~bzr/bzr/bzr.1.5

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bzr-svn
=======

Overview
--------

bzr-svn lets developers use Bazaar as their VCS client on projects
still using a central Subversion repository. Access to Subversion
repositories is largely transparent, i.e. you can use most ``bzr``
commands directly on Subversion repositories exactly the same
as if you were using ``bzr`` on native Bazaar branches.

Many bzr-svn users create a local mirror of the central Subversion
trunk, work in local feature branches, and submit their
overall change back to Subversion when it is ready
to go. This lets them gain many of the advantages of distributed
VCS tools without interrupting existing team-wide processes and
tool integration hooks currently built on top of Subversion. Indeed,
this is a common interim step for teams looking to adopt Bazaar but
who are unable to do so yet for timing or non-technical reasons.

For installation instructions, see the bzr-svn home page:
http://bazaar-vcs.org/BzrForeignBranches/Subversion.


A simple example
----------------

Here's a simple example of how you can use bzr-svn to hack on a
GNOME project like **beagle**. Firstly, setup a local shared repository
for storing your branches in and checkout the trunk::

  bzr init-repo --rich-root-pack beagle-repo
  cd beagle-repo
  bzr checkout svn+ssh://svn.gnome.org/svn/beagle/trunk beagle-trunk

Note that using the ``rich-root-pack`` option to ``init-repo`` is
important as bzr-svn requires some extra metadata not yet supported in Bazaar's
default repository format. Next, create a feature branch and hack away::

  bzr branch beagle-trunk beagle-feature1
  cd beagle-feature1
  *changes*
  bzr commit -m "blah blah blah"
  *changes*
  bzr commit -m "blah blah blah"

When the feature is cooked, refresh your trunk mirror and merge
your change::

  cd ../beagle-trunk
  bzr update
  bzr merge ../beagle-feature1
  bzr commit -m "Complete comment for SVN commit"

As your trunk mirror is a checkout, committing to it implicitly
commits to the real Subversion trunk. That's it!


Using a central repository mirror
---------------------------------

For large projects, it often makes sense to tweak the recipe given above.
In particular, the initial checkout can get quite slow so you may wish
to import the Subversion repository into a Bazaar one once and for all
for your project, and then branch from that native Bazaar repository
instead. bzr-svn provides the ``svn-import`` command for doing this
repository-to-repository conversion. Here's an example of how to use it::

  bzr init-repo --rich-root-pack beagle.bzr
  cd beagle.bzr
  bzr svn-import svn+ssh://svn.gnome.org/svn/beagle

Here's the recipe from above updated to use a central Bazaar mirror::

  bzr init-repo --rich-root-pack beagle-repo
  cd beagle-repo
  bzr branch bzr+ssh://bzr.gnome.org/beagle.bzr/trunk beagle-trunk
  bzr branch beagle-trunk beagle-feature1
  cd beagle-feature1
  *changes*
  bzr commit -m "blah blah blah"
  *changes*
  bzr commit -m "blah blah blah"
  cd ../beagle-trunk
  bzr pull
  bzr merge ../beagle-feature1
  bzr commit -m "Complete comment for SVN commit"
  bzr push

In this case, committing to the trunk only commits the merge locally.
To commit back to the master Subversion trunk, an additional command
(``bzr push``) is required.

Note: You'll need to give ``pull and ``push`` the relevant URLs
the first time you use those commands in the trunk branch. After that,
bzr remembers them.

The final piece of the puzzle in this setup is to put scripts in
place to keep the central Bazaar mirror synchronized with the Subversion
one. This can be done by adding a cron job, using a Subversion hook,
or whatever makes sense in your environment.


Limitations of bzr-svn
----------------------

Bazaar and Subversion are different tools with different capabilities
so there will always be some limited interoperability issues.
Here are some examples current as of bzr-svn 0.4.10:

 * Bazaar doesn't support versioned properties

 * Bazaar doesn't support tracking of file copies.

 * ``bzr push`` to an existing Subversion branch works but 
   ``bzr push`` to a new Subversion branch doesn't. Until
   the relevant bug is fixed (#121875), you need to use
   ``bzr svn-push`` in the latter case.

See the bzr-svn web page,
http://bazaar-vcs.org/BzrForeignBranches/Subversion,
for the current list of constraints.