Subdoc fails with missing modmap files #437
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Same error occurs in clang 17, seems to be something else. Maybe a cmake change? |
danakj
changed the title
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Yeah it's CMake 3.28 which added C++20 module support. CMake's ninja generator puts something like this into the command line for each file: And libclang doesn't seem to know what to do with it. |
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No clang docs seem to mention what the |
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it's from here: https://gitlab.kitware.com/cmake/cmake/-/merge_requests/8611/diffs Which adds the @foo.modmap to the command line, which CL docs say is a command-file which has other commands in it? https://learn.microsoft.com/en-us/cpp/build/reference/cl-command-files?view=msvc-170 But the files don't exist for me after building actual binaries either. The test expects |
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Oh this blog post discusses it: https://nibblestew.blogspot.com/2023/10/the-road-to-hell-is-paved-with-good.html
This is a file that cmake generates before running the compile command. Since clang tools are not cmake... the file does not exist and the resulting compile_commands.json is broken for any other use. Oh no. |
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Since only CMake will generate these files during compilation, we can't use them obviously. I think our only option is to strip them out of the command line. This will work until code actually uses modules at which point CMake will not provide a command line in compile_commands.json that is suitable to reproduce building the C++ file. And we may need to get off of CMake or something. |
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Posted to the cmake discussion here: https://discourse.cmake.org/t/how-to-control-the-location-of-the-c-20-binary-module-interface-bmi-output-directory/7968/13 For now, we will strip out the modmap command-file from the command-line that CMake generates specifically by looking for |
CMake 3.28 adds a modmap command file to the command line that it writes into compile_commands.json but the file does not actually exist outside of cmake compiling. This means the command line in the compile_commands.json fails with an error about the missing file: ``` error: no such file or directory: '@sus/CMakeFiles/subspace_unittests.dir/mem/addressof_unittest.cc.o.modmap' ``` To work around this we can strip out the use of the modmap command-file for now. This will break compilation later when C++ 20 modules are being used though. CMake will need to find a way to provide a command line in the compile_commands.json file which can actually be used by other tools to reproduce the compilation step. CMake discussion: https://discourse.cmake.org/t/how-to-control-the-location-of-the-c-20-binary-module-interface-bmi-output-directory/7968/13 Fixes chromium#437
CMake 3.28 adds a modmap command file to the command line that it writes into compile_commands.json but the file does not actually exist outside of cmake compiling. This means the command line in the compile_commands.json fails with an error about the missing file: ``` error: no such file or directory: '@sus/CMakeFiles/subspace_unittests.dir/mem/addressof_unittest.cc.o.modmap' ``` To work around this we can strip out the use of the modmap command-file for now. This will break compilation later when C++ 20 modules are being used though. CMake will need to find a way to provide a command line in the compile_commands.json file which can actually be used by other tools to reproduce the compilation step. CMake discussion: https://discourse.cmake.org/t/how-to-control-the-location-of-the-c-20-binary-module-interface-bmi-output-directory/7968/13 Fixes #437
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A followup blog post was made about this issue specifically: https://nibblestew.blogspot.com/2023/12/even-more-breakage-in-c-module-world.html |
A recent change in Clang 18 has made subdoc fail to execute the clang tool through libclang, generating an error for every .cc file it attempts to compile:
Subspace is not using modules so there's no modmaps expected.
llvm/llvm-project#75142 looks like it could be the reason.
First appeared on the try run here: #436
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