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 current version of this document is available in the file
15
``doc/developers/HACKING.txt`` in the source tree, or at
16
http://doc.bazaar-vcs.org/bzr.dev/en/developer-guide/HACKING.html
19
`Bazaar Developer Documentation Catalog <../../developers/index.html>`_.
27
Exploring the Bazaar Platform
28
=============================
30
Before making changes, it's a good idea to explore the work already
31
done by others. Perhaps the new feature or improvement you're looking
32
for is available in another plug-in already? If you find a bug,
33
perhaps someone else has already fixed it?
35
To answer these questions and more, take a moment to explore the
36
overall Bazaar Platform. Here are some links to browse:
38
* The Plugins page on the Wiki - http://bazaar-vcs.org/BzrPlugins
40
* The Bazaar product family on Launchpad - https://launchpad.net/bazaar
42
* Bug Tracker for the core product - https://bugs.launchpad.net/bzr/
44
* Blueprint Tracker for the core product - https://blueprints.launchpad.net/bzr/
46
If nothing else, perhaps you'll find inspiration in how other developers
47
have solved their challenges.
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://bazaar-vcs.org/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 on 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
Looking for a 10 minute introduction to submitting a change?
77
See http://bazaar-vcs.org/BzrGivingBack.
79
TODO: Merge that Wiki page into this document.
82
Understanding the Development Process
83
=====================================
85
The development team follows many practices including:
87
* a public roadmap and planning process in which anyone can participate
89
* time based milestones everyone can work towards and plan around
91
* extensive code review and feedback to contributors
93
* complete and rigorous test coverage on any code contributed
95
* automated validation that all tests still pass before code is merged
96
into the main code branch.
98
The key tools we use to enable these practices are:
100
* Launchpad - https://launchpad.net/
102
* Bazaar - http://bazaar-vcs.org/
104
* Bundle Buggy - http://bundlebuggy.aaronbentley.com/
106
* Patch Queue Manager - https://launchpad.net/pqm/
108
For further information, see http://bazaar-vcs.org/BzrDevelopment.
113
Preparing a Sandbox for Making Changes to Bazaar
114
================================================
116
Bazaar supports many ways of organising your work. See
117
http://bazaar-vcs.org/SharedRepositoryLayouts for a summary of the
118
popular alternatives.
120
Of course, the best choice for you will depend on numerous factors:
121
the number of changes you may be making, the complexity of the changes, etc.
122
As a starting suggestion though:
124
* create a local copy of the main development branch (bzr.dev) by using
127
bzr branch http://bazaar-vcs.org/bzr/bzr.dev/ bzr.dev
129
* keep your copy of bzr.dev prestine (by not developing in it) and keep
130
it up to date (by using bzr pull)
132
* create a new branch off your local bzr.dev copy for each issue
133
(bug or feature) you are working on.
135
This approach makes it easy to go back and make any required changes
136
after a code review. Resubmitting the change is then simple with no
137
risk of accidentially including edits related to other issues you may
138
be working on. After the changes for an issue are accepted and merged,
139
the associated branch can be deleted or archived as you wish.
142
Navigating the Code Base
143
========================
145
.. Was at <http://bazaar-vcs.org/NewDeveloperIntroduction>
147
Some of the key files in this directory are:
150
The command you run to start Bazaar itself. This script is pretty
151
short and just does some checks then jumps into bzrlib.
154
This file covers a brief introduction to Bazaar and lists some of its
158
Summary of changes in each Bazaar release that can affect users or
162
Installs Bazaar system-wide or to your home directory. To perform
163
development work on Bazaar it is not required to run this file - you
164
can simply run the bzr command from the top level directory of your
165
development copy. Note: That if you run setup.py this will create a
166
'build' directory in your development branch. There's nothing wrong
167
with this but don't be confused by it. The build process puts a copy
168
of the main code base into this build directory, along with some other
169
files. You don't need to go in here for anything discussed in this
173
Possibly the most exciting folder of all, bzrlib holds the main code
174
base. This is where you will go to edit python files and contribute to
178
Holds documentation on a whole range of things on Bazaar from the
179
origination of ideas within the project to information on Bazaar
180
features and use cases. Within this directory there is a subdirectory
181
for each translation into a human language. All the documentation
182
is in the ReStructuredText markup language.
185
Documentation specifically targetted at Bazaar and plugin developers.
186
(Including this document.)
190
Automatically-generated API reference information is available at
191
<http://starship.python.net/crew/mwh/bzrlibapi/>.
192
(There is an experimental editable version at
193
<http://starship.python.net/crew/mwh/bzrlibapi-oe/>.)
195
See also the `Bazaar Architectural Overview <../../developers/overview.html>`_.
198
The Code Review Process
199
#######################
201
All code changes coming in to Bazaar are reviewed by someone else.
202
Normally changes by core contributors are reviewed by one other core
203
developer, and changes from other people are reviewed by two core
204
developers. Use intelligent discretion if the patch is trivial.
206
Good reviews do take time. They also regularly require a solid
207
understanding of the overall code base. In practice, this means a small
208
number of people often have a large review burden - with knowledge comes
209
responsibility. No one like their merge requests sitting in a queue going
210
nowhere, so reviewing sooner rather than later is strongly encouraged.
214
Sending patches for review
215
==========================
217
If you'd like to propose a change, please post to the
218
bazaar@lists.canonical.com list with a bundle, patch, or link to a
219
branch. Put ``[PATCH]`` or ``[MERGE]`` in the subject so Bundle Buggy
220
can pick it out, and explain the change in the email message text.
