bug#4179: vc-merge with svn: syntax error in revision arg.

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

Dieter Wilhelm <dieter@duenenhof-wilhelm.de> writes:

  > Hi,
  > 
  > when running `vc-merge' for a subversion controlled file (this happens
  > also with Emacs 23.1.50 by the way) with an integer argument (I'd like
  > to specify two svn revision numbers), I'm tumbling into this:
  > 
  > svn: Syntax error in revision argument ':10'
  > 
  > (What I'd like to submit to svn is this: svn merge -r '10:8' ...)
  > 
  > vc-merge (in vc.el) thinks that an integer is a branch ID instead of a
  > svn revision # because of the following function:
  > 
  > (defun vc-branch-p (rev)
  >   "Return t if REV is a branch revision."
  >   (not (eq nil (string-match "\\`[0-9]+\\(\\.[0-9]+\\.[0-9]+\\)*\\'" rev))))

Good catch!  This function is from the time when RCS style revision
numbers where the only thing supported, here's what the comment in the
code says:

;; functions that operate on RCS revision numbers.  This code should
;; also be moved into the backends.  It stays for now, however, since
;; it is used in code below.


Stefan, how would you go about making these functions backend specific:

(defun vc-trunk-p (rev)
(defun vc-branch-p (rev)
(defun vc-branch-part (rev)
(defun vc-minor-part (rev)

It seems to me that only `vc-branch-p' needs to be backend specific, the
rest are only used by RCS and CVS. 

vc-default-{previous,next}-revision use them, but they can go into
vc-rcs (or vc-cvs) and make one use the other (there's a precedent,
vc-cvs-comment-history uses an RCS backend function...).

Do you see an elegant way of dealing with this?