5
This document describes the Bazaar internals and the development process.
6
It's meant for people interested in developing Bazaar, and some parts will
7
also be useful to people developing Bazaar plugins.
9
If you have any questions or something seems to be incorrect, unclear or
10
missing, please talk to us in ``irc://irc.freenode.net/#bzr``, or write to
11
the Bazaar mailing list. To propose a correction or addition to this
12
document, send a merge request or new text to the mailing list.
14
The latest developer documentation can be found online at
15
http://doc.bazaar.canonical.com/developers/.
20
Exploring the Bazaar Platform
21
=============================
23
Before making changes, it's a good idea to explore the work already
24
done by others. Perhaps the new feature or improvement you're looking
25
for is available in another plug-in already? If you find a bug,
26
perhaps someone else has already fixed it?
28
To answer these questions and more, take a moment to explore the
29
overall Bazaar Platform. Here are some links to browse:
31
* The Plugins page on the Wiki - http://wiki.bazaar.canonical.com/BzrPlugins
33
* The Bazaar product family on Launchpad - https://launchpad.net/bazaar
35
* Bug Tracker for the core product - https://bugs.launchpad.net/bzr/
37
If nothing else, perhaps you'll find inspiration in how other developers
38
have solved their challenges.
40
Finding Something To Do
41
=======================
43
Ad-hoc performance work can also be done. One useful tool is the 'evil' debug
44
flag. For instance running ``bzr -Devil commit -m "test"`` will log a backtrace
45
to the bzr log file for every method call which triggers a slow or non-scalable
46
part of the bzr library. So checking that a given command with ``-Devil`` has
47
no backtraces logged to the log file is a good way to find problem function
48
calls that might be nested deep in the code base.
50
Planning and Discussing Changes
51
===============================
53
There is a very active community around Bazaar. Mostly we meet on IRC
54
(#bzr on irc.freenode.net) and on the mailing list. To join the Bazaar
55
community, see http://wiki.bazaar.canonical.com/BzrSupport.
57
If you are planning to make a change, it's a very good idea to mention it
58
on the IRC channel and/or on the mailing list. There are many advantages
59
to involving the community before you spend much time on a change.
62
* you get to build on the wisdom of others, saving time
64
* if others can direct you to similar code, it minimises the work to be done
66
* it assists everyone in coordinating direction, priorities and effort.
68
In summary, maximising the input from others typically minimises the
69
total effort required to get your changes merged. The community is
70
friendly, helpful and always keen to welcome newcomers.
73
Bazaar Development in a Nutshell
74
================================
76
.. was from http://wiki.bazaar.canonical.com/BzrGivingBack
78
One of the fun things about working on a version control system like Bazaar is
79
that the users have a high level of proficiency in contributing back into
80
the tool. Consider the following very brief introduction to contributing back
81
to Bazaar. More detailed instructions are in the following sections.
86
First, get a local copy of the development mainline (See `Why make a local
92
$ bzr branch lp:bzr bzr.dev
94
Now make your own branch::
96
$ bzr branch bzr.dev 123456-my-bugfix
98
This will give you a branch called "123456-my-bugfix" that you can work on
99
and commit in. Here, you can study the code, make a fix or a new feature.
100
Feel free to commit early and often (after all, it's your branch!).
102
Documentation improvements are an easy place to get started giving back to the
103
Bazaar project. The documentation is in the `doc/` subdirectory of the Bazaar
106
When you are done, make sure that you commit your last set of changes as well!
107
Once you are happy with your changes, ask for them to be merged, as described
110
Making a Merge Proposal
111
-----------------------
113
The Bazaar developers use Launchpad to further enable a truly distributed
114
style of development. Anyone can propose a branch for merging into the Bazaar
115
trunk. To start this process, you need to push your branch to Launchpad. To
116
do this, you will need a Launchpad account and user name, e.g.
117
`your_lp_username`. You can push your branch to Launchpad directly from
120
$ bzr push lp:~<your_lp_username>/bzr/meaningful_name_here
122
After you have pushed your branch, you will need to propose it for merging to
123
the Bazaar trunk. Go to
124
<https://launchpad.net/~<your_lp_username>/bzr/meaningful_name_here> and choose
125
"Propose for merging into another branch". Select "lp:bzr" to hand
126
your changes off to the Bazaar developers for review and merging.
