~bzr-pqm/bzr/bzr.dev

=============================
Centralized Workflow Tutorial
=============================


Overview
========

This document describes a possible workflow for using Bazaar_. That of
using Bazaar_, the distributed version control system, in a centralized
manner. Bazaar_ is designed to be very flexible and allows several
different workflows, from fully decentralized to mostly centralized.  The
workflow used here is meant to ease a new user into more advanced usage of
Bazaar_, and allow them to work in a mix of centralized and decentralized
operations.

In general, this document is meant for users coming from a background of
centralized version control systems such as CVS or subversion. It is
common in work settings to have a single central server hosting the
codebase, with several people working on this codebase, keeping their work
in sync.  This workflow is also applicable to a single developer working
on several different machines.

.. _Bazaar: http://bazaar.canonical.com


Initial Setup
=============

These are some reasonably simple steps to setup Bazaar_ so that it works
well for you.


Setting User Email
------------------

Your user identity is stored with each commit. While this doesn't have to
be accurate or unique, it will be used in log messages and
annotations, so it is better to have something real.

::

   % bzr whoami "John Doe <jdoe@organization.com>"


Setting up a local Repository
-----------------------------

Bazaar_ branches generally copy the history information around with them,
which is part of how you can work in a fully decentralized manner. As an
optimization, it is possible for related branches to combine their storage
needs so that you do not need to copy around all of this history
information whenever you create a new branch.

The best way to do this is to create a `Shared Repository`_. In
general, branches will share their storage if they exist in a
subdirectory of a `Shared Repository`_.  So let's set up a `Shared
Repository`_ in our home directory, thus all branches we create
underneath will share their history storage.

::

  % bzr init-repo --trees ~


Setting up a remote Repository
---------------------------------

Many times you want a location where data is stored separately from where
you do your work. This workflow is required by centralized systems
(CVS/SVN).  Usually they are on separate machines, but not always. This is
actually a pretty good setup, especially in a work environment. Since it
ensures a central location where data can be backed up, and means that if
something happens to a developer's machine, no committed work has to be
lost.

So let's set up a shared location for our project on a remote machine
called ``centralhost``. Again, we will use a
`Shared Repository`_ to optimize disk usage.

::

  % bzr init-repo --no-trees bzr+ssh://centralhost/srv/bzr/

You can think of this step as similar to setting up a new cvsroot, or
subversion repository.  The ``--no-trees`` option tells bzr to not
populate the directory with a working tree.  This is appropriate,
since no one will be making changes directly in the branches within
the central repository.

Here we're using a ``bzr+ssh`` URL, which means to use Bazaar's own
protocol on top of the SSH secure shell.  See the Administrator Guide for
information about setting up a bzr+ssh server.  


Migrating an existing project to Bazaar
=======================================

Now that we have a repository, let's create a versioned project. Most of
the time, you will already have some code that you are working with,
that you now want to version using Bazaar_. If the code was originally
in source control, there are many ways to convert the project to Bazaar_
without losing any history. However, this is outside the scope of this
document. See `Tracking Upstream`_ for some possibilities (section
"Converting and keeping history").

.. _Tracking Upstream: http://wiki.bazaar.canonical.com/TrackingUpstream

..
   XXX: We really need a different document for discussing conversion of a
   project. Right now TrackingUpstream is the best we have, though.


Developer 1: Creating the first revision
----------------------------------------

So first, we want to create a branch in our remote Repository, where we
want to host the project.  Let's assume we have a project named
"sigil" that we want to put under version control.

::

  % bzr init bzr+ssh://centralhost/srv/bzr/sigil

This can be thought of as the "HEAD" branch in CVS terms, or as the "trunk"
in Subversion terms. We will call this the ``dev`` branch.

I prefer working in a subdirectory of my home directory to avoid collisions with all
the other files that end up there. Also, we will want a project
directory where we can hold all of the different branches we end up
working on.

::

  % cd ~
  % mkdir work
  % cd work
  % mkdir sigil
  % cd sigil
  % bzr checkout bzr+ssh://centralhost/srv/bzr/sigil dev
  % cd dev
  % cp -ar ~/sigil/* .
  % bzr add
  % bzr commit -m "Initial import of Sigil"


In the previous section, we created an empty branch (the ``/sigil``
branch) on ``centralhost``, and then checkout out this empty branch
onto our workstation to add files from our existing project.  There
are many ways to set up your working directory, but the steps above
make it easy to handle working with feature/bugfix branches. And one
of the strong points of Bazaar_ is how well it works with branches.

At this point, because you have a 'checkout' of the remote branch, any
commits you make in ``~/work/sigil/dev/`` will automatically be saved
both locally, and on ``centralhost``.


Developer N: Getting a working copy of the project
--------------------------------------------------

Since the first developer did all of the work of creating the project,
all other developers would just checkout that branch. **They should
still follow** `Setting User Email`_ and `Setting up a local Repository`_.

To get a copy of the current development tree::

  % cd ~/work/sigil
  % bzr checkout bzr+ssh://centralhost/srv/bzr/sigil dev

Now that two people both have a checkout of
``bzr+ssh://centralhost/srv/bzr/sigil``, there will be times when one of
the checkouts will be out of date with the current version.
At commit time, Bazaar_ will inform the user of this and prevent them from
committing. To get up to date, use ``bzr update`` to update the
tree with the remote changes. This may require resolving conflicts if the
same files have been modified.


