~bzr-pqm/bzr/bzr.dev

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Bazaar plugins

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Information on how to use plugins in Bazaar.

What is a Plugin

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A plugin is an external component for Bazaar that is typically made by

third parties. A plugin is capable of augmenting Bazaar by adding new

functionality.  A plugin can also change current Bazaar behavior by

replacing current functionality. Plugins often work as a way for

developers to test new features for Bazaar prior to inclusion in the

official codebase. Plugins can do a variety of things, including

overriding commands, adding new commands, providing additional network

transports, or customizing log output. The sky is the limit for the

customization that can be done through plugins.

Where to find Plugins 

=====================

We keep our list of plugins on the http://bazaar-vcs.org/BzrPlugins page.

How to Install a plugin 

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Installing a plugin is very easy! One can either install a plugin

system-wide or on a per user basis. Both methods involve creating a

``plugins`` directory. Within this directory one can place plugins in

subdirectories. For example, ``plugins/bzrtools/``.

Two locations are currently checked:  the bzrlib/plugins directory

(typically found in ``/usr/lib/python2.4/site-packages/bzrlib/plugins/``) and

``$HOME/.bazaar/plugins/``.

One can additionally override the home plugins by setting the environment

variable ``BZR_PLUGIN_PATH`` to a directory that contains plugins. The

installation of a plugin can be checked by running ``bzr plugins`` at

any time. New commands can be seen by running ``bzr help commands``.

The commands provided by a plugin are shown followed by the name of the

plugin in brackets.

Plugins work particularly well with Bazaar branches. For example, to

install the bzrtools plugins for your main user account, one can perform

the following:: 

    bzr branch http://panoramicfeedback.com/opensource/bzr/bzrtools

    ~/.bazaar/plugins/bzrtools

When installing plugins the directories that you install them in must

be valid python identifiers. This means that they can only contain

certain characters, notably they cannot contain hyphens (``-``). Rather

than installing ``bzr-gtk`` to ``~/.bazaar/plugins/bzr-gtk``, install it

to ``~/.bazaar/plugins/gtk``.

Writing a plugin

================

Plugins are very similar to bzr core functionality.  They can import

anything in bzrlib.  A plugin may simply override standard functionality,

but most plugins supply new commands.

To create a command, make a new object that derives from

``bzrlib.commands.Command``, and name it ``cmd_foo``, where foo is the name of

your command.  If you create a command whose name contains an underscore,

it will appear in the UI with the underscore turned into a hyphen.  For

example, `cmd_baz_import` will appear as `baz-import`.  For examples of how

to write commands, please see ``builtins.py``.

Once you've created a command you must register the command with

``bzrlib.commands.register_command(cmd_foo)``.  You must register the

command when your file is imported, otherwise bzr will not see it.

Bzr will scan ``bzrlib/plugins`` and ``~/.bazaar/plugins`` for plugins

by default.  You can override this with ``BZR_PLUGIN_PATH``.  Plugins

may be either modules or packages.  If your plugin is a single file,

you can structure it as a module.  If it has multiple files, or if you

want to distribute it as a bzr branch, you should structure it as a

package, i.e. a directory with an ``__init__.py`` file.

Please feel free to contribute your plugin to BzrTools, if you think it

would be useful to other people.