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, 3 insertions, 1 deletions

diff --git a/crates/ra_hir_ty/src/traits/chalk.rs b/crates/ra_hir_ty/src/traits/chalk.rs
index 1bdf13e48..e1e430aeb 100644
--- a/crates/ra_hir_ty/src/traits/chalk.rs
+++ b/crates/ra_hir_ty/src/traits/chalk.rs
@@ -572,8 +572,10 @@ where
             .collect();
 
         let ty: Ty = from_chalk(self.db, parameters[0].assert_ty_ref().clone());
+        let arg: Option<Ty> =
+            parameters.get(1).map(|p| from_chalk(self.db, p.assert_ty_ref().clone()));
 
-        builtin::get_builtin_impls(self.db, self.krate, &ty, trait_, |i| {
+        builtin::get_builtin_impls(self.db, self.krate, &ty, &arg, trait_, |i| {
             result.push(i.to_chalk(self.db))
         });