RE: Reverting but keeping undo

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

> >> FWIW, I just installed a patch in Emacs's trunk which makes that
> >> revert-buffer doesn't discard undo history any more.
> >
> > Hm. So `revert-buffer' no longer removes undo? That has always been a
> > part of what reverting means. And it is clearly intended in the code,
> > not just an unfortunate accident or oversight.
> 
> I think it's a great change.
>
> > And why no discussion beforehand?

Yes, why?  Any good reason?

> > I can't think of a great reason why
> > undo should *always* be removed as part of reverting (as it always has
> > been). But just maybe there is a good reason for doing that, at least
> > some or even most of the time. Why not give Richard et al the benefit
> > of the doubt (30 years of "classic" reverting) and make undo removal
> > optional, at least for a while? (Or is doubt a no-no?)
> 
> Are you, personally, asking for it to be customizable?

Code and users should control whether to get the new behavior or the behavior they've had for the last 3 decades.  (Sure, users can add back code themselves to empty the undo list and get back the former behavior...)

> What's your use case for throwing away the undo list?

That's what reverting is about: returning to an initial state.  The undo list did not exist when the buffer was first visited - a new buffer has no undo.  Reverting generally means starting over from scratch - i.e., putting things in the same state they had at the outset (since the last save).

Yes, there are some exceptions - some buffers have special reverting behavior.  And yes, we can define Emacs to be anything.  We can change what reverting means generally in Emacs, if we want.  But such a basic change calls for a little discussion at emacs-devel, don't you think?

Maybe someone wants to keep some highlighting they applied in the buffer too, or keep some local variables, or...  A similar argument could be made for keeping all sorts of changes to the buffer state after "reversion".  But generally the way to make any such design/behavior change is to first propose and discuss in emacs-devel@gnu.org.  

There might well be someone out there who, "personally" or not (?), has (another) good argument for keeping things the way they were - at least as an option.  Who knows?  As Richard often says (especially for changes to basic, longstanding behavior), why not poll the users?

Do you "personally" know that no one wants to drop the undo list when reverting - whether interactively or in code?

Don't you wonder that this came up now seemingly for the first time?  Do you think that no one has thought before about whether the undo list should be kept or dropped when reverting?  A bit presumptuous, no?

Give those who designed and first implemented buffers and buffer reverting the benefit of the doubt, at least to start with.  They were not necessarily right, but they were not obviously wrong, which is seemingly the way you look at it.  To you it is apparently a no-brainer that undo should not be dropped - how silly they were in the old days...

Has something changed recently that suddenly makes the original design no longer appropriate?  What's new here?  Facebook?  Mobile apps?  The Kardashians?  Why should this behavior be changed now - why not before?

Think about it a bit more.  Open it for discussion on emacs-devel.  Why act so precipitously?  Is that "personally" necessary?