From 4c56758499e5528ad1624894911c9150b66d66a5 Mon Sep 17 00:00:00 2001
From: Mike Maley <michael.r.maley@gmail.com>
Date: Tue, 18 Feb 2025 21:20:18 -0500
Subject: [PATCH 1/2] Update callee.rs

---
 compiler/rustc_hir_typeck/src/callee.rs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index 49ea2181b075a..6b8b1de687458 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -224,8 +224,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             //
             // The simplest fix by far is to just ignore this case and deref again,
             // so we wind up with `FnMut::call_mut(&mut *f, ())`.
-            ty::Ref(..) if autoderef.step_count() == 0 => {
-                return None;
+            ty::Ref(_, deref_ty, _) if autoderef.step_count() == 0 => {
+                match deref_ty.kind() {
+                    ty::Adt(..) => {},
+                    _ => {return None}
+                }
             }
 
             ty::Error(_) => {

From d97eaf80abf2fc88abfe09bd54d1f5669f4d42bd Mon Sep 17 00:00:00 2001
From: Mike Maley <michael.r.maley@gmail.com>
Date: Wed, 19 Feb 2025 06:38:57 -0500
Subject: [PATCH 2/2] Update callee.rs

Added comments and improved formatting.
---
 compiler/rustc_hir_typeck/src/callee.rs | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index 6b8b1de687458..db783f5d5f605 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -223,12 +223,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             //            ^ without this hack `f` would have to be declared as mutable
             //
             // The simplest fix by far is to just ignore this case and deref again,
-            // so we wind up with `FnMut::call_mut(&mut *f, ())`.
+            // so we wind up with `FnMut::call_mut(&mut *f, ())`.  This does not 
+            // apply to structs, enums, or unions; because they should be `mut` 
+            // if they use `call_mut()`.
             ty::Ref(_, deref_ty, _) if autoderef.step_count() == 0 => {
                 match deref_ty.kind() {
-                    ty::Adt(..) => {},
-                    _ => {return None}
-                }
+                    ty::Adt(..) => {}
+                    _ => return None,
+                };
             }
 
             ty::Error(_) => {