bug#5129: 23.1.50; adding font-lock-keywords for face highlight

bug#5129: 23.1.50; adding font-lock-keywords for face highlight

[Roland Winkler]

The highlight face is somehow treated special in an odd way:

If I eval the following in a buffer it will highlight all occurences
of "foo" as expected:

  (font-lock-add-keywords nil '(("foo" . font-lock-constant-face)))

Yet when I do instead

  (font-lock-add-keywords nil '(("foo" . highlight)))

it gives me the message (in the *Messages* buffer)

  Invalid face reference: 0

When I put point at the position of the string "foo" and evaluate

  (get-text-property (point) 'face)

this gives me

  (0 highlight)

which probably explains the "invalid face reference" error.
Why is the face `0' added?


In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.14.4)
 of 2009-12-04 on regnitz
Windowing system distributor `The X.Org Foundation', version 11.0.10502000

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: en_GB.utf8
  value of $LANG: en_US.ISO-8859-15
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-9-unix
  default enable-multibyte-characters: t

bug#5129: 23.1.50; adding font-lock-keywords for face highlight

[Glenn Morris]

"Roland Winkler" wrote:

>   (font-lock-add-keywords nil '(("foo" . font-lock-constant-face)))

works

>   (font-lock-add-keywords nil '(("foo" . highlight)))

doesn't work.

I think you are running into the old issue that faces should be quoted
in font-lock keywords, else they will be treated as variables. For
historical reasons, font-lock-constant-face (etc) as well as being a
face, is a variable whose value is that face.

Instead, try

(font-lock-add-keywords nil '(("foo" . 'highlight)))

bug#5129: marked as done (23.1.50; adding font-lock-keywords for face highlight)

[Emacs bug Tracking System]

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Your message dated Sat, 05 Dec 2009 16:04:29 -0500
with message-id <jwv1vj9nni9.fsf-monnier+emacsbugreports@gnu.org>
and subject line Re: bug#5129: 23.1.50; adding font-lock-keywords for face highlight
has caused the Emacs bug report #5129,
regarding 23.1.50; adding font-lock-keywords for face highlight
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
bug report if necessary, and/or fix the problem forthwith.

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-- 
5129: http://emacsbugs.donarmstrong.com/cgi-bin/bugreport.cgi?bug=5129
Emacs Bug Tracking System
Contact owner@emacsbugs.donarmstrong.com with problems

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From: "Roland Winkler" <Roland.Winkler@physik.uni-erlangen.de>
To: emacs-pretest-bug@gnu.org
Subject: 23.1.50; adding font-lock-keywords for face highlight
Date: Sat, 05 Dec 2009 13:15:31 -0600
Message-ID: <878wdhp6zw.fsf@regnitz.physics.niu.edu>

The highlight face is somehow treated special in an odd way:

If I eval the following in a buffer it will highlight all occurences
of "foo" as expected:

  (font-lock-add-keywords nil '(("foo" . font-lock-constant-face)))

Yet when I do instead

  (font-lock-add-keywords nil '(("foo" . highlight)))

it gives me the message (in the *Messages* buffer)

  Invalid face reference: 0

When I put point at the position of the string "foo" and evaluate

  (get-text-property (point) 'face)

this gives me

  (0 highlight)

which probably explains the "invalid face reference" error.
Why is the face `0' added?


In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.14.4)
 of 2009-12-04 on regnitz
Windowing system distributor `The X.Org Foundation', version 11.0.10502000

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: en_GB.utf8
  value of $LANG: en_US.ISO-8859-15
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-9-unix
  default enable-multibyte-characters: t


[-- Attachment #3: Type: message/rfc822, Size: 2483 bytes --]

From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Roland Winkler <Roland.Winkler@physik.uni-erlangen.de>
Subject: Re: bug#5129: 23.1.50; adding font-lock-keywords for face highlight
Date: Sat, 05 Dec 2009 16:04:29 -0500
Message-ID: <jwv1vj9nni9.fsf-monnier+emacsbugreports@gnu.org>

>   (font-lock-add-keywords nil '(("foo" . font-lock-constant-face)))
                                           ^^^^^^^^^^^^^^^^^^^^^^^
> Yet when I do instead

>   (font-lock-add-keywords nil '(("foo" . highlight)))
                                           ^^^^^^^^^

Thos two things are treated by font-lock as a Lisp expression
to evaluate.  Since font-lock-constant-face is a variable (whose
content is usually the symbol font-lock-constant-face), the first will
work, whereas the second will either signal en error (because the
variable `highlight' doesn't exist) or lead to odd behavior (because
`highlight' just happens to be let-bound by one of the caller).

I.e. you want

   (font-lock-add-keywords nil '(("foo" . 'highlight)))
                                         ^^^

-- Stefan

bug#5129: 23.1.50; adding font-lock-keywords for face highlight

[Roland Winkler]

On Sat Dec 5 2009 Glenn Morris wrote:
> Instead, try
> 
> (font-lock-add-keywords nil '(("foo" . 'highlight)))

Oh well, I thought I ran into this often enough. But still it's too
easy to forget it again.

Thanks for helping me out and sorry for the noise!

Roland