11 files changed, 155 insertions, 142 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index caa760d21..25e5bfb01 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -1597,7 +1597,7 @@ impl Type {
 
     pub fn remove_ref(&self) -> Option<Type> {
         match &self.ty.value.interned(&Interner) {
-            TyKind::Ref(.., substs) => Some(self.derived(substs[0].clone())),
+            TyKind::Ref(.., ty) => Some(self.derived(ty.clone())),
             _ => None,
         }
     }
@@ -1751,10 +1751,30 @@ impl Type {
         return go(&self.ty.value);
 
         fn go(ty: &Ty) -> bool {
-            if ty.is_unknown() {
-                true
-            } else {
-                ty.substs().map_or(false, |substs| substs.iter().any(go))
+            match ty.interned(&Interner) {
+                TyKind::Unknown => true,
+
+                TyKind::Adt(_, substs)
+                | TyKind::AssociatedType(_, substs)
+                | TyKind::Tuple(_, substs)
+                | TyKind::OpaqueType(_, substs)
+                | TyKind::FnDef(_, substs)
+                | TyKind::Closure(_, substs) => substs.iter().any(go),
+
+                TyKind::Array(ty) | TyKind::Slice(ty) | TyKind::Raw(_, ty) | TyKind::Ref(_, ty) => {
+                    go(ty)
+                }
+
+                TyKind::Scalar(_)
+                | TyKind::Str
+                | TyKind::Never
+                | TyKind::Placeholder(_)
+                | TyKind::BoundVar(_)
+                | TyKind::InferenceVar(_, _)
+                | TyKind::Dyn(_)
+                | TyKind::Function(_)
+                | TyKind::Alias(_)
+                | TyKind::ForeignType(_) => false,
             }
         }
     }
@@ -1989,6 +2009,10 @@ impl Type {
                     walk_bounds(db, &type_.derived(ty.clone()), bounds.as_ref(), cb);
                 }
 
+                TyKind::Ref(_, ty) | TyKind::Raw(_, ty) | TyKind::Array(ty) | TyKind::Slice(ty) => {
+                    walk_type(db, &type_.derived(ty.clone()), cb);
+                }
+
                 _ => {}
             }
             if let Some(substs) = ty.substs() {
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index 378c951c5..c1062387e 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -276,20 +276,17 @@ impl HirDisplay for Ty {
             &TyKind::Scalar(Scalar::Float(t)) => write!(f, "{}", primitive::float_ty_to_string(t))?,
             &TyKind::Scalar(Scalar::Int(t)) => write!(f, "{}", primitive::int_ty_to_string(t))?,
             &TyKind::Scalar(Scalar::Uint(t)) => write!(f, "{}", primitive::uint_ty_to_string(t))?,
-            TyKind::Slice(parameters) => {
-                let t = parameters.as_single();
+            TyKind::Slice(t) => {
                 write!(f, "[")?;
                 t.hir_fmt(f)?;
                 write!(f, "]")?;
             }
-            TyKind::Array(parameters) => {
-                let t = parameters.as_single();
+            TyKind::Array(t) => {
                 write!(f, "[")?;
                 t.hir_fmt(f)?;
                 write!(f, "; _]")?;
             }
-            TyKind::Raw(m, parameters) | TyKind::Ref(m, parameters) => {
-                let t = parameters.as_single();
+            TyKind::Raw(m, t) | TyKind::Ref(m, t) => {
                 let ty_display =
                     t.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
 
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 9f29098ee..9c385b845 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -108,6 +108,17 @@ pub struct TypeMismatch {
     pub actual: Ty,
 }
 
