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

[Stefan Monnier <monnier@iro.umontreal.ca>]

> 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

I use the code below for add-hook:

   (byte-defop-compiler-1 remove-hook byte-compile-add-hook)
   (defun byte-compile-add-hook (form)
     (let ((sym (car-safe (cdr-safe form))))
       (when (and (eq 'quote (car-safe sym))
                  (setq sym (car-safe (cdr sym)))
                  (symbolp sym))
         ;; Gross hack: We want to do the sanity checks just as we would for
         ;; a setq so we first do a setq and then pop the byte-code that was
         ;; just pushed by byte-compile-variable-ref.
         (let ((byte-compile-output byte-compile-output)
               (byte-compile-maxdepth byte-compile-maxdepth)
               (byte-compile-depth byte-compile-depth))
           (byte-compile-variable-ref 'byte-varset sym)))
       (byte-compile-normal-call form)))

so I'm in favor of such a change, but it would need to be cleaned up such
that your byte-compile-check-assign is also used for
byte-compile-variable-ref (i.e. the code should be hoisted out of
byte-compile-variable-ref).  Also, note that add-to-list is not only
a "varset" but also a "varref" (it reads the var before assigning to it).


        Stefan