Add --output option to export report to file

[insilications]

If tests are necessary, I could add them.

[kimgr]

Why is this preferable to include-what-you-use t.c > x.log 2>&1?

[insilications]

@kimgr Using IWYU with CMake, for example:

set(CMAKE_CXX_INCLUDE_WHAT_YOU_USE "/usr/bin/include-what-you-use;-Xiwyu;--verbose=1;-Xiwyu;--mapping_file=/usr/share/include-what-you-use/qt5_15.imp;-Xiwyu;--cxx17ns;>fixes.log2>&1")
cmake --build /insilications/apps/Test/Test_Clang-Debug --target all --parallel 16

Doesn't work. The output is never redirected to fixes.log.

set(CMAKE_CXX_INCLUDE_WHAT_YOU_USE "/usr/bin/include-what-you-use;-Xiwyu;--verbose=1;-Xiwyu;--mapping_file=/usr/share/include-what-you-use/qt5_15.imp;-Xiwyu;--cxx17ns;-Xiwyu;>fixes.log2>&1")

Doesn't work either.

With my solution, the intended behavior is perfect:

set(CMAKE_CXX_INCLUDE_WHAT_YOU_USE "/usr/bin/include-what-you-use;-Xiwyu;--verbose=1;-Xiwyu;--mapping_file=/usr/share/include-what-you-use/qt5_15.imp;-Xiwyu;--cxx17ns;-Xiwyu;--output=fixes.log")

[storoj]

Hi @insilications, if I understand it right CMAKE_CXX_INCLUDE_WHAT_YOU_USE command is being applied to every file in the project. If so then every IWYU run will overwrite the same file with an output for every source file. It seems that you open the output file for appending (std::ios::app), but how do you guarantee that the file will be empty before cmake starts calling IWYU? I am also wondering if appending the file from multiple IWYU processes can work reliably.

[kimgr]

@insilications I think @storoj makes some good points wrt concurrency.

The patch is nice and simple, but on plain gut feeling it seems weird to me that IWYU would need file-output if compilers in general don't, so I'd prefer not to do it this way.

As for running with cmake -- the question then becomes: why not just cmake --build . > fixes.log 2>&1?

[insilications]

Hi guys, sorry for the delay. I'm having some real life problems right now. I agree with the problems wrt concurrency, although in my current use case they haven't showed up. But they are definitely real and need to be addressed. I'll be answering you guys later.