221
Remember to update the NEWS file as part of your change if it makes any
222
changes visible to users or plugin developers. Please include a diff
223
against mainline if you're giving a link to a branch.
225
You can generate a merge request like this::
227
bzr send -o bug-1234.patch
229
A ``.patch`` extension is recommended instead of .bundle as many mail clients
230
will send the latter as a binary file.
232
``bzr send`` can also send mail directly if you prefer; see the help.
234
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
235
want it to be merged. If you want comments from developers rather than
236
to be merged, you can put ``[RFC]`` in the subject line.
238
If this change addresses a bug, please put the bug number in the subject
239
line too, in the form ``[#1]`` so that Bundle Buggy can recognize it.
241
If the change is intended for a particular release mark that in the
242
subject too, e.g. ``[1.6]``.
248
Please put a "cover letter" on your merge request explaining:
250
* the reason **why** you're making this change
252
* **how** this change achieves this purpose
254
* anything else you may have fixed in passing
256
* anything significant that you thought of doing, such as a more
257
extensive fix or a different approach, but didn't or couldn't do now
259
A good cover letter makes reviewers' lives easier because they can decide
260
from the letter whether they agree with the purpose and approach, and then
261
assess whether the patch actually does what the cover letter says.
262
Explaining any "drive-by fixes" or roads not taken may also avoid queries
263
from the reviewer. All in all this should give faster and better reviews.
264
Sometimes writing the cover letter helps the submitter realize something
265
else they need to do. The size of the cover letter should be proportional
266
to the size and complexity of the patch.
269
Reviewing proposed changes
270
==========================
272
Anyone is welcome to review code, and reply to the thread with their
275
The simplest way to review a proposed change is to just read the patch on
276
the list or in Bundle Buggy. For more complex changes it may be useful
277
to make a new working tree or branch from trunk, and merge the proposed
278
change into it, so you can experiment with the code or look at a wider
281
There are three main requirements for code to get in:
283
* Doesn't reduce test coverage: if it adds new methods or commands,
284
there should be tests for them. There is a good test framework
285
and plenty of examples to crib from, but if you are having trouble
286
working out how to test something feel free to post a draft patch
289
* Doesn't reduce design clarity, such as by entangling objects
290
we're trying to separate. This is mostly something the more
291
experienced reviewers need to help check.
293
* Improves bugs, features, speed, or code simplicity.
295
Code that goes in should not degrade any of these aspects. Patches are
296
welcome that only cleanup the code without changing the external
297
behaviour. The core developers take care to keep the code quality high
298
and understandable while recognising that perfect is sometimes the enemy
301
It is easy for reviews to make people notice other things which should be
302
fixed but those things should not hold up the original fix being accepted.
303
New things can easily be recorded in the Bug Tracker instead.
305
It's normally much easier to review several smaller patches than one large
306
one. You might want to use ``bzr-loom`` to maintain threads of related
307
work, or submit a preparatory patch that will make your "real" change
311
Checklist for reviewers
312
=======================
314
* Do you understand what the code's doing and why?
316
* Will it perform reasonably for large inputs, both in memory size and
317
run time? Are there some scenarios where performance should be
320
* Is it tested, and are the tests at the right level? Are there both
321
blackbox (command-line level) and API-oriented tests?
323
* If this change will be visible to end users or API users, is it
324
appropriately documented in NEWS?
326
* Does it meet the coding standards below?
328
* If it changes the user-visible behaviour, does it update the help
329
strings and user documentation?
331
* If it adds a new major concept or standard practice, does it update the
332
developer documentation?
334
* (your ideas here...)
337
Bundle Buggy and review outcomes
338
================================
340
Anyone can "vote" on the mailing list by expressing an opinion. Core
341
developers can also vote using Bundle Buggy. Here are the voting codes and
344
:approve: Reviewer wants this submission merged.
345
:tweak: Reviewer wants this submission merged with small changes. (No
347
:abstain: Reviewer does not intend to vote on this patch.
348
:resubmit: Please make changes and resubmit for review.
349
:reject: Reviewer doesn't want this kind of change merged.
350
:comment: Not really a vote. Reviewer just wants to comment, for now.
352
If a change gets two approvals from core reviewers, and no rejections,
353
then it's OK to come in. Any of the core developers can bring it into the
354
bzr.dev trunk and backport it to maintenance branches if required. The
355
Release Manager will merge the change into the branch for a pending
356
release, if any. As a guideline, core developers usually merge their own
357
changes and volunteer to merge other contributions if they were the second
358
reviewer to agree to a change.
360
To track the progress of proposed changes, use Bundle Buggy. See
361
http://bundlebuggy.aaronbentley.com/help for a link to all the
362
outstanding merge requests together with an explanation of the columns.
363
Bundle Buggy will also mail you a link to track just your change.
365
Coding Style Guidelines
366
#######################
371
``hasattr`` should not be used because it swallows exceptions including
372
``KeyboardInterrupt``. Instead, say something like ::
374
if getattr(thing, 'name', None) is None
380
Please write PEP-8__ compliant code.
382
__ http://www.python.org/peps/pep-0008.html
384
One often-missed requirement is that the first line of docstrings
385
should be a self-contained one-sentence summary.
387
We use 4 space indents for blocks, and never use tab characters. (In vim,
390
No trailing white space is allowed.
392
Unix style newlines (LF) are used.
394
Each file must have a newline at the end of it.
396
Lines should be no more than 79 characters if at all possible.