+#[derive(Clone, PartialEq, Eq, Debug)]
+struct InternedStandardTypes {
+    unknown: Ty,
+}
+
+impl Default for InternedStandardTypes {
+    fn default() -> Self {
+        InternedStandardTypes { unknown: TyKind::Unknown.intern(&Interner) }
+    }
+}
+
 /// The result of type inference: A mapping from expressions and patterns to types.
 #[derive(Clone, PartialEq, Eq, Debug, Default)]
 pub struct InferenceResult {
@@ -126,6 +137,8 @@ pub struct InferenceResult {
     pub type_of_expr: ArenaMap<ExprId, Ty>,
     pub type_of_pat: ArenaMap<PatId, Ty>,
     pub(super) type_mismatches: ArenaMap<ExprId, TypeMismatch>,
+    /// Interned Unknown to return references to.
+    standard_types: InternedStandardTypes,
 }
 
 impl InferenceResult {
@@ -170,7 +183,7 @@ impl Index<ExprId> for InferenceResult {
     type Output = Ty;
 
     fn index(&self, expr: ExprId) -> &Ty {
-        self.type_of_expr.get(expr).unwrap_or(&Ty(TyKind::Unknown))
+        self.type_of_expr.get(expr).unwrap_or(&self.standard_types.unknown)
     }
 }
 
@@ -178,7 +191,7 @@ impl Index<PatId> for InferenceResult {
     type Output = Ty;
 
     fn index(&self, pat: PatId) -> &Ty {
-        self.type_of_pat.get(pat).unwrap_or(&Ty(TyKind::Unknown))
+        self.type_of_pat.get(pat).unwrap_or(&self.standard_types.unknown)
     }
 }
 
@@ -723,14 +736,19 @@ impl Expectation {
 
     /// This expresses no expectation on the type.
     fn none() -> Self {
-        Expectation { ty: TyKind::Unknown.intern(&Interner), rvalue_hint: false }
+        Expectation {
+            // FIXME
+            ty: TyKind::Unknown.intern(&Interner),
+            rvalue_hint: false,
+        }
     }
 
-    fn coercion_target(&self) -> &Ty {
+    fn coercion_target(&self) -> Ty {
         if self.rvalue_hint {
-            &Ty(TyKind::Unknown)
+            // FIXME
+            TyKind::Unknown.intern(&Interner)
         } else {
-            &self.ty
+            self.ty.clone()
         }
     }
 }
diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs
index 36670043a..137419264 100644
--- a/crates/hir_ty/src/infer/coerce.rs
+++ b/crates/hir_ty/src/infer/coerce.rs
@@ -71,7 +71,7 @@ impl<'a> InferenceContext<'a> {
         }
 
         // Pointer weakening and function to pointer
-        match (&mut from_ty.0, to_ty.interned(&Interner)) {
+        match (from_ty.interned_mut(), to_ty.interned(&Interner)) {
             // `*mut T` -> `*const T`
             // `&mut T` -> `&T`
             (TyKind::Raw(m1, ..), TyKind::Raw(m2 @ Mutability::Not, ..))
@@ -111,9 +111,7 @@ impl<'a> InferenceContext<'a> {
         // Auto Deref if cannot coerce
         match (from_ty.interned(&Interner), to_ty.interned(&Interner)) {
             // FIXME: DerefMut
-            (TyKind::Ref(_, st1), TyKind::Ref(_, st2)) => {
-                self.unify_autoderef_behind_ref(&st1[0], &st2[0])
-            }
+            (TyKind::Ref(_, st1), TyKind::Ref(_, st2)) => self.unify_autoderef_behind_ref(st1, st2),
 
             // Otherwise, normal unify
             _ => self.unify(&from_ty, to_ty),
@@ -178,11 +176,7 @@ impl<'a> InferenceContext<'a> {
             // Stop when constructor matches.
             if from_ty.equals_ctor(&to_ty) {
                 // It will not recurse to `coerce`.
-                return match (from_ty.substs(), to_ty.substs()) {
-                    (Some(st1), Some(st2)) => self.table.unify_substs(st1, st2, 0),
-                    (None, None) => true,
-                    _ => false,
-                };
+                return self.table.unify(&from_ty, &to_ty);
             } else if self.table.unify_inner_trivial(&derefed_ty, &to_ty, 0) {
                 return true;
             }
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 1a11b146a..f40dec17f 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -503,8 +503,8 @@ impl<'a> InferenceContext<'a> {
                 };
                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
                 match rawness {
-                    Rawness::RawPtr => TyKind::Raw(mutability, Substs::single(inner_ty)),
-                    Rawness::Ref => TyKind::Ref(mutability, Substs::single(inner_ty)),
+                    Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
+                    Rawness::Ref => TyKind::Ref(mutability, inner_ty),
                 }
                 .intern(&Interner)
             }
@@ -685,7 +685,7 @@ impl<'a> InferenceContext<'a> {
             }
             Expr::Array(array) => {
                 let elem_ty = match expected.ty.interned(&Interner) {
-                    TyKind::Array(st) | TyKind::Slice(st) => st.as_single().clone(),
+                    TyKind::Array(st) | TyKind::Slice(st) => st.clone(),
                     _ => self.table.new_type_var(),
                 };
 