Developing on separate branches
===============================

So far everyone is working and committing their changes into the same
branch. This means that everyone needs to update fairly regularly and
deal with other people's changes. Also, if one person commits something
that breaks the codebase, then upon syncing, everyone will get the
problem.

Usually, it is better to do development on different branches, and then
integrate those back into the main branch, once they are stable. This is
one of the biggest changes from working with CVS/SVN. They both allow you
to work on separate branches, but their merging algorithms are fairly
weak, so it is difficult to keep things synchronized. Bazaar_ tracks
what has already been merged, and can even apply changes to files that
have been renamed.


Creating and working on a new branch
------------------------------------

We want to keep our changes available for other people, even if they
aren't quite complete yet. So we will create a new public branch on
``centralhost``, and track it locally.

::

  % cd ~/work/sigil
  % bzr branch bzr+ssh://centralhost/srv/bzr/sigil \
               bzr+ssh://centralhost/srv/bzr/sigil/doodle-fixes
  % bzr checkout bzr+ssh://centralhost/srv/bzr/sigil/doodle-fixes doodle-fixes
  % cd doodle-fixes

We now have a place to make any fixes we need to ``doodle``. And we would
not interrupt people who are working on other parts of the code.  Because
we have a checkout, any commits made in the ``~/work/sigil/doodle-fixes/``
will also show up on ``centralhost``. [#nestedbranches]_ It is also
possible to have two developers collaborate on one of these branches, just
like they would have collaborated on the ``dev`` branch. [#cbranch]_

.. [#nestedbranches] It may look odd to have a branch in a subdirectory of
   another branch. This is just fine, and you can think of it as a
   hierarchical namespace where the nested branch is derived from the
   outer branch.

.. [#cbranch] When using lots of independent branches, having to retype
   the full URL all the time takes a lot of typing. We are looking into
   various methods to help with this, such as branch aliases, etc. For
   now, though, the bzrtools_ plugin provides the ``bzr cbranch`` command.
   Which is designed to take a base branch, create a new public branch,
   and create a checkout of that branch, all with much less typing.
   Configuring ``cbranch`` is outside the scope of this document, but the
   final commands are similar to:

::

   % bzr cbranch dev my-feature-branch

.. _bzrtools: http://wiki.bazaar.canonical.com/BzrTools


Merging changes back
--------------------

When it is decided that some of the changes in ``doodle-fixes`` are ready
to be merged into the main branch, simply do::

  % cd ~/work/sigil/dev
  % bzr merge ../doodle-fixes

Now the changes are available in the ``dev`` branch, but they have not
been committed yet. This is the time when you want to review the final
changes, and double check the code to make sure it compiles cleanly and
passes the test suite. The commands ``bzr status`` and ``bzr diff`` are
good tools to use here. Also, this is the time to resolve any conflicts.
Bazaar_ will prevent you from committing until you have resolved these
conflicts. That way you don't accidentally commit the conflict markers.
The command ``bzr status`` will show the conflicts along with the other
changes, or you can use ``bzr conflicts`` to just list conflicts. Use
``bzr resolve file/name`` or ``bzr resolve --all`` once conflicts have
been handled. [#resolve]_ If you have a conflict that is particularly
difficult to solve you may want to use the ``bzr remerge`` command. It
will let you try different merge algorithms, as well as let you see the
original source lines (``--show-base``).

.. [#resolve] Some systems make you resolve conflicts as part of the merge
   process. We have found that it is usually easier to resolve conflicts
   when you have the view of the entire tree, rather than just a single
   file. It gives you much more context, and also lets you run tests as
   you resolve the problems.


Recommended Branching
---------------------

One very common way to handle all of these branches is to give each
developer their own branch, and their own place to work in the central
location. This can be done with::

  % bzr branch bzr+ssh://centralhost/srv/bzr/sigil \
               bzr+ssh://centralhost/srv/bzr/sigil/user-a
  % bzr branch bzr+ssh://centralhost/srv/bzr/sigil \
               bzr+ssh://centralhost/srv/bzr/sigil/user-b

This gives each developer their own branch to work on. And, they can
easily create a new feature branch for themselves with just [#cbranch]_
::

  % bzr branch bzr+ssh://centralhost/srv/bzr/sigil/user-a \
               bzr+ssh://centralhost/srv/bzr/sigil/user-a/feature
  % cd ~/work/sigil
  % bzr checkout bzr+ssh://centralhost/srv/bzr/sigil/user-a/feature myfeature


Glossary
========

Shared Repository
-----------------

Bazaar_ has the concept of a "Shared Repository". This is similar to
the traditional concept of a repository in other VCSs like CVS and
Subversion. For example, in Subversion you have a remote repository,
which is where all of the history is stored, and locally you don't
have any history information, only a checkout of the working tree
files. Note that "Shared" in this context means shared between
branches. It *may* be shared between people, but standalone branches
can also be shared between people.

In Bazaar_ terms, a "Shared Repository" is a location where multiple
branches can **share** their revision history information. In order to
support decentralized workflows, it is possible for every branch to
store its own revision history information. But this is often
inefficient, since related branches share history, and they might as
well share the storage as well.


..
   vim: tw=74 ft=rst spell spelllang=en_us