bug#34234: 27.0.50; local defvar and special-variable-p

bug#34234: 27.0.50; local defvar and special-variable-p

[Sebastian Miele]

;; Run ./src/emacs -Q, put this into *scratch*, and C-x C-e through
;; what follows outside of comments.
;;
(setq lexical-binding t)
;;
;; The expression
;;
(progn
  (defvar x)
  (special-variable-p 'x))
;;
;; evaluates to nil. But in fact x is special in that context, as
;; described in the Elisp manual, and as witnessed by e.g.
;;
(funcall (progn
           (setq x 0)
           (defvar x)
           (let ((x 1)) (lambda () x))))
;;
;; evaluating to 0.


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.4)
 of 2019-01-28 built on tisch
Repository revision: d81aa8516ef6df79d6d602d4f732d8a65bf1677c
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12003000
System Description: Arch Linux

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set [2 times]
t
nil
0 (#o0, #x0, ?\C-@)
Mark set

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB
NOTIFY INOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS LIBSYSTEMD JSON
CANNOT_DUMP LCMS2 GMP

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
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  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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
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rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils elec-pair
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
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syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
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ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 45936 9112)
 (symbols 48 5860 1)
 (strings 32 14876 2143)
 (string-bytes 1 491285)
 (vectors 16 9479)
 (vector-slots 8 117416 15538)
 (floats 8 17 135)
 (intervals 56 385 20)
 (buffers 992 12))

bug#34234: 27.0.50; local defvar and special-variable-p

[Lars Ingebrigtsen]

Sebastian Miele <sebastian.miele@gmail.com> writes:

> ;; Run ./src/emacs -Q, put this into *scratch*, and C-x C-e through
> ;; what follows outside of comments.
> ;;
> (setq lexical-binding t)
> ;;
> ;; The expression
> ;;
> (progn
>   (defvar x)
>   (special-variable-p 'x))
> ;;
> ;; evaluates to nil. But in fact x is special in that context, as
> ;; described in the Elisp manual, and as witnessed by e.g.
> ;;
> (funcall (progn
>            (setq x 0)
>            (defvar x)
>            (let ((x 1)) (lambda () x))))
> ;;
> ;; evaluating to 0.

But the doc string says:

---
special-variable-p is a built-in function in ‘src/eval.c’.

(special-variable-p SYMBOL)

  Probably introduced at or before Emacs version 24.1.

Return non-nil if SYMBOL’s global binding has been declared special.
A special variable is one that will be bound dynamically, even in a
context where binding is lexical by default.
---

Note "global binding".  So it doesn't say whether x is special in that
context, but whether it's special globally, so I think the function
works as documented.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no