized.apply_solution(self, substs);
                     self.obligations.push(obligation);
                 }
                 Some(_) => {
@@ -355,6 +367,11 @@ impl<'a> InferenceContext<'a> {
         }
     }
 
+    fn push_obligation(&mut self, o: DomainGoal) {
+        self.obligations.push(o);
+        self.last_obligations_check = None;
+    }
+
     fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
         self.table.unify(ty1, ty2)
     }
@@ -390,21 +407,19 @@ impl<'a> InferenceContext<'a> {
                     _ => panic!("resolve_associated_type called with non-associated type"),
                 };
                 let ty = self.table.new_type_var();
-                let substs = Substitution::build_for_def(self.db, res_assoc_ty)
+                let trait_ref = TyBuilder::trait_ref(self.db, trait_)
                     .push(inner_ty)
                     .fill(params.iter().cloned())
                     .build();
-                let trait_ref =
-                    TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs.clone() };
                 let alias_eq = AliasEq {
                     alias: AliasTy::Projection(ProjectionTy {
                         associated_ty_id: to_assoc_type_id(res_assoc_ty),
-                        substitution: substs,
+                        substitution: trait_ref.substitution.clone(),
                     }),
                     ty: ty.clone(),
                 };
-                self.obligations.push(trait_ref.cast(&Interner));
-                self.obligations.push(alias_eq.cast(&Interner));
+                self.push_obligation(trait_ref.cast(&Interner));
+                self.push_obligation(alias_eq.cast(&Interner));
                 self.resolve_ty_as_possible(ty)
             }
             None => self.err_ty(),
@@ -419,7 +434,7 @@ 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.interned(&Interner) {
+        ty.fold(&mut |ty| match ty.kind(&Interner) {
             TyKind::Alias(AliasTy::Projection(proj_ty)) => {
                 self.normalize_projection_ty(proj_ty.clone())
             }
@@ -431,7 +446,7 @@ impl<'a> InferenceContext<'a> {
         let var = self.table.new_type_var();
         let alias_eq = AliasEq { alias: AliasTy::Projection(proj_ty), ty: var.clone() };
         let obligation = alias_eq.cast(&Interner);
-        self.obligations.push(obligation);
+        self.push_obligation(obligation);
         var
     }
 
@@ -453,56 +468,32 @@ impl<'a> InferenceContext<'a> {
             TypeNs::AdtId(AdtId::StructId(strukt)) => {
                 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));
+                let ty = self.insert_type_vars(ty.substitute(&Interner, &substs));
                 forbid_unresolved_segments((ty, Some(strukt.into())), unresolved)
             }
             TypeNs::AdtId(AdtId::UnionId(u)) => {
                 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));
+                let ty = self.insert_type_vars(ty.substitute(&Interner, &substs));
                 forbid_unresolved_segments((ty, Some(u.into())), unresolved)
             }
             TypeNs::EnumVariantId(var) => {
                 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));
+                let ty = self.insert_type_vars(ty.substitute(&Interner, &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 = Substitution::type_params_for_generics(self.db, &generics);
-                let ty = self.db.impl_self_ty(impl_id).subst(&substs);
-                match unresolved {
-                    None => {
-                        let variant = ty_variant(&ty);
-                        (ty, variant)
-                    }
-                    Some(1) => {
-                        let segment = path.mod_path().segments().last().unwrap();
-                        // this could be an enum variant or associated type
-                        if let Some((AdtId::EnumId(enum_id), _)) = ty.as_adt() {
-                            let enum_data = self.db.enum_data(enum_id);
-                            if let Some(local_id) = enum_data.variant(segment) {
-                                let variant = EnumVariantId { parent: enum_id, local_id };
-                                return (ty, Some(variant.into()));
-                            }
-                        }
-                        // FIXME potentially resolve assoc type
-                        (self.err_ty(), None)
-                    }
-                    Some(_) => {
-                        // FIXME diagnostic
-                        (self.err_ty(), None)
-                    }
-                }
+                let substs = generics.type_params_subst(self.db);
+                let ty = self.db.impl_self_ty(impl_id).substitute(&Interner, &substs);
+                self.resolve_variant_on_alias(ty, unresolved, path)
             }
             TypeNs::TypeAliasId(it) => {
-                let substs = Substitution::build_for_def(self.db, it)
+                let ty = TyBuilder::def_ty(self.db, it.into())
                     .fill(std::iter::repeat_with(|| self.table.new_type_var()))
                     .build();
-                let ty = self.db.ty(it.into()).subst(&substs);
-                let variant = ty_variant(&ty);
-                forbid_unresolved_segments((ty, variant), unresolved)
+                self.resolve_variant_on_alias(ty, unresolved, path)
             }
             TypeNs::AdtSelfType(_) => {
                 // FIXME this could happen in array size expressions, once we're checking them
@@ -526,19 +517,46 @@ impl<'a> InferenceContext<'a> {
                 result
             } else {
                 // FIXME diagnostic
-                (TyKind::Unknown.intern(&Interner), None)
+                (TyKind::Error.intern(&Interner), None)
             }
         }
+    }
 
