Always reborrow mutable reference receiver in methods

Author: HKalbasi

crates/hir-ty/src/method_resolution.rs

@@ -952,7 +952,10 @@ fn iterate_method_candidates_with_autoref(
         )
     };
 
-    iterate_method_candidates_by_receiver(receiver_ty, first_adjustment.clone())?;
+    if !matches!(receiver_ty.value.kind(Interner), TyKind::Ref(Mutability::Mut, _, _)) {
+        // We should prefer reborrow in case of mutable references
+        iterate_method_candidates_by_receiver(receiver_ty, first_adjustment.clone())?;
+    }
 
     let refed = Canonical {
         value: TyKind::Ref(Mutability::Not, static_lifetime(), receiver_ty.value.clone())

crates/hir-ty/src/tests/method_resolution.rs

@@ -388,6 +388,25 @@ mod bar_test {
     );
 }
 
+#[test]
+fn infer_trait_method_multiple_mutable_reference() {
+    check_types(
+        r#"
+trait Trait {
+    fn method(&mut self) -> i32 { 5 }
+}
+struct S;
+impl Trait for &mut &mut S {}
+fn test() {
+    let s = &mut &mut &mut S;
+    s.method();
+  //^^^^^^^^^^ i32
+}
+        "#,
+    );
+}
+
+
 #[test]
 fn infer_trait_method_generic_1() {
     // the trait implementation is intentionally incomplete -- it shouldn't matter

crates/ide/src/inlay_hints/adjustment.rs

@@ -322,6 +322,8 @@ fn main() {
    //^^^^^^^^^^^&
    //^^^^^^^^^^^*
     (&mut Struct).by_ref_mut();
+   //^^^^^^^^^^^&mut $
+   //^^^^^^^^^^^*
 
     // Check that block-like expressions don't duplicate hints
     let _: &mut [u32] = (&mut []);
@@ -425,6 +427,10 @@ fn main() {
    //^^^^^^^^^^^.*
    //^^^^^^^^^^^.&
     (&mut Struct).by_ref_mut();
+   //^^^^^^^^^^^(
+   //^^^^^^^^^^^)
+   //^^^^^^^^^^^.*
+   //^^^^^^^^^^^.&mut
 
     // Check that block-like expressions don't duplicate hints
     let _: &mut [u32] = (&mut []);