@@ -709,18 +709,17 @@ impl<'a> InferenceContext<'a> {
                     }
                 }
 
-                TyKind::Array(Substs::single(elem_ty)).intern(&Interner)
+                TyKind::Array(elem_ty).intern(&Interner)
             }
             Expr::Literal(lit) => match lit {
                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
                 Literal::String(..) => {
-                    TyKind::Ref(Mutability::Not, Substs::single(TyKind::Str.intern(&Interner)))
-                        .intern(&Interner)
+                    TyKind::Ref(Mutability::Not, TyKind::Str.intern(&Interner)).intern(&Interner)
                 }
                 Literal::ByteString(..) => {
                     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)
+                    let array_type = TyKind::Array(byte_type).intern(&Interner);
+                    TyKind::Ref(Mutability::Not, array_type).intern(&Interner)
                 }
                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
                 Literal::Int(_v, ty) => match ty {
@@ -799,7 +798,7 @@ impl<'a> InferenceContext<'a> {
                 // we don't even make an attempt at coercion
                 self.table.new_maybe_never_var()
             } else {
-                self.coerce(&Ty::unit(), expected.coercion_target());
+                self.coerce(&Ty::unit(), &expected.coercion_target());
                 Ty::unit()
             }
         };
@@ -854,9 +853,7 @@ 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, Substs::single(derefed_receiver_ty)).intern(&Interner)
-            }
+            Some((_, mutability)) => TyKind::Ref(mutability, derefed_receiver_ty).intern(&Interner),
             _ => derefed_receiver_ty,
         };
         self.unify(&expected_receiver_ty, &actual_receiver_ty);
diff --git a/crates/hir_ty/src/infer/pat.rs b/crates/hir_ty/src/infer/pat.rs
index a16755cda..9e8ca18ef 100644
--- a/crates/hir_ty/src/infer/pat.rs
+++ b/crates/hir_ty/src/infer/pat.rs
@@ -158,12 +158,12 @@ impl<'a> InferenceContext<'a> {
                         if mutability != exp_mut {
                             // FIXME: emit type error?
                         }
-                        inner_ty
+                        inner_ty.clone()
                     }
-                    _ => &Ty(TyKind::Unknown),
+                    _ => self.result.standard_types.unknown.clone(),
                 };
-                let subty = self.infer_pat(*pat, expectation, default_bm);
-                TyKind::Ref(mutability, Substs::single(subty)).intern(&Interner)
+                let subty = self.infer_pat(*pat, &expectation, default_bm);
+                TyKind::Ref(mutability, subty).intern(&Interner)
             }
             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
                 p.as_ref(),
@@ -196,7 +196,7 @@ impl<'a> InferenceContext<'a> {
 
                 let bound_ty = match mode {
                     BindingMode::Ref(mutability) => {
-                        TyKind::Ref(mutability, Substs::single(inner_ty.clone())).intern(&Interner)
+                        TyKind::Ref(mutability, inner_ty.clone()).intern(&Interner)
                     }
                     BindingMode::Move => inner_ty.clone(),
                 };
@@ -206,8 +206,8 @@ impl<'a> InferenceContext<'a> {
             }
             Pat::Slice { prefix, slice, suffix } => {
                 let (container_ty, elem_ty): (fn(_) -> _, _) = match expected.interned(&Interner) {
-                    TyKind::Array(st) => (TyKind::Array, st.as_single().clone()),
-                    TyKind::Slice(st) => (TyKind::Slice, st.as_single().clone()),
+                    TyKind::Array(st) => (TyKind::Array, st.clone()),
+                    TyKind::Slice(st) => (TyKind::Slice, st.clone()),
                     _ => (TyKind::Slice, self.err_ty()),
                 };
 
