bug#6376: 23.2; byte compile add-to-list report free variable

[Kevin Ryde]

I made a mistake with a variable name to add-to-list and wondered if the
byte compiler might report

    (add-to-list 'nosuchvariable ...)

as a free variable, similar to the report for

    (set 'nosuchvariable ...)

The few lines below get the desired effect, but might be a bit rough.
The separate check-assign is with a view to sharing among set, setq,
set-default and maybe others.

Something specific for add-to-list would be vaguely reasonable since
it's a builtin, but it could be worth trying a general way to flag an
arg number as the name of a variable either referenced or assigned.
Something like that might also allow "function not known to be defined"
for quoted symbol args to mapcar, sort, etc.

I suppose this sort of thing might be analysed by elint instead or as
well, but the byte compiler has good information about bindings
available after macro expansion etc and it's much more often run than
elint.



(defun byte-compile-check-assign (symbol)
  (cond ((and (byte-compile-warning-enabled-p 'constants)
              (byte-compile-const-symbol-p symbol t))
         (byte-compile-warn "variable assignment to constant `%s'" symbol))

        ((and (byte-compile-warning-enabled-p 'free-vars)
              (not (memq symbol byte-compile-bound-variables))
              (not (memq symbol byte-compile-free-assignments)))
         (byte-compile-warn "assignment to free variable `%s'" symbol)
         (push symbol byte-compile-free-assignments))))

(defun byte-compile-varsym1 (form)
  ;; arg 1 is a symbol which is the name of a variable which must be found
  ;; eg. (foo 'var ...)
  (cond ((eq 'quote (car-safe (nth 1 form)))
         (let ((var (car-safe (cdr (nth 1 form)))))
           (if (symbolp var)
               (byte-compile-check-assign var))))
        ;; (add-to-list 'nil ...) reaches here as (add-to-list nil ...),
        ;; call the check so as to report nil as a constant
        ((null (nth 1 form))
         (byte-compile-check-assign nil)))
  (byte-compile-normal-call form))

(byte-defop-compiler-1 add-to-list         byte-compile-varsym1)
(byte-defop-compiler-1 add-to-ordered-list byte-compile-varsym1)



In GNU Emacs 23.2.1 (i486-pc-linux-gnu, GTK+ Version 2.20.0)
 of 2010-05-16 on raven, modified by Debian
configured using `configure  '--build' 'i486-linux-gnu' '--build' 
'i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' 
'--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' 
'--mandir=/usr/share/man' '--with-pop=yes' 
'--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.2/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.2/leim'
 '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 
'build_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

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_AU
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-1-unix
  default enable-multibyte-characters: t