Merge #3263

3263: Implement unsizing coercions using Chalk r=matklad a=flodiebold

These are coercions like `&[T; n] -> &[T]`, which are handled by the `Unsize` and `CoerceUnsized` traits. The impls for `Unsize` are all built in to the compiler and require special handling, so we need to provide them to Chalk.

This adds the following `Unsize` impls:
 - `Unsize<[T]> for [T; _]`
 - `Unsize<dyn Trait> for T where T: Trait`
 - `Unsize<dyn SuperTrait> for dyn SubTrait`

Hence we are still missing the 'unsizing the last field of a generic struct' case.

Co-authored-by: Florian Diebold <[email protected]>
Co-authored-by: Florian Diebold <[email protected]>

1 files changed, 0 insertions, 7 deletions

diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 76069eb9c..6e1d268de 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -206,12 +206,6 @@ struct InferenceContext<'a, D: HirDatabase> {
     /// closures, but currently this is the only field that will change there,
     /// so it doesn't make sense.
     return_ty: Ty,
-
-    /// Impls of `CoerceUnsized` used in coercion.
-    /// (from_ty_ctor, to_ty_ctor) => coerce_generic_index
-    // FIXME: Use trait solver for this.
-    // Chalk seems unable to work well with builtin impl of `Unsize` now.
-    coerce_unsized_map: FxHashMap<(TypeCtor, TypeCtor), usize>,
 }
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
@@ -222,7 +216,6 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             obligations: Vec::default(),
             return_ty: Ty::Unknown, // set in collect_fn_signature
             trait_env: TraitEnvironment::lower(db, &resolver),
-            coerce_unsized_map: Self::init_coerce_unsized_map(db, &resolver),
             db,
             owner,
             body: db.body(owner),