397
Lines that continue a long statement may be indented in either of
400
within the parenthesis or other character that opens the block, e.g.::
406
or indented by four spaces::
412
The first is considered clearer by some people; however it can be a bit
413
harder to maintain (e.g. when the method name changes), and it does not
414
work well if the relevant parenthesis is already far to the right. Avoid
417
self.legbone.kneebone.shinbone.toebone.shake_it(one,
423
self.legbone.kneebone.shinbone.toebone.shake_it(one,
429
self.legbone.kneebone.shinbone.toebone.shake_it(
432
For long lists, we like to add a trailing comma and put the closing
433
character on the following line. This makes it easier to add new items in
436
from bzrlib.goo import (
442
There should be spaces between function paramaters, but not between the
443
keyword name and the value::
445
call(1, 3, cheese=quark)
449
;(defface my-invalid-face
450
; '((t (:background "Red" :underline t)))
451
; "Face used to highlight invalid constructs or other uglyties"
454
(defun my-python-mode-hook ()
455
;; setup preferred indentation style.
456
(setq fill-column 79)
457
(setq indent-tabs-mode nil) ; no tabs, never, I will not repeat
458
; (font-lock-add-keywords 'python-mode
459
; '(("^\\s *\t" . 'my-invalid-face) ; Leading tabs
460
; ("[ \t]+$" . 'my-invalid-face) ; Trailing spaces
461
; ("^[ \t]+$" . 'my-invalid-face)); Spaces only
465
(add-hook 'python-mode-hook 'my-python-mode-hook)
467
The lines beginning with ';' are comments. They can be activated
468
if one want to have a strong notice of some tab/space usage
475
* Imports should be done at the top-level of the file, unless there is
476
a strong reason to have them lazily loaded when a particular
477
function runs. Import statements have a cost, so try to make sure
478
they don't run inside hot functions.
480
* Module names should always be given fully-qualified,
481
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
487
Functions, methods or members that are "private" to bzrlib are given
488
a leading underscore prefix. Names without a leading underscore are
489
public not just across modules but to programmers using bzrlib as an
490
API. As a consequence, a leading underscore is appropriate for names
491
exposed across modules but that are not to be exposed to bzrlib API
494
We prefer class names to be concatenated capital words (``TestCase``)
495
and variables, methods and functions to be lowercase words joined by
496
underscores (``revision_id``, ``get_revision``).
498
For the purposes of naming some names are treated as single compound
499
words: "filename", "revno".
501
Consider naming classes as nouns and functions/methods as verbs.
503
Try to avoid using abbreviations in names, because there can be
504
inconsistency if other people use the full name.
510
``revision_id`` not ``rev_id`` or ``revid``
512
Functions that transform one thing to another should be named ``x_to_y``
513
(not ``x2y`` as occurs in some old code.)
519
Python destructors (``__del__``) work differently to those of other
520
languages. In particular, bear in mind that destructors may be called
521
immediately when the object apparently becomes unreferenced, or at some
522
later time, or possibly never at all. Therefore we have restrictions on
523
what can be done inside them.
525
0. If you think you need to use a ``__del__`` method ask another
526
developer for alternatives. If you do need to use one, explain
529
1. Never rely on a ``__del__`` method running. If there is code that
530
must run, do it from a ``finally`` block instead.
532
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
535
3. In some places we raise a warning from the destructor if the object
536
has not been cleaned up or closed. This is considered OK: the warning
537
may not catch every case but it's still useful sometimes.
543
In some places we have variables which point to callables that construct
544
new instances. That is to say, they can be used a lot like class objects,
545
but they shouldn't be *named* like classes:
547
> I think that things named FooBar should create instances of FooBar when
548
> called. Its plain confusing for them to do otherwise. When we have
549
> something that is going to be used as a class - that is, checked for via
550
> isinstance or other such idioms, them I would call it foo_class, so that
551
> it is clear that a callable is not sufficient. If it is only used as a
552
> factory, then yes, foo_factory is what I would use.
558
Several places in Bazaar use (or will use) a registry, which is a
559
mapping from names to objects or classes. The registry allows for
560
loading in registered code only when it's needed, and keeping
561
associated information such as a help string or description.
564
InterObject and multiple dispatch
565
=================================
567
The ``InterObject`` provides for two-way `multiple dispatch`__: matching
568
up for example a source and destination repository to find the right way
569
to transfer data between them.
571
.. __: http://en.wikipedia.org/wiki/Multiple_dispatch
573
There is a subclass ``InterObject`` classes for each type of object that is
574
dispatched this way, e.g. ``InterRepository``. Calling ``.get()`` on this
575
class will return an ``InterObject`` instance providing the best match for
576
those parameters, and this instance then has methods for operations
579
inter = InterRepository.get(source_repo, target_repo)
580
inter.fetch(revision_id)
582
``InterRepository`` also acts as a registry-like object for its
583
subclasses, and they can be added through ``.register_optimizer``. The
584
right one to run is selected by asking each class, in reverse order of
585
registration, whether it ``.is_compatible`` with the relevant objects.
590
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
591
delay importing modules until they are actually used. ``lazy_import`` uses
592
the same syntax as regular python imports. So to import a few modules in a
595
from bzrlib.lazy_import import lazy_import
596
lazy_import(globals(), """
605
revision as _mod_revision,
607
import bzrlib.transport
611
At this point, all of these exist as a ``ImportReplacer`` object, ready to
612
be imported once a member is accessed. Also, when importing a module into
613
the local namespace, which is likely to clash with variable names, it is
614
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
615
the variable is a module, and these object should be hidden anyway, since
616
they shouldn't be imported into other namespaces.
