[Bug c++/103809] New: spurious reporting of structure redefinition

[florin at iucha dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103809

            Bug ID: 103809
           Summary: spurious reporting of structure redefinition
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: florin at iucha dot net
  Target Milestone: ---

Consider the following program:

/*********************************************************/
#include <concepts>

namespace priv
{
    template<typename Value>
    struct Struct {};
}

#ifdef SHOW_BUG

template<std::integral Integral>
struct priv::Struct<Integral> {};

// This way results in:
//  <source>:19:14: error: redefinition of 'struct priv::Struct<Integral>'
//       19 | struct priv::Struct<Float> {};
//          |              ^~~~~~~~~~~~~
template<std::floating_point Float>
struct priv::Struct<Float> {};

#else

namespace priv
{
    template<std::integral Integral>
    struct Struct<Integral> {};

    template<std::floating_point Float>
    struct Struct<Float> {};
}

#endif

int main() {}

/*********************************************************/

Compiling with "g++ -std=c++20 -DSHOW_BUG" results in 

<source>:19:14: error: redefinition of 'struct priv::Struct<Integral>'
   19 | struct priv::Struct<Float> {};
      |              ^~~~~~~~~~~~~
<source>:12:14: note: previous definition of 'struct priv::Struct<Integral>'
   12 | struct priv::Struct<Integral> {};
      |              ^~~~~~~~~~~~~~~~
ASM generation compiler returned: 1
<source>:19:14: error: redefinition of 'struct priv::Struct<Integral>'
   19 | struct priv::Struct<Float> {};
      |              ^~~~~~~~~~~~~
<source>:12:14: note: previous definition of 'struct priv::Struct<Integral>'
   12 | struct priv::Struct<Integral> {};
      |              ^~~~~~~~~~~~~~~~

Compiling without SHOW_BUG results in no error.

(Bug found by my colleague, Ramon Sibello).