GNU bug report logs - #23419
25.0.93; double-click-time

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: martin rudalics <rudalics <at> gmx.at>
To: Bug-Gnu-Emacs <bug-gnu-emacs <at> gnu.org>
Subject: 25.0.93; double-click-time
Date: Mon, 02 May 2016 10:03:22 +0200

The documentation of ‘double-click-time’ is as:

  Maximum time between mouse clicks to make a double-click.
  Measured in milliseconds.  The value nil means disable double-click
  recognition; t means double-clicks have no time limit and are detected
  by position only.

However, most uses of ‘double-click-time’ in the lisp directory silently
assume that the value is a number which typically fails in ‘sit-for’s
like, for example, in help.el's

  (not (sit-for (/ double-click-time 1000.0) t))

when ‘double-click-time’ is either t or nil.

Could someone out there who understands the semantics of these
‘sit-for’s please fix them.  I can eventually do that myself but these
semantics are yet pretty unclear to me.

TIA, martin

Message #8 received at 23419 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: martin rudalics <rudalics <at> gmx.at>
Cc: 23419 <at> debbugs.gnu.org
Subject: Re: bug#23419: 25.0.93; double-click-time
Date: Fri, 14 Aug 2020 20:49:18 -0700

[Message part 1 (text/plain, inline)]

tags 23419 + patch
thanks

martin rudalics <rudalics <at> gmx.at> writes:

> The documentation of ‘double-click-time’ is as:
>
>   Maximum time between mouse clicks to make a double-click.
>   Measured in milliseconds.  The value nil means disable double-click
>   recognition; t means double-clicks have no time limit and are detected
>   by position only.
>
> However, most uses of ‘double-click-time’ in the lisp directory silently
> assume that the value is a number which typically fails in ‘sit-for’s
> like, for example, in help.el's
>
>   (not (sit-for (/ double-click-time 1000.0) t))
>
> when ‘double-click-time’ is either t or nil.
>
> Could someone out there who understands the semantics of these
> ‘sit-for’s please fix them.  I can eventually do that myself but these
> semantics are yet pretty unclear to me.

I can confirm this.  To reproduce the issue in help.el, use:

0. emacs -Q
1. (setq double-click-time nil)
2. C-h k mouse-1

In the attached patch I add a new function `mouse-double-click-time'
which always returns a number.  This seems better than adding
specialized logic everywhere to handle the various cases.

Any comments?

Best regards,
Stefan Kangas

[0001-Fix-handling-double-click-time-nil-or-t-Bug-23419.patch (text/x-diff, attachment)]

Message #15 received at 23419 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Stefan Kangas <stefan <at> marxist.se>
Cc: rudalics <at> gmx.at, 23419 <at> debbugs.gnu.org
Subject: Re: bug#23419: 25.0.93; double-click-time
Date: Sat, 15 Aug 2020 10:01:34 +0300

> From: Stefan Kangas <stefan <at> marxist.se>
> Date: Fri, 14 Aug 2020 20:49:18 -0700
> Cc: 23419 <at> debbugs.gnu.org
> 
> In the attached patch I add a new function `mouse-double-click-time'
> which always returns a number.  This seems better than adding
> specialized logic everywhere to handle the various cases.

I don't see how this resolves the issue pointed out by Martin.  How do
we know that the problematic callers will DTRT with the arbitrary
values your function returns for t and nil?  Using a very large number
for t may be a good approximation (although I'm not even sure in that
case), but using zero for nil?

I'm afraid there's no way around auditing each caller and determining
what those non-numerical values mean in each case.  For example, I'd
actually suggest to avoid the call to sit-for in the nil case, because
a double-click will never be "on the way" in that case.

Thanks.

Message #20 received at 23419 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: rudalics <at> gmx.at, Stefan Kangas <stefan <at> marxist.se>, 23419 <at> debbugs.gnu.org
Subject: Re: bug#23419: 25.0.93; double-click-time
Date: Mon, 02 May 2022 12:04:44 +0200

Eli Zaretskii <eliz <at> gnu.org> writes:

> I'm afraid there's no way around auditing each caller and determining
> what those non-numerical values mean in each case.  For example, I'd
> actually suggest to avoid the call to sit-for in the nil case, because
> a double-click will never be "on the way" in that case.

I've gone through all the usage sites, and I think Stefan's patch is
correct -- they're using double-click-time as a sensible default for
what they're doing, but they're not really interested in the nil logic
(i.e., they're not supposed to be disabled in that case).

So I've now pushed Stefan's patch to Emacs 29.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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