Re: Overlay arrow in *compilation* and *grep* buffers

[Nick Roberts <nickrob@snap.net.nz>]

 > Even on text terminals users might prefer not to scroll the window.
 > Since overlay arrows are problematic on text terminals, there should
 > be an alternative method of highlighting.  I propose to add one of the
 > methods of next-error highlighting for compilation messages, i.e. a
 > persistent overlay fontified in a special face.
 > 
 > The new option compilation-current-message-highlight will support
 > three values: `arrow', t for highlighting the whole current message
 > line, and nil to turn all indications off.
 > 
 > The default value can be selected based on the following conditions:
 > 
 > 1. When left-fringe is available (tested with a condition like you proposed),
 >    use an arrow.
 > 2. Otherwise, if compilation-context-lines is nil, highlight the
 >    current line in a special face with the persistent overlay.
 > 3. If compilation-context-lines is not nil, don't highlight the current
 >    message since the current message is indicated by its location
 >    at the top of the window (by default).
 > 
 > There is a brief list of changes in the patch below:
 > 
 > 1. New defcustom compilation-current-message-highlight.
This value needs to be recomputed at compile time.

 > 2. compilation-context-lines moved up before compilation-context-lines.
                                  before compilation-current-message-highlight?

 > 3. compilation-highlight-overlay renamed to next-error-highlight-overlay,
 >    because this overlay is actually used for highlighting source lines
 >    visited by `next-error'.
 > 4. compilation-highlight-overlay is used for highlighting lines
 >    in the compilation buffer.
 > 6. The value `fringe-arrow' renamed to more general name `arrow'.

Yes, it looks good. The default behaviour matches what was agreed in an earlier
thread.

On a related note, I think that the default value for next-error-highlight
should be nil, as the cursor already points to the source line of interest.

Nick