[Bug c++/100617] New: [modules] Exported namespace not visible from outside when the module imports another module that declares the same namespace

[Bug c++/100617] New: [modules] Exported namespace not visible from outside when the module imports another module that declares the same namespace

[amorvincitomnia.iw at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100617

            Bug ID: 100617
           Summary: [modules] Exported namespace not visible from outside
                    when the module imports another module that declares
                    the same namespace
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amorvincitomnia.iw at gmail dot com
  Target Milestone: ---

See it live: https://wandbox.org/permlink/1Tgk83eCk7VYm3a3


Minimum code to reproduce the error:

//test2.cc
export module test2;
export namespace A{}

//test1.cc
export module test1;
import test2;
export namespace A{
    int a = 3;
}

//prog.cc
import test1;

void g(){
    A::a;
}



Compile it with:

$ g++ "-std=c++20" "-fmodules-ts" "test2.cc" "test1.cc" "prog.cc"



Results in error:

prog.cc: In function 'void g()':
prog.cc:5:5: error: 'A' has not been declared
    5 |     A::a;
      |     ^



Reproduces in both g++ 11.1.0 and g++ 12.0.0 20210510.

[Bug c++/100617] [modules] Exported namespace not visible from outside when the module imports another module that declares the same namespace

[amorvincitomnia.iw at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100617

--- Comment #1 from wang ivor <amorvincitomnia.iw at gmail dot com> ---
A workaround is to create a module that exports only the namespace A and
'export import' it in the module 'test1'.

[Bug c++/100617] [modules] Exported namespace not visible from outside when the module imports another module that declares the same namespace

[asynts+bugs at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100617

Paul Scharnofske <asynts+bugs at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |asynts+bugs at gmail dot com

--- Comment #2 from Paul Scharnofske <asynts+bugs at gmail dot com> ---
I ran into the same issue and produced a slightly different example:

```c++
// foo.cpp
export module foo;

import bar;

namespace foo
{
    export void foo() { }
}
```
```c++
// bar.cpp
export module bar;

namespace foo
{

}
```
```c++
// baz.cpp
export module baz;

import foo;
import bar;

int main() {
    foo::foo();
}
```
```none
$ ~/.local/lib/gcc-trunk/bin/g++ --version
g++ (GCC) 12.0.1 20220211 (experimental)
Copyright (C) 2022 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.
$ ~/.local/lib/gcc-trunk/bin/g++ -Wall -Wextra -std=c++20 -fmodules-ts bar.cpp
foo.cpp baz.cpp
baz.cpp: In function 'int main()':
baz.cpp:8:5: error: 'foo' has not been declared
    8 |     foo::foo();
      |     ^~~
baz.cpp: At global scope:
baz.cpp:2:8: warning: not writing module 'baz' due to errors
    2 | export module baz;
      |        ^~~~~~
```
https://godbolt.org/z/8zMaq6eqr

-   In other words, the 'export' specifier doesn't even have to be mentioned.
    It is enough if the same namespace is mentioned even if it is completely
empty and not exported.

-   The issue disappears if the 'import bar' is removed from 'foo.cpp', in
other words, this only happens
    if that module is actually imported.  It doesn't matter that it's still
imported in 'baz.cpp'.

[Bug c++/100617] [modules] Exported namespace not visible from outside when the module imports another module that declares the same namespace

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100617

--- Comment #3 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
(In reply to wang ivor from comment #1)
> A workaround is to create a module that exports only the namespace A and
> 'export import' it in the module 'test1'.

I did that, but it's not enough. See Bug 102524.

I export a `detail` namespace like this to workaround the issue in its parent
namespace:
```C++
export module waarudo.details.workaround_gcc_bug_100617;

export namespace waarudo::detail {

void workaround_gcc_bug_100617() { }

} // namespace waarudo::detail

```

[Bug c++/100617] [modules] Exported namespace not visible from outside when the module imports another module that declares the same namespace

[nshead at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100617

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=100707
           Assignee|unassigned at gcc dot gnu.org      |nshead at gcc dot gnu.org
   Target Milestone|---                         |14.0
         Resolution|---                         |FIXED
                 CC|                            |nshead at gcc dot gnu.org
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
Fixed with r14-8407-gb433a6f5a0617d.