Flag global namespace pollution in header files. Right now it only triggers on using declarations and directives.

The relevant style guide section is



Note: this option is deprecated, it will be removed in clang-tidy version 19. Please use the global configuration option HeaderFileExtensions.

A comma-separated list of filename extensions of header files (the filename extensions should not contain “.” prefix). Default is “h”. For header files without an extension, use an empty string (if there are no other desired extensions) or leave an empty element in the list. E.g., “h,hh,hpp,hxx,” (note the trailing comma).