-        fn ty_variant(ty: &Ty) -> Option<VariantId> {
-            ty.as_adt().and_then(|(adt_id, _)| match adt_id {
-                AdtId::StructId(s) => Some(VariantId::StructId(s)),
-                AdtId::UnionId(u) => Some(VariantId::UnionId(u)),
-                AdtId::EnumId(_) => {
-                    // FIXME Error E0071, expected struct, variant or union type, found enum `Foo`
-                    None
+    fn resolve_variant_on_alias(
+        &mut self,
+        ty: Ty,
+        unresolved: Option<usize>,
+        path: &Path,
+    ) -> (Ty, Option<VariantId>) {
+        match unresolved {
+            None => {
+                let variant = ty.as_adt().and_then(|(adt_id, _)| match adt_id {
+                    AdtId::StructId(s) => Some(VariantId::StructId(s)),
+                    AdtId::UnionId(u) => Some(VariantId::UnionId(u)),
+                    AdtId::EnumId(_) => {
+                        // FIXME Error E0071, expected struct, variant or union type, found enum `Foo`
+                        None
+                    }
+                });
+                (ty, variant)
+            }
+            Some(1) => {
+                let segment = path.mod_path().segments().last().unwrap();
+                // this could be an enum variant or associated type
+                if let Some((AdtId::EnumId(enum_id), _)) = ty.as_adt() {
+                    let enum_data = self.db.enum_data(enum_id);
+                    if let Some(local_id) = enum_data.variant(segment) {
+                        let variant = EnumVariantId { parent: enum_id, local_id };
+                        return (ty, Some(variant.into()));
+                    }
                 }
-            })
+                // FIXME potentially resolve assoc type
+                (self.err_ty(), None)
+            }
+            Some(_) => {
+                // FIXME diagnostic
+                (self.err_ty(), None)
+            }
         }
     }
 
@@ -676,25 +694,6 @@ impl<'a> InferenceContext<'a> {
     }
 }
 
-/// The kinds of placeholders we need during type inference. There's separate
-/// values for general types, and for integer and float variables. The latter
-/// two are used for inference of literal values (e.g. `100` could be one of
-/// several integer types).
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
-pub struct InferenceVar {
-    index: u32,
-}
-
-impl InferenceVar {
-    fn to_inner(self) -> unify::TypeVarId {
-        unify::TypeVarId(self.index)
-    }
-
-    fn from_inner(unify::TypeVarId(index): unify::TypeVarId) -> Self {
-        InferenceVar { index }
-    }
-}
-
 /// When inferring an expression, we propagate downward whatever type hint we
 /// are able in the form of an `Expectation`.
 #[derive(Clone, PartialEq, Eq, Debug)]
@@ -739,7 +738,7 @@ impl Expectation {
     fn none() -> Self {
         Expectation {
             // FIXME
-            ty: TyKind::Unknown.intern(&Interner),
+            ty: TyKind::Error.intern(&Interner),
             rvalue_hint: false,
         }
     }
@@ -747,7 +746,7 @@ impl Expectation {
     fn coercion_target(&self) -> Ty {
         if self.rvalue_hint {
             // FIXME
-            TyKind::Unknown.intern(&Interner)
+            TyKind::Error.intern(&Interner)
         } else {
             self.ty.clone()
         }
diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs
index 9c62932b1..fd679f444 100644
--- a/crates/hir_ty/src/infer/coerce.rs
+++ b/crates/hir_ty/src/infer/coerce.rs
@@ -7,9 +7,7 @@
 use chalk_ir::{cast::Cast, Mutability, TyVariableKind};
 use hir_def::lang_item::LangItemTarget;
 
-use crate::{
-    autoderef, to_chalk_trait_id, traits::Solution, Interner, Substitution, TraitRef, Ty, TyKind,
-};
+use crate::{autoderef, Canonical, Interner, Solution, Ty, TyBuilder, TyExt, TyKind};
 
 use super::{InEnvironment, InferenceContext};
 
