5 files changed, 242 insertions, 173 deletions

diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs
index 028a4d568..1f463a425 100644
--- a/crates/hir_ty/src/infer/coerce.rs
+++ b/crates/hir_ty/src/infer/coerce.rs
@@ -7,7 +7,7 @@
 use chalk_ir::{cast::Cast, Mutability, TyVariableKind};
 use hir_def::lang_item::LangItemTarget;
 
-use crate::{autoderef, traits::Solution, Interner, Ty, TyBuilder, TyKind};
+use crate::{autoderef, Canonical, Interner, Solution, Ty, TyBuilder, TyExt, TyKind};
 
 use super::{InEnvironment, InferenceContext};
 
@@ -71,17 +71,19 @@ impl<'a> InferenceContext<'a> {
         }
 
         // Pointer weakening and function to pointer
-        match (from_ty.interned_mut(), to_ty.kind(&Interner)) {
+        match (from_ty.kind(&Interner), to_ty.kind(&Interner)) {
             // `*mut T` -> `*const T`
+            (TyKind::Raw(_, inner), TyKind::Raw(m2 @ Mutability::Not, ..)) => {
+                from_ty = TyKind::Raw(*m2, inner.clone()).intern(&Interner);
+            }
             // `&mut T` -> `&T`
-            (TyKind::Raw(m1, ..), TyKind::Raw(m2 @ Mutability::Not, ..))
-            | (TyKind::Ref(m1, ..), TyKind::Ref(m2 @ Mutability::Not, ..)) => {
-                *m1 = *m2;
+            (TyKind::Ref(_, lt, inner), TyKind::Ref(m2 @ Mutability::Not, ..)) => {
+                from_ty = TyKind::Ref(*m2, lt.clone(), inner.clone()).intern(&Interner);
             }
             // `&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);
             }
 
@@ -111,7 +113,9 @@ impl<'a> InferenceContext<'a> {
         // Auto Deref if cannot coerce
         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),
@@ -137,7 +141,7 @@ impl<'a> InferenceContext<'a> {
             b.push(from_ty.clone()).push(to_ty.clone()).build()
         };
 
-        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);
@@ -146,7 +150,14 @@ 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 c584a2c08..50497eecb 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -3,7 +3,7 @@
 use std::iter::{repeat, repeat_with};
 use std::{mem, sync::Arc};
 
-use chalk_ir::{cast::Cast, Mutability, TyVariableKind};
+use chalk_ir::{cast::Cast, fold::Shift, Mutability, TyVariableKind};
 use hir_def::{
     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
     path::{GenericArg, GenericArgs},
@@ -15,15 +15,16 @@ use stdx::always;
 use syntax::ast::RangeOp;
 
 use crate::{
-    autoderef,
+    autoderef, dummy_usize_const,
     lower::lower_to_chalk_mutability,
+    mapping::from_chalk,
     method_resolution, op,
     primitive::{self, UintTy},
-    to_chalk_trait_id,
-    traits::{chalk::from_chalk, FnTrait, InEnvironment},
-    utils::{generics, variant_data, Generics},
-    AdtId, Binders, CallableDefId, FnPointer, FnSig, Interner, Rawness, Scalar, Substitution,
-    TraitRef, Ty, TyBuilder, TyKind,
+    static_lifetime, to_chalk_trait_id,
+    traits::FnTrait,
+    utils::{generics, Generics},
+    AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
+    ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
 };
 
 use super::{
@@ -180,7 +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 {
@@ -259,14 +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::from_iter(&Interner, sig_tys.clone()),
+                    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
@@ -313,7 +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());
 
