https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110158
--- Comment #6 from danakj at orodu dot net --- In case it is of help, here's an even smaller repro that clang reports the error in libstdc++. For whatever reason gcc does not notice the libstdc++ bug here. https://gcc.godbolt.org/z/Phndafeoe ``` #include <string> struct S { constexpr ~S() {} std::string s; }; constexpr std::string foo(const S& s) { return s.s; } static_assert(foo(S("hi")) == "hi"); // Fails. static_assert(foo(S("a longer string works")) == "a longer string works"); int main() {} ``` The error: ``` <source>:11:15: error: static assertion expression is not an integral constant expression static_assert(foo(S("hi")) == "hi"); ^~~~~~~~~~~~~~~~~~~~ /opt/compiler-explorer/gcc-12.2.0/lib/gcc/x86_64-linux-gnu/12.2.0/../../../../include/c++/12.2.0/bits/basic_string.h:356:10: note: assignment to member '_M_local_buf' of union with no active member is not allowed in a constant expression __c = _CharT(); ^ /opt/compiler-explorer/gcc-12.2.0/lib/gcc/x86_64-linux-gnu/12.2.0/../../../../include/c++/12.2.0/bits/basic_string.tcc:229:4: note: in call to '&S(("hi")).s->_M_use_local_data()' _M_use_local_data(); ^ /opt/compiler-explorer/gcc-12.2.0/lib/gcc/x86_64-linux-gnu/12.2.0/../../../../include/c++/12.2.0/bits/basic_string.h:642:2: note: in call to '&S(("hi")).s->_M_construct(&"hi"[0], &"hi"[2], {{}})' _M_construct(__s, __end, forward_iterator_tag()); ^ <source>:11:21: note: in call to 'basic_string(&"hi"[0], std::allocator<char>())' static_assert(foo(S("hi")) == "hi"); ^ 1 error generated. ```
