Fix shifting of binders in FnPointer

 - don't shift in/out for Chalk mapping (we want to have the same
   binders now)
 - do shift in when creating the signature for a closure (though it
   shouldn't matter much)
 - do shift in when lowering a `fn()` type
 - correctly deal with the implied binder in TypeWalk

1 files changed, 13 insertions, 0 deletions

diff --git a/crates/hir_ty/src/walk.rs b/crates/hir_ty/src/walk.rs
index 963eb12c8..e1e77ba37 100644
--- a/crates/hir_ty/src/walk.rs
+++ b/crates/hir_ty/src/walk.rs
@@ -92,6 +92,13 @@ pub trait TypeWalk {
         self
     }
 
+    fn shifted_in(self, _interner: &Interner) -> Self
+    where
+        Self: Sized,
+    {
+        self.shifted_in_from(DebruijnIndex::ONE)
+    }
+
     /// Shifts up debruijn indices of `TyKind::Bound` vars by `n`.
     fn shifted_in_from(self, n: DebruijnIndex) -> Self
     where
@@ -149,6 +156,9 @@ impl TypeWalk for Ty {
             TyKind::Slice(ty) | TyKind::Array(ty) | TyKind::Ref(_, ty) | TyKind::Raw(_, ty) => {
                 ty.walk(f);
             }
+            TyKind::Function(fn_pointer) => {
+                fn_pointer.substitution.0.walk(f);
+            }
             _ => {
                 if let Some(substs) = self.substs() {
                     for t in substs.iter(&Interner) {
@@ -180,6 +190,9 @@ impl TypeWalk for Ty {
             TyKind::Slice(ty) | TyKind::Array(ty) | TyKind::Ref(_, ty) | TyKind::Raw(_, ty) => {
                 ty.walk_mut_binders(f, binders);
             }
+            TyKind::Function(fn_pointer) => {
+                fn_pointer.substitution.0.walk_mut_binders(f, binders.shifted_in());
+            }
             _ => {
                 if let Some(substs) = self.substs_mut() {
                     substs.walk_mut_binders(f, binders);