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The following patch implements the clang -Wheader-guard warning, which warns if a valid multiple inclusion header guard's #ifndef/#if !defined directive is immediately (no other non-line directives nor other (non-comment) tokens in between) followed by #define directive for some different macro, which in get_suggestion rules is close enough to the actual header guard macro (i.e. likely misspelling), the #define is object-like with empty definition (I've followed what clang implements) and the macro isn't defined later on (at least not on the final #endif at the end of a header). In this case it emits a warning, so that #ifndef STDIO_H #define STDOI_H ... #endif or similar misspellings can be caught. clang enables this warning by default, but I've put it into -Wall instead as it still seems to be a style warning, nothing more severe; if a header doesn't survive multiple inclusion because of the misspelling, users will get different diagnostics. 2024-10-02 Jakub Jelinek <jakub@redhat.com> PR preprocessor/96842 libcpp/ * include/cpplib.h (struct cpp_options): Add warn_header_guard member. (enum cpp_warning_reason): Add CPP_W_HEADER_GUARD enumerator. * internal.h (struct cpp_reader): Add mi_def_cmacro, mi_loc and mi_def_loc members. (_cpp_defined_macro_p): Constify type pointed by argument type. Formatting fix. * init.cc (cpp_create_reader): Clear CPP_OPTION (pfile, warn_header_guard). * directives.cc (struct if_stack): Add def_loc and mi_def_cmacro members. (DIRECTIVE_TABLE): Add IF_COND flag to define. (do_define): Set ifs->mi_def_cmacro on a define immediately following #ifndef directive for the guard. Clear pfile->mi_valid. Formatting fix. (do_endif): Copy over pfile->mi_def_cmacro and pfile->mi_def_loc if ifs->mi_def_cmacro is set and pfile->mi_cmacro isn't a defined macro. (push_conditional): Clear mi_def_cmacro and mi_def_loc members. * files.cc (_cpp_pop_file_buffer): Emit -Wheader-guard diagnostics. gcc/ * doc/invoke.texi (Wheader-guard): Document. gcc/c-family/ * c.opt (Wheader-guard): New option. * c.opt.urls: Regenerated. * c-ppoutput.cc (init_pp_output): Initialize also cb->get_suggestion. gcc/testsuite/ * c-c++-common/cpp/Wheader-guard-1.c: New test. * c-c++-common/cpp/Wheader-guard-1-1.h: New test. * c-c++-common/cpp/Wheader-guard-1-2.h: New test. * c-c++-common/cpp/Wheader-guard-1-3.h: New test. * c-c++-common/cpp/Wheader-guard-1-4.h: New test. * c-c++-common/cpp/Wheader-guard-1-5.h: New test. * c-c++-common/cpp/Wheader-guard-1-6.h: New test. * c-c++-common/cpp/Wheader-guard-1-7.h: New test. * c-c++-common/cpp/Wheader-guard-1-8.h: New test. * c-c++-common/cpp/Wheader-guard-1-9.h: New test. * c-c++-common/cpp/Wheader-guard-1-10.h: New test. * c-c++-common/cpp/Wheader-guard-1-11.h: New test. * c-c++-common/cpp/Wheader-guard-1-12.h: New test. * c-c++-common/cpp/Wheader-guard-2.c: New test. * c-c++-common/cpp/Wheader-guard-2.h: New test. * c-c++-common/cpp/Wheader-guard-3.c: New test. * c-c++-common/cpp/Wheader-guard-3.h: New test.
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