[Bug c++/108579] New: Requires-expression that checks constructor on non-template constructor of template class got rejected

[Bug c++/108579] New: Requires-expression that checks constructor on non-template constructor of template class got rejected

[gnaggnoyil at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108579

            Bug ID: 108579
           Summary: Requires-expression that checks constructor on
                    non-template constructor of template class got
                    rejected
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gnaggnoyil at gmail dot com
  Target Milestone: ---

template <typename T>
class foo{
public:
    foo(double, char){}
    foo(int) requires requires { foo(0.0, 'c'); }{}
};

int main(){
    foo<int> x(3);
    (void)x;
    return 0;
}

The above code fails to compile on latest GCC trunk with `-std=c++20` as of the
day of report:

test8.cpp: In instantiation of ‘foo<T>::foo(int) requires requires{foo(0.0,
'c');} [with T = int]’:
test8.cpp:9:17:   required from here
test8.cpp:5:5:   required by the constraints of ‘template<class T>
foo<T>::foo(int) requires requires{foo(0.0, 'c');}’
test8.cpp:5:23:   in requirements  [with T = int]
test8.cpp:5:23: error: satisfaction value of atomic constraint
‘requires{foo(0.0, 'c');} [with T = int]’ changed from ‘false’ to ‘true’
    5 |     foo(int) requires requires { foo(0.0, 'c'); }{}
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~
test8.cpp:2:7: note: satisfaction value first evaluated to ‘false’ from here
    2 | class foo{
      |       ^~~
test8.cpp: In function ‘int main()’:
test8.cpp:9:17: error: no matching function for call to ‘foo<int>::foo(int)’
    9 |     foo<int> x(3);
      |                 ^
test8.cpp:5:5: note: candidate: ‘foo<T>::foo(int) requires requires{foo(0.0,
'c');} [with T = int]’
    5 |     foo(int) requires requires { foo(0.0, 'c'); }{}
      |     ^~~
test8.cpp:5:5: note: constraints not satisfied
test8.cpp:4:5: note: candidate: ‘foo<T>::foo(double, char) [with T = int]’
    4 |     foo(double, char){}
      |     ^~~
test8.cpp:4:5: note:   candidate expects 2 arguments, 1 provided
test8.cpp:2:7: note: candidate: ‘constexpr foo<int>::foo(const foo<int>&)’
    2 | class foo{
      |       ^~~
test8.cpp:2:7: note:   no known conversion for argument 1 from ‘int’ to ‘const
foo<int>&’
test8.cpp:2:7: note: candidate: ‘constexpr foo<int>::foo(foo<int>&&)’
test8.cpp:2:7: note:   no known conversion for argument 1 from ‘int’ to
‘foo<int>&&’

Replacing the "requires {}" part with "is_constructible<foo, double, char>"
will get rejected too, but with different error messages.

Prior releases of GCC like 12.1 or 12.2 can accept both programs without any
problem.

[Bug c++/108579] [13 Regression] Requires-expression that checks constructor on non-template constructor of template class got rejected

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108579

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection,
                   |                            |rejects-valid
   Target Milestone|---                         |13.0
            Summary|Requires-expression that    |[13 Regression]
                   |checks constructor on       |Requires-expression that
                   |non-template constructor of |checks constructor on
                   |template class got rejected |non-template constructor of
                   |                            |template class got rejected

[Bug c++/108579] [13 Regression] Requires-expression that checks constructor on non-template constructor of template class got rejected

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108579

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
           Keywords|needs-bisection             |

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The error started with r13-2968:

c++: fix triviality of class with unsatisfied op=

cxx20_pair is trivially copyable because it has a trivial copy constructor
and only a deleted copy assignment operator; the non-triviality of the
unsatisfied copy assignment overload is not considered.

[Bug c++/108579] [13 Regression] Requires-expression that checks constructor on non-template constructor of template class got rejected

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108579

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
   Last reconfirmed|                            |2023-01-30
     Ever confirmed|0                           |1
                 CC|                            |ppalka at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED

[Bug c++/108579] [13 Regression] Requires-expression that checks constructor on non-template constructor of template class got rejected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108579

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:e7930c6750d03b28d922ebbbace20ba9d8622c6a

commit r13-5682-ge7930c6750d03b28d922ebbbace20ba9d8622c6a
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Feb 3 09:12:31 2023 -0500

    c++: excessive satisfaction in check_methods [PR108579]

    In check_methods we're unnecessarily checking satisfaction for all
    constructors and assignment operators, even those that don't look like
    copy/move special members.  In the testcase below this manifests as an
    unstable satisfaction error because the satisfaction result is first
    determined to be false during check_methods (since A<int> is incomplete
    at this point) and later true after completion of A<int>.

    This patch fixes this simply by swapping the order of the
    constraint_satisfied_p and copy/move_fn_p tests.

            PR c++/108579

    gcc/cp/ChangeLog:

            * class.cc (check_methods): Swap order of constraints_satisfied_p
            and copy/move_fn_p tests.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-pr108579.C: New test.

[Bug c++/108579] [13 Regression] Requires-expression that checks constructor on non-template constructor of template class got rejected

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108579

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13, thanks for the bug report.