@@ -394,16 +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(&Interner));
+                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) {
@@ -415,11 +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));
                 }
@@ -453,7 +464,7 @@ impl<'a> InferenceContext<'a> {
                     match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
                             substs
-                                .interned(&Interner)
+                                .as_slice(&Interner)
                                 .get(idx)
                                 .map(|a| a.assert_ty_ref(&Interner))
                                 .cloned()
@@ -466,7 +477,7 @@ impl<'a> InferenceContext<'a> {
                                 Some(
                                     self.db.field_types((*s).into())[field.local_id]
                                         .clone()
-                                        .subst(&parameters),
+                                        .substitute(&Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -480,7 +491,7 @@ impl<'a> InferenceContext<'a> {
                                 Some(
                                     self.db.field_types((*u).into())[field.local_id]
                                         .clone()
-                                        .subst(&parameters),
+                                        .substitute(&Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -527,7 +538,7 @@ 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)
             }
@@ -702,7 +713,7 @@ impl<'a> InferenceContext<'a> {
             }
             Expr::Array(array) => {
                 let elem_ty = match expected.ty.kind(&Interner) {
-                    TyKind::Array(st) | TyKind::Slice(st) => st.clone(),
+                    TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
                     _ => self.table.new_type_var(),
                 };
 
@@ -726,17 +737,19 @@ 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 {
@@ -853,10 +866,10 @@ 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) {
@@ -872,7 +885,9 @@ 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);
@@ -953,9 +968,11 @@ impl<'a> InferenceContext<'a> {
             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
+                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
@@ -964,8 +981,10 @@ 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());
+                        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 5b70d5e5a..aea354cde 100644
--- a/crates/hir_ty/src/infer/pat.rs
+++ b/crates/hir_ty/src/infer/pat.rs
@@ -7,14 +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::variant_data, Interner, Substitution, Ty, TyBuilder,
-    TyKind,
+    lower::lower_to_chalk_mutability, static_lifetime, Interner, Substitution, Ty, TyBuilder,
+    TyExt, TyKind,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -28,13 +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(&Interner));
+        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 {
@@ -49,7 +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);
         }
@@ -66,25 +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(&Interner));
+        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);
         }
@@ -101,7 +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),
@@ -123,7 +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.as_slice(&Interner),
                     _ => &[],
                 };
 
@@ -159,7 +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?
                         }
@@ -168,10 +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,
@@ -179,7 +178,7 @@ impl<'a> InferenceContext<'a> {
                 *ellipsis,
             ),
             Pat::Record { path: p, args: fields, ellipsis: _ } => {
-                self.infer_record_pat(p.as_ref(), fields, expected, default_bm, pat)
+                self.infer_record_pat(p.as_deref(), fields, expected, default_bm, pat)
             }
             Pat::Path(path) => {
                 // FIXME use correct resolver for the surrounding expression
@@ -201,7 +200,8 @@ impl<'a> InferenceContext<'a> {
 
                 let bound_ty = match mode {
                     BindingMode::Ref(mutability) => {
-                        TyKind::Ref(mutability, inner_ty.clone()).intern(&Interner)
+                        TyKind::Ref(mutability, static_lifetime(), inner_ty.clone())
+                            .intern(&Interner)
                     }
                     BindingMode::Move => inner_ty.clone(),
                 };
@@ -210,17 +210,20 @@ impl<'a> InferenceContext<'a> {
                 return inner_ty;
             }
             Pat::Slice { prefix, slice, suffix } => {
-                let (container_ty, elem_ty): (fn(_) -> _, _) = match expected.kind(&Interner) {
-                    TyKind::Array(st) => (TyKind::Array, st.clone()),
-                    TyKind::Slice(st) => (TyKind::Slice, st.clone()),
-                    _ => (TyKind::Slice, self.err_ty()),
+                let elem_ty = match expected.kind(&Interner) {
+                    TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
+                    _ => self.err_ty(),
                 };
 
                 for pat_id in prefix.iter().chain(suffix) {
                     self.infer_pat(*pat_id, &elem_ty, default_bm);
                 }
 
-                let pat_ty = container_ty(elem_ty).intern(&Interner);
+                let pat_ty = match expected.kind(&Interner) {
+                    TyKind::Array(_, const_) => TyKind::Array(elem_ty, const_.clone()),
+                    _ => TyKind::Slice(elem_ty),
+                }
+                .intern(&Interner);
                 if let Some(slice_pat_id) = slice {
                     self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
                 }
@@ -239,7 +242,7 @@ impl<'a> InferenceContext<'a> {
                     let (inner_ty, alloc_ty) = match expected.as_adt() {
                         Some((adt, subst)) if adt == box_adt => (
                             subst.at(&Interner, 0).assert_ty_ref(&Interner).clone(),
-                            subst.interned(&Interner).get(1).and_then(|a| a.ty(&Interner).cloned()),
+                            subst.as_slice(&Interner).get(1).and_then(|a| a.ty(&Interner).cloned()),
                         ),
                         _ => (self.result.standard_types.unknown.clone(), None),
                     };
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index 671ea355f..495282eba 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -10,7 +10,10 @@ use hir_def::{
 };
 use hir_expand::name::Name;
 
