.clang-tidy not automatically find by clang-tidy 20.1.2

[kenchung285]

I have a project that originally used clang-tidy 19.1.7, and we've recently upgraded to version 20.1.2. After upgrading, I've noticed a change in behavior regarding .clang-tidy file discovery.

In 19.1.7, clang-tidy was able to discover and apply our self-defined .clang-tidy files without explicitly passing the -config-file option. However, in 20.1.2, clang-tidy no longer discovers the .clang-tidy file at the project root unless we explicitly pass -config-file.

Worse, if we do pass the -config-file flag (pointing to the one in the project root), clang-tidy seems to ignore the .clang-tidy file under folder B, even when checking files located in that folder.

Here is the relevant directory structure:

project-root/
├── README.md
├── .clang-tidy           # Full rule config
├── folder A/
│   ├── some source files
│   └── ...
├── folder B/
│   └── .clang-tidy      # Contains "Checks: '-*'" to disable checks in this folder
└── folder C/
    ├── other source files
    └── ...

Expected behavior:

• Without -config-file, clang-tidy should find and respect both the project-root .clang-tidy and the one under folder B.

Actual behavior:

• Without -config-file, .clang-tidy is not found at all in 20.1.2.
• With -config-file, .clang-tidy in folder B is ignored.

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Cheng-Yeh Chung (kenchung285)

I have a project that originally used clang-tidy 19.1.7, and we've recently upgraded to version 20.1.2. After upgrading, I've noticed a change in behavior regarding `.clang-tidy` file discovery.

In 19.1.7, clang-tidy was able to discover and apply our self-defined .clang-tidy files without explicitly passing the -config-file option. However, in 20.1.2, clang-tidy no longer discovers the .clang-tidy file at the project root unless we explicitly pass -config-file.

Worse, if we do pass the -config-file flag (pointing to the one in the project root), clang-tidy seems to ignore the .clang-tidy file under folder B, even when checking files located in that folder.

Here is the relevant directory structure:

project-root/
├── README.md
├── .clang-tidy           # Full rule config
├── folder A/
│   ├── some source files
│   └── ...
├── folder B/
│   └── .clang-tidy      # Contains "Checks: '-*'" to disable checks in this folder
└── folder C/
    ├── other source files
    └── ...

Expected behavior:

• Without -config-file, clang-tidy should discover and respect both the project-root .clang-tidy and the one under folder B.

Actual behavior:

• Without -config-file, .clang-tidy is not discovered at all in 20.1.2.
• With -config-file, .clang-tidy in folder B is ignored.

[vbvictor]

Hi, this bug is possibly related to #134502 which was fixed a couple of weeks ago. Could you try trunk version of clang-tidy to confirm it? If you have debian-based os, you can get clang-tidy-21 from here https://apt.llvm.org/ in "development branch".

[kenchung285]

Hi, do you mean using llvm 20.1.3? I've tried install 20.1.3 version but the clang-tidy still fails to find my .clang-tidy under project root

[vbvictor]

I mean current development branch, which currently has clang-tidy-21. In apt.llvm.org you can find installation guides for nightly builds of clang-tidy-21.
I have a small test repository with multiple configs, and can not reproduce the bug with clang-tidy-21.
Could you make a reproducer that I can run locally? Or at least write contents of .clang-tidy config files with your run-commands so I can mimic your project structure and do your exact steps.

[carlosgalvezp]

The mentioned patch has not been ported to 20.1.3, since I believe it was fixed by my other commit.

@kenchung285 can you elaborate on what's the problem? What are you missing from the top-level file? Checks, HeaderFilter, check options, something else?

Please provide a small reproducible example.

[kenchung285]

Hi, I have sent out a pull request for a small reproducible example base on @vbvictor 's test repository.
PTAL, thanks!
cc @vbvictor @carlosgalvezp

[kenchung285]

@vbvictor I have another problem regarding the installation of nightly version.
In apt.llvm.org the installation instructions are using apt command. However, due to my team's restriction rules, we are not allowed to install packages from apt. I can only download the package and build with cmake on my machine.
Is it possible to do so for nightly version, so that I could make sure if the nightly version works for me? Or just download the main branch and build it?

[carlosgalvezp]

@kenchung285 Thanks for the repro! I notice you are using run-clang-tidy.py. Can you try running the raw clang-tidy binary instead?

Or just download the main branch and build it?

Yes, building from source is the easiest in your case.

[carlosgalvezp]

I re-created your repro in the attached tarball, then run my local build of clang-tidy 20.1.2:

/path/to/llvm-project/build/release/bin/clang-tidy -list-checks main.cpp --

And it prints the checks correctly. It also doesn't print any check if running on lib1/foo.cpp.

So I believe the clang-tidy binary is correct, the problem might be in run-clang-tidy.py.

136659.tar.gz

[kenchung285]

@carlosgalvezp I have try directly using clang-tidy -list-checks in my project and the checks are printed correctly. Thanks for your help!

But I'm still curious about why using the same run-clang-tidy.py displays different result when working with different version of clang-tidy?

[kenchung285]

@carlosgalvezp I found run-clang-tidy executes clang-tidy with -list-checks to displays the enabled checks:

llvm-project/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py

Lines 492 to 517 in 85b35a9

	invocation = get_tidy_invocation(
	"",
	clang_tidy_binary,
	args.checks,
	None,
	build_path,
	args.header_filter,
	args.allow_enabling_alpha_checkers,
	args.extra_arg,
	args.extra_arg_before,
	args.quiet,
	args.config_file,
	args.config,
	args.line_filter,
	args.use_color,
	args.plugins,
	args.warnings_as_errors,
	args.exclude_header_filter,
	args.allow_no_checks,
	)
	invocation.append("-list-checks")
	invocation.append("-")
	# Even with -quiet we still want to check if we can call clang-tidy.
	subprocess.check_call(
	invocation, stdout=subprocess.DEVNULL if args.quiet else None
	)

Therefore, I think if I can display correctly with clang-tidy -list-checks, it should work when using run-clang-tidy.py
Could you try to reproduce my case with the run-clang-tidy.py? So that we could know if I misuse the run-clang-tidy.py or it's a problem lies in run-clang-tidy.py

Besides, the run-clang-tidy.py I'm using is the one I copy directly from the latest main branch of llvm-project.

[carlosgalvezp]

Ok, I can repro as follows:

clang-tidy -p path/to/build --list-checks --

It works if I specify the file:

clang-tidy -p path/to/build --list-checks path/to/foo.cpp --