bug#18059: 24.3.92; defvar and special variables

[Noam Postavsky <npostavs@users.sourceforge.net>]

Noam Postavsky <npostavs@users.sourceforge.net> writes:

> Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
>
>>> I noticed doing (let () (defvar x)) seems to be the same as (progn
>>> (defvar x)), which may be a bug.
>>
>> Both interpretations would make sense, so given the lack of
>> documentation about the intention, we could consider it as a feature as
>> much as a bug.
>>
>> Have you checked whether the behavior is the same with the
>> byte-compiler?
>
> Yes, it's the same.

It's the same when let-binding a lexical variable, but not when binding
a dynamic one.

    ;; -*- lexical-binding: t -*-

    (defvar foo-dynamic 'foo)

    (let ((foo-dynamic 99))
      (defvar x))

    (let ((x 1))
      (setq testfun (lambda () x)))

    (message "%S" (funcall testfun))

gives

    Symbol’s value as variable is void: x

when running the interpreted version, and

    1

when running the compiled version.