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From: "jwjagersma at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107417] New: g++ fails to recognize parameter pack in
 requires-expression
Date: Wed, 26 Oct 2022 15:25:14 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: jwjagersma at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107417

            Bug ID: 107417
           Summary: g++ fails to recognize parameter pack in
                    requires-expression
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jwjagersma at gmail dot com
  Target Milestone: ---

Given the following code:

  $ cat fold.cpp
  template<typename... T>
  requires (requires (T x) { x; } and ...)
  auto func(T...) { }

g++ seems to forget that T is a parameter pack:

  $ g++ -std=3Dc++20 fold.cpp
  fold.cpp:2:11: error: operand of fold expression has no unexpanded parame=
ter
packs
      2 | requires (requires (T x) { x; } and ...)
        |           ^~~~~~~~~~~~~~~~~~~~~

This issue is present on both 12.2 and latest 13.0.  Clang and msvc do acce=
pt
it.=