Re: Default lexical-binding to t

[Richard Stallman <rms@gnu.org>]

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  > - Don't have a `lexical-binding` cookie.
  > - Have code which happens to behave differently under the new dialect
  >   (such code is not rare, but a lot of code works identically in the
  >   two dialects).

  > I believe by the time Emacs-31 will be released, such files will be
  > uncommon, and it is easy to fix them (either by adjusting he code, or
  > by slapping a `lexical-binding` cookie).

It seems that people are forming ideas of how frequent dynamic binding
files are by looking at code in active development.  Of course it is
rare there.  But user have a lot of old Lisp files that they haven't
used for a while.  Some of them, someone will try to use someday.

So we should never expect the user commnity to quickly eliminate
constructs that we plan to break.  We should never rush to break it.

Many users upgrade Emacs only occasionally, and often skip one or more
versions.  And people have Lisp code they have not run in some years
-- but that doesn't mean they never will.  Those disused files may be
more numerous than the files people regularly use.

I think we should prepare for the change in Emacs 31, and go the rest
of the way in Emacs 33 or 34.  Emacs 31 should go all out to urge
users to fix their Lisp files to specify lexical-binding.

For now, we should improve the warning given for a file that fails to
specify lexical-binding.  Let's make it explicitly say what we want
users to do.  "To avoid confusion later, add lexical-binding to the
file's local variables now."

For warning when visiting a file, instead of a cryptic "/d", it whould
show clear instructions.

Can we add that trivial change to 31.2?

The more cases in which we notify users, and the more explicitly we do
so, the sooner users will follow that advice.  With this
encouragement, I think we can expect that few programs that don't
specify lexical-binding will remain after a few more years.


-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)