set-text-properties and jit-lock-mode

set-text-properties and jit-lock-mode

[Alan Schmitt]

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Hello,

I'm tracking down a bug in ledger-mode and I'm now at the point where I
think I need some help about some emacs core code.

The problem: if jit-lock-mode it t, then using set-text-properties to
change the face does not work.

To reproduce: start emacs with -Q. In the scratch buffer, type "foo".
Then evaluate:
(set-text-properties 192 195 (list 'face 'italic))

Nothing changes, and when I do a `describe-char' on one letter of "foo"
I don't see the face.

If I then evaluate
(setq jit-lock-mode nil)
(set-text-properties 192 195 (list 'face 'italic))

then I see the face change to italic, confirmed by `describe-char'.

As `set-text-properties' is a function in C, I don't know how to look at
its source (any pointers on how to do this would be great). Is it
supposed not to work for faces when jit-lock is on?

Thanks,

Alan

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Re: set-text-properties and jit-lock-mode

[Alan Mackenzie]

Hello, Alan.

On Sun, Feb 21, 2016 at 07:02:31PM +0100, Alan Schmitt wrote:
> Hello,

> I'm tracking down a bug in ledger-mode and I'm now at the point where I
> think I need some help about some emacs core code.

> The problem: if jit-lock-mode it t, then using set-text-properties to
> change the face does not work.

> To reproduce: start emacs with -Q. In the scratch buffer, type "foo".
> Then evaluate:
> (set-text-properties 192 195 (list 'face 'italic))

> Nothing changes, and when I do a `describe-char' on one letter of "foo"
> I don't see the face.

At a guess, what's happening here is this: your `set-text-properties'
does indeed work.  But setting text properties is a buffer change.  So
`before-change-functions' and `after-change-functions' will both be
executed.  `a-c-f' contains `jit-lock-after-change', which helpfully
refontifies the line for you.  All this happens before the screen is
redisplayed.

If you bind these hooks to nil around your call, I think it will work:

(let (before-change-functions after-change-functions)
  (set-text-properties 192 195 (list 'face 'italic)))

> If I then evaluate
> (setq jit-lock-mode nil)
> (set-text-properties 192 195 (list 'face 'italic))

> then I see the face change to italic, confirmed by `describe-char'.

> As `set-text-properties' is a function in C, I don't know how to look at
> its source (any pointers on how to do this would be great). Is it
> supposed not to work for faces when jit-lock is on?

> Thanks,

> Alan

-- 
Alan Mackenzie (Nuremberg, Germany).

Re: set-text-properties and jit-lock-mode

[Alan Schmitt]

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On 2016-02-21 20:04, Alan Mackenzie <acm@muc.de> writes:

>> The problem: if jit-lock-mode it t, then using set-text-properties to
>> change the face does not work.
>
>> To reproduce: start emacs with -Q. In the scratch buffer, type "foo".
>> Then evaluate:
>> (set-text-properties 192 195 (list 'face 'italic))
>
>> Nothing changes, and when I do a `describe-char' on one letter of "foo"
>> I don't see the face.
>
> At a guess, what's happening here is this: your `set-text-properties'
> does indeed work.  But setting text properties is a buffer change.  So
> `before-change-functions' and `after-change-functions' will both be
> executed.  `a-c-f' contains `jit-lock-after-change', which helpfully
> refontifies the line for you.  All this happens before the screen is
> redisplayed.
>
> If you bind these hooks to nil around your call, I think it will work:
>
> (let (before-change-functions after-change-functions)
>   (set-text-properties 192 195 (list 'face 'italic)))

Thanks a lot for the suggestion, but unfortunately it does not work. I
guess some other function must be re-fontifying the text.

Alan

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Re: set-text-properties and jit-lock-mode

[Stefan Monnier]

> (let (before-change-functions after-change-functions)
>   (set-text-properties 192 195 (list 'face 'italic)))

Please never ever let-bind those hooks.
Let-bind `inhibit-buffer-modification-hooks' instead, thank you.


        Stefan

Re: set-text-properties and jit-lock-mode

[Eli Zaretskii]

> From: Alan Schmitt <alan.schmitt@polytechnique.org>
> Date: Sun, 21 Feb 2016 19:02:31 +0100
> 
> The problem: if jit-lock-mode it t, then using set-text-properties to
> change the face does not work.
> 
> To reproduce: start emacs with -Q. In the scratch buffer, type "foo".
> Then evaluate:
> (set-text-properties 192 195 (list 'face 'italic))
> 
> Nothing changes, and when I do a `describe-char' on one letter of "foo"
> I don't see the face.
> 
> If I then evaluate
> (setq jit-lock-mode nil)
> (set-text-properties 192 195 (list 'face 'italic))
> 
> then I see the face change to italic, confirmed by `describe-char'.
> 
> As `set-text-properties' is a function in C, I don't know how to look at
> its source (any pointers on how to do this would be great).

You don't need to look at its source.  The documentation clearly says
that it completely replaces the property list of the specified region
with the properties you specify as its arguments.

> Is it supposed not to work for faces when jit-lock is on?

Yes.  Font-lock overwrites the 'face' text properties with its own,
because it uses set-text-properties.

Re: set-text-properties and jit-lock-mode

[Alan Schmitt]

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Hello Eli,

On 2016-02-21 21:30, Eli Zaretskii <eliz@gnu.org> writes:

>> As `set-text-properties' is a function in C, I don't know how to look at
>> its source (any pointers on how to do this would be great).
>
> You don't need to look at its source.  The documentation clearly says
> that it completely replaces the property list of the specified region
> with the properties you specify as its arguments.

Yes, I read that. But as I was not seeing this happen, I wanted to
understand why. I was wrongly assuming set-text-properties was not
changing them, but if I understand your message it does change them, but
they are changed back because of font-lock.

>> Is it supposed not to work for faces when jit-lock is on?
>
> Yes.  Font-lock overwrites the 'face' text properties with its own,
> because it uses set-text-properties.

Is there a way to change the face that plays well with font-lock? I
tried `font-lock-append-text-property' but it did not work.

Thanks,

Alan

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Re: set-text-properties and jit-lock-mode

[Anders Lindgren]

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>
> Is there a way to change the face that plays well with font-lock? I
> tried `font-lock-append-text-property' but it did not work.
>
>
You can set the text property `font-lock-face' instead of `face'. When
`font-lock' is activated, it sets up this as a low-level alias to `face'
but after that doesn't touch it. Effectively, it allows face properties
defined by normal code and by font-lock to live side by side in the same
buffer.

    -- Anders Lindgren

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Re: set-text-properties and jit-lock-mode

[Alan Schmitt]

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On 2016-02-22 09:51, Anders Lindgren <andlind@gmail.com> writes:

>     Is there a way to change the face that plays well with font-lock? I
>     tried `font-lock-append-text-property' but it did not work.
>
> You can set the text property `font-lock-face' instead of `face'. When
> `font-lock' is activated, it sets up this as a low-level alias to `face' but
> after that doesn't touch it. Effectively, it allows face properties defined by
> normal code and by font-lock to live side by side in the same buffer.

It works great, thanks a lot. I think I now see how to get around the
ledger-mode bug.

Thanks again,

Alan

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