bug#10761: 24.0.93; variable declared with defvar is not recognized as special

bug#10761: 24.0.93; variable declared with defvar is not recognized as special

[Oleksandr Manzyuk]

This bug report will be sent to the Bug-GNU-Emacs mailing list
and the GNU bug tracker at debbugs.gnu.org.  Please check that
the From: line contains a valid email address.  After a delay of up
to one day, you should receive an acknowledgement at that address.

Please write in English if possible, as the Emacs maintainers
usually do not have translators for other languages.

Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug.  If you can, give a recipe
starting from `emacs -Q':

The variable `pcomplete-stub' from `pcomplete.el' is declared using
defvar.  The top comment of the file contains -*- lexical-binding: t -*-,
so `pcomplete-stub' should be a special variable.  This is not the case:

1. emacs -Q
2. M-: (boundp 'pcomplete-stub) RET ==> nil
3. M-x shell
4. M-: (boundp 'pcomplete-stub) RET ==> t
5. M-: (special-variable-p 'pcomplete-stub) RET ==> nil
6. Open the file `pcomplete.el' (for example, by looking up the variable
`pcomplete-stub') and M-x eval-buffer.  Now (special-variable-p
'pcomplete-stub) evaluates to t.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
For information about debugging Emacs, please read the file
/home/manzyuk/share/emacs/24.0.93/etc/DEBUG.


In GNU Emacs 24.0.93.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.20.1)
 of 2012-02-07 on paddy
Windowing system distributor `The X.Org Foundation', version 11.0.10706000
Configured using:
 `configure '--prefix=/home/manzyuk''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Emacs-Lisp

Minor modes in effect:
  shell-dirtrack-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<help-echo> M-: ( b o u n d p SPC ' p c o m p l e t
e - s t u b ) <return> M-x s h e l l <return> M-: M-p
<return> M-: ( s p e c i a l - v a r i a b l e - p
SPC ' p c o m p l e t e - s t u b ) <return> C-h v
p c o m p l e t e - s t u b <return> C-x o C-e C-b
C-b C-b C-b <return> M-x e v a l SPC b u f f e r <return>
M-: M-p <return> M-x r e p o r t SPC <tab> <return
>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
nil
t
nil
Type C-x 1 to delete the help window.
uncompressing pcomplete.el.gz...done
Loading vc-git...done
t

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr message format-spec rfc822 mml mml-sec
mm-decode mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mailabbrev mail-utils gmm-utils mailheader
emacsbug cl vc-git jka-compr find-func pp help-mode easymenu view
help-fns ansi-color shell pcomplete comint regexp-opt ring time-date
tooltip ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar
dnd fontset image fringe lisp-mode register page menu-bar rfn-eshadow
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core frame cham georgian utf-8-lang misc-lang vietnamese tibetan
thai tai-viet lao korean japanese hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer loaddefs button faces
cus-face files text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget hashtable-print-readable backquote
make-network-process dbusbind dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

bug#10761: 24.0.93; variable declared with defvar is not recognized as special

[Stefan Monnier]

> 1. emacs -Q
> 2. M-: (boundp 'pcomplete-stub) RET ==> nil
> 3. M-x shell
> 4. M-: (boundp 'pcomplete-stub) RET ==> t
> 5. M-: (special-variable-p 'pcomplete-stub) RET ==> nil
> 6. Open the file `pcomplete.el' (for example, by looking up the variable
> `pcomplete-stub') and M-x eval-buffer.  Now (special-variable-p
> 'pcomplete-stub) evaluates to t.

Thanks for catching this.  It's actually a pretty bad bug.
I've installed the patch below which I believe fixes the problem,


        Stefan


=== modified file 'lisp/ChangeLog'
--- lisp/ChangeLog	2012-02-09 20:27:54 +0000
+++ lisp/ChangeLog	2012-02-09 21:50:23 +0000
@@ -1,3 +1,11 @@
+2012-02-09  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	* emacs-lisp/bytecomp.el (byte-compile-file-form-defvar):
+	Don't fallback on byte-compile-defvar.  Optimize (defvar foo) away.
+	(byte-compile-tmp-var): New const.
+	(byte-compile-defvar): Use it to minimize .elc size.
+	Just use `defvar' rather than simulate it (bug#10761).
+
 2012-02-09  Glenn Morris  <rgm@gnu.org>
 
