Cleanup mutable thunk usage in singular_message

PiperOrigin-RevId: 588482350

src/google/protobuf/compiler/rust/accessors/singular_message.cc

@@ -27,7 +27,7 @@ void SingularMessage::InMsgImpl(Context<FieldDescriptor> field) const {
           {"prefix", prefix},
           {"field", field.desc().name()},
           {"getter_thunk", Thunk(field, "get")},
-          {"getter_mut_thunk", Thunk(field, "mutable")},
+          {"getter_mut_thunk", Thunk(field, "get_mut")},
           {"clearer_thunk", Thunk(field, "clear")},
           {
               "view_body",
@@ -91,7 +91,7 @@ void SingularMessage::InExternC(Context<FieldDescriptor> field) const {
   field.Emit(
       {
           {"getter_thunk", Thunk(field, "get")},
-          {"getter_mut_thunk", Thunk(field, "mutable")},
+          {"getter_mut_thunk", Thunk(field, "get_mut")},
           {"clearer_thunk", Thunk(field, "clear")},
           {"getter_mut",
            [&] {
@@ -130,7 +130,7 @@ void SingularMessage::InThunkCc(Context<FieldDescriptor> field) const {
   field.Emit({{"QualifiedMsg",
                cpp::QualifiedClassName(field.desc().containing_type())},
               {"getter_thunk", Thunk(field, "get")},
-              {"getter_mut_thunk", Thunk(field, "mutable")},
+              {"getter_mut_thunk", Thunk(field, "get_mut")},
               {"clearer_thunk", Thunk(field, "clear")},
               {"field", cpp::FieldName(&field.desc())}},
              R"cc(

src/google/protobuf/compiler/rust/naming.cc

@@ -84,7 +84,10 @@ std::string Thunk(Context<T> field, absl::string_view op) {
   if (field.is_upb() && op == "get") {
     // upb getter is simply the field name (no "get" in the name).
     format = "_$1";
-  } else if (field.is_upb() && (op == "case")) {
+  } else if (field.is_upb() && op == "get_mut") {
+    // same as above, with with `mutable` prefix
+    format = "_mutable_$1";
+  } else if (field.is_upb() && op == "case") {
     // some upb functions are in the order x_op compared to has/set/clear which
     // are in the other order e.g. op_x.
     format = "_$1_$0";