Re: [PATCH] hack-one-local-variable use lexical-binding

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Sun, 29 Nov 2020 03:43:04 -0600
> Cc: tgbugs@gmail.com, emacs-devel@gnu.org
> 
> Once we use lexical-binding t by default in all other cases, it would be
> surprising for it to default to nil in this case.

Once lexical-binding becomes t by default, 'eval' will use
lexical-binding.

> For me, the most important thing is therefore to have a clear idea
> how we can make file local `eval' use lexical-binding by default at
> some point in the future.

My idea is to make it do that by default when lexical-binding is t by
default; until then, if someone wants that in file-local variables, he
or she can use a special construct.

IOW, this change will be a backward-incompatible one no matter what we
do.  IMO, it makes much more sense to make such a change when we
switch to lexical-binding by default rather than now.

> If Eli insists that we can't make this backwards incompatible change
> now, I would suggest instead to introduce `non-lexical-eval' or
> `dynamic-eval' and document that any use of plain `eval' that relies on
> lexical-binding nil is now deprecated.

I don't mind introducing dynamic-eval if people think it could be of
use.  I don't think it's a must, but I won't object to it.