https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103749
Bug ID: 103749 Summary: Misleading error message on template/non-template conflict Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: drepper.fsp+rhbz at gmail dot com Target Milestone: --- This problem isn't new in the trunk version, it exists in all versions I tested. This is the code in question: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ struct foo { template<typename> friend struct bar; }; struct bar { int baz; }; bar var; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This is obviously buggy, the actual definition of 'bar' is not a template class. This is exactly what clang tell me: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ $ clang++ -c u.cc u.cc:6:8: error: redefinition of 'bar' as different kind of symbol struct bar { ^ u.cc:3:17: note: previous definition is here friend struct bar; ^ u.cc:10:1: error: unknown type name 'bar' bar var; ^ 2 errors generated. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ With g++ the error messages are misleading and it also generates a lot more unnecessary text: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ $ g++ -c u.cc u.cc:6:8: error: template argument required for ‘struct bar’ 6 | struct bar { | ^~~ u.cc:10:5: error: class template argument deduction failed: 10 | bar var; | ^~~ u.cc:10:5: error: no matching function for call to ‘bar()’ u.cc:3:17: note: candidate: ‘template<class> bar()-> bar< <template-parameter-1-1> >’ 3 | friend struct bar; | ^~~ u.cc:3:17: note: template argument deduction/substitution failed: u.cc:10:5: note: couldn’t deduce template parameter ‘<template-parameter-1-1>’ 10 | bar var; | ^~~ u.cc:3:17: note: candidate: ‘template<class> bar(bar< <template-parameter-1-1> >)-> bar< <template-parameter-1-1> >’ 3 | friend struct bar; | ^~~ u.cc:3:17: note: template argument deduction/substitution failed: u.cc:10:5: note: candidate expects 1 argument, 0 provided 10 | bar var; | ^~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~