Re: Most of Elisp lacks lexical-binding: t

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> The question is, though, at what point does it become the default?

IIUC Eli is not in a hurry to see it become the default.

> One answer would be, support a "dynamic-binding" cookie line for
> Emacs-27 (which does nothing by default),

You can already use

    -*- lexical-binding:nil -*-

for that.

> incorporate your lexical-binding hack as an option.
> Then, go to lexical by default for Emacs-28.

This sounds rather optimistic to me.  We should at least start by giving
some warnings from the byte-compiler when compiling am Elisp file without
lexical-binding.  Maybe same thing when visiting an Elisp file.

There are also all the calls to `eval` which currently tend to mostly
still use dynamic binding (even in files labeled with
lexical-binding:t).  E.g. we could advertise `eval` as taking a minimum
of 2 args so the byte-compiler would start warning about calls that
don't explicitly request lexical or dynamic binding (and hence fall
back to the default dynamic binding).


        Stefan