byte-compiler warn on quote lexical var?

byte-compiler warn on quote lexical var?

[Stephen Leake]

I've posted bug#21185; it suggests that the byte-compiler should warn
when a lexical variable is quoted.

For example, with this code:

;; -*- lexical-binding: t -*-

(defun display-var (var)
  "Display variable value of VAR (a symbol), if any."
  (cond
   ((boundp var)
    (message "%s: %s" (symbol-name var) (symbol-value var)))

   (t
    (message "%s not bound" (symbol-name var)))))

(defun quote-lexical-var ()
  (let ((my-var "foo"))
    (message "non-quoted my-var: %s" my-var)
    (display-var 'my-var)))

the call to 'display-var' reports "not bound".

I've been bitten by this problem a couple of times when porting code to
lexical binding; I'd like the byte-compiler to warn me about it.

Is that reasonable?

Can anyone point me to where in the byte-compiler code I should look to
start working on adding this?

-- 
-- Stephe

Re: byte-compiler warn on quote lexical var?

[Stefan Monnier]

> Can anyone point me to where in the byte-compiler code I should look to
> start working on adding this?

I think the patch below is what I used.


        Stefan


diff --git a/lisp/emacs-lisp/cconv.el b/lisp/emacs-lisp/cconv.el
index 98eef11..df2865f 100644
--- a/lisp/emacs-lisp/cconv.el
+++ b/lisp/emacs-lisp/cconv.el
@@ -664,6 +675,10 @@
     (`(cond . ,cond-forms)              ; cond special form
      (dolist (forms cond-forms)
        (dolist (form forms) (cconv-analyze-form form env))))
+
+    ;; ((and `(quote ,v . ,_) (guard (assq v env)))
+    ;;  (byte-compile-log-warning
+    ;;   (format "Possible confusion variable/symbol for `%S'" v)))
 
     (`(quote . ,_) nil)                 ; quote form
     (`(function . ,_) nil)              ; same as quote