Subject: bug#24353: 25.1.1: looking-back wrong info

From: [email-masked]
Date: Fri, 02 Sep 2016 20:14:36 -0400

Drew Adams <[email-masked]> writes:
>
> The right way to _encourage_ programmers to use it is to
> tell them precisely that: "Using LIMIT is recommended - it
> typically results in faster code."
>
> Or "strongly recommended".  Or "You're nuts if you omit LIMIT!"
> Or whatever other positive or negative encouragement you think
> might be most effective and appropriate.
>
> Telling them nothing about this and, instead, just showing a
> false signature, does NOT help them.

So something like this:

diff --git i/lisp/subr.el w/lisp/subr.el
index e9e19d3..4d1267a 100644
--- i/lisp/subr.el
+++ w/lisp/subr.el
@@ -3533,7 +3533,10 @@ looking-back
 LIMIT.
 
 As a general recommendation, try to avoid using `looking-back'
-wherever possible, since it is slow."
+wherever possible, since it is slow.
+
+For backwards compatibility LIMIT may be omitted, but this usage
+is deprecated."
   (declare
    (advertised-calling-convention (regexp limit &optional greedy) "25.1"))
   (let ((start (point))

>> > It should be a no-no to just change the advertized
>> > signature of a function, without changing the actual
>> > signature (code) and without otherwise changing the doc.
>> 
>> You have some point there, but mentioning the last argument in the
>> docstring would be rather awkward, considering it's absent in the
>> advertised signature.

The number (and names) of arguments have not been changed.

>
> 2. We removed this sentence, which was the only suggestion
>    related to performance:
>
>    "As a general recommendation, try to avoid using
>     `looking-back' wherever possible, since it is slow."

Not sure which version you're looking at, but that sentence is still
present on both emacs-25 and master branches.