https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95725
Bug ID: 95725 Summary: Confusing error diagnostic in an invalid template Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: haoxintu at gmail dot com Target Milestone: --- This code test.cc, makes GCC get confused while parsing. $cat test.cc template <decltype(= ; $g++-trunk -w -c test.cc test.cc:1:20: error: expected primary-expression before ‘=’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected primary-expression before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected ‘>’ before ‘;’ token test.cc:1:22: error: expected unqualified-id before ‘;’ token $g++-10 -w -c test.cc test.cc:1:20: error: expected primary-expression before ‘=’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected primary-expression before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:21: error: expected ‘)’ before ‘;’ token 1 | template <decltype(= ; | ~ ^~ | ) test.cc:1:22: error: expected ‘>’ before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected unqualified-id before ‘;’ token $g++-9 -w -c test.cc test.cc:1:20: error: expected primary-expression before ‘=’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected primary-expression before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:21: error: expected ‘)’ before ‘;’ token 1 | template <decltype(= ; | ~ ^~ | ) test.cc:1:20: error: expected primary-expression before ‘=’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected primary-expression before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:11: error: expected identifier before ‘decltype’ 1 | template <decltype(= ; | ^~~~~~~~ test.cc:1:20: error: expected primary-expression before ‘=’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected primary-expression before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:21: error: expected ‘)’ before ‘;’ token 1 | template <decltype(= ; | ~ ^~ | ) test.cc:1:20: error: expected primary-expression before ‘=’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected primary-expression before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:20: error: expected primary-expression before ‘=’ token 1 | template <decltype(= ; | ^ test.cc:1:22: error: expected primary-expression before ‘;’ token 1 | template <decltype(= ; | ^ test.cc:1:11: error: expected ‘>’ before ‘decltype’ 1 | template <decltype(= ; | ^~~~~~~~ test.cc:1:22: error: expected unqualified-id before ‘;’ token 1 | template <decltype(= ; | ^ My GCC versions are: $g++-trunk --version g++ (GCC) 11.0.0 20200526 (experimental) Copyright (C) 2020 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. $g++-10 --version g++-10 (Ubuntu 10.1.0-2ubuntu1~18.04) 10.1.0 Copyright (C) 2020 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. $g++-9 --version g++-9 (Ubuntu 9.3.0-11ubuntu0~18.04.1) 9.3.0 Copyright (C) 2019 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. In conclusion, GCC might have two issues in parsing this code: 1. GCC-trunk misses "error: expected ‘)’ before ‘;’ token" message 2. GCC-9 emits too many duplicated error messages.