openin_any removal for TL'26?

There is a Kpathsea configuration variable in texmf.cnf openin_any.
By default it is set to "a", allowing reading of any file. Has anyone
changed that to a different value (for anything besides testing)?

We are contemplating removing openin_any in TL'26, because setting it to
any other value often causes failure of normal runs in practice. For
example, any use of luaotfload fails.

Anyone who wants true security against reading arbitrary files would
need to run in an os-level sandbox anyway (as, e.g., Overleaf does),
instead of relying on this.

Meanwhile, there are obscure cases within the realm of openin_any that
aren't checked for now.  Rather than taking the time to refine a feature
that isn't useful, it seems more sensible to just remove it. I'd keep
all the related functions in the library to avoid unnecessary linking
errors; they'll just always return success.

This potential change has nothing to do with open*out*_any, which is the
important one, and will remain. I implemented openin_any in parallel
with openout_any (umpteen years ago) because it was more or less free to
do so, without thinking about it too hard, but as far as I've heard,
openin_any has never seen any practical use. --thanks, karl.