Plugin API

Status

Date:2008-02-29

bzrlib has a very flexible internal structure allowing plugins for many operations. Plugins can add commands, new storage formats, diff and merge features and more. This document provides an overview of the API and conventions for plugin authors.

Structure of a plugin

Plugins are Python modules under bzrlib.plugins. They can be installed either into the PYTHONPATH in that location, or in ~/.bazaar/plugins.

Plugins should have a setup.py.

As for other Python modules, the name of the directory must match the expected name of the plugin.

Plugin metadata before installation

Plugins can export a summary of what they provide, and what versions of bzrlib they are compatible with. This allows tools to be written to work with plugins, such as to generate a directory of plugins, or install them via a symlink/checkout to ~/.bazaar/plugins.

This interface allows bzr to interrogate a plugin without actually loading it. This is useful because loading a plugin may have side effects such as registering or overriding commands, or the plugin may raise an error, if for example a prerequisite is not present.

Metadata protocol

A plugin that supports the bzr plugin metadata protocol will do two things. Firstly, the setup.py for the plugin will guard the call to setup():

if __name__ == 'main':
    setup(...)

Secondly, the setup module will have one or more of the following variables present at module scope. Any variables that are missing will be given the defaults from the table. An example of every variable is provided after the full list.

Variable Default Definition
bzr_plugin_name None The name the plugin package should be given on disk. The plugin is then available to python at bzrlib.plugins.NAME
bzr_commands [] A list of the commands that the plugin provides. Commands that already exist in bzr and are decorated by the plugin do not need to be listed (but it is not harmful if you do list them).
bzr_plugin_version None A version_info 5-tuple with the plugins version.
bzr_minimum_version None A version_info 3-tuple for comparison with the bzrlib minimum and current version, for determining likely compatibility.
bzr_maximum_version None A version_info 3-tuple like bzr_minimum_version but checking the upper limits supported.
bzr_control_formats {} A dictionary of descriptions of version control directories. See Control Formats below.
bzr_checkout_formats {} A dictionary of tree_format_string -> human description strings, for tree formats that drop into the .bzr/checkout metadir system.
bzr_branch_formats {} As bzr_checkout_formats but for branches.
bzr_repository_formats {} As bzr_checkout_formats but for repositories.

Control Formats

Because disk format detection for formats that bzr does not understand at all can be useful, we allow a declarative description of the shape of a control directory. Each description has a name for showing to users, and a dictonary of relative paths, and the content needed at each path. Paths that end in '/' are required to be directories and the value for that key is ignored. Other paths are required to be regular files, and the value for that key is either None, in which case the file is statted but the content is ignored, or a literal string which is compared against for the content of the file. Thus:

# (look for a .hg directory)
bzr_control_formats = {"Mercurial":{'.hg/': None}}

# (look for a file called .svn/format with contents 4\n).
bzr_control_formats = {"Subversion":{'.svn/format': '4\n'}}

Example

An example setup.py follows:

#!/usr/bin/env python2.4
from distutils.core import setup

bzr_plugin_name = 'demo'
bzr_commands = [
    'new-command',
    ]

bzr_branch_formats = {
    "Branch label on disk\n":"demo branch",
    }

bzr_control_formats = {"Subversion":{'.svn/format': '4\n'}}

bzr_plugin_version = (1, 3, 0, 'dev', 0)
bzr_minimum_version = (1, 0, 0)

if __name__ == 'main':
    setup(name="Demo",
          version="1.3.0dev0",
          description="Demo plugin for plugin metadata.",
          author="Canonical Ltd",
          author_email="bazaar@lists.canonical.com",
          license = "GNU GPL v2",
          url="https://launchpad.net/bzr-demo",
          packages=['bzrlib.plugins.demo',
                    'bzrlib.plugins.demo.tests',
                    ],
          package_dir={'bzrlib.plugins.demo': '.'})

Plugin metadata after installation

After a plugin has been installed, metadata can be more easily obtained. Currently the only metadata used is for API versioning.

API version

Please see API versioning for details on the API metadata protocol used by bzrlib.