@@ -215,7 +215,7 @@ impl<'a> InferenceContext<'a> {
                     self.infer_pat(*pat_id, &elem_ty, default_bm);
                 }
 
-                let pat_ty = container_ty(Substs::single(elem_ty)).intern(&Interner);
+                let pat_ty = container_ty(elem_ty).intern(&Interner);
                 if let Some(slice_pat_id) = slice {
                     self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
                 }
@@ -232,11 +232,11 @@ impl<'a> InferenceContext<'a> {
             Pat::Box { inner } => match self.resolve_boxed_box() {
                 Some(box_adt) => {
                     let inner_expected = match expected.as_adt() {
-                        Some((adt, substs)) if adt == box_adt => substs.as_single(),
-                        _ => &Ty(TyKind::Unknown),
+                        Some((adt, substs)) if adt == box_adt => substs.as_single().clone(),
+                        _ => self.result.standard_types.unknown.clone(),
                     };
 
-                    let inner_ty = self.infer_pat(*inner, inner_expected, default_bm);
+                    let inner_ty = self.infer_pat(*inner, &inner_expected, default_bm);
                     Ty::adt_ty(box_adt, Substs::single(inner_ty))
                 }
                 None => self.err_ty(),
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index ebc612ca9..66f8fe8a3 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -7,8 +7,8 @@ use ena::unify::{InPlaceUnificationTable, NoError, UnifyKey, UnifyValue};
 
 use super::{InferenceContext, Obligation};
 use crate::{
-    BoundVar, Canonical, DebruijnIndex, GenericPredicate, InEnvironment, InferenceVar, Interner,
-    Scalar, Substs, Ty, TyKind, TypeWalk,
+    BoundVar, Canonical, DebruijnIndex, FnPointer, GenericPredicate, InEnvironment, InferenceVar,
+    Interner, Scalar, Substs, Ty, TyKind, TypeWalk,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -108,7 +108,7 @@ 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) = &mut ty.0 {
+                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);
@@ -283,9 +283,23 @@ impl InferenceTable {
         let ty1 = self.resolve_ty_shallow(ty1);
         let ty2 = self.resolve_ty_shallow(ty2);
         if ty1.equals_ctor(&ty2) {
-            match (ty1.substs(), ty2.substs()) {
-                (Some(st1), Some(st2)) => self.unify_substs(st1, st2, depth + 1),
-                (None, None) => true,
+            match (ty1.interned(&Interner), ty2.interned(&Interner)) {
+                (TyKind::Adt(_, substs1), TyKind::Adt(_, substs2))
+                | (TyKind::FnDef(_, substs1), TyKind::FnDef(_, substs2))
+                | (
+                    TyKind::Function(FnPointer { substs: substs1, .. }),
+                    TyKind::Function(FnPointer { substs: substs2, .. }),
+                )
+                | (TyKind::Tuple(_, substs1), TyKind::Tuple(_, substs2))
+                | (TyKind::OpaqueType(_, substs1), TyKind::OpaqueType(_, substs2))
+                | (TyKind::AssociatedType(_, substs1), TyKind::AssociatedType(_, substs2))
+                | (TyKind::Closure(.., substs1), TyKind::Closure(.., substs2)) => {
+                    self.unify_substs(substs1, substs2, depth + 1)
+                }
+                (TyKind::Ref(_, ty1), TyKind::Ref(_, ty2))
+                | (TyKind::Raw(_, ty1), TyKind::Raw(_, ty2))
+                | (TyKind::Array(ty1), TyKind::Array(ty2))
+                | (TyKind::Slice(ty1), TyKind::Slice(ty2)) => self.unify_inner(ty1, ty2, depth + 1),
                 _ => false,
             }
         } else {
@@ -404,7 +418,7 @@ impl InferenceTable {
             if i > 0 {
                 cov_mark::hit!(type_var_resolves_to_int_var);
             }
-            match &ty.0 {
+            match ty.interned(&Interner) {
                 TyKind::InferenceVar(tv, _) => {
                     let inner = tv.to_inner();
                     match self.var_unification_table.inlined_probe_value(inner).known() {
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 484652073..503910dde 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -151,17 +151,17 @@ pub enum TyKind {
     Tuple(usize, Substs),
 
