[Bug c++/113405] New: Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[Bug c++/113405] New: Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[eddiejnolan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

            Bug ID: 113405
           Summary: Can't access member type alias of concept-constrained
                    class template specialization in global module
                    fragment via alias template in different module
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eddiejnolan at gmail dot com
  Target Milestone: ---

This example shows GCC failing to resolve the member type alias "foobar" in a
concept-constrained specialization of class template "corge" when it's accessed
from module2 via an alias template in module1.

Compiler explorer link: https://godbolt.org/z/4sh6xG6P4

Minimal reproduction:

// CMakeLists.txt

cmake_minimum_required(VERSION 3.28)
project(repro CXX)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_library(module1)
target_sources(module1
  PUBLIC
    FILE_SET cxx_modules TYPE CXX_MODULES FILES
   module1.cpp
)
target_include_directories(module1 PRIVATE "include/")

add_library(module2)
target_sources(module2
  PUBLIC
    FILE_SET cxx_modules TYPE CXX_MODULES FILES
   module2.cpp
)
target_link_libraries(module2 PUBLIC module1)

// include/foo.h

template <typename>
concept foo = false;

template <typename>
concept bar = true;

template <typename>
struct corge {};

template <foo T>
struct corge<T> {};

template <bar T>
struct corge<T> {
  using foobar = int;
};

// module1.cpp

module;

#include "foo.h"

export module module1;

export template<class T>
using corge_alias = corge<T>::foobar;

// module2.cpp

export module module2;
import module1;

struct foobaz{};

using quux = corge_alias<foobaz>;

[Bug c++/113405] Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |103524

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It would be useful if you don't use cmake here since it is so simple to figure
out the full command line for building here.


Referenced Bugs:

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

[Bug c++/113405] Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[eddiejnolan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

--- Comment #2 from Eddie Nolan <eddiejnolan at gmail dot com> ---
This series of commands reproduces the issue and does not use CMake:

g++ -g -std=c++20 -E -x c++ ./module2.cpp \
    -MT ./module2.cpp.o.ddi -MD -MF ./module2.cpp.o.ddi.d \
    -fmodules-ts -fdeps-file=./module2.cpp.o.ddi -fdeps-target=./module2.cpp.o
\
    -fdeps-format=p1689r5 -o ./module2.cpp.o.ddi.i
g++ -I./include -g -std=c++20 -E -x c++ ./module1.cpp \
    -MT ./module1.cpp.o.ddi -MD -MF ./module1.cpp.o.ddi.d \
    -fmodules-ts -fdeps-file=./module1.cpp.o.ddi -fdeps-target=./module1.cpp.o
\
    -fdeps-format=p1689r5 -o ./module1.cpp.o.ddi.i
echo "module1 module1.gcm" >> ./module1.cpp.o.modmap
echo "module2 module2.gcm" >> ./module2.cpp.o.modmap
echo "module1 module1.gcm" >> ./module2.cpp.o.modmap
g++ -I./include -g -std=c++20 -MD -MT ./module1.cpp.o -MF ./module1.cpp.o.d \
    -fmodules-ts -fmodule-mapper=./module1.cpp.o.modmap -MD \
    -fdeps-format=p1689r5 -x c++ -o ./module1.cpp.o -c ./module1.cpp
g++ -g -std=c++20 -MD -MT ./module2.cpp.o -MF ./module2.cpp.o.d \
    -fmodules-ts -fmodule-mapper=./module2.cpp.o.modmap -MD \
    -fdeps-format=p1689r5 -x c++ -o ./module2.cpp.o -c ./module2.cpp

[Bug c++/113405] Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[eddiejnolan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

--- Comment #3 from Eddie Nolan <eddiejnolan at gmail dot com> ---
Fixed (first two commands were superfluous):

echo "module1 module1.gcm" >> ./module1.cpp.o.modmap
echo "module2 module2.gcm" >> ./module2.cpp.o.modmap
echo "module1 module1.gcm" >> ./module2.cpp.o.modmap
g++ -I./include -g -std=c++20 -MD -MT ./module1.cpp.o -MF ./module1.cpp.o.d \
    -fmodules-ts -fmodule-mapper=./module1.cpp.o.modmap -MD \
    -fdeps-format=p1689r5 -x c++ -o ./module1.cpp.o -c ./module1.cpp
g++ -g -std=c++20 -MD -MT ./module2.cpp.o -MF ./module2.cpp.o.d \
    -fmodules-ts -fmodule-mapper=./module2.cpp.o.modmap -MD \
    -fdeps-format=p1689r5 -x c++ -o ./module2.cpp.o -c ./module2.cpp

[Bug c++/113405] Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[nathanieloshead at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

Nathaniel Shead <nathanieloshead at gmail dot com> changed:

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

--- Comment #4 from Nathaniel Shead <nathanieloshead at gmail dot com> ---
The issue seems to be that 'depset::hash::add_specializations' only adds the
first of a set of constrained specialisations that use the same arguments. This
comes down to the fact that the 'type_specializations' hashset is only hashed
on the base template and the provided arguments: differently constrained
specialisations just aren't added.

Other parts of the dependency walker seem to handle this OK, by walking the
DECL_TEMPLATE_SPECIALIZATIONS list, but not the base 'specialization_add'
function.

I'm not entirely sure yet what the best way to approach solving this is.

[Bug c++/113405] Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

--- Comment #5 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:6ff54cc0be8dfa9d9bd5922ec65e86c9eb644711

commit r14-8408-g6ff54cc0be8dfa9d9bd5922ec65e86c9eb644711
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date:   Fri Jan 19 22:24:18 2024 +1100

    c++: Handle partial specialisations in GMF [PR113405]

    Currently, when exporting names from the GMF, or within header modules,
    for a set of constrained partial specialisations we only emit the first
    one. This is because the 'type_specialization' list only includes a
    single specialization per template+argument list; constraints are not
    considered here.

    The existing code uses a separate 'partial_specializations' list to
    track this instead, but currently it's only used for declarations in the
    module purview. This patch makes use of this list for all declarations.

            PR c++/113405

    gcc/cp/ChangeLog:

            * module.cc (set_defining_module): Track partial specialisations
            for all declarations.

    gcc/testsuite/ChangeLog:

            * g++.dg/modules/concept-9.h: New test.
            * g++.dg/modules/concept-9_a.C: New test.
            * g++.dg/modules/concept-9_b.C: New test.
            * g++.dg/modules/concept-10_a.H: New test.
            * g++.dg/modules/concept-10_b.C: New test.

    Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>

[Bug c++/113405] Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

[nshead at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
           Assignee|unassigned at gcc dot gnu.org      |nshead at gcc dot gnu.org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
Fixed for GCC 14.