From 182aedaec4a6cfd2465a2c541e5f2485b0aadb58 Mon Sep 17 00:00:00 2001
From: Ollie <69084614+olijeffers0n@users.noreply.github.com>
Date: Sat, 24 Jun 2023 20:19:13 +0100
Subject: [PATCH] Handle empty value objects properly (#481)

Co-authored-by: James Hilton-Balfe <gobot1234yt@gmail.com>
---
 src/betterproto/__init__.py                   |  7 +++++++
 .../google_impl_behavior_equivalence.proto    | 12 +++++++-----
 .../test_google_impl_behavior_equivalence.py  | 19 +++++++++++++++++--
 3 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/src/betterproto/__init__.py b/src/betterproto/__init__.py
index 40be27f..f22a8f7 100644
--- a/src/betterproto/__init__.py
+++ b/src/betterproto/__init__.py
@@ -704,6 +704,13 @@ class Message(ABC):
             return value
 
     def __setattr__(self, attr: str, value: Any) -> None:
+        if (
+            isinstance(value, Message)
+            and hasattr(value, "_betterproto")
+            and not value._betterproto.meta_by_field_name
+        ):
+            value._serialized_on_wire = True
+
         if attr != "_serialized_on_wire":
             # Track when a field has been set.
             self.__dict__["_serialized_on_wire"] = True
diff --git a/tests/inputs/google_impl_behavior_equivalence/google_impl_behavior_equivalence.proto b/tests/inputs/google_impl_behavior_equivalence/google_impl_behavior_equivalence.proto
index 5357a7c..3e9bea9 100644
--- a/tests/inputs/google_impl_behavior_equivalence/google_impl_behavior_equivalence.proto
+++ b/tests/inputs/google_impl_behavior_equivalence/google_impl_behavior_equivalence.proto
@@ -2,14 +2,16 @@ syntax = "proto3";
 
 package google_impl_behavior_equivalence;
 
-message Foo{
-  int64 bar = 1;
-}
+message Foo { int64 bar = 1; }
 
-message Test{
-  oneof group{
+message Test {
+  oneof group {
     string string = 1;
     int64 integer = 2;
     Foo foo = 3;
   }
 }
+
+message Request { Empty foo = 1; }
+
+message Empty {}
\ No newline at end of file
diff --git a/tests/inputs/google_impl_behavior_equivalence/test_google_impl_behavior_equivalence.py b/tests/inputs/google_impl_behavior_equivalence/test_google_impl_behavior_equivalence.py
index 0297692..476d20e 100644
--- a/tests/inputs/google_impl_behavior_equivalence/test_google_impl_behavior_equivalence.py
+++ b/tests/inputs/google_impl_behavior_equivalence/test_google_impl_behavior_equivalence.py
@@ -3,17 +3,20 @@ from google.protobuf import json_format
 
 import betterproto
 from tests.output_betterproto.google_impl_behavior_equivalence import (
+    Empty,
     Foo,
+    Request,
     Test,
 )
 from tests.output_reference.google_impl_behavior_equivalence.google_impl_behavior_equivalence_pb2 import (
+    Empty as ReferenceEmpty,
     Foo as ReferenceFoo,
+    Request as ReferenceRequest,
     Test as ReferenceTest,
 )
 
 
 def test_oneof_serializes_similar_to_google_oneof():
-
     tests = [
         (Test(string="abc"), ReferenceTest(string="abc")),
         (Test(integer=2), ReferenceTest(integer=2)),
@@ -30,7 +33,6 @@ def test_oneof_serializes_similar_to_google_oneof():
 
 
 def test_bytes_are_the_same_for_oneof():
-
     message = Test(string="")
     message_reference = ReferenceTest(string="")
 
@@ -53,3 +55,16 @@ def test_bytes_are_the_same_for_oneof():
 
     assert isinstance(message_reference.foo, ReferenceFoo)
     assert isinstance(message_reference2.foo, ReferenceFoo)
+
+
+def test_empty_message_field():
+    message = Request()
+    reference_message = ReferenceRequest()
+
+    message.foo = Empty()
+    reference_message.foo.CopyFrom(ReferenceEmpty())
+
+    assert betterproto.serialized_on_wire(message.foo)
+    assert reference_message.HasField("foo")
+
+    assert bytes(message) == reference_message.SerializeToString()