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, 3 insertions, 2 deletions

diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index 20bb7dd59..3cbb6ad54 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -178,8 +178,9 @@ impl<'a> TyLoweringContext<'a> {
             }
             TypeRef::Placeholder => TyKind::Error.intern(&Interner),
             TypeRef::Fn(params, is_varargs) => {
-                let substs =
-                    Substitution::from_iter(&Interner, params.iter().map(|tr| self.lower_ty(tr)));
+                let substs = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
+                    Substitution::from_iter(&Interner, params.iter().map(|tr| ctx.lower_ty(tr)))
+                });
                 TyKind::Function(FnPointer {
                     num_binders: 0, // FIXME lower `for<'a> fn()` correctly
                     sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },