[Bug c++/106141] New: Better wording for warning: ‘Child’ has a base ‘Base<(& hello)>’ whose type uses the anonymous namespace [-Wsubobject-linkage]

[jlame646 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106141

            Bug ID: 106141
           Summary: Better wording for warning: ‘Child’ has a base
                    ‘Base<(& hello)>’ whose type uses the anonymous
                    namespace [-Wsubobject-linkage]
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jlame646 at gmail dot com
  Target Milestone: ---

The following program which has undefined behavior NDR produces a warning that
can be worded in a better way:

To reproduce the warning refer to the following:
https://wandbox.org/permlink/M7O7mJS1KJpPuJ05


----base.hh----

#pragma once

#include <iostream>

template<char const *s>
class Base
{
public:
  void print()
  {
    std::cout << s << std::endl;
  }
};

----child.hh----

#pragma once

#include "base.hh"

constexpr char const hello[] = "Hello world!";

class Child : public Base<hello>
{
};


----main.cpp----

#include "child.hh"

int main(void)
{
  Child c;
  c.print();
  return 0;
}


The warning produced from the above program will be:

In file included from main.cpp:1:
child.hh:7:7: warning: ‘Child’ has a base ‘Base<(& hello)>’ whose type uses the
anonymous namespace [-Wsubobject-linkage]
    7 | class Child : public Base<hello>
      |       ^~~~~

------------------------------------------------------------

This warning should instead say:

child.hh:7:7: warning: ‘Child’ has a base ‘Base<(& hello)>’ whose type refers
to an entity with internal linkage [-Wsubobject-linkage]

-------------------------------------------------------------

Note in the above modified/suggested warning we have changed "whose type uses
the anonymous namespace"  to "whose type refers to an entity with internal
linkage"

The reproducible example can be found here:
https://wandbox.org/permlink/M7O7mJS1KJpPuJ05