bug#6830: widget-complete bad completions in :type 'file

[Stefan Monnier]

>> so using either would be fine.
> ??? I don't understand this part.  It maybe OK in this particular
> case, because all you care about is the range of buffer positions
> covered by the overlay.

That's normally the case.  If an application actually cares about which
value of `field' shows up, it'll have to do more work.

>> Now, until here, there's still no bug because indeed it doesn't matter
>> which overlay we use to determine the field.
> See above.  I'm not sure this is correct in general.  And what if one
> of the overlays covers more buffer positions than the other?  Wouldn't
> it sometimes confuse the completion code?

The normal priority rules say that a smaller overlay normally takes
priority, but yes, if there's a small field already defined within the
completion region, then the completion code can become confused.
I don't know how likely this is.

>> Does the patch below fix the problem?
> It does, but on Windows both `before_field' and `field' now have the
> value of the widget, not of `completion'.
> More generally, the overlay returned by get-char-property-and-overlay
> in this situation is still arbitrary after your change, and the Lisp
> application still has no control on which one will be returned.

It has the same control as before: the use of the `priority' property.


        Stefan