Add submsg support for bytes_mut

message.cc:GetterForViewOrMut has been updated to support _mut for byte fields inside submsgs.

PiperOrigin-RevId: 590634540

rust/test/shared/simple_nested_test.rs

@@ -81,6 +81,7 @@ fn test_nested_muts() {
         })
     );
     assert_that!(inner_msg.string_mut().get(), eq(""));
+    assert_that!(inner_msg.bytes_mut().get(), eq(b""));
 
     set_and_test_mut!(inner_msg =>
         double_mut, 543.21;
@@ -95,8 +96,8 @@ fn test_nested_muts() {
         fixed64_mut, 999;
         bool_mut, true;
         string_mut, "hi";
+        bytes_mut, b"bye";
     );
-    // TODO: add mutation test for bytes
 }
 
 #[test]

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

@@ -258,17 +258,43 @@ void GetterForViewOrMut(Context<FieldDescriptor> field, bool is_mut) {
               $maybe_mutator$
             )rs");
   } else if (fieldType == FieldDescriptor::TYPE_BYTES) {
-    field.Emit(
-        {
-            {"field", fieldName},
-            {"self", self},
-            {"getter_thunk", getter_thunk},
-            {"RsType", rsType},
-        },
-        R"rs(
+    field.Emit({{"field", fieldName},
+                {"self", self},
+                {"getter_thunk", getter_thunk},
+                {"setter_thunk", setter_thunk},
+                {"RsType", rsType},
+                {"maybe_mutator",
+                 [&] {
+                   if (is_mut) {
+                     field.Emit({}, R"rs(
+                    pub fn r#$field$_mut(&self) -> $pb$::Mut<'_, $RsType$> {
+                       static VTABLE: $pbi$::BytesMutVTable =
+                        $pbi$::BytesMutVTable::new(
+                          $pbi$::Private,
+                          $getter_thunk$,
+                          $setter_thunk$,
+                        );
+
+                       unsafe {
+                        <$pb$::Mut<$RsType$>>::from_inner(
+                          $pbi$::Private,
+                          $pbi$::RawVTableMutator::new(
+                            $pbi$::Private,
+                            self.inner,
+                            &VTABLE,
+                           )
+                        )
+                      }
+                    }
+                    )rs");
+                   }
+                 }}},
+               R"rs(
               pub fn r#$field$(&self) -> $pb$::View<'_, $RsType$> {
                 unsafe { $getter_thunk$($self$).as_ref() }
               }
+
+              $maybe_mutator$
             )rs");
   } else {
     field.Emit({{"field", fieldName},