RE: [External] : Re: Conditional binding and testing of `lexical-binding'

[Drew Adams <drew.adams@oracle.com>]

> >  (if (and (boundp 'lexical-binding)
> >           lexical-binding)
> >      (lambda (y) (something x y))
> >    `(lambda (y) (something ',x y)))
> 
> You may use `static-if' to benifit from
> byte-compiling.

I see no `static-if' in any Emacs release, from
emacs -Q.  (The most recent Emacs release is 27.2.)

Certainly it's not present in Emacs 23 or earlier,
which is where there's no variable `lexical-let'.
So clearly it can't be used in Emacs 23 to test
whether lexical binding is supported.

I wonder whether you might have misread my post.
This is about a library that intends to be usable
with Emacs releases prior to Emacs 24 (where that
var is introduced), as well as with later Emacs
releases.

This is not about _converting_ a library to always
use `lexical-binding', which would only be useful
for Emacs 24 and later.

It's about being able to take advantage of
`lexical-binding' for Emacs 24+, while still being
compatible with versions earlier than 24.

> > But my question is really about conditionally
> > _setting_ `lexical-binding', so it can be tested.
> 
> I think the "lispy" way is to use: 
> (provide 'lexical-binding)> and use `featurep' to test it.

See above, or reread my first post.  (And none of
my code is providing feature `lexical-binding'.
Just setting that var to t does not "provide" it
as a supported feature.  It's either supported by
a given version of Emacs or it's not.)

> A more reliable way

To do what?  This apparently has nothing to do
with the quoted text it followed (?).

> is to test
> (static-if (assoc 'lexical-binding (buffer-local-variables))
>    (provide 'lexical-binding))
> instead of doing `boundp' test.

Sorry, but that makes no sense to me.  Emacs
support for `lexical-binding' is true (for
Emacs 24+) regardless of whether that var is
buffer-local variable (and with any value).

> > Is this the thing to do?  If not, what advice
> > do you have for adapting a library to use
> > lexical binding when available (Emacs 24+) but
> > to also work when it's unavailable (Emacs < 24)?
>
> > [The doc just tells you how to convert code to
> > use lexical binding.  I see nothing about how
> > to code compatibly for old and new Emacs.]
> 
> Well, I think it's fine to just keep that library as-is.
> Even in the current lastest release there are still many
> builtin packages are not converted to using lexical binding
> at all. Just name a few I know, supercite, enriched-mode

Certainly it's OK to keep such a library as is.
I've been doing that for years.

But I'm asking how to let it take advantage of
lexical binding when that's available.  That's
the question I posed.  I said how I intend to
do that, but I asked if there's a better way.