bug#9432: 24.0.50; doc string of `next-error-highlight'

[Drew Adams]

> > (And FWIW I still think we should also have a value 
> > `until-move' that does the same thing - stay until some
> > other locus replaces it - but using highlighting
> > instead of fringe.  I've been using that for years myself, 
> > so I obviously prefer it - I generally don't show the fringe.)
> 
> But the value `t' already does that - it highlights the locus 
> until some other locus replaces it.

1. No, it does not.  It highlights only until the next command (which is silly,
IMHO).  Move the cursor and poof! it's gone.  Only the fringe has a reasonable
behavior (IMO).


2. FWIW2, the behavior I *actually* prefer is what I implemented for Emacs
20-21, before there was any such highlighting in Emacs: just show the
highlighting forever (or until I remove it - on-demand).  That makes it easy to
notice and compare multiple locations in the source buffer.  It makes it clear
where you've been, which hits you have already visited.

I did not bother with that after Emacs finally added highlighting, since the
highlighting used a different means etc.  Value `until-move' is good enough
(second best).  And I still use Emacs 20 much of the time (since I maintain code
that supports it), and there I enjoy the behavior I prefer.

But IMHO it should also be possible for vanilla Emacs users to keep the
highlighting until some user action (a particular key/command, not just the
*next* command).  One choice for such a key might be `C-0 C-x `' (next-error
with 0 prefix arg).


3. FWIW3: in Emacs -Q, even if I already have the target source file in a
separate frame (e.g. from `C-x 5 b' after having shown it once in the same
frame), and even if that is the *only* place it is currently displayed, `C-x `'
or hit `RET' or click a hit in *grep* still pops up the source file in the same
frame as *grep* and highlights the hit there (does not even highlight it in both
places).

The already displayed source buffer should obviously be used, instead of
multiplying things unnecessarily.  Or the behavior should be optional, under
user control, and the default should be to show hits in a window already
displaying the source buffer.