Hi! I've read the paper and I believe we just implement it with no changes needed (at least since PR67224 and similar libcpp changes in GCC 10), but I could be wrong.
The following patch at least adds a testcase from the start of the paper. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? Do you agree that we can mark the paper as implemented or do you think we need to change something (what?)? 2022-11-04 Jakub Jelinek <ja...@redhat.com> * g++.dg/cpp23/charset1.C: New testcase from C++23 P2314R4. --- gcc/testsuite/g++.dg/cpp23/charset1.C.jj 2022-11-03 10:56:48.114588796 +0100 +++ gcc/testsuite/g++.dg/cpp23/charset1.C 2022-11-03 10:56:39.162711201 +0100 @@ -0,0 +1,10 @@ +// P2314R4 +// { dg-do compile { target c++23 } } +// { dg-options "-finput-charset=UTF-8 -fexec-charset=UTF-8" } + +#define S(x) # x +const char s1[] = S(Köppe); // "Köppe" +const char s2[] = S(K\u00f6ppe); // "Köppe" + +static_assert (sizeof (s1) == 7); +static_assert (sizeof (s2) == 7); Jakub