[clang-tools-extra] [clang-tidy] Header check support for check_clang_tidy.py (PR #175735)

[via cfe-commits]

zeyi2 wrote:

Hi @nico, thanks for reporting!

By looking at the log, it seems that the fixes in header was not applied. But unfortunately the issue is hard to reproduce on my local setup :(

Could you try manually applying this modification in `clang-tools-extra/test/clang-tidy/checkers/modernize/concat-nested-namespaces.cpp` to see if it unblocks your bot if possible?

```diff
@@ -1,5 +1,5 @@
-// RUN: %check_clang_tidy -std=c++17 -check-suffix=NORMAL -check-header %S/Inputs/concat-nested-namespaces/modernize-concat-nested-namespaces.h %s modernize-concat-nested-namespaces %t
-// RUN: %check_clang_tidy -std=c++20 -check-suffixes=NORMAL,CPP20 -check-header %S/Inputs/concat-nested-namespaces/modernize-concat-nested-namespaces.h %s modernize-concat-nested-namespaces %t
+// RUN: %check_clang_tidy -std=c++17 -check-suffix=NORMAL -check-header %S/Inputs/concat-nested-namespaces/modernize-concat-nested-namespaces.h %s modernize-concat-nested-namespaces %t -- -header-filter=.*
+// RUN: %check_clang_tidy -std=c++20 -check-suffixes=NORMAL,CPP20 -check-header %S/Inputs/concat-nested-namespaces/modernize-concat-nested-namespaces.h %s modernize-concat-nested-namespaces %t -- -header-filter=.*
```

https://github.com/llvm/llvm-project/pull/175735