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#73725
Master: Wrong position for byte compiler warning message.
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Message #11 received at 73725 <at> debbugs.gnu.org (full text, mbox):
Hello, Stefan.
Thanks for the reply!
On Fri, Oct 11, 2024 at 19:45:18 -0400, Stefan Monnier wrote:
> > (i) Create the following file, bad-error-position2.el:
> > #########################################################################
> > ;; -*- lexical-binding:t -*-
> > (eval-and-compile
> > (defmacro increase ()
> > `(let ((foo (point-max)))
> > (cond
> > ((consp foo)
> > (message "consp %s" foo)
> > foo)
> > ((numberp foo)
> > (1+ fooo)) ; Note the misspelling.
> > (t (message "Something else: %s" foo))))))
> > (defun call-increase (bar)
> > (cond
> > ((not (or (consp bar)
> > (numberp bar)))
> > bar)
> > (t (increase))))
> > #########################################################################
> > Note the misspelling of `foo' as `fooo' on line 10.
> > (ii) emacs -Q
> > (iii) M-x byte-compile-file /path/to/bad-error-position2.el.
> > (iv) This gives the warning message:
> > bad-error-position2.el:14:4: Warning: reference to free variable `fooo'
> > (v) The position 14:4 is wrong. That is the position of the `cond'
> > symbol in `call-increase'.
> > (vi) The correct message should be:
> > bad-error-position2.el:18:8: Warning: reference to free variable `fooo'
> > .. 18:8 is the position of `increase' on the last line of the file.
> Nitpick: one could also argue that the "correct" message should point to
> line 8 where is the `fooo` typo.
> > +(defun sub-macroexp--posify-form (form call-pos depth)
> > + "Try to apply the transformation of `macroexp--posify-form' to FORM.
> > +FORM and CALL-POS are as in that function. DEPTH is a small integer,
> > +decremented at each recursive call, to prevent infinite recursion.
> > +Return the changed form, or nil if no change happened."
> > + (let (new-form
> > + )
> > + (cond
> > + ((zerop depth) nil)
> > + ((and (consp form)
> > + (symbolp (car form))
> > + (car form))
> > + (setcar form (position-symbol (car form) call-pos))
> > + form)
> > + ((consp form)
> > + (or (when (setq new-form (sub-macroexp--posify-form
> > + (car form) call-pos (1- depth)))
> > + (setcar form new-form)
> > + form)
> > + (when (setq new-form (sub-macroexp--posify-form
> > + (cdr form) call-pos (1- depth)))
> > + (setcdr form new-form)
> > + form)))
> > + ((symbolp form)
> > + (if form ; Don't position nil!
> > + (position-symbol form call-pos)))
> > + ((and (or (vectorp form) (recordp form)))
> > + (let ((len (length form))
> > + (i 0)
> > + )
> > + (while (and (< i len)
> > + (not (setq new-form (sub-macroexp--posify-form
> > + (aref form i) call-pos (1- depth)))))
> > + (setq i (1+ i)))
> > + (when (< i len)
> > + (aset form i new-form)
> > + form))))))
> That sounds potentially costly Have you tried to measure the
> performance impact in some "typical" cases?
I haven't measured it, no, but I doubt it will be costly - the recursion in
sub-macroexp--posify-form will very rarely occur. Virtually every form
passed to it will by a macro invocation or a symbol, I think.
> While reading your description I was naively thinking: we can
> probably fix it with a trivial patch like:
> diff --git a/lisp/emacs-lisp/macroexp.el b/lisp/emacs-lisp/macroexp.el
> index 19daa57b207..5cc471e32f6 100644
> --- a/lisp/emacs-lisp/macroexp.el
> +++ b/lisp/emacs-lisp/macroexp.el
> @@ -246,6 +246,7 @@ macroexp-macroexpand
> (let* ((macroexpand-all-environment env)
> new-form)
> (while (not (eq form (setq new-form (macroexpand-1 form env))))
> + (push form byte-compile-form-stack)
> (let ((fun (car-safe form)))
> (setq form
> (if (and fun (symbolp fun)
> Have you tried something like this?
I haven't, no. It might well work. But I think the `push' form should
go outside of the loop, I'm also a little wary about pushing an item
onto stack when it doesn't get popped again after the form(s) it is
"guarding".
> If it doesn't work, do you happen to know why?
I'm not sure whether it would work for the (similar) bug, bug#73746,
where the symbols with position were getting lost in byte-opt.el.
But I'll give it a try. I'm a bit busy in the next few days, so it might
be next week before I manage it.
> Stefan
--
Alan Mackenzie (Nuremberg, Germany).
This bug report was last modified 106 days ago.
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