[Bug c++/114229] New: [modules] duplicate symbols when including stl in submodule

[nickbegg at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114229

            Bug ID: 114229
           Summary: [modules] duplicate symbols when including stl in
                    submodule
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nickbegg at gmail dot com
  Target Milestone: ---

using the same test src code as PR113930 -

// submod.mpp

module;

#include <iostream>

export module modA:submod;

// modA.mpp

module;

export module modA;

export import :submod;

// main.cpp

#include <string>

import modA;

std::string test_func() {
    return "";
}

Note that this test code causes #113930 to check in a GCC debug build.
With a GCC release build, at link time numerous STL symbols become duplicated -

% /home/nick/inst/gcc-trunk-release/bin/g++ -freport-bug -g
CMakeFiles/moduleMin.dir/main.cpp.o CMakeFiles/moduleMin.dir/submod.mpp.o
CMakeFiles/moduleMin.dir/modA.mpp.o -o moduleMin

/usr/bin/ld: CMakeFiles/moduleMin.dir/modA.mpp.o:(.rodata+0x40): multiple
definition of `vtable for std::basic_ios<wchar_t, std::char_traits<wchar_t> >';
CMakeFiles/moduleMin.dir/main.cpp.o:(.rodata+0x950): first defined here
/usr/bin/ld: CMakeFiles/moduleMin.dir/modA.mpp.o:(.rodata+0x60): multiple
definition of `vtable for std::basic_ostream<wchar_t, std::char_traits<wchar_t>
>'; CMakeFiles/moduleMin.dir/main.cpp.o:(.rodata+0x8f0): first defined here
/usr/bin/ld: CMakeFiles/moduleMin.dir/modA.mpp.o:(.rodata+0xb0): multiple
definition of `VTT for std::basic_ostream<wchar_t, std::char_traits<wchar_t>
>'; CMakeFiles/moduleMin.dir/main.cpp.o:(.rodata+0x940): first defined here
/usr/bin/ld: CMakeFiles/moduleMin.dir/modA.mpp.o:(.rodata+0xc0): multiple
definition of `vtable for std::basic_istream<wchar_t, std::char_traits<wchar_t>
>'; CMakeFiles/moduleMin.dir/main.cpp.o:(.rodata+0x740): first defined here

[snip]

Note that #including <iostream> in both places (rather than string in main.cpp)
resolves the issue - Is the include guard mechanism failing?