impl SettableValue for MsgView

For the cpp runtime, call the `Message::CopyFrom` method.

For the upb runtime, expose the message `MiniTable` and call `upb_Message_DeepCopy`.

PiperOrigin-RevId: 595166276

rust/test/shared/accessors_test.rs

@@ -10,7 +10,7 @@
 use googletest::prelude::*;
 use matchers::{is_set, is_unset};
 use protobuf::Optional;
-use unittest_proto::proto2_unittest::{TestAllTypes, TestAllTypes_};
+use unittest_proto::proto2_unittest::{NestedTestAllTypes, TestAllTypes, TestAllTypes_};
 
 #[test]
 fn test_default_accessors() {
@@ -735,3 +735,15 @@ fn test_oneof_mut_accessors() {
     msg.oneof_bytes_mut().set(b"123");
     assert_that!(msg.oneof_field_mut(), matches_pattern!(OneofBytes(_)));
 }
+
+#[test]
+fn test_set_message_from_view() {
+    use protobuf::MutProxy;
+    let mut m1 = NestedTestAllTypes::new();
+
+    let mut m2 = NestedTestAllTypes::new();
+    m2.payload_mut().optional_int32_mut().set(1);
+
+    m1.payload_mut().set(m2.payload());
+    assert_that!(m1.payload().optional_int32(), eq(1));
+}

rust/upb.rs

@@ -288,6 +288,10 @@ impl<'msg> MutatorMessageRef<'msg> {
     pub fn msg(&self) -> RawMessage {
         self.msg
     }
+
+    pub fn raw_arena(&self, _private: Private) -> RawArena {
+        self.arena.raw()
+    }
 }
 
 pub fn copy_bytes_in_arena_if_needed_by_runtime<'msg>(
@@ -308,6 +312,28 @@ pub fn copy_bytes_in_arena_if_needed_by_runtime<'msg>(
     }
 }
 
+/// Opaque struct containing a upb_MiniTable.
+///
+/// This wrapper is a workaround until stabilization of [`extern type`].
+/// TODO: convert to extern type once stabilized.
+/// [`extern type`]: https://github.com/rust-lang/rust/issues/43467
+#[repr(C)]
+pub struct OpaqueMiniTable {
+    // TODO: consider importing a minitable struct declared in
+    // google3/third_party/upb/bits.
+    _data: [u8; 0],
+    _marker: std::marker::PhantomData<(*mut u8, ::std::marker::PhantomPinned)>,
+}
+
+extern "C" {
+    pub fn upb_Message_DeepCopy(
+        dst: RawMessage,
+        src: RawMessage,
+        mini_table: *const OpaqueMiniTable,
+        arena: RawArena,
+    );
+}
+
 /// The raw type-erased pointer version of `RepeatedMut`.
 ///
 /// Contains a `upb_Array*` as well as `RawArena`, most likely that of the

rust/upb_kernel/BUILD

@@ -10,5 +10,6 @@ cc_library(
     deps = [
         "//upb:mem",
         "//upb:message",
+        "//upb:message_copy",
     ],
 )

rust/upb_kernel/upb_api.c

@@ -10,4 +10,5 @@
 
 #include "upb/mem/arena.h"      // IWYU pragma: keep
 #include "upb/message/array.h"  // IWYU pragma: keep
+#include "upb/message/copy.h"   // IWYU pragma: keep
 #include "upb/message/map.h"    // IWYU pragma: keep

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

@@ -7,6 +7,8 @@
 
 #include "google/protobuf/compiler/rust/message.h"
 
+#include <string>
+
 #include "absl/log/absl_check.h"
 #include "absl/log/absl_log.h"
 #include "absl/strings/str_format.h"
@@ -19,6 +21,7 @@
 #include "google/protobuf/compiler/rust/naming.h"
 #include "google/protobuf/compiler/rust/oneof.h"
 #include "google/protobuf/descriptor.h"
+#include "upb_generator/mangle.h"
 
 namespace google {
 namespace protobuf {
@@ -26,6 +29,10 @@ namespace compiler {
 namespace rust {
 namespace {
 
+std::string UpbMinitableName(const Descriptor& msg) {
+  return upb::generator::MessageInit(msg.full_name());
+}
+
 void MessageNew(Context& ctx, const Descriptor& msg) {
   switch (ctx.opts().kernel) {
     case Kernel::kCpp:
@@ -126,12 +133,14 @@ void MessageExterns(Context& ctx, const Descriptor& msg) {
               {"delete_thunk", ThunkName(ctx, msg, "delete")},
               {"serialize_thunk", ThunkName(ctx, msg, "serialize")},
               {"deserialize_thunk", ThunkName(ctx, msg, "deserialize")},
+              {"copy_from_thunk", ThunkName(ctx, msg, "copy_from")},
           },
           R"rs(
           fn $new_thunk$() -> $pbi$::RawMessage;
           fn $delete_thunk$(raw_msg: $pbi$::RawMessage);
           fn $serialize_thunk$(raw_msg: $pbi$::RawMessage) -> $pbr$::SerializedData;
           fn $deserialize_thunk$(raw_msg: $pbi$::RawMessage, data: $pbr$::SerializedData) -> bool;
+          fn $copy_from_thunk$(dst: $pbi$::RawMessage, src: $pbi$::RawMessage);
         )rs");
       return;
 
