Re: [Emacs-diffs] master 29d1c72: Introduce new value t for compilation-context-lines to eliminate scrolling

[Alan Mackenzie <acm@muc.de>]

Hello, Stefan.

On Sun, Aug 25, 2019 at 14:39:46 -0400, Stefan Monnier wrote:
> Hi Alan,

> I have a few questions abut your change.

> >     * lisp/progmodes/compile.el (compilation-context-lines): Add the new value t.
> >     (compilation-set-window): Amend to handle compilation-context-lines being t.
> >     (overlay-arrow-overlay): New variable holding an overlay with before-string
> >     property "=>".

> 1- Why `overlay-arrow-overlay` without a `compilation-` prefix?

It goes together with overlay-arrow-string, and overlay-arrow-position.

> 2- Why insert a prefix string (an "inserted arrow") instead of using
>    a "regular overwriting arrow"?

Because the overwriting arrow would obliterate the first two characters
of the file name.  I actually tried this first, and it wasn't
satisfactory.  This contrasts with another use of the overwriting arrow
in edebug, where (usually) only WS gets overwritten, and it is important
not to disturb the visible indentation.

> 3- Why link the choice of inserted-arrow vs regular-overwriting-arrow to
>    compilation-context-lines specifically?

Simplicity: mainly confusion on my part as just to where all the bits of
the new code would have to go if the "insertion" arrow were to be made a
general feature.  If the new mechanism is a success, it should be easier
then to make it more general.

> -- Stefan "maybe part of my confusion is that I'm not sufficiently
>            familiar with the behavior when there's no left-fringe"

That behaviour involves scrolling the current line to the top of the
buffer, and several years of that had exceeded my irritation threshold.
I usually run on a Linux tty, where there's no possibility of a fringe.

-- 
Alan Mackenzie (Nuremberg, Germany).