RE: RCS, again: another removed functionality: undo last-checkin

[Drew Adams <drew.adams@oracle.com>]

> > Breaking backward compatibility is about the worst crime package
> > maintainers could commit, in my opinion.  (I know it's not shared by
> > many of the others.)
> 
> This general opinion (and you're not alone holding it) is one of the
> most tedious parts of the Emacs ecosystem, IME. It's not that I *love*
> removing features, but being unable to do that at all makes the burden
> of a maintainer harder when making changes or adding new features.

Emacs is not just for its maintainers.  It is above all for its users.

And plenty of users, for plenty of reasons, do not use the latest &
greatest version of Emacs.  And yes, Emacs is exceptional in its aim
to be especially easy for users to extend.  Emacs is _designed_ for
user extension and customization (as is Lisp, BTW).

> Removing features is always a tradeoff. While no one wants to make old
> users sad, if their needs would still be achievable at the cost of
> workflow changes, we should be able to make that sacrifice.

Whose workflow?  Are you saying that you are willing to sacrifice
a user's workflow & habits, so they can take advantage of the latest
shiny new features you have to offer?  How gracious of you!

> At some point in the future (distant, in all likelihood, so this is just
> a rough example), I imagine that would mean sacrificing support for
> antique VC backends entirely, in favor of simpler VC implementation, or
> better support of the newer backends. There's nothing stopping the
> veterans from adopting modern VCSes, you know.

There can be plenty of things stopping a given user from adopting
your favorite modern whatever, including a VCS.

Many users use tools, including Emacs that are installed
organization-wide (e.g., company-wide).

What percentage of Emacs users do you think build Emacs themselves
for their use at work?  (No, I don't have a figure in mind, but
I'm pretty sure that the average core Emacs maintainer/developer
is not a typical user.)