128
Alternatively, after pushing you can use the ``lp-propose`` command to
129
create the merge proposal.
131
Using a meaningful name for your branch will help you and the reviewer(s)
132
better track the submission. Use a very succint description of your submission
133
and prefix it with bug number if needed (lp:~mbp/bzr/484558-merge-directory
134
for example). Alternatively, you can suffix with the bug number
135
(lp:~jameinel/bzr/export-file-511987).
141
Please put a "cover letter" on your merge request explaining:
143
* the reason **why** you're making this change
145
* **how** this change achieves this purpose
147
* anything else you may have fixed in passing
149
* anything significant that you thought of doing, such as a more
150
extensive fix or a different approach, but didn't or couldn't do now
152
A good cover letter makes reviewers' lives easier because they can decide
153
from the letter whether they agree with the purpose and approach, and then
154
assess whether the patch actually does what the cover letter says.
155
Explaining any "drive-by fixes" or roads not taken may also avoid queries
156
from the reviewer. All in all this should give faster and better reviews.
157
Sometimes writing the cover letter helps the submitter realize something
158
else they need to do. The size of the cover letter should be proportional
159
to the size and complexity of the patch.
162
Why make a local copy of bzr.dev?
163
---------------------------------
165
Making a local mirror of bzr.dev is not strictly necessary, but it means
167
- You can use that copy of bzr.dev as your main bzr executable, and keep it
168
up-to-date using ``bzr pull``.
169
- Certain operations are faster, and can be done when offline. For example:
172
- ``bzr diff -r ancestor:...``
175
- When it's time to create your next branch, it's more convenient. When you
176
have further contributions to make, you should do them in their own branch::
179
$ bzr branch bzr.dev additional_fixes
180
$ cd additional_fixes # hack, hack, hack
184
Understanding the Development Process
185
=====================================
187
The development team follows many practices including:
189
* a public roadmap and planning process in which anyone can participate
191
* time based milestones everyone can work towards and plan around
193
* extensive code review and feedback to contributors
195
* complete and rigorous test coverage on any code contributed
197
* automated validation that all tests still pass before code is merged
198
into the main code branch.
200
The key tools we use to enable these practices are:
202
* Launchpad - https://launchpad.net/
204
* Bazaar - http://bazaar.canonical.com/
206
* Patch Queue Manager - https://launchpad.net/pqm/
208
For further information, see <http://wiki.bazaar.canonical.com/BzrDevelopment>.
213
Preparing a Sandbox for Making Changes to Bazaar
214
================================================
216
Bazaar supports many ways of organising your work. See
217
http://wiki.bazaar.canonical.com/SharedRepositoryLayouts for a summary of the
218
popular alternatives.
220
Of course, the best choice for you will depend on numerous factors:
221
the number of changes you may be making, the complexity of the changes, etc.
222
As a starting suggestion though:
224
* create a local copy of the main development branch (bzr.dev) by using
227
bzr branch lp:bzr bzr.dev
229
* keep your copy of bzr.dev pristine (by not developing in it) and keep
230
it up to date (by using bzr pull)
232
* create a new branch off your local bzr.dev copy for each issue
233
(bug or feature) you are working on.
235
This approach makes it easy to go back and make any required changes
236
after a code review. Resubmitting the change is then simple with no
237
risk of accidentally including edits related to other issues you may
238
be working on. After the changes for an issue are accepted and merged,
239
the associated branch can be deleted or archived as you wish.
242
Navigating the Code Base
243
========================
245
.. Was at <http://wiki.bazaar.canonical.com/NewDeveloperIntroduction>
247
Some of the key files in this directory are:
250
The command you run to start Bazaar itself. This script is pretty
251
short and just does some checks then jumps into bzrlib.
