[Bug c++/99678] New: c++20 trailing requires clauses allows undeclared identifier

[Bug c++/99678] New: c++20 trailing requires clauses allows undeclared identifier

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

            Bug ID: 99678
           Summary: c++20 trailing requires clauses allows undeclared
                    identifier
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

https://godbolt.org/z/reG8qE

====

void bar(auto) requires undeclared_identifier;

====

GCC accepts this code.

[Bug c++/99678] c++20 trailing requires clauses allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nshead at gcc dot gnu.org

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 114946 has been marked as a duplicate of this bug. ***

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|c++20 trailing requires     |[concepts] requires-clause
                   |clauses allows undeclared   |allows undeclared
                   |identifier                  |identifier
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
From PR114946:

(In reply to Nathaniel Shead from comment #0)
> The following sample compiles fine with 'g++ -std=c++20 -pedantic-errors':
> 
>   template <typename T>
>     requires xxxx
>   struct S {};
> 
>   template <typename T>
>     requires xxxx
>   void foo() {}
> 
> Note that 'xxxx' has not been declared or defined.  Both MSVC and Clang
> complain about the undeclared identifier.  GCC does error if we attempt to
> instantiate either of these specialisations, but they always (silently) lose
> to a better match:
> 
>   template <typename T> struct S {};
>   template <typename T> requires xxxx struct S<T> {};
> 
>   template <typename T> void foo() {}
>   template <typename T> requires xxxx void foo() {}
> 
>   int main() {
>     S<int> x;
>     foo<int>();
>   }

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eratchias at gmail dot com

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 115429 has been marked as a duplicate of this bug. ***

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

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
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-06-12

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

--- Comment #4 from GCC 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:d387ecb2b2f44f33fd6a7c5ec7eadaf6dd70efc9

commit r15-1294-gd387ecb2b2f44f33fd6a7c5ec7eadaf6dd70efc9
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jun 13 10:16:10 2024 -0400

    c++: undeclared identifier in requires-clause [PR99678]

    Since the terms of a requires-clause are grammatically primary-expressions
    and not e.g. postfix-expressions, it seems we need to explicitly handle
    and diagnose the case where a term parses to a bare unresolved identifier,
    like cp_parser_postfix_expression does, since cp_parser_primary_expression
    leaves that up to its callers.  Otherwise we incorrectly accept the first
    three requires-clauses below.

    Note that the only occurrences of primary-expression in the grammar are
    postfix-expression and constraint-logical-and-expression, so it's not too
    surprising that we need this special handling here.

            PR c++/99678

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_constraint_primary_expression): Diagnose
            a bare unresolved unqualified-id.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-requires38.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.2

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-14 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:20cda2e85c307096a3856f7f27215b8a28982fb6

commit r14-10320-g20cda2e85c307096a3856f7f27215b8a28982fb6
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jun 13 10:16:10 2024 -0400

    c++: undeclared identifier in requires-clause [PR99678]

    Since the terms of a requires-clause are grammatically primary-expressions
    and not e.g. postfix-expressions, it seems we need to explicitly handle
    and diagnose the case where a term parses to a bare unresolved identifier,
    like cp_parser_postfix_expression does, since cp_parser_primary_expression
    leaves that up to its callers.  Otherwise we incorrectly accept the first
    three requires-clauses below.

    Note that the only occurrences of primary-expression in the grammar are
    postfix-expression and constraint-logical-and-expression, so it's not too
    surprising that we need this special handling here.

            PR c++/99678

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_constraint_primary_expression): Diagnose
            a bare unresolved unqualified-id.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-requires38.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>
    (cherry picked from commit d387ecb2b2f44f33fd6a7c5ec7eadaf6dd70efc9)

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

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

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

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 14.2, thanks for the bug report.