flatc generates invalid C++ code with `--grpc-callback-api`

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
cpp, grpc
Domain
tooling

Research direction

Start by running the grpctest project with flatc --grpc-callback-api and inspect the generated tests/monster_test.grpc.fb.h around the StubInterface and CallbackService declarations. Correct the declaration scope, then verify that the generated code compiles successfully and the grpctest project passes.

Written by the indexing model from the issue text.

Description

When the --grpc-callback-api option is used, flatc generates invalid C++ code that fails to compile.

The grpctest test project fails with the following error:

2>W:\Dev\flatbuffers\tests\monster_test.grpc.fb.h(361,23): error C2039: 'CallbackService': is not a member of 'MyGame::Example::MonsterStorage'
2>(compiling source file '../../Dev/flatbuffers/tests/monster_test.grpc.fb.cc')
2>    W:\Dev\flatbuffers\tests\monster_test.grpc.fb.h(33,7):
2>    see declaration of 'MyGame::Example::MonsterStorage'

After inspecting the generated monster_test.grpc.fb.h file, it appears that the declaration of CallbackService is emitted in the wrong scope.

The generated code effectively declares:

MyGame::Example::MonsterStorage::StubInterface::CallbackService

while it should be declared as:

MyGame::Example::MonsterStorage::CallbackService

I verified this behavior both on the current master branch and on commit deb3d934 (the commit that originally introduced this functionality). The problem is reproducible in both cases.

From what I can see, the fix appears to be trivial: the generated class CallbackService; line simply needs to be swapped with the following line containing the closing brace, so that CallbackService is declared in the scope of MonsterStorage rather than inside StubInterface.

Image

Expected behavior

flatc --grpc-callback-api should generate valid C++ code, and the grpctest project should compile successfully.

Actual behavior

Generated code places CallbackService in the wrong scope, causing compilation errors.

Dominant language
C++
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