bug#64391: buffer narrowing slowdown regression in emacs 29

[Gregory Heytings]

> > Yes.  In fact now that we have a separate function for the labeled 
> > case, we can remove the funcall in both cases.  Patch attached.
>
> Thank you, but are we sure that save-restriction would be used for 
> labelled restrictions in the future? Maybe we should just start with the 
> unlabelled case.

I'm sorry, I don't understand your question.  The only way (except by 
using internal functions) to enter a labeled restriction is to use the 
with-restriction special form with its optional label argument.  That form 
has a save-restriction since day one.

> > > The documentation should also make it clear that `nil` is not a valid 
> > > label.
> >
> > Is that not already clear in the docstring, which says "in which LABEL 
> > is a symbol"?
>
> Well, nil is a symbol.

Indeed, but I'd say it's clear enough from the context that "symbol" means 
a quoted symbol here.