bug#20718: 25.0.50; find-function fails on advised subrs (again)

bug#20718: 25.0.50; find-function fails on advised subrs (again)

[Michael Heerdegen]

Hello,

just as a random example:

  (advice-add 'handle-switch-frame :after #'prin1)

and M-x find-function 'handle-switch-frame RET

==> find-function-search-for-symbol: Don't know where
    `handle-switch-frame' is defined

Works without advicing.  I included the word "again" in the subject
because this had been fixed once in #789 in 2008.

It doesn't work because `find-function-library' performs the subrp test
just on the symbol function of the given function name, which is the
advice, not the original subr.


Thanks,

Michael.



In GNU Emacs 25.0.50.4 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
 of 2015-05-30 on drachen
Windowing system distributor `The X.Org Foundation', version 11.0.11701000
System Description:	Debian GNU/Linux testing (stretch)

bug#20718: 25.0.50; find-function fails on advised subrs (again)

[Dmitry Gutov]

On 06/02/2015 03:49 PM, Michael Heerdegen wrote:

> It doesn't work because `find-function-library' performs the subrp test
> just on the symbol function of the given function name, which is the
> advice, not the original subr.

At a glance, the problem is in find-function-advised-original: it only 
supports the old-style advice, and returns nil for 'handle-switch-frame 
augmented with advice-add.

Something like the patch below should fix it, but then the function 
returns a #<subr> object, instead of function symbol, and several 
callers seem to depend on the return value being the latter (because 
they want to call symbol-function on it).

diff --git a/lisp/emacs-lisp/find-func.el b/lisp/emacs-lisp/find-func.el
index 7ea13d4..75fdfc7 100644
--- a/lisp/emacs-lisp/find-func.el
+++ b/lisp/emacs-lisp/find-func.el
@@ -192,9 +192,9 @@ defined in C.")
    "Return the original function symbol of an advised function FUNC.
  If FUNC is not the symbol of an advised function, just returns FUNC."
    (or (and (symbolp func)
-	   (featurep 'advice)
-	   (let ((ofunc (cdr (assq 'origname (ad-get-advice-info func)))))
-	     (and (fboundp ofunc) ofunc)))
+	   (featurep 'nadvice)
+	   (let ((ofunc (advice--symbol-function func)))
+	     (and (advice--p ofunc) (advice--cd*r ofunc))))
        func))

  (defun find-function-C-source (fun-or-var file type)

bug#20718: 25.0.50; find-function fails on advised subrs (again)

[Stefan Monnier]

> Something like the patch below should fix it, but then the function
> returns a #<subr> object, instead of function symbol, and several callers
> seem to depend on the return value being the latter (because they want to
> call symbol-function on it).

Indeed, even its docstring says that it returns "the original function
symbol", and that's basically meaningless in general (and in the
nadvice case in particular).

So the callers will need to be adjusted.


        Stefan


> diff --git a/lisp/emacs-lisp/find-func.el b/lisp/emacs-lisp/find-func.el
> index 7ea13d4..75fdfc7 100644
> --- a/lisp/emacs-lisp/find-func.el
> +++ b/lisp/emacs-lisp/find-func.el
> @@ -192,9 +192,9 @@ defined in C.")
>    "Return the original function symbol of an advised function FUNC.
>  If FUNC is not the symbol of an advised function, just returns FUNC."
>    (or (and (symbolp func)
> -	   (featurep 'advice)
> -	   (let ((ofunc (cdr (assq 'origname (ad-get-advice-info func)))))
> -	     (and (fboundp ofunc) ofunc)))
> +	   (featurep 'nadvice)
> +	   (let ((ofunc (advice--symbol-function func)))
> +	     (and (advice--p ofunc) (advice--cd*r ofunc))))
>        func))

>  (defun find-function-C-source (fun-or-var file type)

bug#20718: 25.0.50; find-function fails on advised subrs (again)

[Dmitry Gutov]

Version: 25.1

On 06/04/2015 06:55 PM, Stefan Monnier wrote:

> So the callers will need to be adjusted.

Ok, done. I seems to work now.