254
This file covers a brief introduction to Bazaar and lists some of its
258
Installs Bazaar system-wide or to your home directory. To perform
259
development work on Bazaar it is not required to run this file - you
260
can simply run the bzr command from the top level directory of your
261
development copy. Note: That if you run setup.py this will create a
262
'build' directory in your development branch. There's nothing wrong
263
with this but don't be confused by it. The build process puts a copy
264
of the main code base into this build directory, along with some other
265
files. You don't need to go in here for anything discussed in this
269
Possibly the most exciting folder of all, bzrlib holds the main code
270
base. This is where you will go to edit python files and contribute to
274
Holds documentation on a whole range of things on Bazaar from the
275
origination of ideas within the project to information on Bazaar
276
features and use cases. Within this directory there is a subdirectory
277
for each translation into a human language. All the documentation
278
is in the ReStructuredText markup language.
281
Documentation specifically targeted at Bazaar and plugin developers.
282
(Including this document.)
284
doc/en/release-notes/
286
Detailed changes in each Bazaar release (there is one file by series:
287
bzr-2.3.txt, bzr-2.4.txt, etc) that can affect users or plugin
292
High-level summaries of changes in each Bazaar release (there is one
293
file by series: whats-new-in-2.3.txt, whats-new-in-2.4.txt, etc).
296
Automatically-generated API reference information is available at
297
<http://people.canonical.com/~mwh/bzrlibapi/>.
299
See also the `Bazaar Architectural Overview
300
<http://doc.bazaar.canonical.com/developers/overview.html>`_.
309
We don't change APIs in stable branches: any supported symbol in a stable
310
release of bzr must not be altered in any way that would result in
311
breaking existing code that uses it. That means that method names,
312
parameter ordering, parameter names, variable and attribute names etc must
313
not be changed without leaving a 'deprecated forwarder' behind. This even
314
applies to modules and classes.
316
If you wish to change the behaviour of a supported API in an incompatible
317
way, you need to change its name as well. For instance, if I add an optional keyword
318
parameter to branch.commit - that's fine. On the other hand, if I add a
319
keyword parameter to branch.commit which is a *required* transaction
320
object, I should rename the API - i.e. to 'branch.commit_transaction'.
322
(Actually, that may break code that provides a new implementation of
323
``commit`` and doesn't expect to receive the parameter.)
325
When renaming such supported API's, be sure to leave a deprecated_method (or
326
_function or ...) behind which forwards to the new API. See the
327
bzrlib.symbol_versioning module for decorators that take care of the
328
details for you - such as updating the docstring, and issuing a warning
329
when the old API is used.
331
For unsupported API's, it does not hurt to follow this discipline, but it's
332
not required. Minimally though, please try to rename things so that
333
callers will at least get an AttributeError rather than weird results.
336
Deprecation decorators
337
----------------------
339
``bzrlib.symbol_versioning`` provides decorators that can be attached to
340
methods, functions, and other interfaces to indicate that they should no
341
longer be used. For example::
343
@deprecated_method(deprecated_in((0, 1, 4)))
345
return self._new_foo()
347
To deprecate a static method you must call ``deprecated_function``
348
(**not** method), after the staticmethod call::
351
@deprecated_function(deprecated_in((0, 1, 4)))
352
def create_repository(base, shared=False, format=None):
354
When you deprecate an API, you should not just delete its tests, because
355
then we might introduce bugs in them. If the API is still present at all,
356
it should still work. The basic approach is to use
357
``TestCase.applyDeprecated`` which in one step checks that the API gives
358
the expected deprecation message, and also returns the real result from
359
the method, so that tests can keep running.
361
Deprecation warnings will be suppressed for final releases, but not for
362
development versions or release candidates, or when running ``bzr
363
selftest``. This gives developers information about whether their code is
364
using deprecated functions, but avoids confusing users about things they
374
The copyright policy for bzr was recently made clear in this email (edited
375
for grammatical correctness)::
377
The attached patch cleans up the copyright and license statements in
378
the bzr source. It also adds tests to help us remember to add them
379
with the correct text.
381
We had the problem that lots of our files were "Copyright Canonical
382
Development Ltd" which is not a real company, and some other variations
383
on this theme. Also, some files were missing the GPL statements.
