clang-tidy does not find include `<iostream>` with `__run_co_compile`

Code
1

I am wondering why clang-tidy does not find includes with libc++ but does with libstdc++ when configured
with CXX_CLANG_TIDY=clang-tidy:

The compile command which works with linux-clang-libstc++-debug is:

/usr/local/bin/cmake \
-E \
__run_co_compile \
--launcher=/usr/bin/ccache \
--tidy="/usr/bin/clang-tidy;-header-filter=.;-extra-arg=-Wno-unknown-warning-option;-checks=-clang-diagnostic-unused-command-line-argument;-warnings-as-errors=*;--extra-arg-before=--driver-mode=g++" \
--source=/workspaces/cmake-general/tests/project/build/linux-clang-libstdc++-debug/src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.cxx \
-- \
/usr/bin/clang++-13 \
-DCARES_STATICLIB \
-DFMT_SHARED \
-D_GLIBCXX_USE_CXX11_ABI=1 \
-I/workspaces/cmake-general/tests/project/src \
-I/workspaces/cmake-general/tests/project/build/linux-clang-libstdc++-debug/src \
-g \
-fPIE \
-stdlib=libstdc++ \
-fcolor-diagnostics \
-fdebug-default-version=5 \
-Wall \
-Wextra \
-Wshadow \
-Wnon-virtual-dtor \
-Wold-style-cast \
-Wcast-align \
-Wunused \
-Woverloaded-virtual \
-Wpedantic \
-Wconversion \
-Wsign-conversion \
-Wnull-dereference \
-Wdouble-promotion \
-Wformat=2 \
-Wsuggest-override \
-Wmisleading-indentation \
-Werror \
-fsanitize=address \
-fsanitize=undefined,bounds \
-fno-sanitize-recover=undefined,bounds \
-fno-omit-frame-pointer \
-std=c++20 \
-Winvalid-pch \
-fpch-instantiate-templates \
-Xclang \
-emit-pch \
-Xclang \
-include \
-Xclang \
/workspaces/cmake-general/tests/project/build/linux-clang-libstdc++-debug/src/cli/CMakeFiles/cli.dir/cmake_pch.hxx \
-x \
c++-header \
-MD \
-MT \
src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.pch \
-MF \
src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.pch.d \
-o \
src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.pch \
-c \
/workspaces/cmake-general/tests/project/build/linux-clang-libstdc++-debug/src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.cxx

but with linux-clang-libc++-debug

/usr/local/bin/cmake \
-E \
__run_co_compile \
--launcher=/usr/bin/ccache \
--tidy="/usr/bin/clang-tidy;-header-filter=.;-extra-arg=-Wno-unknown-warning-option;-checks=-clang-diagnostic-unused-command-line-argument;-warnings-as-errors=*;--extra-arg-before=--driver-mode=g++" \
--source=/workspaces/cmake-general/tests/project/build/linux-clang-libc++/src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.cxx \
-- \
/usr/bin/clang++-13 \
-DCARES_STATICLIB \
-DFMT_SHARED \
-D_GLIBCXX_USE_CXX11_ABI=1 \
-I/workspaces/cmake-general/tests/project/src \
-I/workspaces/cmake-general/tests/project/build/linux-clang-libc++/src \
-g \
-fPIE \
-stdlib=libc++ \
-fcolor-diagnostics \
-fdebug-default-version=5 \
-Wall \
-Wextra \
-Wshadow \
-Wnon-virtual-dtor \
-Wold-style-cast \
-Wcast-align \
-Wunused \
-Woverloaded-virtual \
-Wpedantic \
-Wconversion \
-Wsign-conversion \
-Wnull-dereference \
-Wdouble-promotion \
-Wformat=2 \
-Wsuggest-override \
-Wmisleading-indentation \
-Werror \
-fsanitize=address \
-fsanitize=undefined,bounds \
-fno-sanitize-recover=undefined,bounds \
-fno-omit-frame-pointer \
-std=c++20 \
-Winvalid-pch \
-fpch-instantiate-templates \
-Xclang \
-emit-pch \
-Xclang \
-include \
-Xclang \
/workspaces/cmake-general/tests/project/build/linux-clang-libc++/src/cli/CMakeFiles/cli.dir/cmake_pch.hxx \
-x \
c++-header \
-MD \
-MT \
src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.pch \
-MF \
src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.pch.d \
-o \
src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.pch \
-c \
/workspaces/cmake-general/tests/project/build/linux-clang-libc++/src/cli/CMakeFiles/cli.dir/cmake_pch.hxx.cxx

it does not find includes

/workspaces/cmake-general/tests/project/build/linux-clang-libc++/src/cli/CMakeFiles/cli.dir/cmake_pch.hxx:5:10:
error: 'iostream' file not found [clang-diagnostic-error]

Both compiler invocations are nearly identica except for path and -stdlib
But also by changing the failing one to libstdc++ it does not work, which is utterly strange?

I am out of luck, how can I debug further here?
It seem its either a clang-tidy bug, or __run_co_compile does something weird? System includes should be handled by clang right?
Also compile_commands.json is generated in the build dir.

Thanks for the help.

2

Also all input files are completely identical.

3

I guess cmake __run_co_compile does some sideeffects depending on the location of --source
which I do not understand

4

What if you run the command without cmake -E? Just run the command from the same directory that cmake is running it from with the same arguments. Sounds like a clang-tidy installation issue to me.

5

I think you mean without the above first part above ?

Because without this it works (?).
So I strangely guess its a __run_co_compile problem? Do you know what it does? Does it inject include directories?

6

Could the error be coming from clang-tidy?