@@ -36,7 +34,7 @@ impl<'a> InferenceContext<'a> {
             ty1.clone()
         } else {
             if let (TyKind::FnDef(..), TyKind::FnDef(..)) =
-                (ty1.interned(&Interner), ty2.interned(&Interner))
+                (ty1.kind(&Interner), ty2.kind(&Interner))
             {
                 cov_mark::hit!(coerce_fn_reification);
                 // Special case: two function types. Try to coerce both to
@@ -44,8 +42,8 @@ impl<'a> InferenceContext<'a> {
                 // https://github.com/rust-lang/rust/blob/7b805396bf46dce972692a6846ce2ad8481c5f85/src/librustc_typeck/check/coercion.rs#L877-L916
                 let sig1 = ty1.callable_sig(self.db).expect("FnDef without callable sig");
                 let sig2 = ty2.callable_sig(self.db).expect("FnDef without callable sig");
-                let ptr_ty1 = Ty::fn_ptr(sig1);
-                let ptr_ty2 = Ty::fn_ptr(sig2);
+                let ptr_ty1 = TyBuilder::fn_ptr(sig1);
+                let ptr_ty2 = TyBuilder::fn_ptr(sig2);
                 self.coerce_merge_branch(&ptr_ty1, &ptr_ty2)
             } else {
                 cov_mark::hit!(coerce_merge_fail_fallback);
@@ -55,7 +53,7 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn coerce_inner(&mut self, mut from_ty: Ty, to_ty: &Ty) -> bool {
-        match (from_ty.interned(&Interner), to_ty.interned(&Interner)) {
+        match (from_ty.kind(&Interner), to_ty.kind(&Interner)) {
             // Never type will make type variable to fallback to Never Type instead of Unknown.
             (TyKind::Never, TyKind::InferenceVar(tv, TyVariableKind::General)) => {
                 self.table.type_variable_table.set_diverging(*tv, true);
@@ -73,7 +71,7 @@ impl<'a> InferenceContext<'a> {
         }
 
         // Pointer weakening and function to pointer
-        match (from_ty.interned_mut(), to_ty.interned(&Interner)) {
+        match (from_ty.interned_mut(), to_ty.kind(&Interner)) {
             // `*mut T` -> `*const T`
             // `&mut T` -> `&T`
             (TyKind::Raw(m1, ..), TyKind::Raw(m2 @ Mutability::Not, ..))
@@ -83,7 +81,7 @@ impl<'a> InferenceContext<'a> {
             // `&T` -> `*const T`
             // `&mut T` -> `*mut T`/`*const T`
             (TyKind::Ref(.., substs), &TyKind::Raw(m2 @ Mutability::Not, ..))
-            | (TyKind::Ref(Mutability::Mut, substs), &TyKind::Raw(m2, ..)) => {
+            | (TyKind::Ref(Mutability::Mut, _, substs), &TyKind::Raw(m2, ..)) => {
                 from_ty = TyKind::Raw(m2, substs.clone()).intern(&Interner);
             }
 
@@ -95,12 +93,12 @@ impl<'a> InferenceContext<'a> {
             (TyKind::FnDef(..), TyKind::Function { .. }) => match from_ty.callable_sig(self.db) {
                 None => return false,
                 Some(sig) => {
-                    from_ty = Ty::fn_ptr(sig);
+                    from_ty = TyBuilder::fn_ptr(sig);
                 }
             },
 
             (TyKind::Closure(.., substs), TyKind::Function { .. }) => {
-                from_ty = substs[0].clone();
+                from_ty = substs.at(&Interner, 0).assert_ty_ref(&Interner).clone();
             }
 
             _ => {}
@@ -111,9 +109,11 @@ impl<'a> InferenceContext<'a> {
         }
 
         // Auto Deref if cannot coerce
-        match (from_ty.interned(&Interner), to_ty.interned(&Interner)) {
+        match (from_ty.kind(&Interner), to_ty.kind(&Interner)) {
             // FIXME: DerefMut
-            (TyKind::Ref(_, st1), TyKind::Ref(_, st2)) => self.unify_autoderef_behind_ref(st1, st2),
+            (TyKind::Ref(.., st1), TyKind::Ref(.., st2)) => {
+                self.unify_autoderef_behind_ref(st1, st2)
+            }
 
             // Otherwise, normal unify
             _ => self.unify(&from_ty, to_ty),
@@ -130,19 +130,16 @@ impl<'a> InferenceContext<'a> {
             _ => return None,
         };
 
-        let generic_params = crate::utils::generics(self.db.upcast(), coerce_unsized_trait.into());
-        if generic_params.len() != 2 {
-            // The CoerceUnsized trait should have two generic params: Self and T.
-            return None;
-        }
+        let trait_ref = {
+            let b = TyBuilder::trait_ref(self.db, coerce_unsized_trait);
+            if b.remaining() != 2 {
+                // The CoerceUnsized trait should have two generic params: Self and T.
+                return None;
+            }
+            b.push(from_ty.clone()).push(to_ty.clone()).build()
+        };
 