385
I want to be clear about the intent of this patch, since copyright can
386
be a little controversial.
388
1) The big motivation for this is not to shut out the community, but
389
just to clean up all of the invalid copyright statements.
391
2) It has been the general policy for bzr that we want a single
392
copyright holder for all of the core code. This is following the model
393
set by the FSF, which makes it easier to update the code to a new
394
license in case problems are encountered. (For example, if we want to
395
upgrade the project universally to GPL v3 it is much simpler if there is
396
a single copyright holder). It also makes it clearer if copyright is
397
ever debated, there is a single holder, which makes it easier to defend
398
in court, etc. (I think the FSF position is that if you assign them
399
copyright, they can defend it in court rather than you needing to, and
400
I'm sure Canonical would do the same).
401
As such, Canonical has requested copyright assignments from all of the
404
3) If someone wants to add code and not attribute it to Canonical, there
405
is a specific list of files that are excluded from this check. And the
406
test failure indicates where that is, and how to update it.
408
4) If anyone feels that I changed a copyright statement incorrectly, just
409
let me know, and I'll be happy to correct it. Whenever you have large
410
mechanical changes like this, it is possible to make some mistakes.
412
Just to reiterate, this is a community project, and it is meant to stay
413
that way. Core bzr code is copyright Canonical for legal reasons, and
414
the tests are just there to help us maintain that.
423
Bazaar has a few facilities to help debug problems by going into pdb_, the
426
.. _pdb: http://docs.python.org/lib/debugger-commands.html
428
If the ``BZR_PDB`` environment variable is set
429
then bzr will go into pdb post-mortem mode when an unhandled exception
432
If you send a SIGQUIT or SIGBREAK signal to bzr then it will drop into the
433
debugger immediately. SIGQUIT can be generated by pressing Ctrl-\\ on
434
Unix. SIGBREAK is generated with Ctrl-Pause on Windows (some laptops have
435
this as Fn-Pause). You can continue execution by typing ``c``. This can
436
be disabled if necessary by setting the environment variable
437
``BZR_SIGQUIT_PDB=0``.
439
All tests inheriting from bzrlib.tests.TestCase can use ``self.debug()``
440
instead of the longer ``import pdb; pdb.set_trace()``. The former also works
441
when ``stdin/stdout`` are redirected (by using the original ``stdin/stdout``
442
file handles at the start of the ``bzr`` script) while the later doesn't.
443
``bzrlib.debug.set_trace()`` also uses the original ``stdin/stdout`` file
449
Bazaar accepts some global options starting with ``-D`` such as
450
``-Dhpss``. These set a value in `bzrlib.debug.debug_flags`, and
451
typically cause more information to be written to the trace file. Most
452
`mutter` calls should be guarded by a check of those flags so that we
453
don't write out too much information if it's not needed.
455
Debug flags may have effects other than just emitting trace messages.
457
Run ``bzr help global-options`` to see them all.
459
These flags may also be set as a comma-separated list in the
460
``debug_flags`` option in e.g. ``~/.bazaar/bazaar.conf``. (Note that it
461
must be in this global file, not in the branch or location configuration,
462
because it's currently only loaded at startup time.) For instance you may
463
want to always record hpss traces and to see full error tracebacks::
465
debug_flags = hpss, error
472
Integer identifier for a revision on the main line of a branch.
473
Revision 0 is always the null revision; others are 1-based
474
indexes into the branch's revision history.
477
Unicode and Encoding Support
478
============================
480
This section discusses various techniques that Bazaar uses to handle
481
characters that are outside the ASCII set.
486
When a ``Command`` object is created, it is given a member variable
487
accessible by ``self.outf``. This is a file-like object, which is bound to
488
``sys.stdout``, and should be used to write information to the screen,
489
rather than directly writing to ``sys.stdout`` or calling ``print``.
490
This file has the ability to translate Unicode objects into the correct
491
representation, based on the console encoding. Also, the class attribute
492
``encoding_type`` will effect how unprintable characters will be
493
handled. This parameter can take one of 3 values:
496
Unprintable characters will be represented with a suitable replacement
497
marker (typically '?'), and no exception will be raised. This is for
498
any command which generates text for the user to review, rather than
499
for automated processing.
