Re: Locking/unlocking file inside with-silent-modifications

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 27 Dec 2017 18:27:24 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> 
> This is a spin-off from bug#29846, where a user complained about very
> slow scrolling due to JIT font-lock, when the buffer visits a file
> that resides on a very slow networked volume.
> 
> The reason for that is that JIT font-lock repeatedly calls
> with-silent-modifications, which calls restore-buffer-modified-p,
> which calls unlock_file.  It does that even if the user disabled
> file-locking (presumably because some other Emacs session could
> have locked the file).
> 
> After thinking about this, I concluded that it makes little sense to
> lock and unlock files in the body run by with-silent-modifications.
> After all, with-silent-modifications is meant to pretend that no
> modifications happened in the first place, so why would we want to
> lock and unlock the buffer's file while performing modifications that
> "never happened"?  Am I missing something?
> 
> There is a way, albeit an undocumented one, of disabling lock/unlock
> inside restore-buffer-modified-p.  So if we agree that it's TRT, the
> change to implement that is easy.

For the record: the followup is in bug#29846, and the change that will
fix this issue will be shortly pushed to the emacs-26 branch.