Subject: Re: bug#32676: Feature request

From: Ernesto Alfonso <[email-masked]>
Date: Thu, 13 Sep 2018 11:18:13 -0700

> You should be able to fix this problem by setting
> hl-line-range-function to a suitable function (which should be quite
> simple, AFAIU).

Not really. I tried, setting hl-line-range-function to the next-error
buffer message line after turning on hl-line:

> (with-current-buffer next-error-last-buffer
>     (make-variable-buffer-local 'hl-line-range-function)
>     (setf hl-line-range-function
>           (lambda ()
>             (save-excursion
>               (goto-char compilation-current-error)
>               (let ((range
>                      (cons (line-beginning-position)
(line-end-position))))
>                 (message "hl-line-range-function caled. range is %s"
range)
>                 range)))))

See gif below where hl-line-function is not called after commands invoked
outside of the next-error buffer:

  highlight-line.gif
<https://drive.google.com/file/d/0ByCqoLLtc4gqSS1pZTQ2WGZWdHI5Qml6MTd1MUFSQm45WjFF/view?usp=drivesdk>

> Basically, the difference is that hl-line uses post-command-hooks to
track the current line and put an overlay
> on it, whereas in this case highlighting only changes whenever
next-error-hook is invoked.
>>
>> Is this really important?  Those are just implementation details, no?

No, this is exactly the reason why hl-line-range-function doesn't work in
the above example. These are
different concepts with different hooks involved that are invoked under
different conditions.

post-command-hook means hook is invoked after movement commands, which
should not affect err msg line
highlighting, it also means that it may not necessarily be invoked upon
next-error.

hl-line-mode hooks:
>   (if hl-line-mode
>       (progn
>         ;; In case `kill-all-local-variables' is called.
>         (add-hook 'change-major-mode-hook #'hl-line-unhighlight nil t)
>         (hl-line-highlight)
>         (setq hl-line-overlay-buffer (current-buffer))
>  (add-hook 'post-command-hook #'hl-line-highlight nil t)
>         (add-hook 'post-command-hook #'hl-line-maybe-unhighlight nil t))
>     (remove-hook 'post-command-hook #'hl-line-highlight t)
>     (hl-line-unhighlight)
>     (remove-hook 'change-major-mode-hook #'hl-line-unhighlight t)
>     (remove-hook 'post-command-hook #'hl-line-maybe-unhighlight t)))

Whereas for this enhancement, the only event that affects highlight region
is next-error.

Additionally, hl-line and error message highlight and face should be
independent:
the user may want current-line highlighting in addition to error message
highlighting.

Ernesto
On Thu, Sep 13, 2018, 9:44 AM Eli Zaretskii <[email-masked]> wrote:

> > From: Ernesto Alfonso <[email-masked]>
> > Date: Thu, 13 Sep 2018 08:02:48 -0700
> > Cc: Eli Zaretskii <[email-masked]>, [email-masked]
> >
> > The problem is that there are two independent* markers, point, and a
> marker at the beginning of the current
> > error line in the next error buffer, for example
> compilation-current-error, where the fringe arrow is displayed.
> >
> > In the same way that the user can move around the point in the
> next-error buffer between calls to
> > {next,previous}-error without affecting the location of the fringe
> arrow, the user should also be able to move
> > point around without affecting highlighting of the current error message
> (for example, to kill part of an error
> > message in the compilation buffer), since this is really a visual
> enhancement to the fringe arrow.
>
> You should be able to fix this problem by setting
> hl-line-range-function to a suitable function (which should be quite
> simple, AFAIU).
>
> > Another problem with hl-line is what the original poster pointed out in
> the screenshot below: hl-line only
> > highlights on the current buffer's window, so if the user were to switch
> to the source code buffer (or if he
> > wasn't there in the first place, e.g. by having invokied next-error form
> the source code buffer via a key
> > binding) then highlighting of error messages is either lost or never
> happens.
>
> This is only true for the global-hl-line-mode; the local mode's
> highlight is "sticky" by default, and shows even in non-selected
> windows.
>
> Moreover, you can customize the global mode so that its highlight is
> sticky as well (not that I see why would you want to in this case).
>
> > Basically, the difference is that hl-line uses post-command-hooks to
> track the current line and put an overlay
> > on it, whereas in this case highlighting only changes whenever
> next-error-hook is invoked.
>
> Is this really important?  Those are just implementation details, no?
>