bug#17453: Framework extending window functions for Follow Mode (etc.).

[Alan Mackenzie]

Hello, Juri.

On Sun, Dec 06, 2015 at 01:06:05AM +0200, Juri Linkov wrote:
> >> I see no problem for follow-mode to add follow-post-command-hook
> >> to both hooks.

> > Because this ties Follow Mode to implementation details of isearch.el,
> > replace.el, and ispell.el.  It is plain ugly for Follow Mode to have to
> > add-hook an obscure hook for every package that attempts lazy
> > highlighting.

> A hook is needed not only for lazy highlighting (in its current state),
> but also for every package that doesn't use the standard command loop.

Yes, I think we're in violent agreement here.

[ .... ]

> > Sorry, I made a typo there.  I really meant replace-update-post-hook.
> > Can we somehow keep this "internal use only", so that we are not
> > bound somehow to keep supporting it should the `query-replace'
> > command loop be reformulated (as believe it should, ASAP)?  The same
> > applies to ispell-update-post-hook, which I've been forced to
> > introduce into ispell.el for the same reason.

> isearch-update-post-hook, replace-update-post-hook, ispell-update-post-hook
> are not just a hack, they will stay as useful hooks even after we'll
> rewrite query-replace/ispell to use the standard command loop.  These hooks
> are for convenience, for the users to be able to set in ~/.emacs, e.g.:

>   (add-hook 'isearch-update-post-hook 'recenter)
>   (add-hook 'replace-update-post-hook 'recenter)

First comment: this sort of thing will wreck Follow Mode, scrolling text
in the current window rather than point moving forward to the next
window.

> How would you do the same without these hooks, using only post-command-hook?

By putting #'recenter into `post-command-hook'?  This should work for
Isearch, and would work for Replace and Ispell if these two used the
Emacs command loop.

> > #########################################################################

> > Anyhow, here's a status update with where I am on making isearch.el and
> > follow.el work together:

> > (i) Yesterday I rebased the scratch/follow branch on the emacs-25 branch.
> > (ii) I haven't yet replaced the GROUP parameter in the windows primitives
> >   with (e.g.) `window-group-start'.
> > (iii) isearch.el now appears to work properly.  For this, I had to swap
> >   the order of invocation of isearch-update-post-hook and i-l-h-new-loop,
> >   like you said.  I restored i-l-h-new-loop pretty much to the way it was
> >   prior to my experimentations.
> > (iv) replace.el now appears to work properly.
> > (v) ispell.el is more troublesome.  See bug #22097.  I have a problem
> >   with ispell putting its *Choices* window at the top of the left hand
> >   Follow Mode window.  Because of FM's sorting algorithm, this causes the
> >   two windows to be logically swapped, leading to confusing results.  I
> >   think the neatest solution would be to put *Choices* at the top of the
> >   rightmost window, preventing this.

I have indeed put *Choices* at the top of the RH window, to preserve
sanity.

I committed those changes, including changes to Ispell this afternoon.  I
think they're close to working fully.

> I believe bug#22097 is easy to fix for lazy highlighting, but what you
> described above is more troublesome, and might require adding support for
> window groups to ispell.el (like you're adding it to isearch.el).

I've put the window group stuff into ispell.el - there wasn't a lot to
change.

This afternoon, lack of lazy highlighting in Ispell (bug #22097) made
itself noticeable again.  I'll see what I can do, here.

-- 
Alan Mackenzie (Nuremberg, Germany).