1 files changed, 142 insertions, 105 deletions

diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 262177ffb..eee3e6ec5 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -18,10 +18,11 @@ use crate::{
     lower::lower_to_chalk_mutability,
     method_resolution, op,
     primitive::{self, UintTy},
-    traits::{FnTrait, InEnvironment},
+    to_assoc_type_id,
+    traits::{chalk::from_chalk, FnTrait, InEnvironment},
     utils::{generics, variant_data, Generics},
-    AdtId, Binders, CallableDefId, FnPointer, FnSig, Obligation, OpaqueTyId, Rawness, Scalar,
-    Substs, TraitRef, Ty,
+    AdtId, Binders, CallableDefId, FnPointer, FnSig, Interner, Obligation, Rawness, Scalar, Substs,
+    TraitRef, Ty, TyKind,
 };
 
 use super::{
@@ -57,7 +58,7 @@ impl<'a> InferenceContext<'a> {
             // Return actual type when type mismatch.
             // This is needed for diagnostic when return type mismatch.
             ty
-        } else if expected.coercion_target() == &Ty::Unknown {
+        } else if expected.coercion_target().is_unknown() {
             ty
         } else {
             expected.ty.clone()
@@ -84,7 +85,7 @@ impl<'a> InferenceContext<'a> {
             arg_tys.push(arg);
         }
         let parameters = param_builder.build();
-        let arg_ty = Ty::Tuple(num_args, parameters);
+        let arg_ty = TyKind::Tuple(num_args, parameters).intern(&Interner);
         let substs =
             Substs::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
 
@@ -97,8 +98,10 @@ impl<'a> InferenceContext<'a> {
         });
         if self.db.trait_solve(krate, goal.value).is_some() {
             self.obligations.push(implements_fn_trait);
-            let output_proj_ty =
-                crate::ProjectionTy { associated_ty: output_assoc_type, parameters: substs };
+            let output_proj_ty = crate::ProjectionTy {
+                associated_ty: to_assoc_type_id(output_assoc_type),
+                parameters: substs,
+            };
             let return_ty = self.normalize_projection_ty(output_proj_ty);
             Some((arg_tys, return_ty))
         } else {
@@ -116,10 +119,13 @@ impl<'a> InferenceContext<'a> {
     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
         let ty = match &body[tgt_expr] {
-            Expr::Missing => Ty::Unknown,
+            Expr::Missing => self.err_ty(),
             Expr::If { condition, then_branch, else_branch } => {
                 // if let is desugared to match, so this is always simple if
-                self.infer_expr(*condition, &Expectation::has_type(Ty::Scalar(Scalar::Bool)));
+                self.infer_expr(
+                    *condition,
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
+                );
 
                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
                 let mut both_arms_diverge = Diverges::Always;
@@ -167,14 +173,15 @@ impl<'a> InferenceContext<'a> {
             Expr::TryBlock { body } => {
                 let _inner = self.infer_expr(*body, expected);
                 // FIXME should be std::result::Result<{inner}, _>
-                Ty::Unknown
+                self.err_ty()
             }
             Expr::Async { body } => {
                 // Use the first type parameter as the output type of future.
                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
                 let inner_ty = self.infer_expr(*body, &Expectation::none());
-                let opaque_ty_id = OpaqueTyId::AsyncBlockTypeImplTrait(self.owner, *body);
-                Ty::OpaqueType(opaque_ty_id, Substs::single(inner_ty))
+                let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
+                let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
+                TyKind::OpaqueType(opaque_ty_id, Substs::single(inner_ty)).intern(&Interner)
             }
             Expr::Loop { body, label } => {
                 self.breakables.push(BreakableContext {
@@ -192,17 +199,20 @@ impl<'a> InferenceContext<'a> {
                 if ctxt.may_break {
                     ctxt.break_ty
                 } else {
-                    Ty::Never
+                    TyKind::Never.intern(&Interner)
                 }
             }
             Expr::While { condition, body, label } => {
                 self.breakables.push(BreakableContext {
                     may_break: false,
-                    break_ty: Ty::Unknown,
+                    break_ty: self.err_ty(),
                     label: label.map(|label| self.body[label].name.clone()),
                 });
                 // while let is desugared to a match loop, so this is always simple while
-                self.infer_expr(*condition, &Expectation::has_type(Ty::Scalar(Scalar::Bool)));
+                self.infer_expr(
+                    *condition,
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
+                );
                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
                 // the body may not run, so it diverging doesn't mean we diverge
@@ -214,7 +224,7 @@ impl<'a> InferenceContext<'a> {
 
