5
This document describes the Breezy internals and the development process.
6
It's meant for people interested in developing Breezy, and some parts will
7
also be useful to people developing Breezy 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 Breezy 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 Breezy 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 Breezy Platform. Here are some links to browse:
31
* The Plugins page on the Wiki - http://wiki.bazaar.canonical.com/BzrPlugins
33
* The Breezy product family on Launchpad - https://launchpad.net/breezy
35
* Bug Tracker for the core product - https://bugs.launchpad.net/brz/
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 ``brz -Devil commit -m "test"`` will log a backtrace
45
to the Breezy log file for every method call which triggers a slow or non-scalable
46
part of the breezy 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 Breezy. Mostly we meet on IRC
54
(#bzr on irc.freenode.net) and on the mailing list. To join the Breezy
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
Breezy 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 Breezy 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 Breezy. More detailed instructions are in the following sections.
86
First, get a local copy of the development mainline (See `Why make a local
92
$ brz branch lp:brz bzr.dev
94
Now make your own branch::
96
$ brz 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
Breezy project. The documentation is in the `doc/` subdirectory of the Breezy
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 Breezy developers use Launchpad to further enable a truly distributed
114
style of development. Anyone can propose a branch for merging into the Breezy
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
$ brz 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 Breezy 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 Breezy 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 brz executable, and keep it
168
up-to-date using ``brz pull``.
169
- Certain operations are faster, and can be done when offline. For example:
172
- ``brz 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
$ brz 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
* Breezy - https://www.breezy-vcs.org/
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 Breezy
214
================================================
216
Breezy 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
brz branch lp:brz bzr.dev
229
* keep your copy of bzr.dev pristine (by not developing in it) and keep
230
it up to date (by using brz 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 Breezy itself. This script is pretty
251
short and just does some checks then jumps into bzrlib.
254
This file covers a brief introduction to Breezy and lists some of its
258
Installs Breezy system-wide or to your home directory. To perform
259
development work on Breezy it is not required to run this file - you
260
can simply run the Breezy 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 Breezy from the
275
origination of ideas within the project to information on Breezy
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 Breezy and plugin developers.
282
(Including this document.)
284
doc/en/release-notes/
286
Detailed changes in each Breezy 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 Breezy 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 `Breezy 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 Breezy 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
377
Breezy has a few facilities to help debug problems by going into pdb_, the
380
.. _pdb: http://docs.python.org/lib/debugger-commands.html
382
If the ``BZR_PDB`` environment variable is set
383
then brz will go into pdb post-mortem mode when an unhandled exception
386
If you send a SIGQUIT or SIGBREAK signal to brz then it will drop into the
387
debugger immediately. SIGQUIT can be generated by pressing Ctrl-\\ on
388
Unix. SIGBREAK is generated with Ctrl-Pause on Windows (some laptops have
389
this as Fn-Pause). You can continue execution by typing ``c``. This can
390
be disabled if necessary by setting the environment variable
391
``BZR_SIGQUIT_PDB=0``.
393
All tests inheriting from bzrlib.tests.TestCase can use ``self.debug()``
394
instead of the longer ``import pdb; pdb.set_trace()``. The former also works
395
when ``stdin/stdout`` are redirected (by using the original ``stdin/stdout``
396
file handles at the start of the ``bzr`` script) while the later doesn't.
397
``bzrlib.debug.set_trace()`` also uses the original ``stdin/stdout`` file
403
Breezy accepts some global options starting with ``-D`` such as
404
``-Dhpss``. These set a value in `bzrlib.debug.debug_flags`, and
405
typically cause more information to be written to the trace file. Most
406
`mutter` calls should be guarded by a check of those flags so that we
407
don't write out too much information if it's not needed.
409
Debug flags may have effects other than just emitting trace messages.
411
Run ``brz help global-options`` to see them all.
413
These flags may also be set as a comma-separated list in the
414
``debug_flags`` option in e.g. ``~/.config/breezy/breezy.conf``. (Note
415
that it must be in this global file, not in the branch or location
416
configuration, because it's currently only loaded at startup time.) For
417
instance you may want to always record hpss traces and to see full error
420
debug_flags = hpss, error
427
Integer identifier for a revision on the main line of a branch.
428
Revision 0 is always the null revision; others are 1-based
429
indexes into the branch's revision history.
432
Unicode and Encoding Support
433
============================
435
This section discusses various techniques that Breezy uses to handle
436
characters that are outside the ASCII set.
441
When a ``Command`` object is created, it is given a member variable
442
accessible by ``self.outf``. This is a file-like object, which is bound to
443
``sys.stdout``, and should be used to write information to the screen,
444
rather than directly writing to ``sys.stdout`` or calling ``print``.
445
This file has the ability to translate Unicode objects into the correct
446
representation, based on the console encoding. Also, the class attribute
447
``encoding_type`` will effect how unprintable characters will be
448
handled. This parameter can take one of 3 values:
451
Unprintable characters will be represented with a suitable replacement
452
marker (typically '?'), and no exception will be raised. This is for
453
any command which generates text for the user to review, rather than
454
for automated processing.
