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

[Dmitry Gutov <dgutov@yandex.ru>]

On 09/23/2015 04:26 PM, Stefan Monnier wrote:

> The "revert" (which IIUC just installs a new change which undoes the
> effect of some earlier change) can mostly be implemented in
> a backend-independent way.

Yep. But then it won't be the "rollback" command that's been requested.

> But the "rollback" (which IIUC can destructively remove an previous
> existing commit, I guess I'd call it "uncommit") is a lot more
> problematic, since various backends support it in very different ways
> with very different limitations.

Ok, if you're sure about that.

> Generalizing the "Amend:" support of
> vc-git.el to other backends would probably cover 99% of the use cases.

We'd have to see more opinions on this - e.g. the use cases for 
vc-uncommit and vc-amend that I can imagine would be slightly different.

Regarding "Amend:", we might want to start with taking care of the main 
annoyance (IME): when there are no changes to files, I can't easily 
amend the current commit with the purpose of changing its message.

How would handle that? Make `C-u C-x v v' ignore the 'up to date' 
status? Create a separate command for "amend"?

> If you feel it's really important that user be able to delete a revision
> from within Emacs, why not provide a vc-rcs-delete-commits command in
> vc-rcs.el?

I don't feel that anything related to RCS can be classified as "really 
important". It would be useful if it's implemented in modern backends. 
But rollback isn't hard to do by hand anyway.

> That would be a lot simpler to implement and wouldn't force us
> to come up with some weird pseudo-generic functionality that might end
> up not even supporting 100% of RCS's use cases.

Naturally: if the semantics are that different between RCS and Git, we 
shouldn't try to force both into something unnatural.