@@ -141,11 +150,15 @@ void MessageExterns(Context& ctx, const Descriptor& msg) {
               {"new_thunk", ThunkName(ctx, msg, "new")},
               {"serialize_thunk", ThunkName(ctx, msg, "serialize")},
               {"deserialize_thunk", ThunkName(ctx, msg, "parse")},
+              {"minitable", UpbMinitableName(msg)},
           },
           R"rs(
           fn $new_thunk$(arena: $pbi$::RawArena) -> $pbi$::RawMessage;
           fn $serialize_thunk$(msg: $pbi$::RawMessage, arena: $pbi$::RawArena, len: &mut usize) -> $NonNull$<u8>;
           fn $deserialize_thunk$(data: *const u8, size: usize, arena: $pbi$::RawArena) -> Option<$pbi$::RawMessage>;
+          /// Opaque wrapper for this message's MiniTable. The only valid way to
+          /// reference this static is with `std::ptr::addr_of!(..)`.
+          static $minitable$: $pbr$::OpaqueMiniTable;
       )rs");
       return;
   }
@@ -169,6 +182,41 @@ bool IsStringOrBytes(FieldDescriptor::Type t) {
   return t == FieldDescriptor::TYPE_STRING || t == FieldDescriptor::TYPE_BYTES;
 }
 
+void MessageSettableValue(Context& ctx, const Descriptor& msg) {
+  switch (ctx.opts().kernel) {
+    case Kernel::kCpp:
+      ctx.Emit({{"copy_from_thunk", ThunkName(ctx, msg, "copy_from")}}, R"rs(
+        impl<'msg> $pb$::SettableValue<$Msg$> for $Msg$View<'msg> {
+          fn set_on<'dst>(
+            self, _private: $pbi$::Private, mutator: $pb$::Mut<'dst, $Msg$>)
+            where $Msg$: 'dst {
+            unsafe { $copy_from_thunk$(mutator.inner.msg(), self.msg) };
+          }
+        }
+      )rs");
+      return;
+
+    case Kernel::kUpb:
+      ctx.Emit({{"minitable", UpbMinitableName(msg)}}, R"rs(
+        impl<'msg> $pb$::SettableValue<$Msg$> for $Msg$View<'msg> {
+          fn set_on<'dst>(
+            self, _private: $pbi$::Private, mutator: $pb$::Mut<'dst, $Msg$>)
+            where $Msg$: 'dst {
+            unsafe { $pbr$::upb_Message_DeepCopy(
+              mutator.inner.msg(),
+              self.msg,
+              $std$::ptr::addr_of!($minitable$),
+              mutator.inner.raw_arena($pbi$::Private),
+            ) };
+          }
+        }
+      )rs");
+      return;
+  }
+
+  ABSL_LOG(FATAL) << "unreachable";
+}
+
 void GetterForViewOrMut(Context& ctx, const FieldDescriptor& field,
                         bool is_mut) {
   auto fieldName = field.name();
@@ -381,7 +429,8 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
             {"accessor_fns_for_views",
              [&] { AccessorsForViewOrMut(ctx, msg, false); }},
             {"accessor_fns_for_muts",
-             [&] { AccessorsForViewOrMut(ctx, msg, true); }}},
+             [&] { AccessorsForViewOrMut(ctx, msg, true); }},
+            {"settable_impl", [&] { MessageSettableValue(ctx, msg); }}},
            R"rs(
         #[allow(non_camel_case_types)]
         // TODO: Implement support for debug redaction
@@ -437,13 +486,7 @@ void GenerateRs(Context& ctx, const Descriptor& msg) {
           }
         }
 
-        impl<'a> $pb$::SettableValue<$Msg$> for $Msg$View<'a> {
+        $settable_impl$
-          fn set_on<'b>(self, _private: $pb$::__internal::Private, _mutator: $pb$::Mut<'b, $Msg$>)
-          where
-            $Msg$: 'b {
-            todo!()
-          }
-        }
 
         #[derive(Debug)]
         #[allow(dead_code)]
@@ -556,6 +599,7 @@ void GenerateThunksCc(Context& ctx, const Descriptor& msg) {
        {"delete_thunk", ThunkName(ctx, msg, "delete")},
        {"serialize_thunk", ThunkName(ctx, msg, "serialize")},
        {"deserialize_thunk", ThunkName(ctx, msg, "deserialize")},
+       {"copy_from_thunk", ThunkName(ctx, msg, "copy_from")},
        {"nested_msg_thunks",
         [&] {
           for (int i = 0; i < msg.nested_type_count(); ++i) {
@@ -590,6 +634,10 @@ void GenerateThunksCc(Context& ctx, const Descriptor& msg) {
           return msg->ParseFromArray(data.data, data.len);
         }
 
+        void $copy_from_thunk$($QualifiedMsg$* dst, const $QualifiedMsg$* src) {
+          dst->CopyFrom(*src);
+        }
+
         $accessor_thunks$
 
         $oneof_thunks$