https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99427
--- Comment #3 from Alexander Lelyakin <alexander.lelyakin at googlemail dot com> --- There is a shorter sequence: /usr/local/bin/g++ -std=c++20 -fmodules-ts -x c++-system-header string_view /usr/local/bin/g++ -std=c++20 -fmodules-ts -x c++-system-header ios /usr/local/bin/g++ -std=c++20 -fmodules-ts -x c++-system-header ccomplex ---- In file included from /usr/local/include/c++/11.0.1/sstream:38, from /usr/local/include/c++/11.0.1/complex:45, from /usr/local/include/c++/11.0.1/ccomplex:39: /usr/local/include/c++/11.0.1/istream: In function ‘std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT (&)[_Num])’: /usr/local/include/c++/11.0.1/istream:840:26: error: non-constant condition for static assertion 840 | static_assert(_Num <= __gnu_cxx::__numeric_traits<streamsize>::__max); | ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /usr/local/include/c++/11.0.1/istream:840:26: error: the value of ‘__gnu_cxx::__numeric_traits_integer<long int>::__max’ is not usable in a constant expression In file included from /usr/local/include/c++/11.0.1/bits/stl_algobase.h:63, from /usr/local/include/c++/11.0.1/bits/char_traits.h:39, from /usr/local/include/c++/11.0.1/string_view:41, of module /usr/local/include/c++/11.0.1/string_view, imported at /usr/local/include/c++/11.0.1/bits/basic_string.h:48, included from /usr/local/include/c++/11.0.1/string:55, from /usr/local/include/c++/11.0.1/bits/locale_classes.h:40, from /usr/local/include/c++/11.0.1/bits/ios_base.h:41, from /usr/local/include/c++/11.0.1/ios:42, of module /usr/local/include/c++/11.0.1/ios, imported at /usr/local/include/c++/11.0.1/istream:38, included from /usr/local/include/c++/11.0.1/sstream:38, from /usr/local/include/c++/11.0.1/complex:45, from /usr/local/include/c++/11.0.1/ccomplex:39: /usr/local/include/c++/11.0.1/ext/numeric_traits.h:75:27: note: ‘__gnu_cxx::__numeric_traits_integer<long int>::__max’ was not initialized with a constant expression 75 | static const _Value __max = __is_signed | ^~~~~ /usr/local/include/c++/11.0.1/ccomplex: At global scope: /usr/local/include/c++/11.0.1/ccomplex: warning: not writing module ‘/usr/local/include/c++/11.0.1/ccomplex’ due to errors ---- g++ (GCC) 11.0.1 20210329 (experimental) Copyright (C) 2021 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.