Re: Filling woes

[Richard Stallman]

    This is a very incompatible change, since adaptive-fill-function's
    return value previously carried no meaning.

Looking at the code, I think you're mistaken.  adaptive-fill-function
returns the string to use as the prefix, or nil.'

The change *is* incompatible, for a different reason.
It would cause adaptive-fill-function to be called in situations
where now it would not be called.  And adaptive-fill-function could
override matching adaptive-fill-regexp.

This can't break anything in Emacs because nothing in Emacs uses
adaptive-fill-function.  It could break some user Lisp code, though.
Pretest is when we are likely to find out about this; mostly users
would change their code.  So if we are going to make this change,
there's no harm doing it now.

However, it could be a good idea to first ask users who use
adaptive-fill-function to tell us how they use it, before deciding
whether to change anything here.

    While the current scheme appears braindead, we could make it somewhat
    saner in a compatible way by allowing adaptive-fill-regexp to be nil,
    in which case adaptive-fill-function would get called unconditionally.

That is how it works now.