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Extending Bazaar with Hooks and Plugins
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=======================================
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Bazaar offers a powerful extension mechanism for adding capabilities. In
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addition to offering full library API access to all of its structures, which
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can be useful for outside programs that would like to interact with Bazaar
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branches, Bazaar can also load *plugins* that perform specific tasks. These
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specific tasks are specified by *hooks* that run during certain steps of the
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version control process.
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For full documentation on the available hooks, see ``bzr help hooks``. Among
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those, some of the most significant hooks from an administration
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standpoint are `pre_commit`, `post_commit` and `post_change_branch_tip`.
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A `pre_commit` hook can inspect a commit before it happens and cancel it if
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some criteria are not met. This can be useful for enforcing policies about
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the code, such as line-endings or whitespace conventions. A
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`post_commit` hook can take actions based on the commit that just happened,
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such as providing various types of notifications. Finally, a
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`post_change_branch_tip` hook is a more general form of a `post_commit`
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hook which is used whenever the tip of a branch changes (which can happen in
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more ways than just committing). This too can be used for notification
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purposes, as well as for backups and mirroring.
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Information on the whole range of Bazaar plugins is available at
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http://doc.bazaar.canonical.com/plugins/en/. For purposes of installation,
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plugins are simply python packages. They can be installed alongside Bazaar in
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the ``bzrlib.plugins`` package using each plugin's ``setup.py``. They can
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also be installed in the plugin path which is the user's ``~/.bazaar/plugins``
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directory or can be specified with the ``BZR_PLUGIN_PATH`` environment
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variable. See ``bzr help configuration`` for more on specifying the location
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A common need is for every change made on a branch to send an email message to
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some address, most often a mailing list. These plugins provide that capability
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in a number of different ways.
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The `email` plugin sends email from each individual developer's computer. This
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can be useful for situations that want to track what each individual developer
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is working on. On the downside, it requires that every developer's branches be
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configured individually to use the same plugin.
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The next two plugins `hookless-email` and `email-notifier` address this concern
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by running on a central server whenever changes happen on centrally stored
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To configure this plugin, simply install the plugin and configure the
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``post_commit_to`` option for each branch. This configuration can be done
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in the ``locations.conf`` file or individually in each branch's
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``branch.conf`` file. The sender's email address can be specified as
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``post_commit_sender`` if it is different than the email address reported by
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``bzr whoami``. The ``post_commit_mailer`` option specifies how the
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mail should be sent. If it isn't set, email is sent via ``/usr/bin/mail``.
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It can also be configured to communicate directly with an SMTP server.
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For more details on configuring this plugin, see
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http://doc.bazaar-vcs.org/plugins/en/email-plugin.html. As examples, consider
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the following two possible configurations. A minimal one (uses
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post_commit_to = projectx-commits@example.com
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and a more complicated one (using all of the options)
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post_commit_url = http://www.example.com/code/projectx/trunk
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post_commit_to = projectx-commits@example.com
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post_commit_sender = donotreply@example.com
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post_commit_mailer = smtplib
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smtp_server = mail.example.com:587
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# smtp_password = 'not specified, will prompt'
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This plugin is basically a server-side version of the `email` plugin. It is
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a program that runs either from the command line or as a daemon that monitors
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the branches specified on the command line for any changes. When a change
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occurs to any of the monitored branches, it will send an email to the
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specified address. Using our simple example, the following command would send
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an email to ``projectx-commits@example.com`` on any of the branches under
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``/srv/bzr`` since the last time the command was run. (This command could be
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set up to run at regular intervals, for example from ``cron``.)
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$ bzr_hookless_email.py --email=projectx-commits@example.com \
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This is a more elaborate version of the `hookless-email` plugin that can send
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templated HTML emails, render wiki-style markup in commit messages and update
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working copies on the server (similar to `push_and_update`_). It can also
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send emails reporting the creation of new branches or the removal of branches
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under a specified directory (here ``/srv/bzr/projectx``). As it is more
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complicated, its configuration is also more complicated and we won't repeat
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its documentation here, but a simple configuration that will send emails on
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commits and creation/deletion of branches is
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server=smtp.example.com
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# If user is not provided then no authentication will be performed.
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# The address to send commit emails to.
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to=projctx-commits@example.com
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from=$revision.committer
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# A Cheetah template used to construct the subject of the email message.
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subject=$relative_path: $revision_number $summary
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to=projectx-commits@example.com
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from=donotreply@example.com
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subject=$relative_path: New branch created
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to=projectx-commits@example.com
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from=donotreply@example.com
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subject=$relative_path: Branch removed
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If this file is stored as ``/srv/bzr/email-notifier.conf``, then the command
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$ bzr-email-notifier.py --config=/srv/bzr/email-notifier.conf /srv/bzr/projectx
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will watch all branches under the given directory for commits, branch
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creations and branch deletions.
