protobuf fails to build with Python 3.9.0b1.

...
./google/protobuf/parse_context.h:397:17: error: comparison is always false due to limited range of data type [-Werror=type-limits]
  397 |     return *ptr == tag;
      |            ~~~~~^~~~~~
./google/protobuf/parse_context.h: In instantiation of 'bool google::protobuf::internal::ExpectTag(const char*) [with unsigned int tag = 138]':
google/protobuf/map_lite_unittest.pb.cc:1635:73:   required from here
./google/protobuf/parse_context.h:397:17: error: comparison is always false due to limited range of data type [-Werror=type-limits]
./google/protobuf/parse_context.h: In instantiation of 'bool google::protobuf::internal::ExpectTag(const char*) [with unsigned int tag = 146]':
google/protobuf/map_lite_unittest.pb.cc:1647:73:   required from here
./google/protobuf/parse_context.h:397:17: error: comparison is always false due to limited range of data type [-Werror=type-limits]
./google/protobuf/parse_context.h: In instantiation of 'bool google::protobuf::internal::ExpectTag(const char*) [with unsigned int tag = 810]':
google/protobuf/map_lite_unittest.pb.cc:4197:73:   required from here
./google/protobuf/parse_context.h:397:17: error: comparison is always false due to limited range of data type [-Werror=type-limits]
./google/protobuf/parse_context.h: In instantiation of 'bool google::protobuf::internal::ExpectTag(const char*) [with unsigned int tag = 818]':
google/protobuf/map_lite_unittest.pb.cc:4210:73:   required from here
./google/protobuf/parse_context.h:397:17: error: comparison is always false due to limited range of data type [-Werror=type-limits]
  CXX      google/protobuf/no_warning_test-unittest_lite.pb.o
In file included from ./google/protobuf/map_type_handler.h:34,
                 from ./google/protobuf/map.h:49,
                 from ./google/protobuf/generated_message_table_driven.h:34,
                 from ./google/protobuf/unittest_lite.pb.h:26,
                 from google/protobuf/unittest_lite.pb.cc:4:
./google/protobuf/parse_context.h: In instantiation of 'bool google::protobuf::internal::ExpectTag(const char*) [with unsigned int tag = 248]':
google/protobuf/unittest_lite.pb.cc:2361:73:   required from here
./google/protobuf/parse_context.h:397:17: error: comparison is always false due to limited range of data type [-Werror=type-limits]
  397 |     return *ptr == tag;
      |            ~~~~~^~~~~~
...

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01396337-protobuf/

For all our attempts to build protobuf with Python 3.9, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/package/protobuf/

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Python 3.9:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/

Let us know here if you have any questions.

Python 3.9 will be included in Fedora 33. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.9.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires), so if this package is required a lot, it's important for us to get it fixed soon.
We'd appreciate help from the people who know this package best, but if you don't want to work on this now, let us know so we can try to work around it on our side.