     /// An array with the given length. Written as `[T; n]`.
-    Array(Substs),
+    Array(Ty),
 
     /// The pointee of an array slice.  Written as `[T]`.
-    Slice(Substs),
+    Slice(Ty),
 
     /// A raw pointer. Written as `*mut T` or `*const T`
-    Raw(Mutability, Substs),
+    Raw(Mutability, Ty),
 
     /// A reference; a pointer with an associated lifetime. Written as
     /// `&'a mut T` or `&'a T`.
-    Ref(Mutability, Substs),
+    Ref(Mutability, Ty),
 
     /// This represents a placeholder for an opaque type in situations where we
     /// don't know the hidden type (i.e. currently almost always). This is
@@ -248,11 +248,11 @@ pub enum TyKind {
 }
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
-pub struct Ty(TyKind);
+pub struct Ty(Arc<TyKind>);
 
 impl TyKind {
     pub fn intern(self, _interner: &Interner) -> Ty {
-        Ty(self)
+        Ty(Arc::new(self))
     }
 }
 
@@ -260,6 +260,14 @@ impl Ty {
     pub fn interned(&self, _interner: &Interner) -> &TyKind {
         &self.0
     }
+
+    pub fn interned_mut(&mut self) -> &mut TyKind {
+        Arc::make_mut(&mut self.0)
+    }
+
+    pub fn into_inner(self) -> TyKind {
+        Arc::try_unwrap(self.0).unwrap_or_else(|a| (*a).clone())
+    }
 }
 
 /// A list of substitutions for generic parameters.
@@ -665,19 +673,15 @@ impl Ty {
 
     pub fn as_reference(&self) -> Option<(&Ty, Mutability)> {
         match self.interned(&Interner) {
-            TyKind::Ref(mutability, parameters) => Some((parameters.as_single(), *mutability)),
+            TyKind::Ref(mutability, ty) => Some((ty, *mutability)),
             _ => None,
         }
     }
 
     pub fn as_reference_or_ptr(&self) -> Option<(&Ty, Rawness, Mutability)> {
         match self.interned(&Interner) {
-            TyKind::Ref(mutability, parameters) => {
-                Some((parameters.as_single(), Rawness::Ref, *mutability))
-            }
-            TyKind::Raw(mutability, parameters) => {
-                Some((parameters.as_single(), Rawness::RawPtr, *mutability))
-            }
+            TyKind::Ref(mutability, ty) => Some((ty, Rawness::Ref, *mutability)),
+            TyKind::Raw(mutability, ty) => Some((ty, Rawness::RawPtr, *mutability)),
             _ => None,
         }
     }
@@ -685,8 +689,8 @@ impl Ty {
     pub fn strip_references(&self) -> &Ty {
         let mut t: &Ty = self;
 
-        while let TyKind::Ref(_mutability, parameters) = t.interned(&Interner) {
-            t = parameters.as_single();
+        while let TyKind::Ref(_mutability, ty) = t.interned(&Interner) {
+            t = ty;
         }
 
         t
@@ -772,8 +776,8 @@ impl Ty {
 
     fn builtin_deref(&self) -> Option<Ty> {
         match self.interned(&Interner) {
-            TyKind::Ref(.., parameters) => Some(Ty::clone(parameters.as_single())),
-            TyKind::Raw(.., parameters) => Some(Ty::clone(parameters.as_single())),
+            TyKind::Ref(.., ty) => Some(ty.clone()),
+            TyKind::Raw(.., ty) => Some(ty.clone()),
             _ => None,
         }
     }
@@ -809,40 +813,11 @@ impl Ty {
         }
     }
 
