14
bzrlib has a very flexible internal structure allowing plugins for many
15
operations. Plugins can add commands, new storage formats, diff and merge
16
features and more. This document provides an overview of the API and
17
conventions for plugin authors.
19
If you're writing a plugin and have questions not addressed by this
20
document, please ask us.
25
* `Bazaar Developer Documentation Catalog <index.html>`_.
26
* <http://bazaar-vcs.org/WritingPlugins> wiki page with many more
27
suggestions about particular APIs
33
Plugins are Python modules under ``bzrlib.plugins``. They can be installed
34
either into the PYTHONPATH in that location, or in ~/.bazaar/plugins.
36
Plugins should have a setup.py.
38
As for other Python modules, the name of the directory must match the
39
expected name of the plugin.
42
Plugin metadata before installation
43
===================================
45
Plugins can export a summary of what they provide, and what versions of bzrlib
46
they are compatible with. This allows tools to be written to work with plugins,
47
such as to generate a directory of plugins, or install them via a
48
symlink/checkout to ~/.bazaar/plugins.
50
This interface allows bzr to interrogate a plugin without actually loading
51
it. This is useful because loading a plugin may have side effects such
52
as registering or overriding commands, or the plugin may raise an error,
53
if for example a prerequisite is not present.
59
A plugin that supports the bzr plugin metadata protocol will do two
60
things. Firstly, the ``setup.py`` for the plugin will guard the call to
63
if __name__ == 'main':
66
Secondly, the setup module will have one or more of the following variables
67
present at module scope. Any variables that are missing will be given the
68
defaults from the table. An example of every variable is provided after
71
+------------------------+---------+----------------------------------------+
72
| Variable | Default | Definition |
73
+========================+=========+========================================+
74
| bzr_plugin_name | None | The name the plugin package should be |
75
| | | given on disk. The plugin is then |
76
| | | available to python at |
77
| | | bzrlib.plugins.NAME |
78
+------------------------+---------+----------------------------------------+
79
| bzr_commands | [] | A list of the commands that the plugin |
80
| | | provides. Commands that already exist |
81
| | | in bzr and are decorated by the plugin |
82
| | | do not need to be listed (but it is not|
83
| | | harmful if you do list them). |
84
+------------------------+---------+----------------------------------------+
85
| bzr_plugin_version | None | A version_info 5-tuple with the plugins|
87
+------------------------+---------+----------------------------------------+
88
| bzr_minimum_version | None | A version_info 3-tuple for comparison |
89
| | | with the bzrlib minimum and current |
90
| | | version, for determining likely |
91
| | | compatibility. |
92
+------------------------+---------+----------------------------------------+
93
| bzr_maximum_version | None | A version_info 3-tuple like |
94
| | | bzr_minimum_version but checking the |
95
| | | upper limits supported. |
96
+------------------------+---------+----------------------------------------+
97
| bzr_control_formats | {} | A dictionary of descriptions of version|
98
| | | control directories. See |
99
| | | `Control Formats` below. |
100
+------------------------+---------+----------------------------------------+
101
| bzr_checkout_formats | {} | A dictionary of tree_format_string -> |
102
| | | human description strings, for tree |
103
| | | formats that drop into the |
104
| | | ``.bzr/checkout`` metadir system. |
105
+------------------------+---------+----------------------------------------+
106
| bzr_branch_formats | {} | As bzr_checkout_formats but for |
108
+------------------------+---------+----------------------------------------+
109
| bzr_repository_formats | {} | As bzr_checkout_formats but for |
110
| | | repositories. |
111
+------------------------+---------+----------------------------------------+
116
Because disk format detection for formats that bzr does not understand at
117
all can be useful, we allow a declarative description of the shape of a
118
control directory. Each description has a name for showing to users, and a
119
dictonary of relative paths, and the content needed at each path. Paths
120
that end in '/' are required to be directories and the value for that key
121
is ignored. Other paths are required to be regular files, and the value
122
for that key is either None, in which case the file is statted but the
123
content is ignored, or a literal string which is compared against for
124
the content of the file. Thus::
126
# (look for a .hg directory)
127
bzr_control_formats = {"Mercurial":{'.hg/': None}}
129
# (look for a file called .svn/format with contents 4\n).
130
bzr_control_formats = {"Subversion":{'.svn/format': '4\n'}}
136
An example setup.py follows::
138
#!/usr/bin/env python2.4
139
from distutils.core import setup
141
bzr_plugin_name = 'demo'
146
bzr_branch_formats = {
147
"Branch label on disk\n":"demo branch",
150
bzr_control_formats = {"Subversion":{'.svn/format': '4\n'}}
152
bzr_plugin_version = (1, 3, 0, 'dev', 0)
153
bzr_minimum_version = (1, 0, 0)
155
if __name__ == 'main':
158
description="Demo plugin for plugin metadata.",
159
author="Canonical Ltd",
160
author_email="bazaar@lists.canonical.com",
161
license = "GNU GPL v2",
162
url="https://launchpad.net/bzr-demo",
163
packages=['bzrlib.plugins.demo',
164
'bzrlib.plugins.demo.tests',
166
package_dir={'bzrlib.plugins.demo': '.'})
169
Plugin metadata after installation
170
==================================
172
After a plugin has been installed, metadata can be more easily obtained by
173
looking inside the module object -- in other words, for variables defined
174
in the plugin's ``__init__.py``.
176
Help and documentation
177
----------------------
179
The module docstring is used as the plugin description shown by ``bzr
180
plugins``. As with all Python docstrings, the first line should be a
181
short complete sentence summarizing the plugin. The full docstring is
182
shown by ``bzr help PLUGIN_NAME``.
184
Remember that to be effective, the module docstring must be the first
185
statement in the file. It may come after comments but it must be before
186
any import statements.
191
Plugins can and should declare that they depend on a particular version of
194
from bzrlib.api import require_api
196
require_api(bzrlib, (1, 11, 0))
198
Please see `API versioning <api-versioning.html>`_ for more details on the API
199
metadata protocol used by bzrlib.
204
The plugin should expose a version tuple to describe its own version.
205
Some plugins use a version number that corresponds to the version of bzr
206
they're released against, but you can use whatever you want. For example::
208
version_info = (1, 10, 0)
211
Detecting whether code's being loaded as a plugin
212
-------------------------------------------------
214
You may have a Python module that can be used as a bzr plugin and also in
215
other places. To detect whether the module is being loaded by bzr, use
216
something like this::
218
if __name__ == 'bzrlib.plugins.loggerhead':
219
# register with bzrlib...
225
Plugins should avoid doing work or loading code from the plugin or
226
external libraries, if they're just installed but not actually active,
227
because this slows down every invocation of bzr. The bzrlib APIs
228
generally allow the plugin to 'lazily' register methods to invoke if a
229
particular disk format or seen or a particular command is run.
235
The plugin ``__init__.py`` runs when the plugin is loaded during bzr
236
startup. Generally the plugin won't want to actually do anything at this
237
time other than register or override functions to be called later.
239
The plugin can import bzrlib and call any function.
240
Some interesting APIs are described in <http://bazaar-vcs.org/WritingPlugins>
243
Publishing your plugin
244
======================
246
When your plugin is basically working you might like to share it with
247
other people. Here are some steps to consider:
249
* make a project on Launchpad.net like
250
<https://launchpad.net/bzr-fastimport>
251
and publish the branches or tarballs there
253
* include the plugin in <http://bazaar-vcs.org/BzrPlugins>
255
* post about it to the ``bazaar-announce`` list at ``lists.canonical.com``
258
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doc/developers/plugin-api.txt
