Use correct, full substs for self type in impl

Without arbitrary self types, the self type could never refer to the method type
parameters, so this wasn't a problem; but with arbitrary self types, it can.

This fixes the crash from #6668; but it doesn't make method resolution work for
these methods.

1 files changed, 7 insertions, 1 deletions

diff --git a/crates/hir_ty/src/method_resolution.rs b/crates/hir_ty/src/method_resolution.rs
index 5a6f0c67f..8a289f52a 100644
--- a/crates/hir_ty/src/method_resolution.rs
+++ b/crates/hir_ty/src/method_resolution.rs
@@ -720,7 +720,13 @@ fn transform_receiver_ty(
             .push(self_ty.value.clone())
             .fill_with_unknown()
             .build(),
-        AssocContainerId::ImplId(impl_id) => inherent_impl_substs(db, impl_id, &self_ty)?,
+        AssocContainerId::ImplId(impl_id) => {
+            let impl_substs = inherent_impl_substs(db, impl_id, &self_ty)?;
+            Substs::build_for_def(db, function_id)
+                .use_parent_substs(&impl_substs)
+                .fill_with_unknown()
+                .build()
+        }
         AssocContainerId::ContainerId(_) => unreachable!(),
     };
     let sig = db.callable_item_signature(function_id.into());