Re: Major modes using `widen' is a good, even essential, programming practice.

[Gregory Heytings <gregory@heytings.org>]

>
> Major modes, like all Emacs Lisp programs, have, by design, access to 
> the full range of Emacs's facilities.  Should it make your task more 
> difficult (and I don't see that it does), that's your problem, not the 
> major modes' maintainers'.
>

I fear it is not my problem, no.

jit-lock-functions is an API, with a contract.  CC Mode decided to break 
that contract.  It is wrong that "arbitrary Lisp can be executed through 
fontification-functions", as you said earlier.  A function called from 
fontification-functions isn't supposed to download a file, or to send an 
email, or to change a user option, or to remove or create a file, or to 
remove or insert text in the buffer, or to kill Emacs or a frame or a 
window or the current buffer, or to change the window layout, and so on 
and so forth.

So far breaching that contract has not posed major problems, except of 
course for CC Mode users, who had to bear its sluggishness.  We now have a 
new feature which assumes, and rightly so, that this contract is obeyed. 
This breaks CC Mode.

From where I stand, there are two options here: either CC Mode disables 
the new feature (which is, on purpose, 100% backward compatible), or CC 
Mode is fixed to obey the jit-lock-functions contract, and to become 
compatible with the new feature (which will likely also, by side-effect 
and as a bonus, fix the aforementioned sluggishness).