Make Python/C++ reject unmatched end-group tag.

This brings it into conformance with our spec and other languages.

PiperOrigin-RevId: 702914786

conformance/failure_list_python_cpp.txt

@@ -7,7 +7,3 @@
 # TODO: insert links to corresponding bugs tracking the issue.
 # Should we use GitHub issues or the Google-internal bug tracker?
 Required.*.JsonInput.Int32FieldQuotedExponentialValue.* # Failed to parse input or produce output.
-Required.*.ProtobufInput.UnmatchedEndGroup                                                                         # Should have failed to parse, but didn't.
-Required.*.ProtobufInput.UnmatchedEndGroupUnknown                                                                  # Should have failed to parse, but didn't.
-Required.*.ProtobufInput.UnmatchedEndGroupWithData                                                                 # Should have failed to parse, but didn't.
-Required.*.ProtobufInput.UnmatchedEndGroupWrongType                                                                # Should have failed to parse, but didn't.

python/google/protobuf/internal/message_test.py

@@ -69,16 +69,12 @@ def testParseErrors(self, message_module):
     msg = message_module.TestAllTypes()
     self.assertRaises(TypeError, msg.FromString, 0)
     self.assertRaises(Exception, msg.FromString, '0')
-    # TODO: Fix cpp extension to raise error instead of warning.
-    # b/27494216
     end_tag = encoder.TagBytes(1, 4)
-    if (api_implementation.Type() == 'python' or
-        api_implementation.Type() == 'upb'):
-      with self.assertRaises(message.DecodeError) as context:
-        msg.FromString(end_tag)
-      if api_implementation.Type() == 'python':
-        # Only pure-Python has an error message this specific.
-        self.assertEqual('Unexpected end-group tag.', str(context.exception))
+    with self.assertRaises(message.DecodeError) as context:
+      msg.FromString(end_tag)
+    if api_implementation.Type() != 'upb':
+      # upb raises a less specific exception.
+      self.assertRegex(str(context.exception), 'Unexpected end-group tag.*')
 
     # Field number 0 is illegal.
     self.assertRaises(message.DecodeError, msg.FromString, b'\3\4')

python/google/protobuf/pyext/message.cc

@@ -1900,10 +1900,9 @@ static PyObject* MergeFromString(CMessage* self, PyObject* arg) {
   // ctx has an explicit limit set (length of string_view), so we have to
   // check we ended at that limit.
   if (!ctx.EndedAtLimit()) {
-    // TODO: Raise error and return NULL instead.
-    // b/27494216
-    PyErr_Warn(nullptr, "Unexpected end-group tag: Not all data was converted");
-    return PyLong_FromLong(data.len - ctx.BytesUntilLimit(ptr));
+    PyErr_Format(DecodeError_class,
+                 "Unexpected end-group tag: Not all data was converted");
+    return nullptr;
   }
   return PyLong_FromLong(data.len);
 }