add_custom_command adds nonsense "driveletter:" to step

CMake Version: 3.17.1

Using the WORKING_DIRECTORY option in add_custom_command completely breaks the generated build step. For an unknown reason, CMake generates an extra line which is usually just “driveletter:” (C:, D:, E:, …).

This is the command that causes that:

	ARGS ${_el}
	WORKING_DIRECTORY ${target_binary_dir}

Which generates:

cd C:\Tools
if %errorlevel% neq 0 goto :cmEnd
C: // <-- This is the problem, where does it even come from?
if %errorlevel% neq 0 goto :cmEnd
"C:\Program Files\LLVM\bin\clang-tidy.exe" D:\Projects\Xaymar\obs-studio\build\64\UI\frontend-plugins\streamfx\source\module.cpp
if %errorlevel% neq 0 goto :cmEnd
endlocal & call :cmErrorLevel %errorlevel% & goto :cmDone
exit /b %1
  • target_binary_dir only contains “C:\Tools”, no other entries.
  • CLANG_TIDY_BIN is the path to clang-tidy.exe
  • _target is the current target name.
  • _el is the target source file

Anyone have any idea why this happens, and how to actually solve it?

I guess add_custom_command expects so called “cmake-style paths”. You can use file(TO_CMAKE_PATH) to convert a native Windows path into a cmake-style path (see for more details).

It is also advised to always double-quote paths, since some function might interpret a single path containing spaces as several space-separated arguments.

I hope this helps!

Neither cmake-style paths or native paths work unfortunately, it was one of the first things I tried. Even manually giving it “…/Tools” (autoformatting turns it into …, but its two .) still added a nonsense C: to it. :confused:

cd C:\Tools changes the working directory of the C: drive to C:\Tools. But if the current drive is X: then an addition C: has to be done to switch the drive.

Is it really adding C: //? Because that would be a problem.
Otherwise why would having C: be a problem at all?

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See actual generated commands in the OP. It adds a 2nd command with just C: and nothing else.

As @fdk17 mentioned, having C: in a batch script is totally valid and necessary in case the current working directory is on another drive.

I made a similar example, though manually in cmd.exe, and from C: to D:


I hope this helps!

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Hi McMartin, you can achieve the same with “cd /D”. The second D: there actually returns a failure, so the script aborts at that moment. Which is my current problem.

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Did some additional testing now. The commands start working when the drive is not a network mounted drive, or an NTFS mounted directory. I suppose that is an acceptable limitation, though ‘cd /D’ doesn’t seem have this limitation. Will just move the project and necessary files to local directories instead.

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cd /D doesn’t work for me…


/D is an option that must be passed to the directory-changing cd command, and means “also change the drive if applicable.” So the correct syntax would be

C:\Users\Alain>cd /D D:\dev