[Bug c++/112737] New: [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[Bug c++/112737] New: [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[hp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

            Bug ID: 112737
           Summary: [14 Regression] g++.dg/modules/xtreme-header-2_b.C
                    -std=c++2b (test for excess errors)
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hp at gcc dot gnu.org
                CC: redi at gcc dot gnu.org
  Target Milestone: ---
            Target: cris-elf

With r14-5794-g7a6a29c455e775 "libstdc++: Define std::ranges::to for C++23
(P1206R7) [PR111055]" this test-suite regression was introduced for various
targets:

Running /x/gcc/testsuite/g++.dg/modules/modules.exp ...
[...]
FAIL: g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

According to g++.log, for cris-elf:

Excess errors:
/src/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error: conflicting
global module declaration 'template<template<class ...> class _Cont, class _Rg,
class ... _Args> using std::ranges::__detail::_DeduceExpr1 = decltype
(_Cont<...auto...>(declval<_Rg>(), (declval<_Args>)()...))'
/src/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error: conflicting
global module declaration 'template<template<class ...> class _Cont, class _Rg,
class ... _Args> using std::ranges::__detail::_DeduceExpr2 = decltype
(_Cont<...auto...>(std::from_range, declval<_Rg>(), (declval<_Args>)()...))'
/src/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error: conflicting
global module declaration 'template<template<class ...> class _Cont, class _Rg,
class ... _Args> using std::ranges::__detail::_DeduceExpr3 = decltype
(_Cont<...auto...>(declval<std::ranges::__detail::_InputIter<_Rg> >(),
declval<std::ranges::__detail::_InputIter<_Rg> >(), (declval<_Args>)()...))'
/src/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error: conflicting
global module declaration 'using std::ranges::__detail::_DeduceExpr1 = decltype
(_Cont<...auto...>(declval<_Rg>(), (declval<_Args>)()...))'
/src/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error: conflicting
global module declaration 'using std::ranges::__detail::_DeduceExpr2 = decltype
(_Cont<...auto...>(std::from_range, declval<_Rg>(), (declval<_Args>)()...))'
/src/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error: conflicting
global module declaration 'using std::ranges::__detail::_DeduceExpr3 = decltype
(_Cont<...auto...>(declval<std::ranges::__detail::_InputIter<_Rg> >(),
declval<std::ranges::__detail::_InputIter<_Rg> >(), (declval<_Args>)()...))'

This appears to happen also for "aarch64":
https://gcc.gnu.org/pipermail/gcc-regression/2023-November/078616.html
and "Linux/x86_64":
https://gcc.gnu.org/pipermail/gcc-regression/2023-November/078617.html
suggesting that most targets are affected.

(Maintainers, please adjust your scripts to include a full gnu target tuple in
your autotester messages in those places where the abbreviated quoted ones are
found, so that readers can cut-and-paste that key information for e.g.
additional targets in bug-reports, QED.  Additional steps such as following
links should not be necessary.)

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=101095
   Last reconfirmed|                            |2023-11-28

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The errors remind me of PR101095. Maybe the fix will be similar.

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[danglin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

John David Anglin <danglin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |danglin at gcc dot gnu.org
             Target|cris-elf                    |cris-elf
                   |                            |hppa-unknown-linux-gnu

--- Comment #2 from John David Anglin <danglin at gcc dot gnu.org> ---
Same errors occur on hppa-linux-gnu.

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
                 CC|                            |ppalka at gcc dot gnu.org

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Created attachment 56858
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56858&action=edit
untested fix

Changing CLASS_PLACEHOLDER_TEMPLATE of a CTAD placeholder that names a ttp to
point to the ttp's TEMPLATE_TEMPLATE_PARM node instead of its TEMPLATE_DECL
seems to fix the issue, but I'm not sure if this is what we really want...

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[danglin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

--- Comment #4 from John David Anglin <danglin at gcc dot gnu.org> ---
On hppa64-hp-hpux11.11:

Excess errors:
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error:
conflicting global module declaration 'template<template<class ...> class
_Cont, class _Rg, class ... _Args> using std::ranges::__detail::_DeduceExpr1 =
decltype (_Cont<...auto...>(declval<_Rg>(), (declval<_Args>)()...))'
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error:
conflicting global module declaration 'template<template<class ...> class
_Cont, class _Rg, class ... _Args> using std::ranges::__detail::_DeduceExpr2 =
decltype (_Cont<...auto...>(std::from_range, declval<_Rg>(),
(declval<_Args>)()...))'
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error:
conflicting global module declaration 'template<template<class ...> class
_Cont, class _Rg, class ... _Args> using std::ranges::__detail::_DeduceExpr3 =
decltype (_Cont<...auto...>(declval<std::ranges::__detail::_InputIter<_Rg> >(),
declval<std::ranges::__detail::_InputIter<_Rg> >(), (declval<_Args>)()...))'
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error:
conflicting global module declaration 'using
std::ranges::__detail::_DeduceExpr1 = decltype
(_Cont<...auto...>(declval<_Rg>(), (declval<_Args>)()...))'
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error:
conflicting global module declaration 'using
std::ranges::__detail::_DeduceExpr2 = decltype
(_Cont<...auto...>(std::from_range, declval<_Rg>(), (declval<_Args>)()...))'
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/modules/xtreme-header-2_a.H: error:
conflicting global module declaration 'using
std::ranges::__detail::_DeduceExpr3 = decltype
(_Cont<...auto...>(declval<std::ranges::__detail::_InputIter<_Rg> >(),
declval<std::ranges::__detail::_InputIter<_Rg> >(), (declval<_Args>)()...))'

