Michael Heerdegen <michael_heerdegen@web.de> writes:
> Ah - ok, now finally I've understood all the parts.
>
> You want to prompt for a directory that is either empty or not yet
> existing.  But with `read-file-name' you only get either (a) non-empty
> directories accepted as input, or (b) failing completion of existing
> non-empty directories, which makes it impossible to choose a directory
> inside an existing directory.
>
> Yes, looks like a bug that this is not possible.  It should be possible
> to complete directory names that do not match.

I'm happy to work on the bug, if others agree that this change is desired.

> Then the documentation needs to be improved: what exactly is accepted
> when both MUSTMATCH and PREDICATE are specified?

I can improve the docs too, once I have the answer that questions.

> Finally, I think the docstring of `read-directory-name' needs to be
> updated: it fails to mention that MUSTMATCH can be a function (the
> argument is passed directly to `read-file-name').

How about the attached patch?

> Michael.