https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93149
Bug ID: 93149 Summary: -fno-concepts silently ignored in c++2a mode Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: nathan at gcc dot gnu.org Target Milestone: --- In testing something out, I discovered that '-std=c++2a -fno-concepts' is concept-enabled. template<typename T> requires (sizeof (T) > 1) void frob (T); nathans@devvm2772:306>./cc1plus conc.cc -quiet -std=c++2a nathans@devvm2772:307>./cc1plus conc.cc -quiet -std=c++2a -fno-concepts nathans@devvm2772:308>./cc1plus conc.cc -quiet -std=c++17 -fno-concepts conc.cc:2:10: error: expected constructor, destructor, or type conversion before '(' token 2 | requires (sizeof (T) > 1) | ^ I expected either: 1) a warning telling me -fno-concepts had no effect with -std=c++2a 2) concepts disabled, in a similar manner to -fno-rtti and -fno-exceptions