pull does not understand lp: URLs in branch.conf

I've just put lp:qbzr/0.18 into the branch.conf of my qbzr development branch.

Trying standard bzr commands:

C:\work\Bazaar\plugins\qbzr>bzr info
Lightweight checkout (format: 2a)
Location:
  light checkout root: .
   checkout of branch: .bzr/branches/0.18
    shared repository: .bzr/branches

Related branches:
  parent branch: .bzr/branches/0.18/lp:qbzr/0.18

C:\work\Bazaar\plugins\qbzr>bzr pull
Using saved parent location: C:/work/Bazaar/plugins/qbzr/.bzr/branches/0.18/lp:qbzr/0.18
bzr: ERROR: Not a branch: "C:/work/Bazaar/plugins/qbzr/.bzr/branches/0.18/lp:qbzr/0.18/".

So as I can see the standard bzr behavior is the same as qbzr one: bzr don't understand directory services in branch.conf. And because qbzr just uses bzr API we get the same problems as bzr core has.

Based on your bug report I don't understand how it actually works for you with plain `bzr pull`.

I'm inclined to mark this bug as Invalid for QBzr or re-assign it to bzr core.

It seems that this is indeed a bug in core bzr. It works for 'bzr push' but not 'bzr pull':

C:\dev\bzr-mac-installers\2.1>bzr info
Repository tree (format: 2a)
Location:
  shared repository: C:/dev/bzr-mac-installers
  repository branch: .

Related branches:
  public branch: lp:bzr-mac-installers/2.1
    push branch: lp:bzr-mac-installers/2.1
  parent branch: lp:bzr-mac-installers/2.1
  submit branch: lp:bzr-mac-installers

C:\dev\bzr-mac-installers\2.1>bzr pull
Using saved parent location: C:/dev/bzr-mac-installers/2.1/lp:bzr-mac-installers/2.1
bzr: ERROR: Not a branch: "C:/dev/bzr-mac-installers/2.1/lp:bzr-mac-installers/2.1/".

C:\dev\bzr-mac-installers\2.1>bzr push
Using saved push location: lp:bzr-mac-installers/2.1
Connected (version 2.0, client Twisted)
Authentication (publickey) successful!
Secsh channel 1 opened.
No new revisions to push.

@Gordon, since you confirmed that the bug is in bzr-core, you can just as well change the status and the importance.
I trust your judgment here :)

So Branch.get_parent() uses urlutils.join() to join the branch base dir and the parent location, I guess in case the parent location is a relative dir (e.g. ../trunk). However, urlutils.join() doesn't recognize lp:blah as an absolute URL, which it would treat specially and return without concatenating. The regex it uses to detect URLs assumes something like "scheme://path".