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Re: Is this a bug?
From: |
Tassilo Horn |
Subject: |
Re: Is this a bug? |
Date: |
Tue, 03 Dec 2013 09:46:19 +0100 |
User-agent: |
Gnus/5.130008 (Ma Gnus v0.8) Emacs/24.3.50 (gnu/linux) |
Perry Smith <pedzsan@gmail.com> writes:
Hi Perry,
> Now the non-working case. Repeat the above after adding advice:
>
> (defadvice load (before load-log activate)
> (message "Loading %s" (ad-get-arg 0)))
>
> and I get an error with the stack:
>
> Debugger entered--Lisp error: (wrong-type-argument subrp (lambda (file
> &optional noerror nomessage n$
> subr-name((lambda (file &optional noerror nomessage nosuffix must-suffix)
It seems like a bug in 24.3 since your example now works with the
current bzr trunk. Nevertheless, the docs explicitly warn about
advising subrs like `load':
,----[ (info "(elisp)Advising Functions") ]
| Unless you know what you are doing, do _not_ advise a primitive
| (*note What Is a Function::). Some primitives are used by the advice
| mechanism; advising them could cause an infinite recursion. Also, many
| primitives are called directly from C code. Calls to the primitive from
| Lisp code will take note of the advice, but calls from C code will
| ignore the advice.
`----
The concrete problem is that `help-C-file-name' assumes that a function
defined in C is a subr. But when you add a piece of advice, the subr
is wrapped in a lisp function, and then `subr-name' fails.
--8<---------------cut here---------------start------------->8---
ELISP> (symbol-function 'load)
#<subr load>
ELISP> (defadvice load (before load-log activate)
(message "Loading %s" (ad-get-arg 0)))
load
ELISP> (symbol-function 'load)
#[128 "\300\301\302.#\207"
[apply ad-Advice-load #<subr load> nil]
5
#("Advised function" 0 16
(dynamic-docstring-function advice--make-docstring))]
--8<---------------cut here---------------end--------------->8---
After defining the advice with the current bzr version, the help buffer
states "load is a compiled Lisp function" without any file link. That's
better than an error, but still not perfect. One could get the original
subr with (ad-get-orig-definition 'load) to also include a link to the C
source.
I just checked: with emacs 23, when you advised load or any other subr,
C-h f still had a link to the C source, so IMHO that counts as a
regression.
Bye,
Tassilo