-    /// If this is a type with type parameters (an ADT or function), replaces
-    /// the `Substs` for these type parameters with the given ones. (So e.g. if
-    /// `self` is `Option<_>` and the substs contain `u32`, we'll have
-    /// `Option<u32>` afterwards.)
-    pub fn apply_substs(mut self, new_substs: Substs) -> Ty {
-        match &mut self.0 {
-            TyKind::Adt(_, substs)
-            | TyKind::Slice(substs)
-            | TyKind::Array(substs)
-            | TyKind::Raw(_, substs)
-            | TyKind::Ref(_, substs)
-            | TyKind::FnDef(_, substs)
-            | TyKind::Function(FnPointer { substs, .. })
-            | TyKind::Tuple(_, substs)
-            | TyKind::OpaqueType(_, substs)
-            | TyKind::AssociatedType(_, substs)
-            | TyKind::Closure(.., substs) => {
-                assert_eq!(substs.len(), new_substs.len());
-                *substs = new_substs;
-            }
-            _ => (),
-        }
-        self
-    }
-
     /// Returns the type parameters of this type if it has some (i.e. is an ADT
     /// or function); so if `self` is `Option<u32>`, this returns the `u32`.
     pub fn substs(&self) -> Option<&Substs> {
         match self.interned(&Interner) {
             TyKind::Adt(_, substs)
-            | TyKind::Slice(substs)
-            | TyKind::Array(substs)
-            | TyKind::Raw(_, substs)
-            | TyKind::Ref(_, substs)
             | TyKind::FnDef(_, substs)
             | TyKind::Function(FnPointer { substs, .. })
             | TyKind::Tuple(_, substs)
@@ -853,13 +828,9 @@ impl Ty {
         }
     }
 
-    pub fn substs_mut(&mut self) -> Option<&mut Substs> {
-        match &mut self.0 {
+    fn substs_mut(&mut self) -> Option<&mut Substs> {
+        match self.interned_mut() {
             TyKind::Adt(_, substs)
-            | TyKind::Slice(substs)
-            | TyKind::Array(substs)
-            | TyKind::Raw(_, substs)
-            | TyKind::Ref(_, substs)
             | TyKind::FnDef(_, substs)
             | TyKind::Function(FnPointer { substs, .. })
             | TyKind::Tuple(_, substs)
@@ -988,7 +959,7 @@ pub trait TypeWalk {
     {
         self.walk_mut_binders(
             &mut |ty_mut, binders| {
-                let ty = mem::replace(ty_mut, Ty(TyKind::Unknown));
+                let ty = mem::replace(ty_mut, TyKind::Unknown.intern(&Interner));
                 *ty_mut = f(ty, binders);
             },
             binders,
@@ -1001,7 +972,7 @@ pub trait TypeWalk {
         Self: Sized,
     {
         self.walk_mut(&mut |ty_mut| {
-            let ty = mem::replace(ty_mut, Ty(TyKind::Unknown));
+            let ty = mem::replace(ty_mut, TyKind::Unknown.intern(&Interner));
             *ty_mut = f(ty);
         });
         self
@@ -1022,7 +993,7 @@ pub trait TypeWalk {
     {
         self.walk_mut_binders(
             &mut |ty, binders| {
-                if let &mut TyKind::BoundVar(bound) = &mut ty.0 {
+                if let &mut TyKind::BoundVar(bound) = ty.interned_mut() {
                     if bound.debruijn >= binders {
                         *ty = substs.0[bound.index].clone().shift_bound_vars(binders);