618
While it is possible for ``lazy_import()`` to import members of a module
619
when using the ``from module import member`` syntax, it is recommended to
620
only use that syntax to load sub modules ``from module import submodule``.
621
This is because variables and classes can frequently be used without
622
needing a sub-member for example::
624
lazy_import(globals(), """
625
from module import MyClass
629
return isinstance(x, MyClass)
631
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
632
object, rather than the real class.
634
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
635
Because the replacer only knows about the original name, it is unable to
636
replace other variables. The ``ImportReplacer`` class will raise an
637
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
638
happened. But it requires accessing a member more than once from the new
639
variable, so some bugs are not detected right away.
645
The null revision is the ancestor of all revisions. Its revno is 0, its
646
revision-id is ``null:``, and its tree is the empty tree. When referring
647
to the null revision, please use ``bzrlib.revision.NULL_REVISION``. Old
648
code sometimes uses ``None`` for the null revision, but this practice is
652
Object string representations
653
=============================
655
Python prints objects using their ``__repr__`` method when they are
656
written to logs, exception tracebacks, or the debugger. We want
657
objects to have useful representations to help in determining what went
660
If you add a new class you should generally add a ``__repr__`` method
661
unless there is an adequate method in a parent class. There should be a
664
Representations should typically look like Python constructor syntax, but
665
they don't need to include every value in the object and they don't need
666
to be able to actually execute. They're to be read by humans, not
667
machines. Don't hardcode the classname in the format, so that we get the
668
correct value if the method is inherited by a subclass. If you're
669
printing attributes of the object, including strings, you should normally
670
use ``%r`` syntax (to call their repr in turn).
672
Try to avoid the representation becoming more than one or two lines long.
673
(But balance this against including useful information, and simplicity of
676
Because repr methods are often called when something has already gone
677
wrong, they should be written somewhat more defensively than most code.
678
The object may be half-initialized or in some other way in an illegal
679
state. The repr method shouldn't raise an exception, or it may hide the
680
(probably more useful) underlying exception.
685
return '%s(%r)' % (self.__class__.__name__,
692
A bare ``except`` statement will catch all exceptions, including ones that
693
really should terminate the program such as ``MemoryError`` and
694
``KeyboardInterrupt``. They should rarely be used unless the exception is
695
later re-raised. Even then, think about whether catching just
696
``Exception`` (which excludes system errors in Python2.5 and later) would
703
All code should be exercised by the test suite. See `Guide to Testing
704
Bazaar <testing.html>`_ for detailed information about writing tests.
713
We have a commitment to 6 months API stability - any supported symbol in a
714
release of bzr MUST NOT be altered in any way that would result in
715
breaking existing code that uses it. That means that method names,
716
parameter ordering, parameter names, variable and attribute names etc must
717
not be changed without leaving a 'deprecated forwarder' behind. This even
718
applies to modules and classes.
720
If you wish to change the behaviour of a supported API in an incompatible
721
way, you need to change its name as well. For instance, if I add an optional keyword
722
parameter to branch.commit - that's fine. On the other hand, if I add a
723
keyword parameter to branch.commit which is a *required* transaction
724
object, I should rename the API - i.e. to 'branch.commit_transaction'.
726
When renaming such supported API's, be sure to leave a deprecated_method (or
727
_function or ...) behind which forwards to the new API. See the
728
bzrlib.symbol_versioning module for decorators that take care of the
729
details for you - such as updating the docstring, and issuing a warning
730
when the old api is used.
732
For unsupported API's, it does not hurt to follow this discipline, but it's
733
not required. Minimally though, please try to rename things so that
734
callers will at least get an AttributeError rather than weird results.
737
Deprecation decorators
738
----------------------
740
``bzrlib.symbol_versioning`` provides decorators that can be attached to
741
methods, functions, and other interfaces to indicate that they should no
742
longer be used. For example::
744
@deprecated_method(deprecated_in((0, 1, 4)))
746
return self._new_foo()
748
To deprecate a static method you must call ``deprecated_function``
749
(**not** method), after the staticmethod call::
752
@deprecated_function(deprecated_in((0, 1, 4)))
753
def create_repository(base, shared=False, format=None):
755
When you deprecate an API, you should not just delete its tests, because
756
then we might introduce bugs in them. If the API is still present at all,
757
it should still work. The basic approach is to use
758
``TestCase.applyDeprecated`` which in one step checks that the API gives
759
the expected deprecation message, and also returns the real result from
760
the method, so that tests can keep running.
762
Deprecation warnings will be suppressed for final releases, but not for
763
development versions or release candidates, or when running ``bzr
764
selftest``. This gives developers information about whether their code is
765
using deprecated functions, but avoids confusing users about things they
772
Processing Command Lines
773
------------------------
775
bzrlib has a standard framework for parsing command lines and calling
776
processing routines associated with various commands. See builtins.py
777
for numerous examples.
780
Standard Parameter Types
781
------------------------
783
There are some common requirements in the library: some parameters need to be
784
unicode safe, some need byte strings, and so on. At the moment we have
785
only codified one specific pattern: Parameters that need to be unicode
786
should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
787
input into unicode in a consistent fashion, allowing trivial strings to be
788
used for programmer convenience, but not performing unpredictably in the
789
presence of different locales.
795
(The strategy described here is what we want to get to, but it's not
796
consistently followed in the code at the moment.)