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A related concept to sending out emails when branches change is the generation
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of news feeds from changes on each branch. Interested parties can then choose
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to follow those news feeds in order to see what is happening on a branch.
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This plugin creates an ATOM feed for every branch on every branch change
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(commit, etc.). It stores these files as ``.bzr/branch/branch.atom`` inside
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each branch. Currently, it includes the 20 most recent changes in each feed.
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To use it, simply install the plugin and set your feed reader to follow the
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``branch.atom`` files.
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In addition, there are other tools that are not plugins for creating news
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feeds from Bazaar branches. See http://bazaar-vcs.org/FeedGenerators for more
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Sometimes it is useful to ensure that one branch exists as an exact copy of
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another. This can be used to provide simple backup facilities or redundancy
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(see `Back-up and restore <backup.html>`_ for more details on backups). One
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way to do this using Bazaar's workflows is to make the branch where changes
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happen into a bound branch of the mirror branch. Then, when commits happen on
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the working branch, they will also happen on the mirror branch. Note that
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commits to bound branches do *not* update the mirror branch's working copy, so
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if the mirror branch is more than just a backup of the complete history of the
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branch, for example if it is being served as a web page, then additional
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plugins are necessary.
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This plugin updates Bazaar's ``push`` command to also update the remote
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working copy. It can only work over connections that imply filesystem or SSH
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access to the remote working copy (``bzr+ssh://``, ``sftp://`` and
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``file://``). Also, it is only useful when the remote branch is updated with
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an explicit ``push`` command.
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This plugin is similar to `push_and_update` in that it updates the working
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copy of a remote branch. The difference is that this plugin is designed to
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update the remote branch on every change to the working branch. To configure
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this, set the ``post_commit_mirror = URL`` option on a branch. This option
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can include multiple branch URLs separated by commas to create multiple
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mirrors. For example, if we want to mirror our ``/srv/bzr/projectx/trunk``
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branch to the URL ``sftp://www.example.com/var/www/projectx`` (for example if
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ProjectX were a web project that we wanted to access at
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``http://www.example.com/projectx``), then we could include
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post_commit_mirror = sftp://www.example.com/var/www/branches/trunk
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in the file ``/srv/bzr/projectx/trunk/.bzr/branch/branch.conf``.
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Facilitating interaction with `PQM
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<integration.html#patch-queue-manager-pqm>`_, this plugin provides support for
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submitting merge requests to a remote Patch Queue Manager. PQM provides
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a way to automatically run the test suite before merging changes to the
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Sometimes referred to as the poor man's PQM, this plugin runs a single command
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on the updated revision (in a temporary directory) and if the command returns
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0, then the revision can be committed to that branch. For example, if the
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testsuite is run with the command ``nosetests`` in the root of the branch
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(which returns 0 if the test suite passes and 1 if it doesn't pass), then one
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pre_change_branch_tip_test_command = nosetests
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in ``.bzr/branch/branch.conf``.
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This plugin is an example of a `pre_commit` hook that checks the revision
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being committed for meeting some policy. In this case, it checks that all of
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the files have the specified line endings. It uses a configuration file
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``.bzreol`` in the root of the working tree (similar to the ``.bzrignore``
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file). This configuration file has sections for line feed endings (LF),
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carriage return/line-feed endings (CRLF) and carriage return endings (CR).
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For an unusual example that specifies different line endings for different
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files, that file might look like
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or if you simply want to enforce a single line ending convention on the branch
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This plugin needs to be installed on the server where the branch updates will
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happen, and the ``.bzreol`` file must be in each branch where line ending
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policies will be enforced. (Adding it to the branch with ``bzr add .bzreol``
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is an easy way to ensure this, although it means that branches on the server
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must have working trees.)
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This plugin is a more advanced version of `checkeol` that can check such
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coding style guidelines such as trailing whitespace, long lines and files that
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don't end with a newline. It is configured using Bazaar's built in rules
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specification in ``BZR_HOME/rules`` (see ``bzr help rules`` for more
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information. For different types of undesired changes, you can specify
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different types of actions. For example
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trailing_whitespace=fail
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newline_at_eof=ignore
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trailing_whitespace=fail
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will prevent changes from adding new trailing whitespace to the specified
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files and keep all python source files free of tabs and lines over 78
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characters. To commit while violating these rules, one can pass the
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``--text-check-warn-only`` option to commit.
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doc/en/admin-guide/hooks-plugins.txt
