bug#68815: Unexpected behavior with read-file-name and functional REQUIRE-MATCH argument

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

>> Also, performance can be a concern (in many cases it makes more sense
>> to make the caller pass the unquoted name rather than force it to quote
>> the name only for PRED to unquote it).
>
> The REQUIRE-MATCH function is only called once when the user attempts to
> exit the minibuffer.  Would you please explain the performance concern?

Oh, sorry, I got confused.  Indeed, you're wrapping the REQUIRE-MATCH
arg, not the PRED arg I was ranting about.  Duh!

It would be OK for `emacs-29`, indeed.  Eli?  Stefan?  Any objection?

In the mean time, could you update the docs to clarify the behavior.
E.g. currently the docstring of `read-file-name` says:

    - a function, which will be called with the input as the
      argument.  [...]

which could be understood to suggest it really receives the contents of
the minibuffer (i.e. the quoted file name) rather than the value we'd
extract from it (the unquoted file name).


        Stefan