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

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

>> 1- Why `overlay-arrow-overlay` without a `compilation-` prefix?
> It goes together with overlay-arrow-string, and overlay-arrow-position.

I can see the logic of the name, but if it's in compile.el it should
have a `compilation-` prefix, IMO.  If you intend it to be a new generic
feature, then it should not be in compile.el.

>> 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.

I see.  Indeed, I guess most other uses of overlay-arrow will typically
end up overwriting whitespace whereas in *compilation* the first two
chars will usually not be whitespace.

Maybe worth a comment in the code.

>> 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.

Fair enough.

>> -- 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.

IIUC previously, in the absence of a left-fringe the position of the
error was indicated by the cursor, right?  So your change is to offer an
option "don't scroll" (or rather, let the redisplay scroll to keep point
visible but only when needed), and you added to it the
overlay-arrow-overlay because the cursor was not visible enough?

If so another option might be to replace the scrolling-or-overlayarrow
with some kind of transient highlighting.  Can be annoying as well, tho.


        Stefan