455
For example: ``brz log`` should not fail if one of the entries has text
456
that cannot be displayed.
459
Attempting to print an unprintable character will cause a UnicodeError.
460
This is for commands that are intended more as scripting support, rather
461
than plain user review.
462
For example: ``brz ls`` is designed to be used with shell scripting. One
463
use would be ``brz ls --null --unknowns | xargs -0 rm``. If ``bzr``
464
printed a filename with a '?', the wrong file could be deleted. (At the
465
very least, the correct file would not be deleted). An error is used to
466
indicate that the requested action could not be performed.
469
Do not attempt to automatically convert Unicode strings. This is used
470
for commands that must handle conversion themselves.
471
For example: ``brz diff`` needs to translate Unicode paths, but should
472
not change the exact text of the contents of the files.
475
``bzrlib.urlutils.unescape_for_display``
476
----------------------------------------
478
Because Transports work in URLs (as defined earlier), printing the raw URL
479
to the user is usually less than optimal. Characters outside the standard
480
set are printed as escapes, rather than the real character, and local
481
paths would be printed as ``file://`` URLs. The function
482
``unescape_for_display`` attempts to unescape a URL, such that anything
483
that cannot be printed in the current encoding stays an escaped URL, but
484
valid characters are generated where possible.
490
We write some extensions in C using Cython. We design these to work in
493
* User with no C compiler
494
* User with C compiler
497
The recommended way to install Breezy is to have a C compiler so that the
498
extensions can be built, but if no C compiler is present, the pure python
499
versions we supply will work, though more slowly.
501
For developers we recommend that Cython be installed, so that the C
502
extensions can be changed if needed.
504
For the C extensions, the extension module should always match the
505
original python one in all respects (modulo speed). This should be
506
maintained over time.
508
To create an extension, add rules to setup.py for building it with Cython ,
509
and with distutils. Now start with an empty .pyx file. At the top add
510
"include 'yourmodule.py'". This will import the contents of foo.py into this
511
file at build time - remember that only one module will be loaded at
512
runtime. Now you can subclass classes, or replace functions, and only your
513
changes need to be present in the .pyx file.
515
Making Installers for OS Windows
516
================================
517
To build a win32 installer, see the instructions on the wiki page:
518
http://wiki.bazaar.canonical.com/BzrWin32Installer
526
What is a Core Developer?
527
-------------------------
529
While everyone in the Breezy community is welcome and encouraged to
530
propose and submit changes, a smaller team is reponsible for pulling those
531
changes together into a cohesive whole. In addition to the general developer
532
stuff covered above, "core" developers have responsibility for:
536
* managing releases (see `Releasing Breezy <http://doc.bazaar.canonical.com/developers/releasing.html>`_)
539
Removing barriers to community participation is a key reason for adopting
540
distributed VCS technology. While DVCS removes many technical barriers,
541
a small number of social barriers are often necessary instead.
542
By documenting how the above things are done, we hope to
543
encourage more people to participate in these activities, keeping the
544
differences between core and non-core contributors to a minimum.
547
Communicating and Coordinating
548
------------------------------
550
While it has many advantages, one of the challenges of distributed
551
development is keeping everyone else aware of what you're working on.
552
There are numerous ways to do this:
554
#. Assign bugs to yourself in Launchpad
555
#. Mention it on the mailing list
558
As well as the email notifcations that occur when merge requests are sent
559
and reviewed, you can keep others informed of where you're spending your
560
energy by emailing the **bazaar-commits** list implicitly. To do this,
561
install and configure the Email plugin. One way to do this is add these
562
configuration settings to your central configuration file (e.g.
563
``~/.config/breezy/breezy.conf``)::
566
email = Joe Smith <joe.smith@internode.on.net>
567
smtp_server = mail.internode.on.net:25
569
Then add these lines for the relevant branches in ``locations.conf``::
571
post_commit_to = bazaar-commits@lists.canonical.com
572
post_commit_mailer = smtplib
574
While attending a sprint, RobertCollins' Dbus plugin is useful for the
575
same reason. See the documentation within the plugin for information on
576
how to set it up and configure it.
587
Keeping on top of bugs reported is an important part of ongoing release
588
planning. Everyone in the community is welcome and encouraged to raise
589
bugs, confirm bugs raised by others, and nominate a priority. Practically
590
though, a good percentage of bug triage is often done by the core
591
developers, partially because of their depth of product knowledge.
593
With respect to bug triage, core developers are encouraged to play an
594
active role with particular attention to the following tasks:
596
* keeping the number of unconfirmed bugs low
597
* ensuring the priorities are generally right (everything as critical - or
598
medium - is meaningless)
599
* looking out for regressions and turning those around sooner rather than later.
602
As well as prioritizing bugs and nominating them against a
603
target milestone, Launchpad lets core developers offer to mentor others in
added
removed
doc/developers/HACKING.txt
