[Bug c++/104221] New: member functions defined in separate files of classes declared in module partitions won't compile

[Bug c++/104221] New: member functions defined in separate files of classes declared in module partitions won't compile

[f.b.brokken at rug dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104221

            Bug ID: 104221
           Summary: member functions defined in separate files of classes
                    declared in module partitions won't compile
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: f.b.brokken at rug dot nl
  Target Milestone: ---

The following source file (full.cc) compiles OK:

-----------------------------
export module mod:partition;
export class Data
{
    int d_value = 10;
    public:
        int value() const;
};
int Data::value() const 
{
    return d_value;
}
void fun();
-----------------------------

The function fun() can be implemented in a separate file, and also compiles OK
(fun.cc):

-------------------------
module;
#include <iostream>
module mod:partition;
using namespace std;
void fun()
{
    cout << "hi\n";    
}
-------------------------

When implementing int Data::value() const in a separate file a compilation
error results. 

Here's the modified module interface file (partition.cc):

-----------------------------
export module mod:partition;
export class Data
{
    int d_value = 10;
    public:
        int value() const;
};
void fun();               
-----------------------------

and the source defining int Data::value() (value.cc):

------------------------
module mod:partition;
int Data::value() const
{
    return d_value;
}
------------------------

The function void fun() compiles OK.

When compiling 
   g++ --std=c++20 -Wall -Wextra -fno-strict-aliasing -fwrapv -c -fmodules-ts \
       partition.cc fun.cc value.cc

using g++-12 on an updated Debian linux system
(g++ (Debian 12-20211217-1) 12.0.0 20211217 (experimental) [master
r12-6027-g774269aa4b9] the compiler reports:

--------------------------------------------------------------------------
value.cc:3:5: error: ‘Data’ has not been declared
    3 | int Data::value() const
      |     ^~~~
value.cc:3:19: error: non-member function ‘int value()’ cannot have
cv-qualifier
    3 | int Data::value() const
      |                   ^~~~~
value.cc: In function ‘int value()’:
value.cc:5:12: error: ‘d_value’ was not declared in this scope; did you mean
‘value’?
    5 |     return d_value;
      |            ^~~~~~~
      |            value
value.cc: At global scope:
value.cc:1:1: warning: not writing module ‘mod:partition’ due to errors
    1 | module mod:partition;
      | ^~~~~~
--------------------------------------------------------------------------

If any additional information is required, please let me know.

Kind regards,

Frank.

[Bug c++/104221] member functions defined in separate files of classes declared in module partitions won't compile

[nathanieloshead at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104221

Nathaniel Shead <nathanieloshead at gmail dot com> changed:

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

--- Comment #1 from Nathaniel Shead <nathanieloshead at gmail dot com> ---
I think this is IFNDR; you cannot have more than one partition with the same
name. See https://eel.is/c++draft/module.unit#3:

> A module partition is a module unit whose module-declaration contains
> a module-partition. A named module shall not contain multiple module
> partitions with the same module-partition. All module partitions of a
> module that are module interface units shall be directly or indirectly
> exported by the primary module interface unit ([module.import]).
> No diagnostic is required for a violation of these rules.

And in particular, unlike a module implementation unit, a module partition does
not implicitly import anything; see https://eel.is/c++draft/module.unit#8 which
says:

> A module-declaration that contains neither an export-keyword nor a
> module-partition implicitly imports the primary module interface unit
> of the module as if by a module-import-declaration.

So this is working as specified. I don't think there'd be any good way of
improving the diagnostics for this either.