bug#24518: 25.2.50; dired-mark-extension with prefix arg fails

[Eli Zaretskii <eliz@gnu.org>]

> From: Tino Calancha <tino.calancha@gmail.com>
> Date: Sat, 24 Sep 2016 21:30:11 +0900 (JST)
> cc: Tino Calancha <tino.calancha@gmail.com>, 24518@debbugs.gnu.org
> 
> 
> On Sat, 24 Sep 2016, Eli Zaretskii wrote:
> 
> > This loses the feature whereby the user could also specify the
> > character to use as the marker.  Try "C-u 65 * . el RET" to see what
> > that does.
> That feature has never being available since `dired-x' was added to Emacs
> in 1994: the bug came from the very first commit.  No user will miss
> that feature because nobody ever could use it.

??? The example I gave works with the unmodified sources.  When used
as I've shown, there's no bug, and the command does what I expect.  So
how can we be sure no one ever used it that way and won't miss this
optional behavior?

Can you explain your logic here?

> > While using the numeric code of a character sounds like a kludge, the
> > current implementation seems to do that deliberately.  It might make 
> > sense to use 'c' instead of 'P' there, I think, but your patch totally
> > changes the semantics of the prefix argument, so I'm not sure I can 
> > endorse such a change.
> Sure, we could use 'c' and fix it.  We could provide such feature not working
> in >20 years without nobody oppening a bug report.  That sounds like a
> not useful feature at all.

It's an existing feature.  I won't agree to removing features that
existed for the last 22 years without a very good reason.  We have no
good means of finding out whether anyone out there uses this; if
someone does, removing this feature will most probably be a source of
aggravation for them.

> Believe me, using a prefix argument for unmark is very useful.

I believe you.  But we will have to provide this feature without
breaking other existing features.

> For me this uniform behaviour between these two marking commands is
> a very nice thing.

I don't disagree.  I just don't want to break existing features.

Thanks.