Make resolve_ty_shallow return Ty

crates/hir_ty/src/infer.rs

@@ -13,8 +13,6 @@
 //! to certain types. To record this, we use the union-find implementation from
 //! the `ena` crate, which is extracted from rustc.
 
-use std::borrow::Cow;
-
 use std::ops::Index;
 use std::sync::Arc;
 
@@ -384,7 +382,7 @@ impl<'a> InferenceContext<'a> {
         self.table.resolve_ty_as_possible(ty)
     }
 
-    fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
+    fn resolve_ty_shallow(&mut self, ty: &Ty) -> Ty {
         self.table.resolve_ty_shallow(ty)
     }
 

crates/hir_ty/src/infer/coerce.rs

@@ -23,7 +23,7 @@ impl<'a> InferenceContext<'a> {
         if to_ty.is_unknown() {
             return true;
         }
-        let from_ty = self.resolve_ty_shallow(from_ty).into_owned();
+        let from_ty = self.resolve_ty_shallow(from_ty);
         let to_ty = self.resolve_ty_shallow(to_ty);
         match self.coerce_inner(from_ty, &to_ty) {
             Ok(_result) => {
@@ -46,9 +46,7 @@ impl<'a> InferenceContext<'a> {
     ///    least upper bound.
     pub(super) fn coerce_merge_branch(&mut self, ty1: &Ty, ty2: &Ty) -> Ty {
         let ty1 = self.resolve_ty_shallow(ty1);
-        let ty1 = ty1.as_ref();
         let ty2 = self.resolve_ty_shallow(ty2);
-        let ty2 = ty2.as_ref();
         // Special case: two function types. Try to coerce both to
         // pointers to have a chance at getting a match. See
         // https://github.com/rust-lang/rust/blob/7b805396bf46dce972692a6846ce2ad8481c5f85/src/librustc_typeck/check/coercion.rs#L877-L916
@@ -80,9 +78,9 @@ impl<'a> InferenceContext<'a> {
         // type is a type variable and the new one is `!`, trying it the other
         // way around first would mean we make the type variable `!`, instead of
         // just marking it as possibly diverging.
-        if self.coerce(ty2, ty1) {
+        if self.coerce(&ty2, &ty1) {
             ty1.clone()
-        } else if self.coerce(ty1, ty2) {
+        } else if self.coerce(&ty1, &ty2) {
             ty2.clone()
         } else {
             // TODO record a type mismatch

crates/hir_ty/src/infer/unify.rs

@@ -1,6 +1,6 @@
 //! Unification and canonicalization logic.
 
-use std::{borrow::Cow, fmt, mem, sync::Arc};
+use std::{fmt, mem, sync::Arc};
 
 use chalk_ir::{
     cast::Cast, fold::Fold, interner::HasInterner, zip::Zip, FloatTy, IntTy, TyVariableKind,
@@ -340,11 +340,8 @@ impl<'a> InferenceTable<'a> {
 
     /// If `ty` is a type variable with known type, returns that type;
     /// otherwise, return ty.
-    // FIXME this could probably just return Ty
-    pub(crate) fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
-        self.var_unification_table
-            .normalize_ty_shallow(&Interner, ty)
-            .map_or(Cow::Borrowed(ty), Cow::Owned)
+    pub(crate) fn resolve_ty_shallow(&mut self, ty: &Ty) -> Ty {
+        self.var_unification_table.normalize_ty_shallow(&Interner, ty).unwrap_or_else(|| ty.clone())
     }
 
     /// Resolves the type as far as currently possible, replacing type variables