798
bzrlib is intended to be a generically reusable library. It shouldn't
799
write messages to stdout or stderr, because some programs that use it
800
might want to display that information through a GUI or some other
803
We can distinguish two types of output from the library:
805
1. Structured data representing the progress or result of an
806
operation. For example, for a commit command this will be a list
807
of the modified files and the finally committed revision number
810
These should be exposed either through the return code or by calls
811
to a callback parameter.
813
A special case of this is progress indicators for long-lived
814
operations, where the caller should pass a ProgressBar object.
816
2. Unstructured log/debug messages, mostly for the benefit of the
817
developers or users trying to debug problems. This should always
818
be sent through ``bzrlib.trace`` and Python ``logging``, so that
819
it can be redirected by the client.
821
The distinction between the two is a bit subjective, but in general if
822
there is any chance that a library would want to see something as
823
structured data, we should make it so.
825
The policy about how output is presented in the text-mode client
826
should be only in the command-line tool.
833
Bazaar has online help for various topics through ``bzr help COMMAND`` or
834
equivalently ``bzr command -h``. We also have help on command options,
835
and on other help topics. (See ``help_topics.py``.)
837
As for python docstrings, the first paragraph should be a single-sentence
838
synopsis of the command.
840
The help for options should be one or more proper sentences, starting with
841
a capital letter and finishing with a full stop (period).
843
All help messages and documentation should have two spaces between
847
Handling Errors and Exceptions
848
==============================
850
Commands should return non-zero when they encounter circumstances that
851
the user should really pay attention to - which includes trivial shell
854
Recommended values are:
857
1. Conflicts in merge-like operations, or changes are present in
858
diff-like operations.
859
2. Unrepresentable diff changes (i.e. binary files that we cannot show
861
3. An error or exception has occurred.
862
4. An internal error occurred (one that shows a traceback.)
864
Errors are handled through Python exceptions. Exceptions should be defined
865
inside bzrlib.errors, so that we can see the whole tree at a glance.
867
We broadly classify errors as either being either internal or not,
868
depending on whether ``internal_error`` is set or not. If we think it's our
869
fault, we show a backtrace, an invitation to report the bug, and possibly
870
other details. This is the default for errors that aren't specifically
871
recognized as being caused by a user error. Otherwise we show a briefer
872
message, unless -Derror was given.
874
Many errors originate as "environmental errors" which are raised by Python
875
or builtin libraries -- for example IOError. These are treated as being
876
our fault, unless they're caught in a particular tight scope where we know
877
that they indicate a user errors. For example if the repository format
878
is not found, the user probably gave the wrong path or URL. But if one of
879
the files inside the repository is not found, then it's our fault --
880
either there's a bug in bzr, or something complicated has gone wrong in
881
the environment that means one internal file was deleted.
883
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
884
to be added near the place where they are used.
886
Exceptions are formatted for the user by conversion to a string
887
(eventually calling their ``__str__`` method.) As a convenience the
888
``._fmt`` member can be used as a template which will be mapped to the
889
error's instance dict.
891
New exception classes should be defined when callers might want to catch
892
that exception specifically, or when it needs a substantially different
895
#. If it is something that a caller can recover from, a custom exception
898
#. If it is a data consistency issue, using a builtin like
899
``ValueError``/``TypeError`` is reasonable.
901
#. If it is a programmer error (using an api incorrectly)
902
``AssertionError`` is reasonable.
904
#. Otherwise, use ``BzrError`` or ``InternalBzrError``.
906
Exception strings should start with a capital letter and should not have a
907
final fullstop. If long, they may contain newlines to break the text.
913
Do not use the Python ``assert`` statement, either in tests or elsewhere.
914
A source test checks that it is not used. It is ok to explicitly raise
919
* It makes the behaviour vary depending on whether bzr is run with -O
920
or not, therefore giving a chance for bugs that occur in one case or
921
the other, several of which have already occurred: assertions with
922
side effects, code which can't continue unless the assertion passes,
923
cases where we should give the user a proper message rather than an
925
* It's not that much shorter than an explicit if/raise.
926
* It tends to lead to fuzzy thinking about whether the check is
927
actually needed or not, and whether it's an internal error or not
928
* It tends to cause look-before-you-leap patterns.
929
* It's unsafe if the check is needed to protect the integrity of the
931
* It tends to give poor messages since the developer can get by with
932
no explanatory text at all.
933
* We can't rely on people always running with -O in normal use, so we
934
can't use it for tests that are actually expensive.
935
* Expensive checks that help developers are better turned on from the
936
test suite or a -D flag.
937
* If used instead of ``self.assert*()`` in tests it makes them falsely pass with -O.
943
When you change bzrlib, please update the relevant documentation for the
944
change you made: Changes to commands should update their help, and
945
possibly end user tutorials; changes to the core library should be
946
reflected in API documentation.
951
If you make a user-visible change, please add a note to the NEWS file.
952
The description should be written to make sense to someone who's just
953
a user of bzr, not a developer: new functions or classes shouldn't be
954
mentioned, but new commands, changes in behaviour or fixed nontrivial
955
bugs should be listed. See the existing entries for an idea of what
958
Within each release, entries in the news file should have the most
959
user-visible changes first. So the order should be approximately:
961
* changes to existing behaviour - the highest priority because the
962
user's existing knowledge is incorrect
963
* new features - should be brought to their attention
964
* bug fixes - may be of interest if the bug was affecting them, and
965
should include the bug number if any
966
* major documentation changes
967
* changes to internal interfaces
969
People who made significant contributions to each change are listed in
970
parenthesis. This can include reporting bugs (particularly with good
971
details or reproduction recipes), submitting patches, etc.