-use crate::{method_resolution, Interner, Substitution, Ty, TyBuilder, TyKind, ValueTyDefId};
+use crate::{
+    method_resolution, Interner, Substitution, TraitRefExt, Ty, TyBuilder, TyExt, TyKind,
+    ValueTyDefId,
+};
 
 use super::{ExprOrPatId, InferenceContext, TraitRef};
 
@@ -81,9 +84,9 @@ impl<'a> InferenceContext<'a> {
             ValueNs::ImplSelf(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
                 let substs = generics.type_params_subst(self.db);
-                let ty = self.db.impl_self_ty(impl_id).subst(&substs);
+                let ty = self.db.impl_self_ty(impl_id).substitute(&Interner, &substs);
                 if let Some((AdtId::StructId(struct_id), substs)) = ty.as_adt() {
-                    let ty = self.db.value_ty(struct_id.into()).subst(&substs);
+                    let ty = self.db.value_ty(struct_id.into()).substitute(&Interner, &substs);
                     return Some(ty);
                 } else {
                     // FIXME: diagnostic, invalid Self reference
@@ -98,7 +101,7 @@ impl<'a> InferenceContext<'a> {
         let substs = ctx.substs_from_path(path, typable, true);
         let ty = TyBuilder::value_ty(self.db, typable)
             .use_parent_substs(&parent_substs)
-            .fill(substs.interned(&Interner)[parent_substs.len(&Interner)..].iter().cloned())
+            .fill(substs.as_slice(&Interner)[parent_substs.len(&Interner)..].iter().cloned())
             .build();
         Some(ty)
     }
@@ -142,7 +145,7 @@ impl<'a> InferenceContext<'a> {
                     remaining_segments_for_ty,
                     true,
                 );
-                if let TyKind::Unknown = ty.kind(&Interner) {
+                if let TyKind::Error = ty.kind(&Interner) {
                     return None;
                 }
 
@@ -207,7 +210,7 @@ impl<'a> InferenceContext<'a> {
         name: &Name,
         id: ExprOrPatId,
     ) -> Option<(ValueNs, Option<Substitution>)> {
-        if let TyKind::Unknown = ty.kind(&Interner) {
+        if let TyKind::Error = ty.kind(&Interner) {
             return None;
         }
 
@@ -243,7 +246,8 @@ impl<'a> InferenceContext<'a> {
                         let impl_substs = TyBuilder::subst_for_def(self.db, impl_id)
                             .fill(iter::repeat_with(|| self.table.new_type_var()))
                             .build();
-                        let impl_self_ty = self.db.impl_self_ty(impl_id).subst(&impl_substs);
+                        let impl_self_ty =
+                            self.db.impl_self_ty(impl_id).substitute(&Interner, &impl_substs);
                         self.unify(&impl_self_ty, &ty);
                         Some(impl_substs)
                     }
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index a04b935ef..a887e20b0 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -2,13 +2,17 @@
 
 use std::borrow::Cow;
 
-use chalk_ir::{FloatTy, IntTy, TyVariableKind, UniverseIndex, VariableKind};
+use chalk_ir::{
+    cast::Cast, fold::Fold, interner::HasInterner, FloatTy, IntTy, TyVariableKind, UniverseIndex,
+    VariableKind,
+};
 use ena::unify::{InPlaceUnificationTable, NoError, UnifyKey, UnifyValue};
 
 use super::{DomainGoal, InferenceContext};
 use crate::{
-    AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds, DebruijnIndex, FnPointer,
-    InEnvironment, InferenceVar, Interner, Scalar, Substitution, Ty, TyKind, TypeWalk, WhereClause,
+    fold_tys, static_lifetime, AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds,
+    DebruijnIndex, FnPointer, FnSubst, InEnvironment, InferenceVar, Interner, Scalar, Substitution,
+    Ty, TyExt, TyKind, WhereClause,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -33,7 +37,10 @@ where
 }
 
