Package: emacs;
Reported by: Kévin Le Gouguec <kevin.legouguec <at> gmail.com>
Date: Sun, 28 Apr 2019 17:12:02 UTC
Severity: normal
Tags: fixed, patch
Fixed in version 27.1
Done: Noam Postavsky <npostavs <at> gmail.com>
Bug is archived. No further changes may be made.
View this message in rfc822 format
From: Kévin Le Gouguec <kevin.legouguec <at> gmail.com>
To: 35476 <at> debbugs.gnu.org
Cc: Stefan Monnier <monnier <at> IRO.UMontreal.CA>, Nicolas Goaziou <mail <at> nicolasgoaziou.fr>
Subject: bug#35476: [PATCH] 27.0.50; font-lock-{append,prepend}-text-property and anonymous faces
Date: Sun, 28 Apr 2019 19:11:06 +0200
[Message part 1 (text/plain, inline)]
Hello,
This is a follow-up to the mails I sent to emacs-orgmode[1] and
help-gnu-emacs[2].
tl;dr I believe font-lock-{append,prepend}-text-property do not handle
anonymous faces correctly: they splice their attributes, producing
lists mixing keyword attributes and named faces such as this one:
(:strike-through t org-level-1)
The patch I attach changes this to:
((:strike-through t) org-level-1)
To summarize my findings:
1. With org.el from Emacs's master branch (commit 88c91f53df), in an
Org buffer with a heading such as this one:
* *foo* /bar/ _baz_ +quux+
foo (resp. bar and baz) show both the heading face and the bold
(resp. italic and underline) decoration, whereas quux only shows
the strike-through decoration, without the heading face.
2. C-u C-x = on quux says:
> face (:strike-through t org-level-1)
A hasty look at org.el showed that it used
`font-lock-prepend-text-property`. I sent a trivial patch to
emacs-orgmode which uses `font-lock-append-text-property` instead,
although I wasn't sure that it was sound. With this patch, C-u
C-x = says instead:
> face (org-level-1 :strike-through t)
… and quux shows both the org-level-1 foreground and the
strike-through decoration.
3. On help-gnu-emacs, Stefan confirmed that my patch relies on
undefined behavior.
4. Meanwhile, Nicolas applied it to the org-mode repository (commit
42abf5c69).
I have now come to the conclusion that a patch such as the one I
attached in this report might be more appropriate.
[0001-Refrain-from-splicing-anonymous-faces-in-text-proper.patch (text/x-diff, attachment)]
[Message part 3 (text/plain, inline)]
I am not an expert on font-lock though, so this patch might not be
correct. <excuses>Also, since I'm on a laptop running on battery
power, I don't intend to run make check right now.</excuses> I am
sharing this patch in case someone well-versed in font-lock finds it
"obviously correct".
If that is the case, I have two more questions for additional patches:
1. Would it make sense to stuff most of these two functions's code
into a third function called e.g.
font-lock--add-text-property (start end prop value object append)
in order to reduce duplication?
2. I guess some new automated tests would be appreciated?
Thank you for your time.
Kévin
[1]: http://lists.gnu.org/archive/html/emacs-orgmode/2019-04/msg00101.html
[2]: http://lists.gnu.org/archive/html/help-gnu-emacs/2019-04/msg00240.html
In GNU Emacs 27.0.50 (build 1, i686-pc-linux-gnu, GTK+ Version 3.22.11)
of 2019-04-18 built on nc10-laptop
Repository revision: a18336a8dc754fa1c68e16dd8009466cf409271b
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11902000
System Description: BunsenLabs GNU/Linux 9.8 (Helium)
Recent messages:
Saving file /home/peniblec/drafts/font-lock.md...
Wrote /home/peniblec/drafts/font-lock.md
Saving file /home/peniblec/drafts/font-lock.md...
Wrote /home/peniblec/drafts/font-lock.md
Mark set
Saving file /home/peniblec/drafts/font-lock.md...
Wrote /home/peniblec/drafts/font-lock.md
next-line: End of buffer [4 times]
Mark set [3 times]
Undo!
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