public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "ed at catmur dot uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/105425] New: ambiguous template instantiation with hana::when
Date: Thu, 28 Apr 2022 15:10:49 +0000	[thread overview]
Message-ID: <bug-105425-4@http.gcc.gnu.org/bugzilla/> (raw)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105425

            Bug ID: 105425
           Summary: ambiguous template instantiation with hana::when
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ed at catmur dot uk
  Target Milestone: ---

Simplified:

template<bool> struct when;
template<int> constexpr int B = 1;
template<class, class> struct A;
template<class T, bool K> struct A<T, when<K>> {}; // fallback
template<class C> struct A<C, when<B<0> == 1>> {};
A<int, when<true>> a;

"B<0> == 1" is sufficiently complex (?) to trigger the bug (it doesn't need to
be dependent on C) but "B<0>" on its own isn't.

This affects hana since it uses the when<true> pattern heavily.

Per godbolt 11.3.0 is good, 12.0.1 20220426 is bad.

             reply	other threads:[~2022-04-28 15:10 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-28 15:10 ed at catmur dot uk [this message]
2022-04-28 15:46 ` [Bug c++/105425] " mpolacek at gcc dot gnu.org
2022-04-28 15:56 ` [Bug c++/105425] [12/13 Regression] " ppalka at gcc dot gnu.org
2022-04-28 17:11 ` cvs-commit at gcc dot gnu.org
2022-04-28 18:07 ` cvs-commit at gcc dot gnu.org
2022-04-28 18:49 ` ppalka 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-105425-4@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: link
Be 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).