bug#43572: Feature request: make it possible to choose whether the first lines of the minibuffer should be displayed instead of the last ones

[Stefan Monnier <monnier@iro.umontreal.ca>]

> So I agree with Stefan that the text inserted into the minibuffer
> should itself indicate to the display engine that it wants to be
> displayed starting at BOB.  That way we don't have to worry about
> inadvertently affecting other users of the mini-window.

It might be difficult/inconvenient to have the info directly in the
text, tho.  Having it in a variable is not great (one of the
problems with it is that it depends on things like point so it's really
more "per-window" whereas variables are "per-buffer"), tho for the case
of minibuffers at least those buffers are normally never shown in more
than one window.

How 'bout using a window-parameter whose value should be an overlay
indicating the "area of focus", and then only obey this parameter if:
- the overlay is in the buffer that's being displayed.
- and window-point is lies within this overlay.

One more thing: there's a good argument to make that icomplete-vertical
should list the completions *above* the minibuffer's prompt rather than
below (so as not to affect the positions of the minibuffer's prompt so
much).  But in that case, the part of the overlay's after/before string
(when too long) which should be truncated (when the mini-window is too
small) is the beginning, whereas IIUC the current redisplay is unable to
display "the end" of an overlay's after/before string unless it also
shows its beginning.


        Stefan