-        let substs = Substitution::build_for_generics(&generic_params)
-            .push(from_ty.clone())
-            .push(to_ty.clone())
-            .build();
-        let trait_ref =
-            TraitRef { trait_id: to_chalk_trait_id(coerce_unsized_trait), substitution: substs };
-        let goal = InEnvironment::new(self.trait_env.env.clone(), trait_ref.cast(&Interner));
+        let goal = InEnvironment::new(&self.trait_env.env, trait_ref.cast(&Interner));
 
         let canonicalizer = self.canonicalizer();
         let canonicalized = canonicalizer.canonicalize_obligation(goal);
@@ -151,7 +148,14 @@ impl<'a> InferenceContext<'a> {
 
         match solution {
             Solution::Unique(v) => {
-                canonicalized.apply_solution(self, v.0);
+                canonicalized.apply_solution(
+                    self,
+                    Canonical {
+                        binders: v.binders,
+                        // FIXME handle constraints
+                        value: v.value.subst,
+                    },
+                );
             }
             _ => return None,
         };
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 3f3187ea2..9841988c5 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -15,15 +15,16 @@ use stdx::always;
 use syntax::ast::RangeOp;
 
 use crate::{
-    autoderef,
+    autoderef, dummy_usize_const,
     lower::lower_to_chalk_mutability,
     method_resolution, op,
     primitive::{self, UintTy},
-    to_assoc_type_id, to_chalk_trait_id,
-    traits::{chalk::from_chalk, FnTrait, InEnvironment},
-    utils::{generics, variant_data, Generics},
-    AdtId, Binders, CallableDefId, DomainGoal, FnPointer, FnSig, Interner, Rawness, Scalar,
-    Substitution, TraitRef, Ty, TyKind,
+    static_lifetime, to_chalk_trait_id,
+    traits::{chalk::from_chalk, FnTrait},
+    utils::{generics, Generics},
+    AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
+    ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
+    TypeWalk,
 };
 
 use super::{
@@ -73,38 +74,33 @@ impl<'a> InferenceContext<'a> {
         let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
         let output_assoc_type =
             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
-        let generic_params = generics(self.db.upcast(), fn_once_trait.into());
-        if generic_params.len() != 2 {
-            return None;
-        }
 
-        let mut param_builder = Substitution::builder(num_args);
         let mut arg_tys = vec![];
-        for _ in 0..num_args {
-            let arg = self.table.new_type_var();
-            param_builder = param_builder.push(arg.clone());
-            arg_tys.push(arg);
-        }
-        let parameters = param_builder.build();
-        let arg_ty = TyKind::Tuple(num_args, parameters).intern(&Interner);
-        let substs =
-            Substitution::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
+        let arg_ty = TyBuilder::tuple(num_args)
+            .fill(repeat_with(|| {
+                let arg = self.table.new_type_var();
+                arg_tys.push(arg.clone());
+                arg
+            }))
+            .build();
+
+        let projection = {
+            let b = TyBuilder::assoc_type_projection(self.db, output_assoc_type);
+            if b.remaining() != 2 {
+                return None;
+            }
+            b.push(ty.clone()).push(arg_ty).build()
+        };
 
         let trait_env = self.trait_env.env.clone();
-        let implements_fn_trait: DomainGoal =
-            TraitRef { trait_id: to_chalk_trait_id(fn_once_trait), substitution: substs.clone() }
-                .cast(&Interner);
-        let goal = self.canonicalizer().canonicalize_obligation(InEnvironment {
-            goal: implements_fn_trait.clone(),
+        let obligation = InEnvironment {
+            goal: projection.trait_ref(self.db).cast(&Interner),
             environment: trait_env,
-        });
-        if self.db.trait_solve(krate, goal.value).is_some() {
-            self.obligations.push(implements_fn_trait);
-            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);
+        };
+        let canonical = self.canonicalizer().canonicalize_obligation(obligation.clone());
+        if self.db.trait_solve(krate, canonical.value).is_some() {
+            self.push_obligation(obligation.goal);
+            let return_ty = self.normalize_projection_ty(projection);
             Some((arg_tys, return_ty))
         } else {
             None
@@ -119,6 +115,8 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
+        self.db.check_canceled();
+
         let body = Arc::clone(&self.body); // avoid borrow checker problem
         let ty = match &body[tgt_expr] {
             Expr::Missing => self.err_ty(),
@@ -136,7 +134,7 @@ impl<'a> InferenceContext<'a> {
                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
                 let else_ty = match else_branch {
                     Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
-                    None => Ty::unit(),
+                    None => TyBuilder::unit(),
                 };
                 both_arms_diverge &= self.diverges;
 