 #[derive(Debug)]
-pub(super) struct Canonicalized<T> {
+pub(super) struct Canonicalized<T>
+where
+    T: HasInterner<Interner = Interner>,
+{
     pub(super) value: Canonical<T>,
     free_vars: Vec<(InferenceVar, TyVariableKind)>,
 }
@@ -47,11 +54,16 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
         })
     }
 
-    fn do_canonicalize<T: TypeWalk>(&mut self, t: T, binders: DebruijnIndex) -> T {
-        t.fold_binders(
-            &mut |ty, binders| match ty.kind(&Interner) {
+    fn do_canonicalize<T: Fold<Interner, Result = T> + HasInterner<Interner = Interner>>(
+        &mut self,
+        t: T,
+        binders: DebruijnIndex,
+    ) -> T {
+        fold_tys(
+            t,
+            |ty, binders| match ty.kind(&Interner) {
                 &TyKind::InferenceVar(var, kind) => {
-                    let inner = var.to_inner();
+                    let inner = from_inference_var(var);
                     if self.var_stack.contains(&inner) {
                         // recursive type
                         return self.ctx.table.type_variable_table.fallback_value(var, kind);
@@ -65,7 +77,7 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
                         result
                     } else {
                         let root = self.ctx.table.var_unification_table.find(inner);
-                        let position = self.add(InferenceVar::from_inner(root), kind);
+                        let position = self.add(to_inference_var(root), kind);
                         TyKind::BoundVar(BoundVar::new(binders, position)).intern(&Interner)
                     }
                 }
@@ -75,7 +87,10 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
         )
     }
 
-    fn into_canonicalized<T>(self, result: T) -> Canonicalized<T> {
+    fn into_canonicalized<T: HasInterner<Interner = Interner>>(
+        self,
+        result: T,
+    ) -> Canonicalized<T> {
         let kinds = self
             .free_vars
             .iter()
@@ -102,25 +117,18 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
             DomainGoal::Holds(wc) => {
                 DomainGoal::Holds(self.do_canonicalize(wc, DebruijnIndex::INNERMOST))
             }
+            _ => unimplemented!(),
         };
         self.into_canonicalized(InEnvironment { goal: result, environment: obligation.environment })
     }
 }
 
-impl<T> Canonicalized<T> {
-    pub(super) fn decanonicalize_ty(&self, mut ty: Ty) -> Ty {
-        ty.walk_mut_binders(
-            &mut |ty, binders| {
-                if let &mut TyKind::BoundVar(bound) = ty.interned_mut() {
-                    if bound.debruijn >= binders {
-                        let (v, k) = self.free_vars[bound.index];
-                        *ty = TyKind::InferenceVar(v, k).intern(&Interner);
-                    }
-                }
-            },
-            DebruijnIndex::INNERMOST,
-        );
-        ty
+impl<T: HasInterner<Interner = Interner>> Canonicalized<T> {
+    pub(super) fn decanonicalize_ty(&self, ty: Ty) -> Ty {
+        crate::fold_free_vars(ty, |bound, _binders| {
+            let (v, k) = self.free_vars[bound.index];
+            TyKind::InferenceVar(v, k).intern(&Interner)
+        })
     }
 
