bug#36832: Supply option to suppress scrolling in compilation mode buffers.

[Alan Mackenzie <acm@muc.de>]

Hello, Eli.

On Tue, Jul 30, 2019 at 19:17:45 +0300, Eli Zaretskii wrote:
> > Date: Tue, 30 Jul 2019 15:59:37 +0000
> > Cc: 36832@debbugs.gnu.org
> > From: Alan Mackenzie <acm@muc.de>

> > > With this setting, how would the user know which error line is the
> > > "current" one, whose source is displayed above?

> > Either by remembering it (she's just hit <CR> on it, after all), or by
> > doing C-x o to move to that line, then C-x o to move back again.

> > The new option is intended for users who find being reminded of the
> > current error line less important than being able to see the error lines
> > above the current one "in context".

> > A possible modification would be to highlight the current line in the
> > compilation mode buffer, but that's beginning to feel like a lot of work
> > for a feature which might not really be wanted by anybody.

> If this feature will not be wanted by anybody, why are we discussing
> its addition?

To attempt to guess whether anybody will want it.

> I'm okay with adding the value you suggest if there will be some means
> for delineating the current error line, either automatically when the
> value t is in use or by an independent optional feature.

I suppose we could put something like ">" or "=>" in column 0 of the
pertinent line, the way that edebug does, when there's no fringe.

> > This is an option, a non-default option, one which nobody is forced to
> > use.  Having hacked it up a couple of days ago, I find it less stressful
> > to use than the setting where the buffer jumps when I hit <CR> on it.

> I understand, but I don't want us to introduce options that look like
> we didn't think them through.

OK.

The current code does two things, sometimes, on <CR> being hit: (i) it
puts an indicator into the fringe; (ii) it scrolls the compile mode
window upwards, the pertinent line moving either to the top, or to a
specified window line.

Unfortunately, the code which does these things seems to be fragmented,
and there is just one user option to control (i) and (ii) above.

One solution would be always to mark to the line in the compile mode
window, whether by an indicator in the fringe or a ">" or "=>" at column
0.  Then only scroll the compile mode window when the user has explicitly
requested this by the user option compilation-context-lines.

Why do these little things so often turn out to be so complicated?  ;-(

-- 
Alan Mackenzie (Nuremberg, Germany).