https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106729
Bug ID: 106729 Summary: Missing diagnostic for violation of 9.2.8.5 Product: gcc Version: 12.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: whh8b at obs dot cr Target Milestone: --- According to 9.2.8.5 of the C++ standard, the following code should produce a diagnostic: void testing() { return; } inline void testing(); int main() { return 0; } I can confirm that clang++ v 14.0.0 produces the proper diagnostic.