Fix message vtable::clear

Needed to pass in the message as a parameter to the clearer thunk!

Now the clear() augmentations in accessors_test.rs are working as expected.

PiperOrigin-RevId: 603394469

rust/test/shared/accessors_test.rs

@@ -707,8 +707,7 @@ fn test_message_opt_set() {
     assert_that!(msg.optional_nested_message_opt().is_set(), eq(true));
 
     msg.optional_nested_message_mut().clear();
-    // TODO: b/323222163
-    // assert_that!(msg.optional_nested_message_mut().is_set(), eq(false));
+    assert_that!(msg.optional_nested_message_mut().is_set(), eq(false));
 }
 
 #[test]
@@ -724,8 +723,7 @@ fn test_setting_submsg() {
     assert_that!(msg.optional_nested_message_mut().is_set(), eq(true));
 
     msg.optional_nested_message_mut().clear();
-    // TODO: b/323222163
-    // assert_that!(msg.optional_nested_message_mut().is_set(), eq(false));
+    assert_that!(msg.optional_nested_message_mut().is_set(), eq(false));
 }
 
 #[test]
@@ -738,8 +736,7 @@ fn test_msg_or_default() {
     assert_that!(msg.optional_nested_message_mut().is_set(), eq(true));
 
     msg.optional_nested_message_mut().clear();
-    // TODO: b/323222163
-    //assert_that!(msg.optional_nested_message_mut().is_set(), eq(false));
+    assert_that!(msg.optional_nested_message_mut().is_set(), eq(false));
 }
 
 #[test]

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

@@ -637,8 +637,7 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
              -> Self::AbsentMutData<'_> {
              // SAFETY: The raw ptr msg_ref is valid
             unsafe {
-              (present_mutator.optional_vtable().clearer);
-              (present_mutator.msg_ref().msg());
+              (present_mutator.optional_vtable().clearer)(present_mutator.msg_ref().msg());
 
              $pbi$::RawVTableOptionalMutatorData::new($pbi$::Private,
                present_mutator.msg_ref(),