[Bug c++/114600] New: [modules] redefinition errors when using certain std headers in GMF

[Bug c++/114600] New: [modules] redefinition errors when using certain std headers in GMF

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

            Bug ID: 114600
           Summary: [modules] redefinition errors when using certain std
                    headers in GMF
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: m.cencora at gmail dot com
  Target Milestone: ---

$ cat std.cpp
module;

#include <type_traits>

export module std;

$ cat main.cpp
import std;

#include <type_traits>

int main()
{
}

$ g++ -std=c++20 -fmodules-ts -c std.cpp
$ g++ -std=c++20 -fmodules-ts main.cpp -o main

In file included from main.cpp:3:
/usr/include/c++/14/type_traits:89:36: error: template definition of
non-template ‘constexpr const _Tp std::integral_constant<_Tp, __v>::value’
   89 |       static constexpr _Tp value = __v;
      |                                    ^~~
/usr/include/c++/14/type_traits:90:29: error: template definition of
non-template ‘using std::integral_constant<_Tp, __v>::value_type = _Tp’
   90 |       using value_type = _Tp;
      |                             ^
/usr/include/c++/14/type_traits:91:47: error: template definition of
non-template ‘using std::integral_constant<_Tp, __v>::type = struct
std::integral_constant<_Tp, __v>’
   91 |       using type = integral_constant<_Tp, __v>;
      |                                               ^
/usr/include/c++/14/type_traits:92:45: error: template definition of
non-template ‘constexpr std::integral_constant<_Tp, __v>::operator value_type()
const’
   92 |       constexpr operator value_type() const noexcept { return value; }
      |                                             ^~~~~~~~
/usr/include/c++/14/type_traits:95:47: error: template definition of
non-template ‘constexpr std::integral_constant<_Tp, __v>::value_type
std::integral_constant<_Tp, __v>::operator()() const’
   95 |       constexpr value_type operator()() const noexcept { return value;
}
      |                                               ^~~~~~~~
/usr/include/c++/14/type_traits:963:26: error: redefinition of default argument
for ‘class _Up’
  963 |   template<typename _Tp, typename _Up = _Tp&&>
      |                          ^~~~~~~~
In file included from std.cpp:3,
of module std, imported at main.cpp:1:
/usr/include/c++/14/type_traits:963:26: note: original definition appeared here
  963 |   template<typename _Tp, typename _Up = _Tp&&>
      |                          ^~~~~~~~
/usr/include/c++/14/type_traits:2470:10: error: redefinition of ‘template<class
_Tp> decltype (__declval<_Tp>(0)) std::declval()’
 2470 |     auto declval() noexcept -> decltype(__declval<_Tp>(0))
      |          ^~~~~~~
/usr/include/c++/14/type_traits:2470:10: note: ‘template<class _Tp> decltype
(__declval<_Tp>(0)) std::declval@std()’ previously declared here


===
Seems like merging of GMFs does not work sometimes.
Also if I create a preprocessed file for <type_traits>
$ g++- -std=c++20 -fmodules-ts -x c++-system-header -E type_traits -o
common.hpp

and include this "common.hpp" instead of <type_traits> in both cpp files, then
compilation succeeds.

This works fine on gcc-13 (at least for <type_traits> header)

[Bug c++/114600] [modules] redefinition errors when using certain std headers in GMF

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #1 from m.cencora at gmail dot com ---
gcc version info:

g++-14 (Ubuntu 14-20240330-1ubuntu2) 14.0.1 20240330 (experimental) [master
r14-9728-g6fc84f680d0]
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nshead at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org
           Keywords|                            |rejects-valid
   Target Milestone|---                         |14.0
             Blocks|                            |103524
            Summary|[modules] redefinition      |[14 Regression] [modules]
                   |errors when using certain   |redefinition errors when
                   |std headers in GMF          |using certain std headers
                   |                            |in GMF
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-04-05
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed, started with r14-6978.

Mechanical reduction:

$ cat 114600.h
namespace std {
template <typename> struct integral_constant {
  typedef integral_constant type;
};
template <bool> using __enable_if_t = int;
template <typename> auto __and_fn() -> integral_constant<bool>;
template <typename... _Bn> struct __and_ : decltype(__and_fn<_Bn...>) {};
template <typename... _Cond>
using _Require = __enable_if_t<__and_<_Cond...>::value>;
template <typename _Tp> _Require<_Tp> swap();
namespace __swappable_details {
using std::swap;
}
} // namespace std

$ cat 114600_a.C
module;

#include "114600.h"

export module std;

$ cat 114600_b.C
import std;

#include "114600.h"

int main()
{
}

$ g++ -fmodules-ts 114600_*.C
114600.h:3:29: error: template definition of non-template 'typedef struct
std::integral_constant< <template-parameter-1-1> > std::integral_constant<
<template-parameter-1-1> >::type'


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103524
[Bug 103524] [meta-bug] modules issue

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=109679
           Keywords|                            |ice-on-valid-code

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Shorter reduction demonstrating an ICE:

$ cat 114600.h # other files same as before
namespace std {
  template<class T> struct A { int n; };
  template<class T> A<T> f();
  namespace __swappable_details { using std::f; }
}

internal compiler error: in finish_member_declaration, at cp/semantics.cc:3771

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[nshead at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

Nathaniel Shead <nshead at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=99000

--- Comment #4 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
In general we don't yet implement merging of textual redefinitions; I guess
this ultimately falls under that, but I'm not sure we have a dedicated bug
report for that yet? Maybe PR99000.

