Add SettableValue<Msg> for owned Msg.

Right now this just does as_view().set_on(), but can be optimized to avoid a copy in a followup.

PiperOrigin-RevId: 602807430

rust/test/shared/accessors_test.rs

@@ -9,7 +9,7 @@
 
 use googletest::prelude::*;
 use matchers::{is_set, is_unset};
-use protobuf::Optional;
+use protobuf::{MutProxy, Optional};
 use unittest_proto::{TestAllTypes, TestAllTypes_};
 
 #[test]
@@ -668,16 +668,22 @@ fn test_nonempty_default_string_accessors() {
 
 #[test]
 fn test_singular_msg_field() {
-    use TestAllTypes_::{NestedMessageMut, NestedMessageView};
+    use TestAllTypes_::*;
 
     let mut msg = TestAllTypes::new();
     let msg_view: NestedMessageView = msg.optional_nested_message();
     // testing reading an int inside a view
     assert_that!(msg_view.bb(), eq(0));
 
-    let msg_mut: NestedMessageMut = msg.optional_nested_message_mut().or_default();
+    let mut nested_msg_mut: NestedMessageMut = msg.optional_nested_message_mut().or_default();
     // test reading an int inside a mut
-    assert_that!(msg_mut.bb(), eq(0));
+    assert_that!(nested_msg_mut.bb(), eq(0));
+
+    // Test setting an owned NestedMessage onto another message.
+    let mut new_nested = NestedMessage::new();
+    new_nested.bb_mut().set(7);
+    nested_msg_mut.set(new_nested);
+    assert_that!(nested_msg_mut.bb(), eq(7));
 }
 
 #[test]

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

@@ -192,7 +192,7 @@ void MessageDrop(Context& ctx, const Descriptor& msg) {
   )rs");
 }
 
-void MessageSettableValue(Context& ctx, const Descriptor& msg) {
+void MessageSettableValueForView(Context& ctx, const Descriptor& msg) {
   switch (ctx.opts().kernel) {
     case Kernel::kCpp:
       ctx.Emit({{"copy_from_thunk", ThunkName(ctx, msg, "copy_from")}}, R"rs(
@@ -519,7 +519,8 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
                                    AccessorCase::MUT);
           }
         }},
-       {"settable_impl", [&] { MessageSettableValue(ctx, msg); }},
+       {"settable_impl_for_view",
+        [&] { MessageSettableValueForView(ctx, msg); }},
        {"repeated_impl", [&] { MessageProxiedInRepeated(ctx, msg); }},
        {"unwrap_upb",
         [&] {
@@ -655,7 +656,18 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
           }
         }
 
-        $settable_impl$
+        $settable_impl_for_view$
+
+        impl $pb$::SettableValue<$Msg$> for $Msg$ {
+          fn set_on<'dst>(
+            self, _private: $pbi$::Private, mutator: $pb$::Mut<'dst, $Msg$>)
+            where $Msg$: 'dst {
+            //~ TODO: b/320701507 - This current will copy the message and then
+            //~ drop it, this copy would be avoided on upb kernel.
+            self.as_view().set_on($pbi$::Private, mutator);
+          }
+        }
+
         $repeated_impl$
 
         #[derive(Debug)]