                 self.breakables.push(BreakableContext {
                     may_break: false,
-                    break_ty: Ty::Unknown,
+                    break_ty: self.err_ty(),
                     label: label.map(|label| self.body[label].name.clone()),
                 });
                 let pat_ty =
@@ -249,12 +259,15 @@ impl<'a> InferenceContext<'a> {
                     None => self.table.new_type_var(),
                 };
                 sig_tys.push(ret_ty.clone());
-                let sig_ty = Ty::Function(FnPointer {
+                let sig_ty = TyKind::Function(FnPointer {
                     num_args: sig_tys.len() - 1,
                     sig: FnSig { variadic: false },
                     substs: Substs(sig_tys.clone().into()),
-                });
-                let closure_ty = Ty::Closure(self.owner, tgt_expr, Substs::single(sig_ty));
+                })
+                .intern(&Interner);
+                let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
+                let closure_ty =
+                    TyKind::Closure(closure_id, Substs::single(sig_ty)).intern(&Interner);
 
                 // Eagerly try to relate the closure type with the expected
                 // type, otherwise we often won't have enough information to
@@ -295,7 +308,7 @@ impl<'a> InferenceContext<'a> {
                             args.len(),
                         )
                     })
-                    .unwrap_or((Vec::new(), Ty::Unknown));
+                    .unwrap_or((Vec::new(), self.err_ty()));
                 self.register_obligations_for_call(&callee_ty);
                 self.check_call_arguments(args, &param_tys);
                 self.normalize_associated_types_in(ret_ty)
@@ -305,8 +318,11 @@ impl<'a> InferenceContext<'a> {
             Expr::Match { expr, arms } => {
                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 
-                let mut result_ty =
-                    if arms.is_empty() { Ty::Never } else { self.table.new_type_var() };
+                let mut result_ty = if arms.is_empty() {
+                    TyKind::Never.intern(&Interner)
+                } else {
+                    self.table.new_type_var()
+                };
 
                 let matchee_diverges = self.diverges;
                 let mut all_arms_diverge = Diverges::Always;
@@ -317,7 +333,7 @@ impl<'a> InferenceContext<'a> {
                     if let Some(guard_expr) = arm.guard {
                         self.infer_expr(
                             guard_expr,
-                            &Expectation::has_type(Ty::Scalar(Scalar::Bool)),
+                            &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
                         );
                     }
 
@@ -333,9 +349,9 @@ impl<'a> InferenceContext<'a> {
             Expr::Path(p) => {
                 // FIXME this could be more efficient...
                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
-                self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(Ty::Unknown)
+                self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(self.err_ty())
             }
-            Expr::Continue { .. } => Ty::Never,
+            Expr::Continue { .. } => TyKind::Never.intern(&Interner),
             Expr::Break { expr, label } => {
                 let val_ty = if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none())
@@ -347,7 +363,7 @@ impl<'a> InferenceContext<'a> {
                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
                         ctxt.break_ty.clone()
                     } else {
-                        Ty::Unknown
+                        self.err_ty()
                     };
 