500
For example: ``bzr log`` should not fail if one of the entries has text
501
that cannot be displayed.
504
Attempting to print an unprintable character will cause a UnicodeError.
505
This is for commands that are intended more as scripting support, rather
506
than plain user review.
507
For example: ``bzr ls`` is designed to be used with shell scripting. One
508
use would be ``bzr ls --null --unknowns | xargs -0 rm``. If ``bzr``
509
printed a filename with a '?', the wrong file could be deleted. (At the
510
very least, the correct file would not be deleted). An error is used to
511
indicate that the requested action could not be performed.
514
Do not attempt to automatically convert Unicode strings. This is used
515
for commands that must handle conversion themselves.
516
For example: ``bzr diff`` needs to translate Unicode paths, but should
517
not change the exact text of the contents of the files.
520
``bzrlib.urlutils.unescape_for_display``
521
----------------------------------------
523
Because Transports work in URLs (as defined earlier), printing the raw URL
524
to the user is usually less than optimal. Characters outside the standard
525
set are printed as escapes, rather than the real character, and local
526
paths would be printed as ``file://`` URLs. The function
527
``unescape_for_display`` attempts to unescape a URL, such that anything
528
that cannot be printed in the current encoding stays an escaped URL, but
529
valid characters are generated where possible.
535
We write some extensions in C using pyrex. We design these to work in
538
* User with no C compiler
539
* User with C compiler
542
The recommended way to install bzr is to have a C compiler so that the
543
extensions can be built, but if no C compiler is present, the pure python
544
versions we supply will work, though more slowly.
546
For developers we recommend that pyrex be installed, so that the C
547
extensions can be changed if needed.
549
For the C extensions, the extension module should always match the
550
original python one in all respects (modulo speed). This should be
551
maintained over time.
553
To create an extension, add rules to setup.py for building it with pyrex,
554
and with distutils. Now start with an empty .pyx file. At the top add
555
"include 'yourmodule.py'". This will import the contents of foo.py into this
556
file at build time - remember that only one module will be loaded at
557
runtime. Now you can subclass classes, or replace functions, and only your
558
changes need to be present in the .pyx file.
560
Note that pyrex does not support all 2.4 programming idioms, so some
561
syntax changes may be required. I.e.
563
- 'from foo import (bar, gam)' needs to change to not use the brackets.
564
- 'import foo.bar as bar' needs to be 'import foo.bar; bar = foo.bar'
566
If the changes are too dramatic, consider
567
maintaining the python code twice - once in the .pyx, and once in the .py,
568
and no longer including the .py file.
571
Making Installers for OS Windows
572
================================
573
To build a win32 installer, see the instructions on the wiki page:
574
http://wiki.bazaar.canonical.com/BzrWin32Installer
582
What is a Core Developer?
583
-------------------------
585
While everyone in the Bazaar community is welcome and encouraged to
586
propose and submit changes, a smaller team is reponsible for pulling those
587
changes together into a cohesive whole. In addition to the general developer
588
stuff covered above, "core" developers have responsibility for:
592
* managing releases (see `Releasing Bazaar <http://doc.bazaar.canonical.com/developers/releasing.html>`_)
595
Removing barriers to community participation is a key reason for adopting
596
distributed VCS technology. While DVCS removes many technical barriers,
597
a small number of social barriers are often necessary instead.
598
By documenting how the above things are done, we hope to
599
encourage more people to participate in these activities, keeping the
600
differences between core and non-core contributors to a minimum.
603
Communicating and Coordinating
604
------------------------------
606
While it has many advantages, one of the challenges of distributed
607
development is keeping everyone else aware of what you're working on.
608
There are numerous ways to do this:
610
#. Assign bugs to yourself in Launchpad
611
#. Mention it on the mailing list
614
As well as the email notifcations that occur when merge requests are sent
615
and reviewed, you can keep others informed of where you're spending your
616
energy by emailing the **bazaar-commits** list implicitly. To do this,
617
install and configure the Email plugin. One way to do this is add these
618
configuration settings to your central configuration file (e.g.
