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From: "barry.revzin at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/101883] New: class template argument deduction in non-type
 template parameter allows explicit deduction guide
Date: Thu, 12 Aug 2021 15:29:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101883

            Bug ID: 101883
           Summary: class template argument deduction in non-type template
                    parameter allows explicit deduction guide
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

Reduced example:

template <class T> struct C { constexpr C(int) {} };
explicit C(int) -> C<int>;

template <C c> struct X { };
X<1> x;

This should fail to compile, because the deduction guide is explicit and so
should not be a candidate, but gcc accepts this example.

gcc does correctly reject:

C y =3D 1;

Which is the same kind of thing.=