                 let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
@@ -360,7 +376,7 @@ impl<'a> InferenceContext<'a> {
                         expr: tgt_expr,
                     });
                 }
-                Ty::Never
+                TyKind::Never.intern(&Interner)
             }
             Expr::Return { expr } => {
                 if let Some(expr) = expr {
@@ -369,14 +385,14 @@ impl<'a> InferenceContext<'a> {
                     let unit = Ty::unit();
                     self.coerce(&unit, &self.return_ty.clone());
                 }
-                Ty::Never
+                TyKind::Never.intern(&Interner)
             }
             Expr::Yield { expr } => {
                 // FIXME: track yield type for coercion
                 if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none());
                 }
-                Ty::Never
+                TyKind::Never.intern(&Interner)
             }
             Expr::RecordLit { path, fields, spread } => {
                 let (ty, def_id) = self.resolve_variant(path.as_ref());
@@ -404,8 +420,9 @@ impl<'a> InferenceContext<'a> {
                     if let Some(field_def) = field_def {
                         self.result.record_field_resolutions.insert(field.expr, field_def);
                     }
-                    let field_ty = field_def
-                        .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
+                    let field_ty = field_def.map_or(self.err_ty(), |it| {
+                        field_types[it.local_id].clone().subst(&substs)
+                    });
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
                 if let Some(expr) = spread {
@@ -424,27 +441,33 @@ impl<'a> InferenceContext<'a> {
                         environment: self.trait_env.clone(),
                     },
                 )
-                .find_map(|derefed_ty| match canonicalized.decanonicalize_ty(derefed_ty.value) {
-                    Ty::Tuple(_, substs) => {
-                        name.as_tuple_index().and_then(|idx| substs.0.get(idx).cloned())
-                    }
-                    Ty::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
-                        self.db.struct_data(s).variant_data.field(name).map(|local_id| {
-                            let field = FieldId { parent: s.into(), local_id };
-                            self.write_field_resolution(tgt_expr, field);
-                            self.db.field_types(s.into())[field.local_id].clone().subst(&parameters)
-                        })
-                    }
-                    Ty::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
-                        self.db.union_data(u).variant_data.field(name).map(|local_id| {
-                            let field = FieldId { parent: u.into(), local_id };
-                            self.write_field_resolution(tgt_expr, field);
-                            self.db.field_types(u.into())[field.local_id].clone().subst(&parameters)
-                        })
+                .find_map(|derefed_ty| {
+                    match canonicalized.decanonicalize_ty(derefed_ty.value).interned(&Interner) {
+                        TyKind::Tuple(_, substs) => {
+                            name.as_tuple_index().and_then(|idx| substs.0.get(idx).cloned())
+                        }
+                        TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
+                            self.db.struct_data(*s).variant_data.field(name).map(|local_id| {
+                                let field = FieldId { parent: (*s).into(), local_id };
+                                self.write_field_resolution(tgt_expr, field);
+                                self.db.field_types((*s).into())[field.local_id]
+                                    .clone()
+                                    .subst(&parameters)
+                            })
+                        }
+                        TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
+                            self.db.union_data(*u).variant_data.field(name).map(|local_id| {
+                                let field = FieldId { parent: (*u).into(), local_id };
+                                self.write_field_resolution(tgt_expr, field);
+                                self.db.field_types((*u).into())[field.local_id]
+                                    .clone()
+                                    .subst(&parameters)
+                            })
