Re: Reading directory names with read-file-name

[Richard Stallman]

    Fourth arg MUSTMATCH non-nil means require existing file's name.
     Non-nil and non-t means also require confirmation after completion.

    I've looked through the *.el files, and I've found at least the
    following non-nil and non-t values:
        lambda, confirm, must-match, yes

    It seems difficult to me to extend the MUSTMATCH argument to cover
    both a predicate and the current tri-state behaviour, and do it
    in a way which is compatible with locate-file.

I overlooked that--I must have been too sleepy.  That is too bad.

It is not necessarily fatal.  We could nominate some specific value to
mean "confirm after completion too", and fix the callers.  But that is
not as clean as I hoped it would be.

    Instead, read-file-name could specbind read-file-name-predicate
    to the predicate argument, and read-file-name-internal could check
    that predicate.

That seems reasonable.