Add impl Clone for Rust proto owned messages.

PiperOrigin-RevId: 633265290

rust/test/shared/accessors_test.rs

@@ -779,6 +779,18 @@ fn test_submsg_setter() {
     assert_that!(parent.optional_nested_message().bb(), eq(7));
 }
 
+#[test]
+fn test_clone() {
+    let mut m = TestAllTypes::new();
+    m.set_optional_int32(42);
+    let clone = m.clone();
+    assert_that!(clone.optional_int32(), eq(42));
+    m.clear_optional_int32();
+    assert_that!(m.has_optional_int32(), eq(false));
+    assert_that!(clone.has_optional_int32(), eq(true));
+    assert_that!(clone.optional_int32(), eq(42));
+}
+
 #[test]
 fn test_to_owned() {
     let mut m = TestAllTypes::new();

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

@@ -1102,6 +1102,12 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
           }
         }
 
+        impl $std$::clone::Clone for $Msg$ {
+          fn clone(&self) -> Self {
+            self.as_view().to_owned()
+          }
+        }
+
         extern "C" {
           $Msg_externs$