UPSTREAM PR #26957: Propagate descriptor errors from MessageMeta

[loci-dev]

Note

Source pull request: protocolbuffers/protobuf#26957

Summary

• stop rewriting non-AttributeError failures to AttributeError in PyUpb_MessageMeta_GetAttr
• add a focused regression test covering KeyboardInterrupt, MemoryError, and SystemExit

Impact

• message class descriptors can currently hide control-flow and fatal exceptions behind a missing-attribute error
• this keeps the protobuf dynamic attribute fallback for real misses while preserving descriptor-raised exceptions

Testing

• cmake -S . -B build-cmake -G Ninja -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_CXX_STANDARD=17 -Dprotobuf_BUILD_TESTS=ON -Dprotobuf_BUILD_CONFORMANCE=OFF -Dprotobuf_BUILD_SHARED_LIBS=OFF -Dprotobuf_BUILD_EXAMPLES=OFF -Dprotobuf_WITH_ZLIB=ON
• cmake --build build-cmake --parallel 8
• ctest --test-dir build-cmake --output-on-failure -R '^(lite-test|full-test|upb-test)$'
• build-cmake/protoc --version
• in a temporary Python 3.10 venv using a repo-backed _message build sourced from this checkout:
  • python setup.py build_ext --inplace
  • python python/google/protobuf/internal/message_meta_getattr_test.py

Notes

• this addresses bug 2 from #26596

[loci-review]

No summary available at this time.

[loci-review]

No meaningful performance changes were detected across 10155 analyzed functions in the following binaries: build.protoc-stable.

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