     pub(super) fn apply_solution(
@@ -132,15 +140,17 @@ impl<T> Canonicalized<T> {
         let new_vars = Substitution::from_iter(
             &Interner,
             solution.binders.iter(&Interner).map(|k| match k.kind {
-                VariableKind::Ty(TyVariableKind::General) => ctx.table.new_type_var(),
-                VariableKind::Ty(TyVariableKind::Integer) => ctx.table.new_integer_var(),
-                VariableKind::Ty(TyVariableKind::Float) => ctx.table.new_float_var(),
-                // HACK: Chalk can sometimes return new lifetime variables. We
-                // want to just skip them, but to not mess up the indices of
-                // other variables, we'll just create a new type variable in
-                // their place instead. This should not matter (we never see the
-                // actual *uses* of the lifetime variable).
-                VariableKind::Lifetime => ctx.table.new_type_var(),
+                VariableKind::Ty(TyVariableKind::General) => {
+                    ctx.table.new_type_var().cast(&Interner)
+                }
+                VariableKind::Ty(TyVariableKind::Integer) => {
+                    ctx.table.new_integer_var().cast(&Interner)
+                }
+                VariableKind::Ty(TyVariableKind::Float) => {
+                    ctx.table.new_float_var().cast(&Interner)
+                }
+                // Chalk can sometimes return new lifetime variables. We just use the static lifetime everywhere
+                VariableKind::Lifetime => static_lifetime().cast(&Interner),
                 _ => panic!("const variable in solution"),
             }),
         );
@@ -149,7 +159,7 @@ impl<T> Canonicalized<T> {
             // eagerly replace projections in the type; we may be getting types
             // e.g. from where clauses where this hasn't happened yet
             let ty = ctx.normalize_associated_types_in(
-                ty.assert_ty_ref(&Interner).clone().subst_bound_vars(&new_vars),
+                new_vars.apply(ty.assert_ty_ref(&Interner).clone(), &Interner),
             );
             ctx.table.unify(&TyKind::InferenceVar(v, k).intern(&Interner), &ty);
         }
@@ -170,8 +180,8 @@ pub(crate) fn unify(tys: &Canonical<(Ty, Ty)>) -> Option<Substitution> {
             // fallback to Unknown in the end (kind of hacky, as below)
             .map(|_| table.new_type_var()),
     );
-    let ty1_with_vars = tys.value.0.clone().subst_bound_vars(&vars);
-    let ty2_with_vars = tys.value.1.clone().subst_bound_vars(&vars);
+    let ty1_with_vars = vars.apply(tys.value.0.clone(), &Interner);
+    let ty2_with_vars = vars.apply(tys.value.1.clone(), &Interner);
     if !table.unify(&ty1_with_vars, &ty2_with_vars) {
         return None;
     }
@@ -204,17 +214,17 @@ impl TypeVariableTable {
     }
 
     pub(super) fn set_diverging(&mut self, iv: InferenceVar, diverging: bool) {
-        self.inner[iv.to_inner().0 as usize].diverging = diverging;
+        self.inner[from_inference_var(iv).0 as usize].diverging = diverging;
     }
 
     fn is_diverging(&mut self, iv: InferenceVar) -> bool {
-        self.inner[iv.to_inner().0 as usize].diverging
+        self.inner[from_inference_var(iv).0 as usize].diverging
     }
 
     fn fallback_value(&self, iv: InferenceVar, kind: TyVariableKind) -> Ty {
         match kind {
-            _ if self.inner[iv.to_inner().0 as usize].diverging => TyKind::Never,
-            TyVariableKind::General => TyKind::Unknown,
+            _ if self.inner[from_inference_var(iv).0 as usize].diverging => TyKind::Never,
+            TyVariableKind::General => TyKind::Error,
             TyVariableKind::Integer => TyKind::Scalar(Scalar::Int(IntTy::I32)),
             TyVariableKind::Float => TyKind::Scalar(Scalar::Float(FloatTy::F64)),
         }
@@ -247,7 +257,7 @@ impl InferenceTable {
         self.type_variable_table.push(TypeVariableData { diverging });
         let key = self.var_unification_table.new_key(TypeVarValue::Unknown);
         assert_eq!(key.0 as usize, self.type_variable_table.inner.len() - 1);
-        TyKind::InferenceVar(InferenceVar::from_inner(key), kind).intern(&Interner)
+        TyKind::InferenceVar(to_inference_var(key), kind).intern(&Interner)
     }
 
