Re: add-hook sets hook globally if buffer-local hook is nil

[Lute Kamstra]

Stefan Monnier <address@hidden> writes:

>>> This new behavior is intended; it is documented in the docstring of
>>> add-hook and in the section on hooks in the Lisp Reference manual.
>
> Where is it documented exactly ?  Could you quote the text you're
> referring to ?

E.g., from add-hook's docstring:

  The optional fourth argument, LOCAL, if non-nil, says to modify
  the hook's buffer-local value rather than its default value.

I understand this as: if LOCAL is nil, modify the default value.  I
understand default value as in (default-value HOOK).

>> Gack, that's even worse.
>
> Indeed, I think it's a bug.  It's introduced by the change below
> which I think should be reverted.  What was the reason for the change ?
>
> @@ -856,9 +870,7 @@
>             (set (make-local-variable hook) (list t)))
>      ;; Detect the case where make-local-variable was used on a hook
>      ;; and do what we used to do.

Whoops, I forgot that the code checks for this situation.  This check,
although probably sane with respect to backward compatibility, is not
in agreement with the docstring.

> -    (when (and (local-variable-p hook)
> -            (not (and (consp (symbol-value hook))
> -                      (memq t (symbol-value hook)))))
> +    (unless (and (consp (symbol-value hook)) (memq t (symbol-value hook)))
>        (setq local t)))
>    (let ((hook-value (if local (symbol-value hook) (default-value hook))))
>      ;; If the hook value is a single function, turn it into a list.

I guess Richard overlooked the (make-variable-buffer-local HOOK)
possibility that does not immediately create a buffer-local variable.

  Lute.