public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/97407] New: Expanding alias template in concept satisfaction error is undesirable Date: Tue, 13 Oct 2020 19:04:13 +0000 [thread overview] Message-ID: <bug-97407-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97407 Bug ID: 97407 Summary: Expanding alias template in concept satisfaction error is undesirable Product: gcc Version: 10.2.1 Status: UNCONFIRMED Keywords: diagnostic Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: redi at gcc dot gnu.org Target Milestone: --- Compiling this with -std=c++20: #include <ranges> template<typename T> concept False = false; template<typename R> requires False<std::ranges::iterator_t<R>> void f(R&) { } int main() { int a[2]; f(a); } Produces the expected error: alias.C: In function ‘int main()’: alias.C:13:6: error: use of function ‘void f(R&) [with R = int [2]]’ with unsatisfied constraints alias.C:7:6: note: declared here alias.C:7:6: note: constraints not satisfied alias.C: In instantiation of ‘void f(R&) [with R = int [2]]’: alias.C:13:6: required from here alias.C:3:30: required for the satisfaction of ‘False<decltype (std::__detail::__ranges_begin(declval<_Container&>()))>’ [with _Container = int[2]] alias.C:3:38: note: the expression ‘false’ evaluated to ‘false’ However the second to last line refers to std::__detail::__ranges_begin(declval<_Container&>())) This is meaningless to users, and "_Container" is not used in the definitions of ranges::iterator_t or anything it uses. The compiler seems drunk and is remembering the template argument of a different, unrelated use of the same alias template. That's probably PR 95310. I think it would be better to leave that alias unexpanded, as std::ranges::iterator_t<R>.
next reply other threads:[~2020-10-13 19:04 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-13 19:04 redi at gcc dot gnu.org [this message] 2020-10-13 19:10 ` [Bug c++/97407] " redi at gcc dot gnu.org 2020-10-13 19:16 ` redi at gcc dot gnu.org 2020-10-13 20:00 ` ppalka at gcc dot gnu.org 2021-06-10 11:45 ` redi at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-97407-4@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).