619
``~/.bazaar/bazaar.conf``)::
622
email = Joe Smith <joe.smith@internode.on.net>
623
smtp_server = mail.internode.on.net:25
625
Then add these lines for the relevant branches in ``locations.conf``::
627
post_commit_to = bazaar-commits@lists.canonical.com
628
post_commit_mailer = smtplib
630
While attending a sprint, RobertCollins' Dbus plugin is useful for the
631
same reason. See the documentation within the plugin for information on
632
how to set it up and configure it.
643
Keeping on top of bugs reported is an important part of ongoing release
644
planning. Everyone in the community is welcome and encouraged to raise
645
bugs, confirm bugs raised by others, and nominate a priority. Practically
646
though, a good percentage of bug triage is often done by the core
647
developers, partially because of their depth of product knowledge.
649
With respect to bug triage, core developers are encouraged to play an
650
active role with particular attention to the following tasks:
652
* keeping the number of unconfirmed bugs low
653
* ensuring the priorities are generally right (everything as critical - or
654
medium - is meaningless)
655
* looking out for regressions and turning those around sooner rather than later.
658
As well as prioritizing bugs and nominating them against a
659
target milestone, Launchpad lets core developers offer to mentor others in
1
============================
2
guidelines for modifying bzr
3
============================
5
* New functionality should have test cases. Preferably write the
6
test before writing the code.
8
In general, you can test at either the command-line level or the
9
internal API level. Choose whichever is appropriate: if adding a
10
new command, or a new command option, then call through run_bzr().
11
It is not necessary to do both.
13
* Before fixing a bug, write a test case so that it does not regress.
15
* Exceptions should be defined inside bzrlib.errors, so that we can
16
see the whole tree at a glance.
18
* Imports should be done at the top-level of the file, unless there is
19
a strong reason to have them lazily loaded when a particular
20
function runs. Import statements have a cost, so try to make sure
21
they don't run inside hot functions.
23
* Please write PEP-8__ compliant code.
25
One often-missed requirement is that the first line of docstrings
26
should be a self-contained one-sentence summary.
28
__ http://www.python.org/peps/pep-0008.html
30
* Module names should always be given fully-qualified,
31
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
38
If you change the behaviour of a command, please update its docstring
39
in bzrlib/commands.py. This is displayed by the 'bzr help' command.
41
If you make a user-visible change, please add a note to the NEWS file.
42
The description should be written to make sense to someone who's just
43
a user of bzr, not a developer: new functions or classes shouldn't be
44
mentioned, but new commands, changes in behaviour or fixed nontrivial
45
bugs should be listed. See the existing entries for an idea of what
53
(The strategy described here is what we want to get to, but it's not
54
consistently followed in the code at the moment.)
56
bzrlib is intended to be a generically reusable library. It shouldn't
57
write messages to stdout or stderr, because some programs that use it
58
might want to display that information through a GUI or some other
61
We can distinguish two types of output from the library:
63
1. Structured data representing the progress or result of an
64
operation. For example, for a commit command this will be a list
65
of the modified files and the finally committed revision number
68
These should be exposed either through the return code or by calls
69
to a callback parameter.
71
A special case of this is progress indicators for long-lived
72
operations, where the caller should pass a ProgressBar object.
74
2. Unstructured log/debug messages, mostly for the benefit of the
75
developers or users trying to debug problems. This should always
76
be sent through ``bzrlib.trace`` and Python ``logging``, so that
77
it can be redirected by the client.
79
The distinction between the two is a bit subjective, but in general if
80
there is any chance that a library would want to see something as
81
structured data, we should make it so.
83
The policy about how output is presented in the text-mode client
84
should be only in the command-line tool.
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In general tests should be placed in a file named test_FOO.py where
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FOO is the logical thing under test. That file should be placed in the
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tests subdirectory under the package being tested.
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For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
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Currently, bzr selftest is used to invoke tests.
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You can provide a pattern argument to run a subset. For example,
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to run just the whitebox tests, run bzr selftest --pattern .*whitebox.*
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HACKING