976
The docstring of a command is used by ``bzr help`` to generate help output
977
for the command. The list 'takes_options' attribute on a command is used by
978
``bzr help`` to document the options for the command - the command
979
docstring does not need to document them. Finally, the '_see_also'
980
attribute on a command can be used to reference other related help topics.
985
Functions, methods, classes and modules should have docstrings
986
describing how they are used.
988
The first line of the docstring should be a self-contained sentence.
990
For the special case of Command classes, this acts as the user-visible
991
documentation shown by the help command.
993
The docstrings should be formatted as reStructuredText_ (like this
994
document), suitable for processing using the epydoc_ tool into HTML
997
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
998
.. _epydoc: http://epydoc.sourceforge.net/
1007
The copyright policy for bzr was recently made clear in this email (edited
1008
for grammatical correctness)::
1010
The attached patch cleans up the copyright and license statements in
1011
the bzr source. It also adds tests to help us remember to add them
1012
with the correct text.
1014
We had the problem that lots of our files were "Copyright Canonical
1015
Development Ltd" which is not a real company, and some other variations
1016
on this theme. Also, some files were missing the GPL statements.
1018
I want to be clear about the intent of this patch, since copyright can
1019
be a little controversial.
1021
1) The big motivation for this is not to shut out the community, but
1022
just to clean up all of the invalid copyright statements.
1024
2) It has been the general policy for bzr that we want a single
1025
copyright holder for all of the core code. This is following the model
1026
set by the FSF, which makes it easier to update the code to a new
1027
license in case problems are encountered. (For example, if we want to
1028
upgrade the project universally to GPL v3 it is much simpler if there is
1029
a single copyright holder). It also makes it clearer if copyright is
1030
ever debated, there is a single holder, which makes it easier to defend
1031
in court, etc. (I think the FSF position is that if you assign them
1032
copyright, they can defend it in court rather than you needing to, and
1033
I'm sure Canonical would do the same).
1034
As such, Canonical has requested copyright assignments from all of the
1037
3) If someone wants to add code and not attribute it to Canonical, there
1038
is a specific list of files that are excluded from this check. And the
1039
test failure indicates where that is, and how to update it.
1041
4) If anyone feels that I changed a copyright statement incorrectly, just
1042
let me know, and I'll be happy to correct it. Whenever you have large
1043
mechanical changes like this, it is possible to make some mistakes.
1045
Just to reiterate, this is a community project, and it is meant to stay
1046
that way. Core bzr code is copyright Canonical for legal reasons, and
1047
the tests are just there to help us maintain that.
1050
Miscellaneous Topics
1051
####################
1056
Bazaar has a few facilities to help debug problems by going into pdb_, the
1059
.. _pdb: http://docs.python.org/lib/debugger-commands.html
1061
If the ``BZR_PDB`` environment variable is set
1062
then bzr will go into pdb post-mortem mode when an unhandled exception
1065
If you send a SIGQUIT signal to bzr, which can be done by pressing
1066
Ctrl-\\ on Unix, bzr will go into the debugger immediately. You can
1067
continue execution by typing ``c``. This can be disabled if necessary
1068
by setting the environment variable ``BZR_SIGQUIT_PDB=0``.
1075
Integer identifier for a revision on the main line of a branch.
1076
Revision 0 is always the null revision; others are 1-based
1077
indexes into the branch's revision history.
1080
Unicode and Encoding Support
1081
============================
1083
This section discusses various techniques that Bazaar uses to handle
1084
characters that are outside the ASCII set.
1089
When a ``Command`` object is created, it is given a member variable
1090
accessible by ``self.outf``. This is a file-like object, which is bound to
1091
``sys.stdout``, and should be used to write information to the screen,
1092
rather than directly writing to ``sys.stdout`` or calling ``print``.
1093
This file has the ability to translate Unicode objects into the correct
1094
representation, based on the console encoding. Also, the class attribute
1095
``encoding_type`` will effect how unprintable characters will be
1096
handled. This parameter can take one of 3 values:
1099
Unprintable characters will be represented with a suitable replacement
1100
marker (typically '?'), and no exception will be raised. This is for
1101
any command which generates text for the user to review, rather than
1102
for automated processing.
1103
For example: ``bzr log`` should not fail if one of the entries has text
1104
that cannot be displayed.
1107
Attempting to print an unprintable character will cause a UnicodeError.
1108
This is for commands that are intended more as scripting support, rather
1109
than plain user review.
1110
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
1111
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
1112
printed a filename with a '?', the wrong file could be deleted. (At the
1113
very least, the correct file would not be deleted). An error is used to
1114
indicate that the requested action could not be performed.
1117
Do not attempt to automatically convert Unicode strings. This is used
1118
for commands that must handle conversion themselves.
1119
For example: ``bzr diff`` needs to translate Unicode paths, but should
1120
not change the exact text of the contents of the files.
1123
``bzrlib.urlutils.unescape_for_display``
1124
----------------------------------------
1126
Because Transports work in URLs (as defined earlier), printing the raw URL
1127
to the user is usually less than optimal. Characters outside the standard
1128
set are printed as escapes, rather than the real character, and local
1129
paths would be printed as ``file://`` urls. The function
1130
``unescape_for_display`` attempts to unescape a URL, such that anything
1131
that cannot be printed in the current encoding stays an escaped URL, but
1132
valid characters are generated where possible.
1138
The ``bzrlib.osutils`` module has many useful helper functions, including
1139
some more portable variants of functions in the standard library.
1141
In particular, don't use ``shutil.rmtree`` unless it's acceptable for it
1142
to fail on Windows if some files are readonly or still open elsewhere.
