cmake + clang_tidy - disable checking in directory

Question

I have large project using CMake. I want to add clang_tidy-8 support with following code:

set(BORG_CLANG_TIDY OFF CACHE STRING "If enabled, clang-tidy will be used. If set to 'fix', fixes will be done on source")
set_property(CACHE BORG_CLANG_TIDY PROPERTY STRINGS ON OFF fix)
if(BORG_CLANG_TIDY)
    if (BORG_CLANG_TIDY STREQUAL "fix")
        set(maybe_fix -fix)
    endif()

    set(CMAKE_CXX_CLANG_TIDY clang-tidy-8 -extra-arg=-Wno-unknown-warning-option -format-style=file ${maybe_fix} )
endif()

I put proper .clang-tidy in root directory of project (proper = with desired checks). However, there are directories that I don't want clang tidy to check/fix (3rdparty and legacy code that can't be modified because it is brittle). So I tried putting empty .clang-tidy file in those directories (empty = with -checks=-*). This doesn't work because Error: no checks enabled.

I hoped to find some some fake -checks=-*,hello-world-do-nothing-check but nothing presented itself.

Is there other way to disable checks in selected subdirectories (/subtrees)? Those directories are static and may be hardcoded in CMake if needed.

Answer 1

If you want a dummy check that would do nothing there's at least one that's pretty easy to disable by its options: misc-definitions-in-headers

The HeaderFileExtensions option can be used to make the check work with only certain header file suffixes. If you set it to something non-existent line "x" then you have a hello-world-do-nothing-check alternative. Your clang-tidy file would then look something like this:

Checks: '-*,misc-definitions-in-headers'
CheckOptions:
  - { key: HeaderFileExtensions,          value: "x" }

You can also check https://stackoverflow.com/a/56319752/9874699 and try to adapt the line-filter to filter out files from certain directories.

Answer 2

Is there other way to disable checks in selected subdirectories (/subtrees)?

In CMakeList.txt files contained in those subdirectories, add the following line:

set(CMAKE_CXX_CLANG_TIDY "")

But this is not a good solution: it creates a binding between the build system and a toolchain-specific tool. CMAKE_CXX_CLANG_TIDY should only ever be set via the configuration command (or possibly via a tool-chain file).