Assertion error in protoc.exe built by VS2017: CHECK failed: file != NULL

[jtattermusch]

protoc v3.6.0 on windows (built using VS2017)

protoc.exe  --grpc_out=generate_mock_code=true:C:/Users/jtattermusch/github/grpc/cmake/build/gens --cpp_out=C:/Users/jtattermusch/github/grpc/cmake/build/gens --plugin=protoc-gen-grpc=C:/Users/jtattermusch/github/grpc/cmake/build/Debug/grpc_cpp_plugin.exe -I . -I C:/Users/jtattermusch/github/grpc/third_party/protobuf/src src/proto/grpc/health/v1/health.proto                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       protoc.exe

crashes with an assertion:
[libprotobuf FATAL C:\Users\jtattermusch\github\grpc\third_party\protobuf\src\google\protobuf\generated_message_reflection.cc:2372] CHECK failed: file != NULL

[jtattermusch]

Minimal repro:
protoc.exe --cpp_out=. src/proto/grpc/health/v1/health.proto (using health.proto from grpc's repo https://github.com/grpc/grpc/blob/master/src/proto/grpc/health/v1/health.proto)
still crashes with the same assertion error.

https://github.com/google/protobuf/blob/79700b56b99fa5c8c22ddef78e6c9557ff711379/src/google/protobuf/generated_message_reflection.cc#L2372

[sigiesec]

I think this is the same as #4773

[jtattermusch]

Interestingly, when building with VS2015, I don't see protoc crashing - I only see it for VS2017 (see grpc's build https://source.cloud.google.com/results/invocations/1322c557-38df-4b30-b5bc-a1d70f21a93d/targets/github%2Fgrpc%2Faggregate_tests/tests;passed=true)

[jtattermusch]

@sigiesec you're right, thanks! There seems to be a fix for this in progress, I'll try to expedite it and push for protobuf 3.6.1 patch release.

[xfxyjwf]

Closing as this is a duplicate of #4773