@@ -183,7 +181,8 @@ impl<'a> InferenceContext<'a> {
                 let inner_ty = self.infer_expr(*body, &Expectation::none());
                 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, Substitution::single(inner_ty)).intern(&Interner)
+                TyKind::OpaqueType(opaque_ty_id, Substitution::from1(&Interner, inner_ty))
+                    .intern(&Interner)
             }
             Expr::Loop { body, label } => {
                 self.breakables.push(BreakableContext {
@@ -191,7 +190,7 @@ impl<'a> InferenceContext<'a> {
                     break_ty: self.table.new_type_var(),
                     label: label.map(|label| self.body[label].name.clone()),
                 });
-                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 
                 let ctxt = self.breakables.pop().expect("breakable stack broken");
                 if ctxt.may_break {
@@ -215,11 +214,11 @@ impl<'a> InferenceContext<'a> {
                     *condition,
                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
                 );
-                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
                 // the body may not run, so it diverging doesn't mean we diverge
                 self.diverges = Diverges::Maybe;
-                Ty::unit()
+                TyBuilder::unit()
             }
             Expr::For { iterable, body, pat, label } => {
                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
@@ -234,11 +233,11 @@ impl<'a> InferenceContext<'a> {
 
                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 
-                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
                 // the body may not run, so it diverging doesn't mean we diverge
                 self.diverges = Diverges::Maybe;
-                Ty::unit()
+                TyBuilder::unit()
             }
             Expr::Lambda { body, args, ret_type, arg_types } => {
                 assert_eq!(args.len(), arg_types.len());
@@ -262,14 +261,17 @@ impl<'a> InferenceContext<'a> {
                 };
                 sig_tys.push(ret_ty.clone());
                 let sig_ty = TyKind::Function(FnPointer {
-                    num_args: sig_tys.len() - 1,
+                    num_binders: 0,
                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
-                    substs: Substitution(sig_tys.clone().into()),
+                    substitution: FnSubst(
+                        Substitution::from_iter(&Interner, sig_tys.clone()).shifted_in(&Interner),
+                    ),
                 })
                 .intern(&Interner);
                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
                 let closure_ty =
-                    TyKind::Closure(closure_id, Substitution::single(sig_ty)).intern(&Interner);
+                    TyKind::Closure(closure_id, Substitution::from1(&Interner, sig_ty))
+                        .intern(&Interner);
 
                 // Eagerly try to relate the closure type with the expected
                 // type, otherwise we often won't have enough information to
@@ -316,7 +318,13 @@ impl<'a> InferenceContext<'a> {
                 self.normalize_associated_types_in(ret_ty)
             }
             Expr::MethodCall { receiver, args, method_name, generic_args } => self
-                .infer_method_call(tgt_expr, *receiver, &args, &method_name, generic_args.as_ref()),
+                .infer_method_call(
+                    tgt_expr,
+                    *receiver,
+                    &args,
+                    &method_name,
+                    generic_args.as_deref(),
+                ),
             Expr::Match { expr, arms } => {
                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 
@@ -358,7 +366,7 @@ impl<'a> InferenceContext<'a> {
                 let val_ty = if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none())
                 } else {
-                    Ty::unit()
+                    TyBuilder::unit()
                 };
 
                 let last_ty =
@@ -384,7 +392,7 @@ impl<'a> InferenceContext<'a> {
                 if let Some(expr) = expr {
                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
                 } else {
-                    let unit = Ty::unit();
+                    let unit = TyBuilder::unit();
                     self.coerce(&unit, &self.return_ty.clone());
                 }
                 TyKind::Never.intern(&Interner)
@@ -397,16 +405,19 @@ impl<'a> InferenceContext<'a> {
                 TyKind::Never.intern(&Interner)
             }
             Expr::RecordLit { path, fields, spread } => {
-                let (ty, def_id) = self.resolve_variant(path.as_ref());
+                let (ty, def_id) = self.resolve_variant(path.as_deref());
                 if let Some(variant) = def_id {
                     self.write_variant_resolution(tgt_expr.into(), variant);
                 }
 
                 self.unify(&ty, &expected.ty);
 
