Re: something like linum.el ought to be added

[Joe Wells <jbw@macs.hw.ac.uk>]

Richard Stallman <rms@gnu.org> writes:

>     I see what you mean; the main complication is that existing overlays
>     can still be necessary in other windows that show the same buffer.
>
> That is true.
>
> 								       So
>     making all overlays available for (re-)consumption would entail
>     walking all visible windows and adjusting (new or existing) overlays
>     where necessary,
>
> Indeed, the after-change-functions hook will need to deal with
> all the windows.  That is not very hard, with buffer-window-list.
>
> If each overlay records which windows it is meant for, the
> window-scroll-functions can could delete and redo only those that
> pertain to the current window.  Each window will run the
> window-scroll-functions to recompute the overlays it needs.

And the “window” overlay property can allow the overlays for the
different windows to be completely independent of each other.  There
could be two overlays for a given line and only one would be displayed
in each window.

> (We can add a primitive to select overlays based on a certain
> property value, to make that faster.)

Like next-single-property-change except for overlays instead of text
properties?

> We could also add this as a display feature.
> It might not be very hard.

By the way, it might help if there was an easier interface to the data
returned by (format-mode-line "%l" WINDOW).  That cached information
is potentially a big speedup, but hard to access in a nice way.

-- 
Joe