     pub(crate) fn new_type_var(&mut self) -> Ty {
@@ -284,7 +294,7 @@ impl InferenceTable {
         substs2: &Substitution,
         depth: usize,
     ) -> bool {
-        substs1.0.iter().zip(substs2.0.iter()).all(|(t1, t2)| {
+        substs1.iter(&Interner).zip(substs2.iter(&Interner)).all(|(t1, t2)| {
             self.unify_inner(t1.assert_ty_ref(&Interner), t2.assert_ty_ref(&Interner), depth)
         })
     }
@@ -305,8 +315,8 @@ impl InferenceTable {
                 (TyKind::Adt(_, substs1), TyKind::Adt(_, substs2))
                 | (TyKind::FnDef(_, substs1), TyKind::FnDef(_, substs2))
                 | (
-                    TyKind::Function(FnPointer { substs: substs1, .. }),
-                    TyKind::Function(FnPointer { substs: substs2, .. }),
+                    TyKind::Function(FnPointer { substitution: FnSubst(substs1), .. }),
+                    TyKind::Function(FnPointer { substitution: FnSubst(substs2), .. }),
                 )
                 | (TyKind::Tuple(_, substs1), TyKind::Tuple(_, substs2))
                 | (TyKind::OpaqueType(_, substs1), TyKind::OpaqueType(_, substs2))
@@ -314,9 +324,11 @@ impl InferenceTable {
                 | (TyKind::Closure(.., substs1), TyKind::Closure(.., substs2)) => {
                     self.unify_substs(substs1, substs2, depth + 1)
                 }
-                (TyKind::Ref(_, ty1), TyKind::Ref(_, ty2))
+                (TyKind::Array(ty1, c1), TyKind::Array(ty2, c2)) if c1 == c2 => {
+                    self.unify_inner(ty1, ty2, depth + 1)
+                }
+                (TyKind::Ref(_, _, ty1), TyKind::Ref(_, _, ty2))
                 | (TyKind::Raw(_, ty1), TyKind::Raw(_, ty2))
-                | (TyKind::Array(ty1), TyKind::Array(ty2))
                 | (TyKind::Slice(ty1), TyKind::Slice(ty2)) => self.unify_inner(ty1, ty2, depth + 1),
                 _ => true, /* we checked equals_ctor already */
             }
@@ -327,7 +339,7 @@ impl InferenceTable {
 
     pub(super) fn unify_inner_trivial(&mut self, ty1: &Ty, ty2: &Ty, depth: usize) -> bool {
         match (ty1.kind(&Interner), ty2.kind(&Interner)) {
-            (TyKind::Unknown, _) | (_, TyKind::Unknown) => true,
+            (TyKind::Error, _) | (_, TyKind::Error) => true,
 
