Fix a python bug that UPB and Python C++ extension assume MessageSet extensions are ordered first

PiperOrigin-RevId: 698430014

python/google/protobuf/internal/message_set_extensions.proto

@@ -19,6 +19,9 @@ message TestMessageSet {
 }
 
 message TestMessageSetExtension1 {
+  extend TestMessageSet {
+    optional TestExtension first_extension = 2534113;
+  }
   extend TestMessageSet {
     optional TestMessageSetExtension1 message_set_extension = 98418603;
   }
@@ -36,6 +39,10 @@ message TestMessageSetExtension3 {
   optional string text = 35;
 }
 
+message TestExtension {
+  optional string str = 1;
+}
+
 extend TestMessageSet {
   optional TestMessageSetExtension3 message_set_extension3 = 98418655;
 }

python/google/protobuf/internal/text_format_test.py

@@ -1411,6 +1411,23 @@ class Proto2Tests(TextFormatBase):
         '  text: \"bar\"\n'
         '}\n')
 
+  def testMessageSetExtensionNotFirst(self):
+    desc = message_set_extensions_pb2.TestMessageSetExtension1.DESCRIPTOR
+    self.assertEqual('first_extension', desc.extensions[0].name)
+    self.assertEqual('message_set_extension', desc.extensions[1].name)
+    message = message_set_extensions_pb2.TestMessageSet()
+    ext = (
+        message_set_extensions_pb2.TestMessageSetExtension1.message_set_extension
+    )
+    message.Extensions[ext].i = 123
+    expected_str = (
+        '[google.protobuf.internal.TestMessageSetExtension1] {\n  i: 123\n}\n'
+    )
+    self.CompareToGoldenText(text_format.MessageToString(message), expected_str)
+    parsed = message_set_extensions_pb2.TestMessageSet()
+    text_format.Parse(expected_str, parsed)
+    self.CompareToGoldenText(text_format.MessageToString(parsed), expected_str)
+
   def testPrintMessageSetByFieldNumber(self):
     out = text_format.TextWriter(False)
     message = unittest_mset_pb2.TestMessageSetContainer()

python/google/protobuf/pyext/extension_dict.cc

@@ -207,6 +207,21 @@ int ass_subscript(ExtensionDict* self, PyObject* key, PyObject* value) {
   return 0;
 }
 
+static const FieldDescriptor* FindMessageSetExtension(
+    const Descriptor* message_descriptor) {
+  for (int i = 0; i < message_descriptor->extension_count(); i++) {
+    const FieldDescriptor* extension = message_descriptor->extension(i);
+    if (extension->is_extension() &&
+        extension->containing_type()->options().message_set_wire_format() &&
+        extension->type() == FieldDescriptor::TYPE_MESSAGE &&
+        extension->label() == FieldDescriptor::LABEL_OPTIONAL &&
+        extension->message_type() == message_descriptor) {
+      return extension;
+    }
+  }
+  return nullptr;
+}
+
 PyObject* _FindExtensionByName(ExtensionDict* self, PyObject* arg) {
   char* name;
   Py_ssize_t name_size;
@@ -221,14 +236,8 @@ PyObject* _FindExtensionByName(ExtensionDict* self, PyObject* arg) {
     // Is is the name of a message set extension?
     const Descriptor* message_descriptor =
         pool->pool->FindMessageTypeByName(absl::string_view(name, name_size));
-    if (message_descriptor && message_descriptor->extension_count() > 0) {
-      const FieldDescriptor* extension = message_descriptor->extension(0);
-      if (extension->is_extension() &&
-          extension->containing_type()->options().message_set_wire_format() &&
-          extension->type() == FieldDescriptor::TYPE_MESSAGE &&
-          extension->label() == FieldDescriptor::LABEL_OPTIONAL) {
-        message_extension = extension;
-      }
+    if (message_descriptor) {
+      message_extension = FindMessageSetExtension(message_descriptor);
     }
   }
   if (message_extension == nullptr) {

upb/reflection/def_pool.c

@@ -12,6 +12,7 @@
 #include "upb/hash/str_table.h"
 #include "upb/mem/alloc.h"
 #include "upb/mem/arena.h"
+#include "upb/reflection/def.h"
 #include "upb/reflection/def_type.h"
 #include "upb/reflection/file_def.h"
 #include "upb/reflection/internal/def_builder.h"
@@ -236,9 +237,15 @@ const upb_FieldDef* upb_DefPool_FindExtensionByNameWithSize(
       return _upb_DefType_Unpack(v, UPB_DEFTYPE_FIELD);
     case UPB_DEFTYPE_MSG: {
       const upb_MessageDef* m = _upb_DefType_Unpack(v, UPB_DEFTYPE_MSG);
-      return _upb_MessageDef_InMessageSet(m)
-                 ? upb_MessageDef_NestedExtension(m, 0)
-                 : NULL;
+      if (_upb_MessageDef_InMessageSet(m)) {
+        for (int i = 0; i < upb_MessageDef_NestedExtensionCount(m); i++) {
+          const upb_FieldDef* ext = upb_MessageDef_NestedExtension(m, i);
+          if (upb_FieldDef_MessageSubDef(ext) == m) {
+            return ext;
+          }
+        }
+      }
+      return NULL;
     }
     default:
       break;