                     }
@@ -1039,7 +1010,7 @@ pub trait TypeWalk {
         Self: Sized,
     {
         self.fold_binders(
-            &mut |ty, binders| match &ty.0 {
+            &mut |ty, binders| match ty.interned(&Interner) {
                 TyKind::BoundVar(bound) if bound.debruijn >= binders => {
                     TyKind::BoundVar(bound.shifted_in_from(n)).intern(&Interner)
                 }
@@ -1068,6 +1039,9 @@ impl TypeWalk for Ty {
                     p.walk(f);
                 }
             }
+            TyKind::Slice(ty) | TyKind::Array(ty) | TyKind::Ref(_, ty) | TyKind::Raw(_, ty) => {
+                ty.walk(f);
+            }
             _ => {
                 if let Some(substs) = self.substs() {
                     for t in substs.iter() {
@@ -1084,7 +1058,7 @@ impl TypeWalk for Ty {
         f: &mut impl FnMut(&mut Ty, DebruijnIndex),
         binders: DebruijnIndex,
     ) {
-        match &mut self.0 {
+        match self.interned_mut() {
             TyKind::Alias(AliasTy::Projection(p_ty)) => {
                 p_ty.substitution.walk_mut_binders(f, binders);
             }
@@ -1096,6 +1070,9 @@ impl TypeWalk for Ty {
             TyKind::Alias(AliasTy::Opaque(o_ty)) => {
                 o_ty.substitution.walk_mut_binders(f, binders);
             }
+            TyKind::Slice(ty) | TyKind::Array(ty) | TyKind::Ref(_, ty) | TyKind::Raw(_, ty) => {
+                ty.walk_mut_binders(f, binders);
+            }
             _ => {
                 if let Some(substs) = self.substs_mut() {
                     substs.walk_mut_binders(f, binders);
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index d026310f4..b4c650fa1 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -160,21 +160,19 @@ impl<'a> TyLoweringContext<'a> {
             }
             TypeRef::RawPtr(inner, mutability) => {
                 let inner_ty = self.lower_ty(inner);
-                TyKind::Raw(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
-                    .intern(&Interner)
+                TyKind::Raw(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
             }
             TypeRef::Array(inner) => {
                 let inner_ty = self.lower_ty(inner);
-                TyKind::Array(Substs::single(inner_ty)).intern(&Interner)
+                TyKind::Array(inner_ty).intern(&Interner)
             }
             TypeRef::Slice(inner) => {
                 let inner_ty = self.lower_ty(inner);
-                TyKind::Slice(Substs::single(inner_ty)).intern(&Interner)
+                TyKind::Slice(inner_ty).intern(&Interner)
             }
             TypeRef::Reference(inner, _, mutability) => {
                 let inner_ty = self.lower_ty(inner);
-                TyKind::Ref(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
-                    .intern(&Interner)
+                TyKind::Ref(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
             }
             TypeRef::Placeholder => TyKind::Unknown.intern(&Interner),
             TypeRef::Fn(params, is_varargs) => {
@@ -993,7 +991,7 @@ pub(crate) fn generic_defaults_query(
 