             (TyKind::Placeholder(p1), TyKind::Placeholder(p2)) if *p1 == *p2 => true,
 
@@ -364,8 +376,12 @@ impl InferenceTable {
                 == self.type_variable_table.is_diverging(*tv2) =>
             {
                 // both type vars are unknown since we tried to resolve them
-                if !self.var_unification_table.unioned(tv1.to_inner(), tv2.to_inner()) {
-                    self.var_unification_table.union(tv1.to_inner(), tv2.to_inner());
+                if !self
+                    .var_unification_table
+                    .unioned(from_inference_var(*tv1), from_inference_var(*tv2))
+                {
+                    self.var_unification_table
+                        .union(from_inference_var(*tv1), from_inference_var(*tv2));
                     self.revision += 1;
                 }
                 true
@@ -402,7 +418,7 @@ impl InferenceTable {
             ) => {
                 // the type var is unknown since we tried to resolve it
                 self.var_unification_table.union_value(
-                    tv.to_inner(),
+                    from_inference_var(*tv),
                     TypeVarValue::Known(other.clone().intern(&Interner)),
                 );
                 self.revision += 1;
@@ -457,7 +473,7 @@ impl InferenceTable {
             }
             match ty.kind(&Interner) {
                 TyKind::InferenceVar(tv, _) => {
-                    let inner = tv.to_inner();
+                    let inner = from_inference_var(*tv);
                     match self.var_unification_table.inlined_probe_value(inner).known() {
                         Some(known_ty) => {
                             // The known_ty can't be a type var itself
@@ -478,55 +494,63 @@ impl InferenceTable {
     /// be resolved as far as possible, i.e. contain no type variables with
     /// known type.
     fn resolve_ty_as_possible_inner(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
-        ty.fold(&mut |ty| match ty.kind(&Interner) {
-            &TyKind::InferenceVar(tv, kind) => {
-                let inner = tv.to_inner();
-                if tv_stack.contains(&inner) {
-                    cov_mark::hit!(type_var_cycles_resolve_as_possible);
-                    // recursive type
-                    return self.type_variable_table.fallback_value(tv, kind);
-                }
-                if let Some(known_ty) =
-                    self.var_unification_table.inlined_probe_value(inner).known()
-                {
-                    // known_ty may contain other variables that are known by now
-                    tv_stack.push(inner);
-                    let result = self.resolve_ty_as_possible_inner(tv_stack, known_ty.clone());
-                    tv_stack.pop();
-                    result
-                } else {
-                    ty
+        fold_tys(
+            ty,
+            |ty, _| match ty.kind(&Interner) {
+                &TyKind::InferenceVar(tv, kind) => {
+                    let inner = from_inference_var(tv);
+                    if tv_stack.contains(&inner) {
+                        cov_mark::hit!(type_var_cycles_resolve_as_possible);
+                        // recursive type
+                        return self.type_variable_table.fallback_value(tv, kind);
+                    }
+                    if let Some(known_ty) =
+                        self.var_unification_table.inlined_probe_value(inner).known()
+                    {
+                        // known_ty may contain other variables that are known by now
+                        tv_stack.push(inner);
+                        let result = self.resolve_ty_as_possible_inner(tv_stack, known_ty.clone());
+                        tv_stack.pop();
+                        result
+                    } else {
+                        ty
+                    }
                 }
-            }
-            _ => ty,
-        })
+                _ => ty,
+            },
+            DebruijnIndex::INNERMOST,
+        )
     }
 
     /// Resolves the type completely; type variables without known type are
     /// replaced by TyKind::Unknown.
     fn resolve_ty_completely_inner(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
-        ty.fold(&mut |ty| match ty.kind(&Interner) {
-            &TyKind::InferenceVar(tv, kind) => {
-                let inner = tv.to_inner();
-                if tv_stack.contains(&inner) {
-                    cov_mark::hit!(type_var_cycles_resolve_completely);
-                    // recursive type
-                    return self.type_variable_table.fallback_value(tv, kind);
-                }
-                if let Some(known_ty) =
-                    self.var_unification_table.inlined_probe_value(inner).known()
-                {
-                    // known_ty may contain other variables that are known by now
-                    tv_stack.push(inner);
-                    let result = self.resolve_ty_completely_inner(tv_stack, known_ty.clone());
-                    tv_stack.pop();
-                    result
-                } else {
-                    self.type_variable_table.fallback_value(tv, kind)
+        fold_tys(
+            ty,
+            |ty, _| match ty.kind(&Interner) {
+                &TyKind::InferenceVar(tv, kind) => {
+                    let inner = from_inference_var(tv);
+                    if tv_stack.contains(&inner) {
+                        cov_mark::hit!(type_var_cycles_resolve_completely);
+                        // recursive type
+                        return self.type_variable_table.fallback_value(tv, kind);
+                    }
+                    if let Some(known_ty) =
+                        self.var_unification_table.inlined_probe_value(inner).known()
+                    {
+                        // known_ty may contain other variables that are known by now
+                        tv_stack.push(inner);
+                        let result = self.resolve_ty_completely_inner(tv_stack, known_ty.clone());
+                        tv_stack.pop();
+                        result
+                    } else {
+                        self.type_variable_table.fallback_value(tv, kind)
+                    }
                 }
-            }
-            _ => ty,
-        })
+                _ => ty,
+            },
+            DebruijnIndex::INNERMOST,
+        )
     }
 }
 
@@ -550,6 +574,14 @@ impl UnifyKey for TypeVarId {
     }
 }
 
+fn from_inference_var(var: InferenceVar) -> TypeVarId {
+    TypeVarId(var.index())
+}
+
+fn to_inference_var(TypeVarId(index): TypeVarId) -> InferenceVar {
+    index.into()
+}
+
 /// The value of a type variable: either we already know the type, or we don't
 /// know it yet.
 #[derive(Clone, PartialEq, Eq, Debug)]