Hierarchical .clang-tidy HeaderFilterRegex Settings Ignored in Clang-Tidy 19

[sfc-gh-mheimel]

Summary

Our project uses a hierarchical .clang-tidy files to selectively enable checks for specific folders. Previously (in Clang-Tidy 18.1.x), we could rely on HeaderFilterRegex to exclude headers in other directories from checks that were only enabled in certain subfolders. After updating to Clang-Tidy 19.1.x, the subfolder’s HeaderFilterRegex seems to be ignored, causing unwanted warnings for headers outside the subfolder.

We traced this regression to PR #91400; reverting that PR makes Clang-Tidy 19 behave like 18 again.

Steps to Reproduce

Folder Structure

.clang-tidy
test.hpp
a/
 ├─ .clang-tidy
 └─ main.cpp

File Contents

1. Root .clang-tidy:

HeaderFilterRegex: '.*'
Checks: -.*

2. Root test.hpp:

int test() {
  return (int)4.0;  // violates google-readability-casting
}

3. Subfolder a/.clang-tidy:

InheritParentConfig: true
HeaderFilterRegex: '.*a/.*'
Checks: google-readability-casting

4. Subfolder a/main.cpp:

#include "test.hpp"

int main() {
  return test();
}

Steps to reproduce

With clang-18 (Expected Behavior)

> clang-tidy-18 a/main.cpp --quiet -- -I.
1 warning generated.

With clang-19 (Regression)

> clang-tidy-19 a/main.cpp --quiet -- -I.
1 warning generated.
./test.hpp:2:10: error: C-style casts are discouraged; use static_cast [google-readability-casting,-warnings-as-errors]
   2 |   return (int)4.0;
     |          ^~~~~
     |          static_cast<int>( )

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Max Heimel (sfc-gh-mheimel)

# Summary Our project uses a hierarchical `.clang-tidy` files to selectively enable checks for specific folders. Previously (in Clang-Tidy 18.1.x), we could rely on `HeaderFilterRegex` to exclude headers in other directories from checks that were only enabled in certain subfolders. After updating to Clang-Tidy 19.1.x, the subfolder’s `HeaderFilterRegex` seems to be ignored, causing unwanted warnings for headers outside the subfolder.

We traced this regression to PR #91400; reverting that PR makes Clang-Tidy 19 behave like 18 again.

Steps to Reproduce

Folder Structure

.clang-tidy
test.hpp
a/
 ├─ .clang-tidy
 └─ main.cpp

File Contents

1. Root .clang-tidy:

HeaderFilterRegex: '.*'
Checks: -.*

2. Root test.hpp:

int test() {
  return (int)4.0;  // violates google-readability-casting
}

3. Subfolder a/.clang-tidy:

InheritParentConfig: true
HeaderFilterRegex: '.*a/.*'
Checks: google-readability-casting

4. Subfolder a/main.cpp:

#include "test.hpp"

int main() {
  return test();
}

Steps to reproduce

With clang-18 (Expected Behavior)

> clang-tidy-18 a/main.cpp --quiet -- -I.
1 warning generated.

With clang-19 (Regression)

> clang-tidy-19 a/main.cpp --quiet -- -I.
1 warning generated.
./test.hpp:2:10: error: C-style casts are discouraged; use static_cast [google-readability-casting,-warnings-as-errors]
   2 |   return (int)4.0;
     |          ^~~~~
     |          static_cast<int>( )

[Deewiant]

This looks like a duplicate of #118009.