1143
Use ``bzrlib.osutils.rmtree`` instead.
1149
We write some extensions in C using pyrex. We design these to work in
1152
* User with no C compiler
1153
* User with C compiler
1156
The recommended way to install bzr is to have a C compiler so that the
1157
extensions can be built, but if no C compiler is present, the pure python
1158
versions we supply will work, though more slowly.
1160
For developers we recommend that pyrex be installed, so that the C
1161
extensions can be changed if needed.
1163
For the C extensions, the extension module should always match the
1164
original python one in all respects (modulo speed). This should be
1165
maintained over time.
1167
To create an extension, add rules to setup.py for building it with pyrex,
1168
and with distutils. Now start with an empty .pyx file. At the top add
1169
"include 'yourmodule.py'". This will import the contents of foo.py into this
1170
file at build time - remember that only one module will be loaded at
1171
runtime. Now you can subclass classes, or replace functions, and only your
1172
changes need to be present in the .pyx file.
1174
Note that pyrex does not support all 2.4 programming idioms, so some
1175
syntax changes may be required. I.e.
1177
- 'from foo import (bar, gam)' needs to change to not use the brackets.
1178
- 'import foo.bar as bar' needs to be 'import foo.bar; bar = foo.bar'
1180
If the changes are too dramatic, consider
1181
maintaining the python code twice - once in the .pyx, and once in the .py,
1182
and no longer including the .py file.
1185
Making Installers for OS Windows
1186
================================
1187
To build a win32 installer, see the instructions on the wiki page:
1188
http://bazaar-vcs.org/BzrWin32Installer
1191
Core Developer Tasks
1192
####################
1197
What is a Core Developer?
1198
-------------------------
1200
While everyone in the Bazaar community is welcome and encouraged to
1201
propose and submit changes, a smaller team is reponsible for pulling those
1202
changes together into a cohesive whole. In addition to the general developer
1203
stuff covered above, "core" developers have responsibility for:
1206
* reviewing blueprints
1208
* managing releases (see the `Releasing Bazaar <../../developers/releasing.html>`_)
1211
Removing barriers to community participation is a key reason for adopting
1212
distributed VCS technology. While DVCS removes many technical barriers,
1213
a small number of social barriers are often necessary instead.
1214
By documenting how the above things are done, we hope to
1215
encourage more people to participate in these activities, keeping the
1216
differences between core and non-core contributors to a minimum.
1219
Communicating and Coordinating
1220
------------------------------
1222
While it has many advantages, one of the challenges of distributed
1223
development is keeping everyone else aware of what you're working on.
1224
There are numerous ways to do this:
1226
#. Assign bugs to yourself in Launchpad
1227
#. Mention it on the mailing list
1228
#. Mention it on IRC
1230
As well as the email notifcations that occur when merge requests are sent
1231
and reviewed, you can keep others informed of where you're spending your
1232
energy by emailing the **bazaar-commits** list implicitly. To do this,
1233
install and configure the Email plugin. One way to do this is add these
1234
configuration settings to your central configuration file (e.g.
1235
``~/.bazaar/bazaar.conf`` on Linux)::
1238
email = Joe Smith <joe.smith@internode.on.net>
1239
smtp_server = mail.internode.on.net:25
1241
Then add these lines for the relevant branches in ``locations.conf``::
1243
post_commit_to = bazaar-commits@lists.canonical.com
1244
post_commit_mailer = smtplib
1246
While attending a sprint, RobertCollins' Dbus plugin is useful for the
1247
same reason. See the documentation within the plugin for information on
1248
how to set it up and configure it.
1257
Of the many workflows supported by Bazaar, the one adopted for Bazaar
1258
development itself is known as "Decentralized with automatic gatekeeper".
1259
To repeat the explanation of this given on
1260
http://bazaar-vcs.org/Workflows:
1263
In this workflow, each developer has their own branch or
1264
branches, plus read-only access to the mainline. A software gatekeeper
1265
(e.g. PQM) has commit rights to the main branch. When a developer wants
1266
their work merged, they request the gatekeeper to merge it. The gatekeeper
1267
does a merge, a compile, and runs the test suite. If the code passes, it
1268
is merged into the mainline.
1270
In a nutshell, here's the overall submission process:
1272
#. get your work ready (including review except for trivial changes)
1273
#. push to a public location
1274
#. ask PQM to merge from that location
1277
At present, PQM always takes the changes to merge from a branch
1278
at a URL that can be read by it. For Bazaar, that means a public,
1279
typically http, URL.
1281
As a result, the following things are needed to use PQM for submissions:
1283
#. A publicly available web server
1284
#. Your OpenPGP key registered with PQM (contact RobertCollins for this)
1285
#. The PQM plugin installed and configured (not strictly required but
1286
highly recommended).
1289
Selecting a Public Branch Location
1290
----------------------------------
1292
If you don't have your own web server running, branches can always be
1293
pushed to Launchpad. Here's the process for doing that:
1295
Depending on your location throughout the world and the size of your
1296
repository though, it is often quicker to use an alternative public
1297
location to Launchpad, particularly if you can set up your own repo and
1298
push into that. By using an existing repo, push only needs to send the
1299
changes, instead of the complete repository every time. Note that it is
1300
easy to register branches in other locations with Launchpad so no benefits
1301
are lost by going this way.
1304
For Canonical staff, http://people.ubuntu.com/~<user>/ is one
1305
suggestion for public http branches. Contact your manager for information
1306
on accessing this system if required.