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Reduced:

$ cat 112737.h
template<template<class> class _Cont>
using _DeduceExpr1 = decltype(_Cont{});

$ cat 112737_a.H
#include "112737.h"

$ cat 112737_b.C
import "112737_a.H";
#include "112737.h"

$ g++ -fmodules-ts 112737_a.H 112737_b.C
In file included from 112737_b.C:2:
112737.h:2:7: error: conflicting declaration of template
‘template<template<class> class _Cont> using _DeduceExpr1 = decltype
(_Cont<...auto...>{})’
    2 | using _DeduceExpr1 = decltype(_Cont{});
      |       ^~~~~~~~~~~~
In file included from 112737_a.H:1,
of module ./112737_a.H, imported at 112737_b.C:1:
112737.h:2:7: note: previous declaration ‘template<template<class> class _Cont>
using _DeduceExpr1 = decltype (_Cont<...auto...>{})’
    2 | using _DeduceExpr1 = decltype(_Cont{});
      |       ^~~~~~~~~~~~

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Ah, this seems to be a general declaration matching issue not specific to
modules.  Here's a non-modules testcase:

template<template<class> class TT, class T>
decltype(TT{T()}) f(); // #1

template<template<class> class TT, class T>
decltype(TT{T()}) f(); // #2, should be considered a redeclaration of #1

template<class T> struct A { A(T); };

int main() {
  f<A, int>(); // ambiguity error
}

We (wrongly?) consider the return types of the two f's to be different, because
the CTAD placeholders refer to different TEMPLATE_DECLs (of a logically
equivalent ttp) and structural_comptypes uses pointer identity here.  Perhaps
we need to relax structural_comptypes in this case.

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

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

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

--- Comment #7 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #6)
> Perhaps we need to relax structural_comptypes in this case.

I guess I can submit a patch to that effect.

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

--- Comment #8 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:3ba5be16a2be3eaedf2870ca1e25cfe826945948

commit r14-8705-g3ba5be16a2be3eaedf2870ca1e25cfe826945948
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Feb 1 13:17:48 2024 -0500

    c++: ttp TEMPLATE_DECL equivalence [PR112737]

    Here during declaration matching we undesirably consider the two TT{42}
    CTAD expressions to be non-equivalent ultimately because for CTAD
    placeholder equivalence we compare the TEMPLATE_DECLs via pointer identity,
    and here the corresponding TEMPLATE_DECLs for TT are different since
    they're from different scopes.  On the other hand, the corresponding
    TEMPLATE_TEMPLATE_PARMs are deemed equivalent according to cp_tree_equal
    (since they have the same position and template parameters).  This turns
    out to be the root cause of some of the xtreme-header modules regressions.

    So this patch relaxes ttp CTAD placeholder equivalence accordingly, by
    comparing the TEMPLATE_TEMPLATE_PARM instead of the TEMPLATE_DECL.  It
    turns out this issue also affects function template-id equivalence as
    with g<TT> in the second testcase, so it makes sense to relax TEMPLATE_DECL
    equivalence more generally in cp_tree_equal.  In passing this patch
    improves ctp_hasher::hash for CTAD placeholders, so that they don't
    all get the same hash.

            PR c++/112737

    gcc/cp/ChangeLog:

            * pt.cc (iterative_hash_template_arg) <case TEMPLATE_DECL>:
            Adjust hashing to match cp_tree_equal.
            (ctp_hasher::hash): Also hash CLASS_PLACEHOLDER_TEMPLATE.
            * tree.cc (cp_tree_equal) <case TEMPLATE_DECL>: Return true
            for ttp TEMPLATE_DECLs if their TEMPLATE_TEMPLATE_PARMs are
            equivalent.
            * typeck.cc (structural_comptypes) <case TEMPLATE_TYPE_PARM>:
            Use cp_tree_equal to compare CLASS_PLACEHOLDER_TEMPLATE.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/ttp42.C: New test.
            * g++.dg/template/ttp43.C: New test.

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

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

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

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

--- Comment #9 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed.

[Bug c++/112737] [14 Regression] g++.dg/modules/xtreme-header-2_b.C -std=c++2b (test for excess errors)

[hp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737

--- Comment #10 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
Looks like this also fixed one of the remaining FAILs logged in PR112580,
specifically
"FAIL: g++.dg/modules/xtreme-header_b.C -std=c++2b (test for excess errors)".