+                        }
+                        _ => None,
                     }
-                    _ => None,
                 })
-                .unwrap_or(Ty::Unknown);
+                .unwrap_or(self.err_ty());
                 let ty = self.insert_type_vars(ty);
                 self.normalize_associated_types_in(ty)
             }
@@ -481,9 +504,10 @@ impl<'a> InferenceContext<'a> {
                 };
                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
                 match rawness {
-                    Rawness::RawPtr => Ty::Raw(mutability, Substs::single(inner_ty)),
-                    Rawness::Ref => Ty::Ref(mutability, Substs::single(inner_ty)),
+                    Rawness::RawPtr => TyKind::Raw(mutability, Substs::single(inner_ty)),
+                    Rawness::Ref => TyKind::Ref(mutability, Substs::single(inner_ty)),
                 }
+                .intern(&Interner)
             }
             Expr::Box { expr } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
@@ -499,7 +523,7 @@ impl<'a> InferenceContext<'a> {
                     sb = sb.fill(repeat_with(|| self.table.new_type_var()));
                     Ty::adt_ty(box_, sb.build())
                 } else {
-                    Ty::Unknown
+                    self.err_ty()
                 }
             }
             Expr::UnaryOp { expr, op } => {
@@ -519,31 +543,31 @@ impl<'a> InferenceContext<'a> {
                                 Some(derefed_ty) => {
                                     canonicalized.decanonicalize_ty(derefed_ty.value)
                                 }
-                                None => Ty::Unknown,
+                                None => self.err_ty(),
                             }
                         }
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     UnaryOp::Neg => {
-                        match &inner_ty {
+                        match inner_ty.interned(&Interner) {
                             // Fast path for builtins
-                            Ty::Scalar(Scalar::Int(_))
-                            | Ty::Scalar(Scalar::Uint(_))
-                            | Ty::Scalar(Scalar::Float(_))
-                            | Ty::InferenceVar(_, TyVariableKind::Integer)
-                            | Ty::InferenceVar(_, TyVariableKind::Float) => inner_ty,
+                            TyKind::Scalar(Scalar::Int(_))
+                            | TyKind::Scalar(Scalar::Uint(_))
+                            | TyKind::Scalar(Scalar::Float(_))
+                            | TyKind::InferenceVar(_, TyVariableKind::Integer)
+                            | TyKind::InferenceVar(_, TyVariableKind::Float) => inner_ty,
                             // Otherwise we resolve via the std::ops::Neg trait
                             _ => self
                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
                         }
                     }
                     UnaryOp::Not => {
-                        match &inner_ty {
+                        match inner_ty.interned(&Interner) {
                             // Fast path for builtins
-                            Ty::Scalar(Scalar::Bool)
-                            | Ty::Scalar(Scalar::Int(_))
-                            | Ty::Scalar(Scalar::Uint(_))
-                            | Ty::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
+                            TyKind::Scalar(Scalar::Bool)
+                            | TyKind::Scalar(Scalar::Int(_))
+                            | TyKind::Scalar(Scalar::Uint(_))
+                            | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
                             // Otherwise we resolve via the std::ops::Not trait
                             _ => self
                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
@@ -554,7 +578,9 @@ impl<'a> InferenceContext<'a> {
             Expr::BinaryOp { lhs, rhs, op } => match op {
                 Some(op) => {
                     let lhs_expectation = match op {
-                        BinaryOp::LogicOp(..) => Expectation::has_type(Ty::Scalar(Scalar::Bool)),
+                        BinaryOp::LogicOp(..) => {
+                            Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
+                        }
                         _ => Expectation::none(),
                     };
                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
@@ -563,7 +589,7 @@ impl<'a> InferenceContext<'a> {
 