I'm not yet sure exactly why my patch caused this to start failing though; it
sounds like it's exporting some using-decls even though they aren't directly
exported, which I suppose is still a bug in its own right.

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Nathaniel Shead from comment #4)
> In general we don't yet implement merging of textual redefinitions; I guess
> this ultimately falls under that, but I'm not sure we have a dedicated bug
> report for that yet? Maybe PR99000.
Makes sense.

> I'm not yet sure exactly why my patch caused this to start failing though;
> it sounds like it's exporting some using-decls even though they aren't
> directly exported, which I suppose is still a bug in its own right.
Hmm, should the check added to add_binding_entity
  flags & (WMB_Using | WMB_Export)
instead be
  (flags & WMB_Using) && (flags & WMB_Export)
?

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[nshead at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #6 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #5)
> (In reply to Nathaniel Shead from comment #4)
> > I'm not yet sure exactly why my patch caused this to start failing though;
> > it sounds like it's exporting some using-decls even though they aren't
> > directly exported, which I suppose is still a bug in its own right.
> Hmm, should the check added to add_binding_entity
>   flags & (WMB_Using | WMB_Export)
> instead be
>   (flags & WMB_Using) && (flags & WMB_Export)
> ?

Right, of course, thanks.  This fixes this issue, but while constructing some
test cases I've found a number of other issues with exported using-decls.  I'll
submit a patch series hopefully soonish to fix the issues I can.

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #7 from m.cencora at gmail dot com ---
Created attachment 57921
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57921&action=edit
Full "std" module

FYI if you want to stress test the modules impl w.r.t. similar issues, here is
std.cpp for almost whole Standard Library.

Some code is disabled (with 'bug' comment).

This is based on semi-preprocessed and hand-adjusted 'std' module code from
libc++

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Thanks. I hope we'll end up auto-generating a file like that from
../gcc/cp/cxxapi-data.csv

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #9 from m.cencora at gmail dot com ---
(In reply to Jonathan Wakely from comment #8)
> Thanks. I hope we'll end up auto-generating a file like that from
> ../gcc/cp/cxxapi-data.csv

Hmm, then that file will have to be extended because we need information about
inline namespaces, e.g. std::literals::chrono_literals.

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

m.cencora at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #57921|0                           |1
        is obsolete|                            |

--- Comment #10 from m.cencora at gmail dot com ---
Created attachment 57924
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57924&action=edit
Full "std' modules with workarounds

Here is an improved version of "std" module, with workarounds for:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114683
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114685

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #11 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Nathaniel Shead <nshead@gcc.gnu.org>:

https://gcc.gnu.org/g:3878e9aeb30cb192f769997c52743daf8190744c

commit r14-9961-g3878e9aeb30cb192f769997c52743daf8190744c
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date:   Mon Apr 8 23:34:42 2024 +1000

    c++: Only emit exported GMF usings [PR114600]

    A typo in r14-6978 made us emit too many things. This ensures that we
    don't emit using-declarations from the GMF that we don't need to.

            PR c++/114600

    gcc/cp/ChangeLog:

            * module.cc (depset::hash::add_binding_entity): Require both
            WMB_Using and WMB_Export for GMF entities.

    gcc/testsuite/ChangeLog:

            * g++.dg/modules/using-14.C: New test.

    Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
    Co-authored-by: Patrick Palka <ppalka@redhat.com>

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

--- Comment #12 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to m.cencora from comment #10)
> Created attachment 57924 [details]
> Full "std' modules with workarounds
> 
> Here is an improved version of "std" module, with workarounds for:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114683
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114685

Interesting, thanks!

IIUC in light of these 'export using' bugs the most robust way to implement the
std module in GCC 14 is probably:

$ cat std.C
export module std;
export import <bits/stdc++.h>;

$ g++ -fmodules-ts -x c++-system-header bits/stdc++.h -x c++ std.C

This has the disadvantage of exposing implementation-detail entities and
requiring an additional step to build the <bits/stdc++.h> header module, but
should otherwise just work.

[Bug c++/114600] [14 Regression] [modules] redefinition errors when using certain std headers in GMF

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114600

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

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

--- Comment #13 from Patrick Palka <ppalka at gcc dot gnu.org> ---
IIUC the regression is fixed.