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I have a simple setup where CMake produces the following compile command:

cd /workspaces/cmake-general/tests/project/build/examples/hello-world && /usr/local/bin/cmake -E __run_co_compile 
--iwyu=/usr/local/bin/include-what-you-use 
--tidy="/usr/bin/clang-tidy;-extra-arg=-Wno-unknown-warning-option;-warnings-as-errors=*;--extra-arg-before=--driver-mode=g++" 
--source=/workspaces/cmake-general/tests/project/build/examples/hello-world/CMakeFiles/example-hello-world.dir/cmake_pch.hxx.cxx -- 
/usr/bin/c++  
-I/workspaces/cmake-general/tests/project/examples/hello-world/src 
-I/workspaces/cmake-general/tests/project/build -O3 -DNDEBUG -stdlib=libc++ 
-fcolor-diagnostics -Wall -Wextra -Wshadow -Wnon-virtual-dtor -Wold-style-cast -Wcast-align -Wunused -Woverloaded-virtual -Wpedantic -Wconversion 
-Wsign-conversion -Wnull-dereference -Wdouble-promotion 
-Wformat=2 -Werror -std=c++20 -Winvalid-pch -fpch-instantiate-templates 
-Xclang -emit-pch -Xclang -include 
-Xclang /workspaces/cmake-general/tests/project/build/examples/hello-world/CMakeFiles/example-hello-world.dir/cmake_pch.hxx 
-x c++-header -MD -MT examples/hello-world/CMakeFiles/example-hello-world.dir/cmake_pch.hxx.pch -MF 
CMakeFiles/example-hello-world.dir/cmake_pch.hxx.pch.d -o CMakeFiles/example-hello-world.dir/cmake_pch.hxx.pch 
-c /workspaces/cmake-general/tests/project/build/examples/hello-world/CMakeFiles/example-hello-world.dir/cmake_pch.hxx.cxx

which errors our with not finding

/workspaces/cmake-general/tests/project/build/examples/example-sanitizer/CMakeFiles/example-sanitizer-address.dir/cmake_pch.hxx:5:10: error: 'iostream' file not found [clang-diagnostic-error]
#include <iostream>
         ^
3 errors generated.

When I take --tidy="..." stuff out of the command. It fully compiles, (also if I dont specify PCHs in the CMakeLists.txt) it works. I am not sure what the problem is exactly.

Do PCH and clang-tidy somehow not work? Why are the include directories somehow missing? I am using LLVM-12, clang-12 on Ubuntu. Also adding -I/usr/lib/llvm-12/include/c++/v1 does not help.

Gabriel
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  • Also the compile command in `compile-commands.json` [from here](https://cmake.org/cmake/help/latest/variable/CMAKE_EXPORT_COMPILE_COMMANDS.html#variable:CMAKE_EXPORT_COMPILE_COMMANDS) work without a problem. maybe thats a cmake internal problem? – Gabriel Sep 09 '21 at 06:50

1 Answers1

2

If you're using CMake with precompiled headers, clang-tidy won't work using compile_commands.json unless you're actually compiling with clang. clang-tidy only understands clang precompiled-headers, not GCC or MSVC, and will produce an error if it encounters the latter.

There doesn't seem to be any way to work around this currently.

I recently ran into the same issue. The only satisfactory workaround I've found is to have a CMAKE preset that builds the project with clang instead of GCC, and use that for running clang-tidy on the whole project.

J Kohn
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  • Thanks for this answer, we also did this. We only configure clang tidy when using clang toolchain. – Gabriel Aug 22 '23 at 09:00