-                let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
+                let substs = ty
+                    .as_adt()
+                    .map(|(_, s)| s.clone())
+                    .unwrap_or_else(|| Substitution::empty(&Interner));
                 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));
+                let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
                 for field in fields.iter() {
                     let field_def =
                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
@@ -418,11 +429,8 @@ impl<'a> InferenceContext<'a> {
                                 None
                             }
                         });
-                    if let Some(field_def) = field_def {
-                        self.result.record_field_resolutions.insert(field.expr, field_def);
-                    }
                     let field_ty = field_def.map_or(self.err_ty(), |it| {
-                        field_types[it.local_id].clone().subst(&substs)
+                        field_types[it.local_id].clone().substitute(&Interner, &substs)
                     });
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
@@ -453,10 +461,10 @@ impl<'a> InferenceContext<'a> {
                             })
                             .unwrap_or(true)
                     };
-                    match canonicalized.decanonicalize_ty(derefed_ty.value).interned(&Interner) {
-                        TyKind::Tuple(_, substs) => {
-                            name.as_tuple_index().and_then(|idx| substs.0.get(idx).cloned())
-                        }
+                    match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
+                        TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
+                            substs.interned().get(idx).map(|a| a.assert_ty_ref(&Interner)).cloned()
+                        }),
                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
                             let field = FieldId { parent: (*s).into(), local_id };
@@ -465,7 +473,7 @@ impl<'a> InferenceContext<'a> {
                                 Some(
                                     self.db.field_types((*s).into())[field.local_id]
                                         .clone()
-                                        .subst(&parameters),
+                                        .substitute(&Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -479,7 +487,7 @@ impl<'a> InferenceContext<'a> {
                                 Some(
                                     self.db.field_types((*u).into())[field.local_id]
                                         .clone()
-                                        .subst(&parameters),
+                                        .substitute(&Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -526,24 +534,17 @@ impl<'a> InferenceContext<'a> {
                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
                 match rawness {
                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
-                    Rawness::Ref => TyKind::Ref(mutability, inner_ty),
+                    Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
                 }
                 .intern(&Interner)
             }
             Expr::Box { expr } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 if let Some(box_) = self.resolve_boxed_box() {
-                    let mut sb =
-                        Substitution::build_for_generics(&generics(self.db.upcast(), box_.into()));
-                    sb = sb.push(inner_ty);
-                    match self.db.generic_defaults(box_.into()).get(1) {
-                        Some(alloc_ty) if !alloc_ty.value.is_unknown() && sb.remaining() > 0 => {
-                            sb = sb.push(alloc_ty.value.clone());
-                        }
-                        _ => (),
-                    }
-                    sb = sb.fill(repeat_with(|| self.table.new_type_var()));
-                    Ty::adt_ty(box_, sb.build())
+                    TyBuilder::adt(self.db, box_)
+                        .push(inner_ty)
+                        .fill_with_defaults(self.db, || self.table.new_type_var())
+                        .build()
                 } else {
                     self.err_ty()
                 }
@@ -571,7 +572,7 @@ impl<'a> InferenceContext<'a> {
                         None => self.err_ty(),
                     },
                     UnaryOp::Neg => {
-                        match inner_ty.interned(&Interner) {
+                        match inner_ty.kind(&Interner) {
                             // Fast path for builtins
                             TyKind::Scalar(Scalar::Int(_))
                             | TyKind::Scalar(Scalar::Uint(_))
@@ -584,7 +585,7 @@ impl<'a> InferenceContext<'a> {
                         }
                     }
                     UnaryOp::Not => {
-                        match inner_ty.interned(&Interner) {
+                        match inner_ty.kind(&Interner) {
                             // Fast path for builtins
                             TyKind::Scalar(Scalar::Bool)
                             | TyKind::Scalar(Scalar::Int(_))
@@ -633,31 +634,31 @@ impl<'a> InferenceContext<'a> {
                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
                 match (range_type, lhs_ty, rhs_ty) {
                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
-                        Some(adt) => Ty::adt_ty(adt, Substitution::empty()),
+                        Some(adt) => TyBuilder::adt(self.db, adt).build(),
                         None => self.err_ty(),
                     },
                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
-                        Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
+                        Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
                         None => self.err_ty(),
                     },
                     (RangeOp::Inclusive, None, Some(ty)) => {
                         match self.resolve_range_to_inclusive() {
-                            Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
+                            Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
                             None => self.err_ty(),
                         }
                     }
                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
-                        Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
+                        Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
                         None => self.err_ty(),
                     },
                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
                         match self.resolve_range_inclusive() {
-                            Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
+                            Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
                             None => self.err_ty(),
                         }
                     }
                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
-                        Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
+                        Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
                         None => self.err_ty(),
                     },
                     (RangeOp::Inclusive, _, None) => self.err_ty(),
@@ -690,10 +691,10 @@ impl<'a> InferenceContext<'a> {
                 }
             }
             Expr::Tuple { exprs } => {
-                let mut tys = match expected.ty.interned(&Interner) {
+                let mut tys = match expected.ty.kind(&Interner) {
                     TyKind::Tuple(_, substs) => substs
-                        .iter()
-                        .cloned()
+                        .iter(&Interner)
+                        .map(|a| a.assert_ty_ref(&Interner).clone())
                         .chain(repeat_with(|| self.table.new_type_var()))
                         .take(exprs.len())
                         .collect::<Vec<_>>(),
@@ -704,11 +705,11 @@ impl<'a> InferenceContext<'a> {
                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
                 }
 
