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Advice only applies in all cases after re-evaluating the function called by the recommended function

In my .emacs file, I have:

(defadvice narrow-to-region (around test activate)
   (message "advice")
   ad-do-it)

When I call a narrow area, the advice works and prints "advice" before the narrowing.

When I call narrow-defunun it is not.

I found that narrow-defunct is defined - in lisp.el, and re-evaluated the function. At this stage, the council began to work.

What could be causing this?

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2 answers


The problem appears to be byte-compilation related, and therefore the inability to advise narrowing primitives ( narrow-to-region

is primitive, narrow-to-defun

invocation narrow-to-region

).

The next post in the Null Program ( "Emacs Advice Limitations" ) details this issue in detail. Here's a short version from deep within the post:



It turns out to be narrow-to-region

so special - perhaps because it is used very often - it gets its own bytecode. A call to a primitive function is compiled into one command. This means that my advice will not count in byte-compiled code. Drain it. The same is true for widen

(code 126).

As for why the advice started working after re-evaluating narrow-to-defun

: I am guessing it is because you ended up replacing the byte compiled version on re-evaluating.

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@Dan described the problem well. Here's some information to help you get around it.

What you can do is advise (or override) as well narrow-to-defun

(and possibly narrow-to-page

), so it acts similarly.

FWIW, I am doing something similar in a library wide-n.el

(see Multiple Nodes ).

I advise narrow-to-region

. But I also override narrow-to-defun

and narrow-to-page

. In all three cases, I make the same change to record the details of each taper so you can come back to them later. Here's a tip, for example:



 (defadvice narrow-to-region (before push-wide-n-restrictions activate)
   "Push the region limits to `wide-n-restrictions'.
 You can use `C-x n x...' to widen to previous buffer restrictions."
   (when (or (interactive-p) wide-n-push-anyway-p)
     (wide-n-push (ad-get-arg 0) (ad-get-arg 1)))) ; Args START and END.

And here is the relevant part of the override narrow-to-defun

:

  ...
  (goto-char end)
  (re-search-backward "^\n" (- (point) 1) t)
  (when (or (interactive-p)  wide-n-push-anyway-p) (wide-n-push beg end)) ; <=====
  (narrow-to-region beg end))))
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