GNU bug report logs - #53155
Use overlays in hi-lock

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Juri Linkov <juri <at> linkov.net>
To: bug-gnu-emacs <at> gnu.org
Subject: Use overlays in hi-lock
Date: Mon, 10 Jan 2022 10:17:15 +0200

[Message part 1 (text/plain, inline)]

When diff-refine overlays take precedence over hi-lock text properties,
then hi-lock can't be used to review diffs.  Hi-lock provides two modes:
font-lock highlighting and highlighting with overlays.  Using overlays
solves the problem.  But how to decide when overlays should be used?
Detecting whether the buffer is read-only, so no more text is expected
to be added to the buffer?  Then add overlays instead of using font-lock?
But this heuristics doesn't work in read-only *vc-change-log* buffers
where expanding commits inserts new text that should be highlighted
with font-lock.

Thus the following patch adds a new variable hi-lock-use-overlays
that can be used like:

#+begin_src emacs-lisp
(add-hook 'diff-mode-hook
            (lambda ()
              (setq-local hi-lock-use-overlays t)))
#+end_src

[hi-lock-use-overlays.patch (text/x-diff, inline)]

diff --git a/lisp/hi-lock.el b/lisp/hi-lock.el
index fbd698e234..99e908ad07 100644
--- a/lisp/hi-lock.el
+++ b/lisp/hi-lock.el
@@ -738,6 +738,17 @@ hi-lock-read-face-name
       (add-to-list 'hi-lock-face-defaults face t))
     (intern face)))
 
+(defvar hi-lock-use-overlays nil
+  "Whether to always use overlays instead of font-lock rules.
+When font-lock-mode is enabled and the buffer specifies font-lock rules,
+highlighting is performed by adding new font-lock rules to the existing ones,
+so when new matching strings are added, they are highlighted by font-lock.
+Otherwise, overlays are used, but new highlighting overlays are not added
+when new matching strings are inserted to the buffer.
+However, sometimes overlays are still preferable even in buffers
+where font-lock is enabled, because hi-lock overlays take precedence
+over other overlays in the same buffer, such as diff-refine overlays, etc.")
+
 (defun hi-lock-set-pattern (regexp face &optional subexp lighter case-fold spaces-regexp)
   "Highlight SUBEXP of REGEXP with face FACE.
 If omitted or nil, SUBEXP defaults to zero, i.e. the entire
@@ -759,7 +770,8 @@ hi-lock-set-pattern
         (add-to-list 'hi-lock--unused-faces (face-name face))
       (push pattern hi-lock-interactive-patterns)
       (push (cons (or lighter regexp) pattern) hi-lock-interactive-lighters)
-      (if (and font-lock-mode (font-lock-specified-p major-mode))
+      (if (and font-lock-mode (font-lock-specified-p major-mode)
+               (not hi-lock-use-overlays))
 	  (progn
 	    (font-lock-add-keywords nil (list pattern) t)
 	    (font-lock-flush))
@@ -781,6 +793,7 @@ hi-lock-set-pattern
                                            (match-end subexp))))
                 (overlay-put overlay 'hi-lock-overlay t)
                 (overlay-put overlay 'hi-lock-overlay-regexp (or lighter regexp))
+                (overlay-put overlay 'priority 1)
                 (overlay-put overlay 'face face))
               (goto-char (match-end 0)))
             (when no-matches

Message #8 received at 53155 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Juri Linkov <juri <at> linkov.net>
Cc: 53155 <at> debbugs.gnu.org
Subject: Re: bug#53155: Use overlays in hi-lock
Date: Thu, 13 Jan 2022 10:08:08 +0100

Juri Linkov <juri <at> linkov.net> writes:

> But this heuristics doesn't work in read-only *vc-change-log* buffers
> where expanding commits inserts new text that should be highlighted
> with font-lock.
>
> Thus the following patch adds a new variable hi-lock-use-overlays
> that can be used like:

I guess that makes sense...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #11 received at 53155 <at> debbugs.gnu.org (full text, mbox):

From: Juri Linkov <juri <at> linkov.net>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 53155 <at> debbugs.gnu.org
Subject: Re: bug#53155: Use overlays in hi-lock
Date: Mon, 24 Jan 2022 21:17:31 +0200

close 53155 29.0.50
stop

>> But this heuristics doesn't work in read-only *vc-change-log* buffers
>> where expanding commits inserts new text that should be highlighted
>> with font-lock.
>>
>> Thus the following patch adds a new variable hi-lock-use-overlays
>> that can be used like:
>
> I guess that makes sense...

So now pushed to master and closed.  I'm not sure if the new
variable 'hi-lock-use-overlays' needs to be mentioned in NEWS.

Message #16 received at 53155 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Juri Linkov <juri <at> linkov.net>
Cc: 53155 <at> debbugs.gnu.org
Subject: Re: bug#53155: Use overlays in hi-lock
Date: Tue, 25 Jan 2022 12:59:43 +0100

Juri Linkov <juri <at> linkov.net> writes:

> So now pushed to master and closed.  I'm not sure if the new
> variable 'hi-lock-use-overlays' needs to be mentioned in NEWS.

No, probably not.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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