Following last week's SG16 meeting that discussed, among other things,
plans to remove the codecvt<char16, char, mbstate_t> and other
specializations, I did some testing and was surprised to discover that
the libstdc++ implementation of that specialization did not behave as I
expected using gcc 11.4. I investigated and found I was hitting the
issue at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86419 (originally
reported in 2018) that was fixed in January for gcc 13
<https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=02dab998665dda0f6df31740e8897c42de3d740f>.

This might be an indication that these specializations do see some use
in the wild.

Dimitrij and Jonathan, are there any details you can share regarding
what lead to the discovery and resolution of this bug? The bug report
indicates the issue was exposed by new tests written by Dimitrij. I'm
curious if that testing was motivated by use in the community or just
part of a test improvement effort. Jonathan, anything you can share
about what motivated fixing the bug this year?

Tom.