Re: vc commit clears undo history

[Dan Nicolaescu <dann@ics.uci.edu>]

Sam Steingold <sds@gnu.org> writes:

  > David Kastrup wrote:
  > > "Sam Steingold" <ssteingold@janestcapital.com> writes:
  > > 
  > >> GNU Emacs 23.0.50.29 (x86_64-unknown-linux-gnu, GTK+ Version 2.8.20)
  > >>  of 2007-12-03 on nyc-qws-005
  > >>  '-with-gtk' '-with-gif=no'
  > >>
  > >> a long-standing bug (bad feature?) is that when a file is committed
  > >> using vc (C-x v v) or pcvs (c in *cvs* buffer), it buffer's undo history
  > >> is discarder.

I have a patch that tries to avoid discarding the undo by looking at the
md5 checksum of the buffer contents and the file on disk. But I am not
100% confident that it is entirely correct....

  > > I think the rationale for that might be that in order to have the files
  > > identifiable as unmodified, some version control systems might do a
  > > recheckout on them, and replace strings like $Id: whatever$ with
  > > different information.  In any case, a revert-buffer is done on the file
  > > after checking it in, I believe.
  > > 
  > > It might not be easy to get consistent undo information in this case.
  > 
  > fwiw, "other vc interfaces", such as dvc (which interfaces to
  > distributed VCs (haz/hg/git &c), do not discard the undo information
  > after a commit.

How does it deal with the case when the file contains keywords that are
expanded on commit?
BTW VC interfaces with distributed VCs just fine.