                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 
-                    if ret == Ty::Unknown {
+                    if ret.is_unknown() {
                         cov_mark::hit!(infer_expr_inner_binary_operator_overload);
 
                         self.resolve_associated_type_with_params(
@@ -575,7 +601,7 @@ impl<'a> InferenceContext<'a> {
                         ret
                     }
                 }
-                _ => Ty::Unknown,
+                _ => self.err_ty(),
             },
             Expr::Range { lhs, rhs, range_type } => {
                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
@@ -586,33 +612,33 @@ impl<'a> InferenceContext<'a> {
                 match (range_type, lhs_ty, rhs_ty) {
                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
                         Some(adt) => Ty::adt_ty(adt, Substs::empty()),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
                         Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     (RangeOp::Inclusive, None, Some(ty)) => {
                         match self.resolve_range_to_inclusive() {
                             Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                            None => Ty::Unknown,
+                            None => self.err_ty(),
                         }
                     }
                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
                         Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
                         match self.resolve_range_inclusive() {
                             Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                            None => Ty::Unknown,
+                            None => self.err_ty(),
                         }
                     }
                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
                         Some(adt) => Ty::adt_ty(adt, Substs::single(ty)),
-                        None => Ty::Unknown,
+                        None => self.err_ty(),
                     },
-                    (RangeOp::Inclusive, _, None) => Ty::Unknown,
+                    (RangeOp::Inclusive, _, None) => self.err_ty(),
                 }
             }
             Expr::Index { base, index } => {
@@ -631,19 +657,19 @@ impl<'a> InferenceContext<'a> {
                         index_trait,
                     );
                     let self_ty =
-                        self_ty.map_or(Ty::Unknown, |t| canonicalized.decanonicalize_ty(t.value));
+                        self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
                     self.resolve_associated_type_with_params(
                         self_ty,
                         self.resolve_ops_index_output(),
                         &[index_ty],
                     )
                 } else {
-                    Ty::Unknown
+                    self.err_ty()
                 }
             }
             Expr::Tuple { exprs } => {
-                let mut tys = match &expected.ty {
-                    Ty::Tuple(_, substs) => substs
+                let mut tys = match expected.ty.interned(&Interner) {
+                    TyKind::Tuple(_, substs) => substs
                         .iter()
                         .cloned()
                         .chain(repeat_with(|| self.table.new_type_var()))
@@ -656,11 +682,11 @@ impl<'a> InferenceContext<'a> {
                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
                 }
 
-                Ty::Tuple(tys.len(), Substs(tys.into()))
+                TyKind::Tuple(tys.len(), Substs(tys.into())).intern(&Interner)
             }
             Expr::Array(array) => {
-                let elem_ty = match &expected.ty {
-                    Ty::Array(st) | Ty::Slice(st) => st.as_single().clone(),
+                let elem_ty = match expected.ty.interned(&Interner) {
+                    TyKind::Array(st) | TyKind::Slice(st) => st.as_single().clone(),
                     _ => self.table.new_type_var(),
                 };
 
@@ -677,43 +703,51 @@ impl<'a> InferenceContext<'a> {
                         );
                         self.infer_expr(
                             *repeat,
-                            &Expectation::has_type(Ty::Scalar(Scalar::Uint(UintTy::Usize))),
+                            &Expectation::has_type(
+                                TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
+                            ),
                         );
                     }
                 }
 
-                Ty::Array(Substs::single(elem_ty))
+                TyKind::Array(Substs::single(elem_ty)).intern(&Interner)
             }
             Expr::Literal(lit) => match lit {
-                Literal::Bool(..) => Ty::Scalar(Scalar::Bool),
-                Literal::String(..) => Ty::Ref(Mutability::Not, Substs::single(Ty::Str)),
+                Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
+                Literal::String(..) => {
+                    TyKind::Ref(Mutability::Not, Substs::single(TyKind::Str.intern(&Interner)))
+                        .intern(&Interner)
+                }
                 Literal::ByteString(..) => {
-                    let byte_type = Ty::Scalar(Scalar::Uint(UintTy::U8));
-                    let array_type = Ty::Array(Substs::single(byte_type));
-                    Ty::Ref(Mutability::Not, Substs::single(array_type))
+                    let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
+                    let array_type = TyKind::Array(Substs::single(byte_type)).intern(&Interner);
+                    TyKind::Ref(Mutability::Not, Substs::single(array_type)).intern(&Interner)
                 }
-                Literal::Char(..) => Ty::Scalar(Scalar::Char),
+                Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
                 Literal::Int(_v, ty) => match ty {
                     Some(int_ty) => {
-                        Ty::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
+                        TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
+                            .intern(&Interner)
                     }
                     None => self.table.new_integer_var(),
                 },
                 Literal::Uint(_v, ty) => match ty {
                     Some(int_ty) => {
-                        Ty::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
+                        TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
+                            .intern(&Interner)
                     }
                     None => self.table.new_integer_var(),
                 },
                 Literal::Float(_v, ty) => match ty {
                     Some(float_ty) => {
-                        Ty::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
+                        TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
+                            .intern(&Interner)
                     }
                     None => self.table.new_float_var(),
                 },
             },
         };
-        // use a new type variable if we got Ty::Unknown here
+        // use a new type variable if we got unknown here
         let ty = self.insert_type_vars_shallow(ty);
         let ty = self.resolve_ty_as_possible(ty);
         self.write_expr_ty(tgt_expr, ty.clone());
@@ -730,7 +764,7 @@ impl<'a> InferenceContext<'a> {
             match stmt {
                 Statement::Let { pat, type_ref, initializer } => {
                     let decl_ty =
-                        type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(Ty::Unknown);
+                        type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(self.err_ty());
 
