bug#36830: 26.2; find-file-visit-truename is not honored as file local variable

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: gusbrs.2016@gmail.com,  36830@debbugs.gnu.org
> Date: Sun, 25 Aug 2019 07:39:29 +0200
> 
> > Maybe we should just document that this variable cannot be file-local.
> 
> files.el has this:
> 
> (put 'find-file-visit-truename 'safe-local-variable 'booleanp)
> 
> It was changed to booleanp in 2007 (from the presumably invalid
> `boolean'), so it didn't work before 2007 for that reason, and it hasn't
> worked after 2007 because it's checked too late.
> 
> So perhaps the fix here is to just remove that `put'?

Fine with me.

> On the other hand, it would be nice if it worked, because it seems like
> a pretty useful thing to be able to customise on a per-file basis.

I agree.  If someone can come up with a way to resolve the race, I'm
all ears.

We have similar problems in startup.el, with variables that depend on
potentially customizable other variables, and the solutions are... not
pretty and quite fragile.  In particular, that kind of problems was
the main reason why we introduced the early-init file.