-                TyKind::Tuple(tys.len(), Substitution(tys.into())).intern(&Interner)
+                TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
             }
             Expr::Array(array) => {
-                let elem_ty = match expected.ty.interned(&Interner) {
-                    TyKind::Array(st) | TyKind::Slice(st) => st.clone(),
+                let elem_ty = match expected.ty.kind(&Interner) {
+                    TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
                     _ => self.table.new_type_var(),
                 };
 
@@ -732,17 +733,19 @@ impl<'a> InferenceContext<'a> {
                     }
                 }
 
-                TyKind::Array(elem_ty).intern(&Interner)
+                TyKind::Array(elem_ty, dummy_usize_const()).intern(&Interner)
             }
             Expr::Literal(lit) => match lit {
                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
                 Literal::String(..) => {
-                    TyKind::Ref(Mutability::Not, TyKind::Str.intern(&Interner)).intern(&Interner)
+                    TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(&Interner))
+                        .intern(&Interner)
                 }
                 Literal::ByteString(..) => {
                     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)
+                    let array_type =
+                        TyKind::Array(byte_type, dummy_usize_const()).intern(&Interner);
+                    TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(&Interner)
                 }
                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
                 Literal::Int(_v, ty) => match ty {
@@ -767,6 +770,7 @@ impl<'a> InferenceContext<'a> {
                     None => self.table.new_float_var(),
                 },
             },
+            Expr::MacroStmts { tail } => self.infer_expr(*tail, expected),
         };
         // use a new type variable if we got unknown here
         let ty = self.insert_type_vars_shallow(ty);
@@ -821,8 +825,8 @@ 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());
-                Ty::unit()
+                self.coerce(&TyBuilder::unit(), &expected.coercion_target());
+                TyBuilder::unit()
             }
         };
         ty
@@ -858,10 +862,10 @@ 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, self.err_ty()), None),
+            None => (receiver_ty, Binders::empty(&Interner, 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);
+        let method_ty = method_ty.substitute(&Interner, &substs);
         let method_ty = self.insert_type_vars(method_ty);
         self.register_obligations_for_call(&method_ty);
         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
@@ -877,7 +881,9 @@ impl<'a> InferenceContext<'a> {
         // 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)) => TyKind::Ref(mutability, derefed_receiver_ty).intern(&Interner),
+            Some((_, lifetime, mutability)) => {
+                TyKind::Ref(mutability, lifetime, derefed_receiver_ty).intern(&Interner)
+            }
             _ => derefed_receiver_ty,
         };
         self.unify(&expected_receiver_ty, &actual_receiver_ty);
@@ -950,18 +956,20 @@ impl<'a> InferenceContext<'a> {
             substs.push(self.err_ty());
         }
         assert_eq!(substs.len(), total_len);
-        Substitution(substs.into())
+        Substitution::from_iter(&Interner, substs)
     }
 
     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
-        if let TyKind::FnDef(fn_def, parameters) = callable_ty.interned(&Interner) {
+        if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(&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, binders) =
-                    predicate.clone().subst(parameters).into_value_and_skipped_binders();
-                always!(binders == 0); // quantified where clauses not yet handled
-                self.obligations.push(predicate.cast(&Interner));
+                let (predicate, binders) = predicate
+                    .clone()
+                    .substitute(&Interner, parameters)
+                    .into_value_and_skipped_binders();
+                always!(binders.len(&Interner) == 0); // quantified where clauses not yet handled
+                self.push_obligation(predicate.cast(&Interner));
             }
             // add obligation for trait implementation, if this is a trait method
             match def {
@@ -969,9 +977,11 @@ impl<'a> InferenceContext<'a> {
                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
                     {
                         // construct a TraitRef
-                        let substs =
-                            parameters.prefix(generics(self.db.upcast(), trait_.into()).len());
-                        self.obligations.push(
+                        let substs = crate::subst_prefix(
+                            &*parameters,
+                            generics(self.db.upcast(), trait_.into()).len(),
+                        );
+                        self.push_obligation(
                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
                                 .cast(&Interner),
                         );
diff --git a/crates/hir_ty/src/infer/pat.rs b/crates/hir_ty/src/infer/pat.rs
index 474363709..a41e8e116 100644
--- a/crates/hir_ty/src/infer/pat.rs
+++ b/crates/hir_ty/src/infer/pat.rs
@@ -7,15 +7,13 @@ use chalk_ir::Mutability;
 use hir_def::{
     expr::{BindingAnnotation, Expr, Literal, Pat, PatId, RecordFieldPat},
     path::Path,
-    FieldId,
 };
 use hir_expand::name::Name;
 
 use super::{BindingMode, Expectation, InferenceContext};
 use crate::{
-    lower::lower_to_chalk_mutability,
-    utils::{generics, variant_data},
-    Interner, Substitution, Ty, TyKind,
+    lower::lower_to_chalk_mutability, static_lifetime, Interner, Substitution, Ty, TyBuilder,
+    TyExt, TyKind,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -29,13 +27,14 @@ impl<'a> InferenceContext<'a> {
         ellipsis: Option<usize>,
     ) -> Ty {
         let (ty, def) = self.resolve_variant(path);
-        let var_data = def.map(|it| variant_data(self.db.upcast(), it));
+        let var_data = def.map(|it| it.variant_data(self.db.upcast()));
         if let Some(variant) = def {
             self.write_variant_resolution(id.into(), variant);
         }
         self.unify(&ty, expected);
 