                     // Always use the declared type when specified
                     let mut ty = decl_ty.clone();
@@ -738,7 +772,7 @@ impl<'a> InferenceContext<'a> {
                     if let Some(expr) = initializer {
                         let actual_ty =
                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
-                        if decl_ty == Ty::Unknown {
+                        if decl_ty.is_unknown() {
                             ty = actual_ty;
                         }
                     }
@@ -802,7 +836,7 @@ impl<'a> InferenceContext<'a> {
                 self.write_method_resolution(tgt_expr, func);
                 (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
             }
-            None => (receiver_ty, Binders::new(0, Ty::Unknown), None),
+            None => (receiver_ty, Binders::new(0, self.err_ty()), None),
         };
         let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
         let method_ty = method_ty.subst(&substs);
@@ -813,15 +847,17 @@ impl<'a> InferenceContext<'a> {
                 if !sig.params().is_empty() {
                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
                 } else {
-                    (Ty::Unknown, Vec::new(), sig.ret().clone())
+                    (self.err_ty(), Vec::new(), sig.ret().clone())
                 }
             }
-            None => (Ty::Unknown, Vec::new(), Ty::Unknown),
+            None => (self.err_ty(), Vec::new(), self.err_ty()),
         };
         // Apply autoref so the below unification works correctly
         // FIXME: return correct autorefs from lookup_method
         let actual_receiver_ty = match expected_receiver_ty.as_reference() {
-            Some((_, mutability)) => Ty::Ref(mutability, Substs::single(derefed_receiver_ty)),
+            Some((_, mutability)) => {
+                TyKind::Ref(mutability, Substs::single(derefed_receiver_ty)).intern(&Interner)
+            }
             _ => derefed_receiver_ty,
         };
         self.unify(&expected_receiver_ty, &actual_receiver_ty);
@@ -837,7 +873,7 @@ impl<'a> InferenceContext<'a> {
         // that we have more information about the types of arguments when we
         // type-check the functions. This isn't really the right way to do this.
         for &check_closures in &[false, true] {
-            let param_iter = param_tys.iter().cloned().chain(repeat(Ty::Unknown));
+            let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
             for (&arg, param_ty) in args.iter().zip(param_iter) {
                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
                 if is_closure != check_closures {
@@ -867,7 +903,7 @@ impl<'a> InferenceContext<'a> {
                 if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
                     substs.push(receiver_ty.clone());
                 } else {
-                    substs.push(Ty::Unknown);
+                    substs.push(self.err_ty());
                 }
             }
         }
@@ -891,14 +927,15 @@ impl<'a> InferenceContext<'a> {
         };
         let supplied_params = substs.len();
         for _ in supplied_params..total_len {
-            substs.push(Ty::Unknown);
+            substs.push(self.err_ty());
         }
         assert_eq!(substs.len(), total_len);
         Substs(substs.into())
     }
 
     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
-        if let &Ty::FnDef(def, ref parameters) = callable_ty {
+        if let TyKind::FnDef(fn_def, parameters) = callable_ty.interned(&Interner) {
+            let def: CallableDefId = from_chalk(self.db, *fn_def);
             let generic_predicates = self.db.generic_predicates(def.into());
             for predicate in generic_predicates.iter() {
                 let predicate = predicate.clone().subst(parameters);