[Bug c++/97246] New: [10.1 regression] mismatched argument pack lengths

[Bug c++/97246] New: [10.1 regression] mismatched argument pack lengths

[wjwray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

            Bug ID: 97246
           Summary: [10.1 regression] mismatched argument pack lengths
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wjwray at gmail dot com
  Target Milestone: ---

A deduced <typename... T> argument pack T... v now gives a
"mismatched argument pack lengths" error for T... and v...

i.e. static_assert( sizeof...(T) == sizeof...(v) ); // Fail !!

Here's a sample, working on 9.3, rejected since 10.1
https://godbolt.org/z/oM9ve5

  template <int... Is, typename T>
  T arg_T(decltype(Is)..., T, ...);

  template <int I, int... Is>
  inline constexpr auto get =
   []<typename... T>(decltype(Is)..., T... v, ...) {
     static_assert( sizeof...(T) == sizeof...(v) );
     if constexpr ( sizeof...(T) == 1 )
       return (v,...);
     else {
       using V = decltype(arg_T<__integer_pack(I)...>(v...));
       return get<I,__integer_pack(I)...>.template operator()<V>(v...);
     }
   };

   static_assert( get<0>('\0', short{1}, 2, long{3}) == 0 );

(Will try to simplify & post a reduced sample in a later comment).

Note: the 'mismatched length' error shows when both T and v are used together
e.g. with forwarding references <typename... T> : (T&&... v) : ((T&&)v...)

[Bug c++/97246] [10/11 regression] mismatched argument pack lengths

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10.1 regression]           |[10/11 regression]
                   |mismatched argument pack    |mismatched argument pack
                   |lengths                     |lengths
           Keywords|                            |rejects-valid
      Known to fail|                            |10.1.0
      Known to work|                            |9.3.0
   Target Milestone|---                         |10.3

[Bug c++/97246] [10/11 regression] mismatched argument pack lengths since r10-7865-gaedd04caa945260e

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-09-30
     Ever confirmed|0                           |1
            Summary|[10/11 regression]          |[10/11 regression]
                   |mismatched argument pack    |mismatched argument pack
                   |lengths                     |lengths since
                   |                            |r10-7865-gaedd04caa945260e
             Status|UNCONFIRMED                 |NEW
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
      Known to fail|                            |11.0

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed, started with r10-7865-gaedd04caa945260e.

[Bug c++/97246] [10/11 regression] mismatched argument pack lengths since r10-7865-gaedd04caa945260e

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/97246] [10/11 regression] mismatched argument pack lengths since r10-7865-gaedd04caa945260e

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org

[Bug c++/97246] [10/11 regression] mismatched argument pack lengths since r10-7865-gaedd04caa945260e

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

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

https://gcc.gnu.org/g:ac001ddd0cb635dec0145bf577ac796894bda398

commit r11-7204-gac001ddd0cb635dec0145bf577ac796894bda398
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Feb 11 19:45:22 2021 -0500

    c++: variadic lambda template and empty pack [PR97246]

    In get<0>, Is is empty, so the first parameter pack of the lambda is empty,
    but after the fix for PR94546 we were wrongly associating it with the
    partial instantiation of 'v'.

    gcc/cp/ChangeLog:

            PR c++/97246
            PR c++/94546
            * pt.c (extract_fnparm_pack): Check DECL_PACK_P here.
            (register_parameter_specializations): Not here.

    gcc/testsuite/ChangeLog:

            PR c++/97246
            * g++.dg/cpp2a/lambda-generic-variadic21.C: New test.

[Bug c++/97246] [10 regression] mismatched argument pack lengths since r10-7865-gaedd04caa945260e

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:f98a3c8a58b3cb39d4073e8a5b2671a5d68b8ce4

commit r10-9393-gf98a3c8a58b3cb39d4073e8a5b2671a5d68b8ce4
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Feb 11 19:45:22 2021 -0500

    c++: variadic lambda template and empty pack [PR97246]

    In get<0>, Is is empty, so the first parameter pack of the lambda is empty,
    but after the fix for PR94546 we were wrongly associating it with the
    partial instantiation of 'v'.

    gcc/cp/ChangeLog:

            PR c++/97246
            PR c++/94546
            * pt.c (extract_fnparm_pack): Check DECL_PACK_P here.
            (register_parameter_specializations): Not here.

    gcc/testsuite/ChangeLog:

            PR c++/97246
            * g++.dg/cpp2a/lambda-generic-variadic21.C: New test.

[Bug c++/97246] [10 regression] mismatched argument pack lengths since r10-7865-gaedd04caa945260e

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.3                        |10.4

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10.3 is being released, retargeting bugs to GCC 10.4.

[Bug c++/97246] [10 regression] mismatched argument pack lengths since r10-7865-gaedd04caa945260e

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.3
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed in 10.3.