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From: "boris at kolpackov dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99377] New: [modules] undefined std::string_view::empty()
 if referenced in inline exported function
Date: Thu, 04 Mar 2021 07:43:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99377

            Bug ID: 99377
           Summary: [modules] undefined std::string_view::empty() if
                    referenced in inline exported function
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: boris at kolpackov dot net
  Target Milestone: ---

cat <<EOF >hello.mxx
export module hello;

import <string_view>;

export namespace hello
{
  inline bool check (const std::string_view& n)
  {
    return !n.empty ();
  }
}
EOF

cat <<EOF >main.cxx
import hello;

int main ()
{
  return hello::check ("World") ? 0 : 1;
}
EOF

g++ -std=3Dc++2a -fmodules-ts -fmodule-header -x c++-header
.../include/c++/11.0.1/string_view
g++ -std=3Dc++2a -fmodules-ts -c -x c++ hello.mxx
g++ -std=3Dc++2a -fmodules-ts -c -x c++ main.cxx=20
g++ -std=3Dc++2a -fmodules-ts hello.o main.o=20

main.o: In function `hello::check(std::basic_string_view<char,
std::char_traits<char> > const&)':
main.cxx:(.text._ZN5hello5checkERKSt17basic_string_viewIcSt11char_traitsIcE=
E[_ZN5hello5checkERKSt17basic_string_viewIcSt11char_traitsIcEE]+0x14):
undefined reference to `std::basic_string_view<char, std::char_traits<char>
>::empty() const'

The error goes away if hello::check is made non-inline.=