1 files changed, 10 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/assembly.rs b/compiler/rustc_trait_selection/src/solve/assembly.rs
index e44fd82ba22..e6c36d37ffb 100644
--- a/compiler/rustc_trait_selection/src/solve/assembly.rs
+++ b/compiler/rustc_trait_selection/src/solve/assembly.rs
@@ -173,6 +173,14 @@ pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy + Eq {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx>;
+
+    // Implement unsizing. The most common forms of unsizing are array to slice,
+    // and concrete (Sized) type into a `dyn Trait`. ADTs and Tuples can also
+    // have their final field unsized if it's generic.
+    fn consider_builtin_unsize_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {
@@ -303,6 +311,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             G::consider_builtin_future_candidate(self, goal)
         } else if lang_items.gen_trait() == Some(trait_def_id) {
             G::consider_builtin_generator_candidate(self, goal)
+        } else if lang_items.unsize_trait() == Some(trait_def_id) {
+            G::consider_builtin_unsize_candidate(self, goal)
         } else {
             Err(NoSolution)
         };