font lock woes

[Joost Kremers <joostkremers@yahoo.com>]

EN:SiS(9)
Hi all,

I'm writing a minor mode that (among other things) adds some font lock
patterns to the buffer's font-lock-keywords, using
font-lock-add-keywords, but I'm running into some problems.

First, one of the things I'm trying to do is to add some additional text
properties beside a face spec. (info "(elisp) Search-based Fontification")
has the following to say on this:

,----
| `(MATCHER . FACESPEC)'
| [...]
|      However, FACESPEC can also evaluate to a list of this form:
| 
|           (face FACE PROP1 VAL1 PROP2 VAL2...)
| 
|      to specify the face FACE and various additional text properties to
|      put on the text that matches.  If you do this, be sure to add the
|      other text property names that you set in this way to the value of
|      `font-lock-extra-managed-props' so that the properties will also
|      be cleared out when they are no longer appropriate.
`----

This suggests to me that I should be able to do:

,----
| (font-lock-add-keywords nil `((,(regexp-quote "{++") . '(face cm-addition-face read-only t))) t)
`----

but for some reason, the only thing that works is:

,----
| (font-lock-add-keywords nil `((,(regexp-quote "{++") 0 '(face cm-addition-face read-only t))
`----

Am I misunderstanding the info node, or is Info wrong? (I'm running GNU
Emacs 24.3.50.1, BTW).

A second thing I don't understand is how to remove the read-only
property again when the mode is deactivated. I was thinking I should be
able to do the following:

,----
| (font-lock-remove-keywords nil `((,(regexp-quote "{++") 0 '(face cm-addition-face read-only t))))
| (let ((inhibit-read-only t))
|   (font-lock-fontify-buffer))
| (setq font-lock-extra-managed-props (delq 'read-only font-lock-extra-managed-props))
`----

I figured if I remove the relevant matcher from font-lock-keywords, then
refontify the buffer and only then remove the read-only property from
font-lock-extra-managed-props, things should work. But they don't: the
text that was made read-only with font-lock remains read-only.

Only if I don't remove 'read-only from font-lock-extra-managed-props at
all, does it work: in that case, the read-only property is removed. But I
don't like the idea that font-lock-extra-managed-props isn't restored to
its original value. So I'm wondering if there's a better way of doing
this.

It's the first time I'm trying to do anything with font-lock. I'd
appreciate any and all comments!


TIA


-- 
Joost Kremers                                   joostkremers@fastmail.fm
Selbst in die Unterwelt dringt durch Spalten Licht