1308
It should also be noted that best practice in this area is subject to
1309
change as things evolve. For example, once the Bazaar smart server on
1310
Launchpad supports server-side branching, the performance situation will
1311
be very different to what it is now (Jun 2007).
1314
Configuring the PQM Plug-In
1315
---------------------------
1317
While not strictly required, the PQM plugin automates a few things and
1318
reduces the chance of error. Before looking at the plugin, it helps to
1319
understand a little more how PQM operates. Basically, PQM requires an
1320
email indicating what you want it to do. The email typically looks like
1323
star-merge source-branch target-branch
1327
star-merge http://bzr.arbash-meinel.com/branches/bzr/jam-integration http://bazaar-vcs.org/bzr/bzr.dev
1329
Note that the command needs to be on one line. The subject of the email
1330
will be used for the commit message. The email also needs to be ``gpg``
1331
signed with a key that PQM accepts.
1333
The advantages of using the PQM plugin are:
1335
#. You can use the config policies to make it easy to set up public
1336
branches, so you don't have to ever type the full paths you want to merge
1339
#. It checks to make sure the public branch last revision matches the
1340
local last revision so you are submitting what you think you are.
1342
#. It uses the same public_branch and smtp sending settings as bzr-email,
1343
so if you have one set up, you have the other mostly set up.
1345
#. Thunderbird refuses to not wrap lines, and request lines are usually
1346
pretty long (you have 2 long URLs in there).
1348
Here are sample configuration settings for the PQM plugin. Here are the
1349
lines in bazaar.conf::
1352
email = Joe Smith <joe.smith@internode.on.net>
1353
smtp_server=mail.internode.on.net:25
1355
And here are the lines in ``locations.conf`` (or ``branch.conf`` for
1356
dirstate-tags branches)::
1358
[/home/joe/bzr/my-integration]
1359
push_location = sftp://joe-smith@bazaar.launchpad.net/%7Ejoe-smith/bzr/my-integration/
1360
push_location:policy = norecurse
1361
public_branch = http://bazaar.launchpad.net/~joe-smith/bzr/my-integration/
1362
public_branch:policy = appendpath
1363
pqm_email = Bazaar PQM <pqm@bazaar-vcs.org>
1364
pqm_branch = http://bazaar-vcs.org/bzr/bzr.dev
1366
Note that the push settings will be added by the first ``push`` on
1367
a branch. Indeed the preferred way to generate the lines above is to use
1368
``push`` with an argument, then copy-and-paste the other lines into
1375
Here is one possible recipe once the above environment is set up:
1377
#. pull bzr.dev => my-integration
1378
#. merge patch => my-integration
1379
#. fix up any final merge conflicts (NEWS being the big killer here).
1385
The ``push`` step is not required if ``my-integration`` is a checkout of
1388
Because of defaults, you can type a single message into commit and
1389
pqm-commit will reuse that.
1392
Tracking Change Acceptance
1393
--------------------------
1395
The web interface to PQM is https://pqm.bazaar-vcs.org/. After submitting
1396
a change, you can visit this URL to confirm it was received and placed in
1399
When PQM completes processing a change, an email is sent to you with the
1403
Reviewing Blueprints
1404
====================
1406
Blueprint Tracking Using Launchpad
1407
----------------------------------
1409
New features typically require a fair amount of discussion, design and
1410
debate. For Bazaar, that information is often captured in a so-called
1411
"blueprint" on our Wiki. Overall tracking of blueprints and their status
1412
is done using Launchpad's relevant tracker,
1413
https://blueprints.launchpad.net/bzr/. Once a blueprint for ready for
1414
review, please announce it on the mailing list.
1416
Alternatively, send an email begining with [RFC] with the proposal to the
1417
list. In some cases, you may wish to attach proposed code or a proposed
1418
developer document if that best communicates the idea. Debate can then
1419
proceed using the normal merge review processes.
1422
Recording Blueprint Review Feedback
1423
-----------------------------------
1425
Unlike its Bug Tracker, Launchpad's Blueprint Tracker doesn't currently
1426
(Jun 2007) support a chronological list of comment responses. Review
1427
feedback can either be recorded on the Wiki hosting the blueprints or by
1428
using Launchpad's whiteboard feature.
1437
As the two senior developers, Martin Pool and Robert Collins coordinate
1438
the overall Bazaar product development roadmap. Core developers provide
1439
input and review into this, particularly during sprints. It's totally
1440
expected that community members ought to be working on things that
1441
interest them the most. The roadmap is valuable though because it provides
1442
context for understanding where the product is going as a whole and why.
1445
Using Releases and Milestones in Launchpad
1446
------------------------------------------
1448
TODO ... (Exact policies still under discussion)
1454
Keeping on top of bugs reported is an important part of ongoing release
1455
planning. Everyone in the community is welcome and encouraged to raise
1456
bugs, confirm bugs raised by others, and nominate a priority. Practically
1457
though, a good percentage of bug triage is often done by the core
1458
developers, partially because of their depth of product knowledge.
1460
With respect to bug triage, core developers are encouraged to play an
1461
active role with particular attention to the following tasks:
1463
* keeping the number of unconfirmed bugs low
1464
* ensuring the priorities are generally right (everything as critical - or
1465
medium - is meaningless)
1466
* looking out for regressions and turning those around sooner rather than later.
1469
As well as prioritizing bugs and nominating them against a
1470
target milestone, Launchpad lets core developers offer to mentor others in
1475
vim: ft=rst tw=74 ai
added
removed
doc/developers/HACKING.txt
