Fix handling of the binders in dyn/impl Trait

We need to be more careful now when substituting bound variables (previously, we
didn't have anything that used bound variables except Chalk, so it was not a
problem).

This is obviously quite ad-hoc; Chalk has more infrastructure for handling this
in a principled way, which we maybe should adopt.

1 files changed, 4 insertions, 3 deletions

diff --git a/crates/ra_hir/src/ty/traits.rs b/crates/ra_hir/src/ty/traits.rs
index 771525deb..99dbab99e 100644
--- a/crates/ra_hir/src/ty/traits.rs
+++ b/crates/ra_hir/src/ty/traits.rs
@@ -165,9 +165,9 @@ impl TypeWalk for ProjectionPredicate {
         self.ty.walk(f);
     }
 
-    fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
-        self.projection_ty.walk_mut(f);
-        self.ty.walk_mut(f);
+    fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize) {
+        self.projection_ty.walk_mut_binders(f, binders);
+        self.ty.walk_mut_binders(f, binders);
     }
 }
 
@@ -188,6 +188,7 @@ pub(crate) fn trait_solve_query(
     }
 
     let canonical = goal.to_chalk(db).cast();
+
     // We currently don't deal with universes (I think / hope they're not yet
     // relevant for our use cases?)
     let u_canonical = chalk_ir::UCanonical { canonical, universes: 1 };