bug#14772: 24.3; defvar and lexical-binding in interpreted elisp code

[Jisang Yoo <jisang.yoo.ac+org@gmail.com>]

Short description:

Declaring a special variable affects lexical local variables of the
same name (in interpreted code) in a half measure way, thereby
deviating from both the newbies expectation and the common lisp
expectation.



Long description:

contents of alice.el:

;; -*- lexical-binding: t; -*-
;; two functions that are supposed to do the same thing
(defun alice-multiplier-1 (foo)
  (lambda (n) (* n foo)))
(defun alice-multiplier-2 (num)
  (let ((foo num))
    (lambda (n) (* n foo))))
;; breaking bad
(defvar foo 1000)
;; time to see its effects
(print
 (list
  :R3 (mapcar (alice-multiplier-1 10) (list 1 2 3))
  :R4 (mapcar (alice-multiplier-2 10) (list 1 2 3))))

Output from emacs -q --load alice.el:

(:R3 (10 20 30) :R4 (1000 2000 3000))

What I expected:

Either (:R3 (10 20 30) :R4 (10 20 30))  or (:R3 (1000 2000 3000) :R4
(1000 2000 3000))

One answer in
http://stackoverflow.com/questions/17400556/strange-interaction-between-lexical-binding-and-defvar-in-emacs-lisp
suggests that (:R3 (1000 2000 3000) :R4 (1000 2000 3000)) should be
the right output, which is the same as the CLIST output according to
my test.