Re: vc-diff in non-VC buffer

[Richard Stallman <rms@gnu.org>]

    Yes.  For that particular operation, and some other non-modifying ones
    such as printing change-history logs, what users often want is a
    fallback rule for computing selected filesets that says, in effect:
    if the selected fileset is empty, look at all version-controlled 
    files beneath the current directory.  

Is that really the right condition?  I think it is not quite right.
I do not want it to search your tree when that is not wanted.

    I'm testing code that errors out if you (a) have an empty fileset, and
    (b) no files are registered immediately under default-directory.  Juanma
    thinks this will cover his use case.

What will this do in the original case:
you visit a file in your home dir and tyoe C-x v =.
In that case, do you have a nonempty fileset?
If so, it sounds like the criterion for the error
would not be met, and it would search your whole tree.