[Bug c++/107168] New: Wrong errors for concepts with default lambda not-type argument

[Bug c++/107168] New: Wrong errors for concepts with default lambda not-type argument

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107168

            Bug ID: 107168
           Summary: Wrong errors for concepts with default lambda not-type
                    argument
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

The following code in accepted in Clang and MSVC, but GCC emits seemingly wrong
errors:

template <typename, auto = []{}> concept x = true;
struct S {
    // GCC error: template argument 2 is invalid
    operator x auto() { return 42; }
    // GCC error: wrong number of template arguments (0, should be at least 1)
    operator x<> auto() const { return 43; }
};

Online demo: https://godbolt.org/z/a3494qrG3

[Bug c++/107168] [11/12/13 Regression] Wrong errors for concepts with default lambda not-type argument since r11-3714-gc1c62aec6751678e

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107168

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Wrong errors for concepts   |[11/12/13 Regression] Wrong
                   |with default lambda         |errors for concepts with
                   |not-type argument           |default lambda not-type
                   |                            |argument since
                   |                            |r11-3714-gc1c62aec6751678e
   Target Milestone|---                         |11.5
     Ever confirmed|0                           |1
                 CC|                            |marxin at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-10-06

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r11-3714-gc1c62aec6751678e.

[Bug c++/107168] [11/12/13 Regression] Wrong errors for concepts with default lambda not-type argument since r11-3714-gc1c62aec6751678e

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107168

Jason Merrill <jason at gcc dot gnu.org> changed:

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

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
The problem here is that
tsubst_lambda_expr->pushtag->maybe_process_template_type_declaration->push_template_decl
fails because processing_template_decl is set but current_template_parms is
not.

[Bug c++/107168] [11/12/13/14 Regression] Wrong errors for concepts with default lambda not-type argument since r11-3714-gc1c62aec6751678e

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107168

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
      Known to work|                            |10.3.0
      Known to fail|                            |10.4.0, 11.1.0

[Bug c++/107168] [11/12/13 Regression] Wrong errors for concepts with default lambda not-type argument since r11-3714-gc1c62aec6751678e

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107168

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |14.0
            Summary|[11/12/13/14 Regression]    |[11/12/13 Regression] Wrong
                   |Wrong errors for concepts   |errors for concepts with
                   |with default lambda         |default lambda not-type
                   |not-type argument since     |argument since
                   |r11-3714-gc1c62aec6751678e  |r11-3714-gc1c62aec6751678e

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed on the trunk for GCC 14 by the recent lambda template patches.

[Bug c++/107168] [11/12/13 Regression] Wrong errors for concepts with default lambda not-type argument since r11-3714-gc1c62aec6751678e

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107168

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED
   Target Milestone|11.5                        |14.0

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Backporting is unlikely, the patch is kind of risky and this worked earlier
only by accident.