             // Each default can only refer to previous parameters.
             ty.walk_mut_binders(
-                &mut |ty, binders| match &mut ty.0 {
+                &mut |ty, binders| match ty.interned_mut() {
                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
                         if *index >= idx {
                             // type variable default referring to parameter coming
diff --git a/crates/hir_ty/src/method_resolution.rs b/crates/hir_ty/src/method_resolution.rs
index c7055bee5..741440006 100644
--- a/crates/hir_ty/src/method_resolution.rs
+++ b/crates/hir_ty/src/method_resolution.rs
@@ -435,8 +435,7 @@ fn iterate_method_candidates_with_autoref(
     }
     let refed = Canonical {
         kinds: deref_chain[0].kinds.clone(),
-        value: TyKind::Ref(Mutability::Not, Substs::single(deref_chain[0].value.clone()))
-            .intern(&Interner),
+        value: TyKind::Ref(Mutability::Not, deref_chain[0].value.clone()).intern(&Interner),
     };
     if iterate_method_candidates_by_receiver(
         &refed,
@@ -452,8 +451,7 @@ fn iterate_method_candidates_with_autoref(
     }
     let ref_muted = Canonical {
         kinds: deref_chain[0].kinds.clone(),
-        value: TyKind::Ref(Mutability::Mut, Substs::single(deref_chain[0].value.clone()))
-            .intern(&Interner),
+        value: TyKind::Ref(Mutability::Mut, deref_chain[0].value.clone()).intern(&Interner),
     };
     if iterate_method_candidates_by_receiver(
         &ref_muted,
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index 05a4bf0df..6a8b6752e 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -24,9 +24,9 @@ use super::*;
 impl ToChalk for Ty {
     type Chalk = chalk_ir::Ty<Interner>;
     fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Ty<Interner> {
-        match self.0 {
-            TyKind::Ref(m, parameters) => ref_to_chalk(db, m, parameters),
-            TyKind::Array(parameters) => array_to_chalk(db, parameters),
+        match self.into_inner() {
+            TyKind::Ref(m, ty) => ref_to_chalk(db, m, ty),
+            TyKind::Array(ty) => array_to_chalk(db, ty),
             TyKind::Function(FnPointer { sig, substs, .. }) => {
                 let substitution = chalk_ir::FnSubst(substs.to_chalk(db).shifted_in(&Interner));
                 chalk_ir::TyKind::Function(chalk_ir::FnPointer {
@@ -54,13 +54,11 @@ impl ToChalk for Ty {
                 let substitution = substs.to_chalk(db);
                 chalk_ir::TyKind::Tuple(cardinality.into(), substitution).intern(&Interner)
             }
-            TyKind::Raw(mutability, substs) => {
-                let ty = substs[0].clone().to_chalk(db);
+            TyKind::Raw(mutability, ty) => {
+                let ty = ty.to_chalk(db);
                 chalk_ir::TyKind::Raw(mutability, ty).intern(&Interner)
             }
-            TyKind::Slice(substs) => {
-                chalk_ir::TyKind::Slice(substs[0].clone().to_chalk(db)).intern(&Interner)
-            }
+            TyKind::Slice(ty) => chalk_ir::TyKind::Slice(ty.to_chalk(db)).intern(&Interner),
             TyKind::Str => chalk_ir::TyKind::Str.intern(&Interner),
             TyKind::FnDef(id, substs) => {
                 let substitution = substs.to_chalk(db);
@@ -114,7 +112,7 @@ impl ToChalk for Ty {
     fn from_chalk(db: &dyn HirDatabase, chalk: chalk_ir::Ty<Interner>) -> Self {
         match chalk.data(&Interner).kind.clone() {
             chalk_ir::TyKind::Error => TyKind::Unknown,
-            chalk_ir::TyKind::Array(ty, _size) => TyKind::Array(Substs::single(from_chalk(db, ty))),
+            chalk_ir::TyKind::Array(ty, _size) => TyKind::Array(from_chalk(db, ty)),
             chalk_ir::TyKind::Placeholder(idx) => TyKind::Placeholder(idx),
             chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Projection(proj)) => {
                 let associated_ty = proj.associated_ty_id;
@@ -168,12 +166,10 @@ impl ToChalk for Ty {
             chalk_ir::TyKind::Tuple(cardinality, subst) => {
                 TyKind::Tuple(cardinality, from_chalk(db, subst))
             }
-            chalk_ir::TyKind::Raw(mutability, ty) => {
-                TyKind::Raw(mutability, Substs::single(from_chalk(db, ty)))
-            }
-            chalk_ir::TyKind::Slice(ty) => TyKind::Slice(Substs::single(from_chalk(db, ty))),
+            chalk_ir::TyKind::Raw(mutability, ty) => TyKind::Raw(mutability, from_chalk(db, ty)),
+            chalk_ir::TyKind::Slice(ty) => TyKind::Slice(from_chalk(db, ty)),
             chalk_ir::TyKind::Ref(mutability, _lifetime, ty) => {
-                TyKind::Ref(mutability, Substs::single(from_chalk(db, ty)))
+                TyKind::Ref(mutability, from_chalk(db, ty))
             }
             chalk_ir::TyKind::Str => TyKind::Str,
             chalk_ir::TyKind::Never => TyKind::Never,
@@ -197,17 +193,17 @@ impl ToChalk for Ty {
 fn ref_to_chalk(
     db: &dyn HirDatabase,
     mutability: chalk_ir::Mutability,
-    subst: Substs,
+    ty: Ty,
 ) -> chalk_ir::Ty<Interner> {
-    let arg = subst[0].clone().to_chalk(db);
+    let arg = ty.to_chalk(db);
     let lifetime = LifetimeData::Static.intern(&Interner);
     chalk_ir::TyKind::Ref(mutability, lifetime, arg).intern(&Interner)
 }
 
 /// We currently don't model constants, but Chalk does. So, we have to insert a
 /// fake constant here, because Chalks built-in logic may expect it to be there.
-fn array_to_chalk(db: &dyn HirDatabase, subst: Substs) -> chalk_ir::Ty<Interner> {
-    let arg = subst[0].clone().to_chalk(db);
+fn array_to_chalk(db: &dyn HirDatabase, ty: Ty) -> chalk_ir::Ty<Interner> {
+    let arg = ty.to_chalk(db);
     let usize_ty = chalk_ir::TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner);
     let const_ = chalk_ir::ConstData {
         ty: usize_ty,