Re: Font Locking issue: Need help/advice

[Yuan Fu <casouri@gmail.com>]

> On Apr 3, 2020, at 6:36 PM, David Engster <deng@randomsample.de> wrote:
> 
>> - What happens on the GIF?  How I can fix this? How to avoid similar
>>  in the future?
> 
> What happens here is that the initial font-lock goes over the whole
> currently visible section, but as soon as you edit one line, font-lock
> will be called only for the part of the buffer that has changed, and it
> seems your font-lock rules work differently in this case because the
> context has changed.
> 
>> - In fact, I would like to be able to independently receive the
>>  answer to the question "Why did this happen?" so I'm interesting
>>  on debugging practices.  How to debug similar issues?
> 
> For better understanding how font-lock actually works, I highly
> recommend using font-lock-studio
> 
> https://github.com/Lindydancer/font-lock-studio
> 
> Also, take a look at the other linked packages in the description. In
> your case, 'highlight-refontification' could be useful to see which
> parts of the buffer actually get refontified when you edit it.
> 
> -David
> 

It is also helpful to look at jit-lock.el since that’s the default on-the-fly fortification facility. Basically it marks all text after the changed region (including the region) as “unfontified” when you edit the buffer. And the redisplay (C) code will call jit-lock functions (which calls font-lock functions) to fontify the unfontified text when it needs to display them. IIUC jit-lock is given chunks of unfontified text (several thousand characters) each time. 

Yuan