Allow open enums from editions files in proto3.

The old check assumed all non-proto3 enums were closed, which is no longer true.

PiperOrigin-RevId: 582411371

src/google/protobuf/descriptor.cc

@@ -7711,17 +7711,13 @@ void DescriptorBuilder::ValidateProto3Field(const FieldDescriptor* field,
              "Explicit default values are not allowed in proto3.");
   }
   if (field->cpp_type() == FieldDescriptor::CPPTYPE_ENUM &&
-      field->enum_type() &&
-      FileDescriptorLegacy(field->enum_type()->file()).syntax() !=
-          FileDescriptorLegacy::Syntax::SYNTAX_PROTO3 &&
-      FileDescriptorLegacy(field->enum_type()->file()).syntax() !=
-          FileDescriptorLegacy::Syntax::SYNTAX_UNKNOWN) {
-    // Proto3 messages can only use Proto3 enum types; otherwise we can't
+      field->enum_type() && field->enum_type()->is_closed()) {
+    // Proto3 messages can only use open enum types; otherwise we can't
     // guarantee that the default value is zero.
     AddError(
         field->full_name(), proto, DescriptorPool::ErrorCollector::TYPE, [&] {
           return absl::StrCat("Enum type \"", field->enum_type()->full_name(),
-                              "\" is not a proto3 enum, but is used in \"",
+                              "\" is not an open enum, but is used in \"",
                               field->containing_type()->full_name(),
                               "\" which is a proto3 message type.");
         });

src/google/protobuf/descriptor_unittest.cc

@@ -7034,10 +7034,73 @@ TEST_F(ValidationErrorTest, ValidateProto3EnumFromProto2) {
       "    field { name:'bar' number:1 label:LABEL_OPTIONAL type:TYPE_ENUM "
       "            type_name: 'foo.FooEnum' }"
       "}",
-      "bar.proto: Foo.bar: TYPE: Enum type \"foo.FooEnum\" is not a proto3 "
+      "bar.proto: Foo.bar: TYPE: Enum type \"foo.FooEnum\" is not an open "
       "enum, but is used in \"Foo\" which is a proto3 message type.\n");
 }
 
+TEST_F(ValidationErrorTest, ValidateProto3ClosedEnum) {
+  // Define a closed enum in an editions file.
+  BuildFile(R"pb(name: 'foo.proto'
+                 package: 'foo'
+                 syntax: 'editions'
+                 edition: EDITION_2023
+                 enum_type {
+                   name: 'FooEnum'
+                   value { name: 'DEFAULT_OPTION' number: 0 }
+                   options { features { enum_type: CLOSED } }
+                 })pb");
+
+  BuildFileWithErrors(
+      R"pb(name: 'bar.proto'
+           dependency: 'foo.proto'
+           syntax: 'proto3'
+           message_type {
+             name: 'Foo'
+             field {
+               name: 'bar'
+               number: 1
+               label: LABEL_OPTIONAL
+               type: TYPE_ENUM
+               type_name: 'foo.FooEnum'
+             }
+           })pb",
+      "bar.proto: Foo.bar: TYPE: Enum type \"foo.FooEnum\" is not an open "
+      "enum, but is used in \"Foo\" which is a proto3 message type.\n");
+}
+
+TEST_F(ValidationErrorTest, ValidateProto3OpenEnum) {
+  // Define an open enum in an editions file.
+  const FileDescriptor* foo =
+      BuildFile(R"pb(name: 'foo.proto'
+                     package: 'foo'
+                     syntax: 'editions'
+                     edition: EDITION_2023
+                     enum_type {
+                       name: 'FooEnum'
+                       value { name: 'DEFAULT_OPTION' number: 0 }
+                     })pb");
+  const EnumDescriptor* enm = foo->enum_type(0);
+  ASSERT_NE(enm, nullptr);
+
+  const FileDescriptor* bar = BuildFile(
+      R"pb(name: 'bar.proto'
+           dependency: 'foo.proto'
+           syntax: 'proto3'
+           message_type {
+             name: 'Foo'
+             field {
+               name: 'bar'
+               number: 1
+               label: LABEL_OPTIONAL
+               type: TYPE_ENUM
+               type_name: 'foo.FooEnum'
+             }
+           })pb");
+  ASSERT_NE(bar, nullptr);
+
+  EXPECT_EQ(bar->message_type(0)->field(0)->enum_type(), enm);
+}
+
 TEST_F(ValidationErrorTest, ValidateProto3Extension) {
   // Valid for options.
   DescriptorPool pool;