-        let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
+        let substs =
+            ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(&Interner));
 
         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
         let (pre, post) = match ellipsis {
@@ -50,7 +49,9 @@ impl<'a> InferenceContext<'a> {
             let expected_ty = var_data
                 .as_ref()
                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
-                .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
+                .map_or(self.err_ty(), |field| {
+                    field_tys[field].clone().substitute(&Interner, &substs)
+                });
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat, &expected_ty, default_bm);
         }
@@ -67,25 +68,22 @@ impl<'a> InferenceContext<'a> {
         id: PatId,
     ) -> Ty {
         let (ty, def) = self.resolve_variant(path);
-        let var_data = def.map(|it| variant_data(self.db.upcast(), it));
+        let var_data = def.map(|it| it.variant_data(self.db.upcast()));
         if let Some(variant) = def {
             self.write_variant_resolution(id.into(), variant);
         }
 
         self.unify(&ty, expected);
 
-        let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
+        let substs =
+            ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(&Interner));
 
         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
         for subpat in subpats {
             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
-            if let Some(local_id) = matching_field {
-                let field_def = FieldId { parent: def.unwrap(), local_id };
-                self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
-            }
-
-            let expected_ty = matching_field
-                .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
+            let expected_ty = matching_field.map_or(self.err_ty(), |field| {
+                field_tys[field].clone().substitute(&Interner, &substs)
+            });
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat.pat, &expected_ty, default_bm);
         }
@@ -102,7 +100,7 @@ impl<'a> InferenceContext<'a> {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
 
         if is_non_ref_pat(&body, pat) {
-            while let Some((inner, mutability)) = expected.as_reference() {
+            while let Some((inner, _lifetime, mutability)) = expected.as_reference() {
                 expected = inner;
                 default_bm = match default_bm {
                     BindingMode::Move => BindingMode::Ref(mutability),
@@ -124,7 +122,7 @@ impl<'a> InferenceContext<'a> {
         let ty = match &body[pat] {
             &Pat::Tuple { ref args, ellipsis } => {
                 let expectations = match expected.as_tuple() {
-                    Some(parameters) => &*parameters.0,
+                    Some(parameters) => &*parameters.interned().as_slice(),
                     _ => &[],
                 };
 
@@ -134,7 +132,8 @@ impl<'a> InferenceContext<'a> {
                 };
                 let n_uncovered_patterns = expectations.len().saturating_sub(args.len());
                 let err_ty = self.err_ty();
-                let mut expectations_iter = expectations.iter().chain(repeat(&err_ty));
+                let mut expectations_iter =
+                    expectations.iter().map(|a| a.assert_ty_ref(&Interner)).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());
@@ -142,7 +141,8 @@ 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));
 
-                TyKind::Tuple(inner_tys.len(), Substitution(inner_tys.into())).intern(&Interner)
+                TyKind::Tuple(inner_tys.len(), Substitution::from_iter(&Interner, inner_tys))
+                    .intern(&Interner)
             }
             Pat::Or(ref pats) => {
                 if let Some((first_pat, rest)) = pats.split_first() {
@@ -158,7 +158,7 @@ impl<'a> InferenceContext<'a> {
             Pat::Ref { pat, mutability } => {
                 let mutability = lower_to_chalk_mutability(*mutability);
                 let expectation = match expected.as_reference() {
-                    Some((inner_ty, exp_mut)) => {
+                    Some((inner_ty, _lifetime, exp_mut)) => {
                         if mutability != exp_mut {
                             // FIXME: emit type error?
                         }
@@ -167,10 +167,10 @@ impl<'a> InferenceContext<'a> {
                     _ => self.result.standard_types.unknown.clone(),
                 };
                 let subty = self.infer_pat(*pat, &expectation, default_bm);
-                TyKind::Ref(mutability, subty).intern(&Interner)
+                TyKind::Ref(mutability, static_lifetime(), subty).intern(&Interner)
             }
             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
-                p.as_ref(),
+                p.as_deref(),
                 subpats,
                 expected,
                 default_bm,
@@ -178,7 +178,7 @@ impl<'a> InferenceContext<'a> {
                 *ellipsis,
             ),
             Pat::Record { path: p, args: fields, ellipsis: _ } => {