 	* files.el (rename-uniquely): Doc fix.  (Bug#3806)

=== modified file 'lisp/emacs-lisp/bytecomp.el'
--- lisp/emacs-lisp/bytecomp.el	2012-01-19 07:21:25 +0000
+++ lisp/emacs-lisp/bytecomp.el	2012-02-09 19:09:21 +0000
@@ -2237,10 +2237,6 @@
 (put 'defvar   'byte-hunk-handler 'byte-compile-file-form-defvar)
 (put 'defconst 'byte-hunk-handler 'byte-compile-file-form-defvar)
 (defun byte-compile-file-form-defvar (form)
-  (if (null (nth 3 form))
-      ;; Since there is no doc string, we can compile this as a normal form,
-      ;; and not do a file-boundary.
-      (byte-compile-keep-pending form)
     (when (and (symbolp (nth 1 form))
                (not (string-match "[-*/:$]" (symbol-name (nth 1 form))))
                (byte-compile-warning-enabled-p 'lexical))
@@ -2249,6 +2245,9 @@
     (push (nth 1 form) byte-compile-bound-variables)
     (if (eq (car form) 'defconst)
 	(push (nth 1 form) byte-compile-const-variables))
+  (if (and (null (cddr form))		;No `value' provided.
+           (eq (car form) 'defvar))     ;Just a declaration.
+      nil
     (cond ((consp (nth 2 form))
 	   (setq form (copy-sequence form))
 	   (setcar (cdr (cdr form))
@@ -4124,8 +4123,10 @@
     (push (nth 1 (nth 1 form)) byte-compile-global-not-obsolete-vars))
   (byte-compile-normal-call form))
 
+(defconst byte-compile-tmp-var (make-symbol "def-tmp-var"))
+
 (defun byte-compile-defvar (form)
-  ;; This is not used for file-level defvar/consts with doc strings.
+  ;; This is not used for file-level defvar/consts.
   (when (and (symbolp (nth 1 form))
              (not (string-match "[-*/:$]" (symbol-name (nth 1 form))))
              (byte-compile-warning-enabled-p 'lexical))
@@ -4148,32 +4149,21 @@
     (push var byte-compile-bound-variables)
     (if (eq fun 'defconst)
 	(push var byte-compile-const-variables))
-    (byte-compile-body-do-effect
-     (list
-      ;; Put the defined variable in this library's load-history entry
-      ;; just as a real defvar would, but only in top-level forms.
-      (when (and (cddr form) (null byte-compile-current-form))
-	`(setq current-load-list (cons ',var current-load-list)))
-      (when (> (length form) 3)
 	(when (and string (not (stringp string)))
 	    (byte-compile-warn "third arg to `%s %s' is not a string: %s"
 			       fun var string))
-	`(put ',var 'variable-documentation ,string))
+    (byte-compile-form-do-effect
       (if (cddr form)		; `value' provided
-	  (let ((byte-compile-not-obsolete-vars (list var)))
-	    (if (eq fun 'defconst)
-		;; `defconst' sets `var' unconditionally.
-		(let ((tmp (make-symbol "defconst-tmp-var")))
                   ;; Quote with `quote' to prevent byte-compiling the body,
                   ;; which would lead to an inf-loop.
-		  `(funcall '(lambda (,tmp) (defconst ,var ,tmp))
-			    ,value))
-	      ;; `defvar' sets `var' only when unbound.
-	      `(if (not (default-boundp ',var)) (setq-default ,var ,value))))
-	(when (eq fun 'defconst)
+         `(funcall '(lambda (,byte-compile-tmp-var)
+                      (,fun ,var ,byte-compile-tmp-var ,@(nthcdr 3 form)))
+                   ,value)
+        (if (eq fun 'defconst)
 	  ;; This will signal an appropriate error at runtime.
-	  `(eval ',form)))
-      `',var))))
+            `(eval ',form)
+          ;; A simple (defvar foo) just returns foo.
+          `',var)))))
 
 (defun byte-compile-autoload (form)
   (byte-compile-set-symbol-position 'autoload)