[Bug c++/82619] New: C++17 std::apply treated as in global namespace under certain circumstances

[tower120 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82619

            Bug ID: 82619
           Summary: C++17 std::apply treated as in global namespace under
                    certain circumstances
           Product: gcc
           Version: 7.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tower120 at gmail dot com
  Target Milestone: ---

Created attachment 42403
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42403&action=edit
cmake project. Look at test/main.cpp

Under certain circumstances C++17's std::apply treated as if it is in global
namespace.

See attached cmake project. Specially src/reactive/oberver.h. Project is fail
to compile, with function is ambiguous error.

uncommenting /src/reactive/oberver.h line 49 makes it compilable.