bug#2157: 23.0.90; bzr support: vc-diff doesn't work with prefix argument on unchanged files

[Dan Nicolaescu]

Torsten Bronger <bronger@physik.rwth-aachen.de> writes:

  > Hallöchen!
  > 
  > Dan Nicolaescu writes:
  > 
  > > Torsten Bronger <bronger@physik.rwth-aachen.de> writes:
  > >
  > >> If I visit an unchanged file under bzr revision control, i.e. the
  > >> modeline says "Bzr-" (NOT "Bzr:"), I can't use C-u C-x v =,
  > >> i.e. vc-diff but with explicit revision parameters.  The error
  > >> message is:
  > >> 
  > >> vc-bzr-previous-revision: Wrong type argument: stringp, nil
  > >
  > > I can't reproduce this on my GNU/Linux machine.  What version of
  > > bzr are you using?
  > 
  > 1.11
  > 
  > > Can you do: Options / Enter debugger on error and then please
  > > email here the contents of the *Backtrace* buffer that appears
  > > when the error occurs.
  > 
  > I hope this is what you need:
  > 
  > Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  >   string-match("\\`[0-9]+\\'" nil)
  >   
vc-bzr-previous-revision("/home/bronger/src/chantal/current/chantal/samples/remote_client/la2chantal.py"
 nil)
  >   apply(vc-bzr-previous-revision 
("/home/bronger/src/chantal/current/chantal/samples/remote_client/la2chantal.py"
 nil))
  >   vc-call-backend(Bzr previous-revision 
"/home/bronger/src/chantal/current/chantal/samples/remote_client/la2chantal.py" 
nil)
  >   (setq rev1-default (vc-call-backend backend (quote previous-revision) 
first (vc-working-revision first)))

This shows that (vc-working-revision 
"/home/bronger/src/chantal/current/chantal/samples/remote_client/la2chantal.py")
 

returns nil.  So probably for some reason
(vc-bzr-working-revision 
"/home/bronger/src/chantal/current/chantal/samples/remote_client/la2chantal.py")
 

returns nil.  Can you try to debug why that happens?