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/en/developer-guide/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>`_.
1
============================
2
Guidelines for modifying bzr
3
============================
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/>.
193
See also the `Bazaar Architectural Overview <../../developers/overview.html>`_.
196
The Code Review Process
197
#######################
199
All code changes coming in to Bazaar are reviewed by someone else.
200
Normally changes by core contributors are reviewed by one other core
201
developer, and changes from other people are reviewed by two core
202
developers. Use intelligent discretion if the patch is trivial.
204
Good reviews do take time. They also regularly require a solid
205
understanding of the overall code base. In practice, this means a small
206
number of people often have a large review burden - with knowledge comes
207
responsibility. No one like their merge requests sitting in a queue going
208
nowhere, so reviewing sooner rather than later is strongly encouraged.
217
Please put a "cover letter" on your merge request explaining:
219
* the reason **why** you're making this change
221
* **how** this change achieves this purpose
223
* anything else you may have fixed in passing
225
* anything significant that you thought of doing, such as a more
226
extensive fix or a different approach, but didn't or couldn't do now
228
A good cover letter makes reviewers' lives easier because they can decide
229
from the letter whether they agree with the purpose and approach, and then
230
assess whether the patch actually does what the cover letter says.
231
Explaining any "drive-by fixes" or roads not taken may also avoid queries
232
from the reviewer. All in all this should give faster and better reviews.
233
Sometimes writing the cover letter helps the submitter realize something
234
else they need to do. The size of the cover letter should be proportional
235
to the size and complexity of the patch.
238
Reviewing proposed changes
239
==========================
241
Anyone is welcome to review code, and reply to the thread with their
244
The simplest way to review a proposed change is to just read the patch on
245
the list or in Bundle Buggy. For more complex changes it may be useful
246
to make a new working tree or branch from trunk, and merge the proposed
247
change into it, so you can experiment with the code or look at a wider
250
There are three main requirements for code to get in:
252
* Doesn't reduce test coverage: if it adds new methods or commands,
253
there should be tests for them. There is a good test framework
254
and plenty of examples to crib from, but if you are having trouble
255
working out how to test something feel free to post a draft patch
258
* Doesn't reduce design clarity, such as by entangling objects
259
we're trying to separate. This is mostly something the more
260
experienced reviewers need to help check.
262
* Improves bugs, features, speed, or code simplicity.
264
Code that goes in should not degrade any of these aspects. Patches are
265
welcome that only cleanup the code without changing the external
266
behaviour. The core developers take care to keep the code quality high
267
and understandable while recognising that perfect is sometimes the enemy
270
It is easy for reviews to make people notice other things which should be
271
fixed but those things should not hold up the original fix being accepted.
272
New things can easily be recorded in the Bug Tracker instead.
274
It's normally much easier to review several smaller patches than one large
275
one. You might want to use ``bzr-loom`` to maintain threads of related
276
work, or submit a preparatory patch that will make your "real" change
280
Checklist for reviewers
281
=======================
283
* Do you understand what the code's doing and why?
285
* Will it perform reasonably for large inputs, both in memory size and
286
run time? Are there some scenarios where performance should be
289
* Is it tested, and are the tests at the right level? Are there both
290
blackbox (command-line level) and API-oriented tests?
292
* If this change will be visible to end users or API users, is it
293
appropriately documented in NEWS?
295
* Does it meet the coding standards below?
297
* If it changes the user-visible behaviour, does it update the help
298
strings and user documentation?
300
* If it adds a new major concept or standard practice, does it update the
301
developer documentation?
303
* (your ideas here...)
309
From May 2009 on, we prefer people to propose code reviews through
312
* <https://launchpad.net/+tour/code-review>
314
* <https://help.launchpad.net/Code/Review>
316
Anyone can propose or comment on a merge propsal just by creating a
319
There are two ways to create a new merge proposal: through the web
320
interface or by email.
323
Proposing a merge through the web
324
---------------------------------
326
To create the propsal through the web: push your branch to Launchpad, eg::
328
bzr push lp:~mbp/bzr/doc
330
then go to the branch's web page, which in this case would be
331
<https://code.launchpad.net/~mbp/bzr/doc>. You can automate that by just
336
You can then click "Propose for merging into another branch", and enter a
337
cover letter into the web form. Typically you'll want to merge into
338
``~bzr/bzr/trunk`` which will be the default; you might also want to
339
nominate merging into a release branch for a bug fix. There is the option
340
to specify a specific reviewer or type of review, and you shouldn't
341
normally change those.
343
Submitting the form takes you to the new page about the merge proposal
344
containing the diff of the changes, comments by interested people, and
345
controls to comment or vote on the change.
347
Proposing a merge by mail
348
-------------------------
350
To propose a merge by mail, send a bundle to ``merge@code.launchpad.net``.
352
You can generate a merge request like this::
354
bzr send -o bug-1234.diff
356
``bzr send`` can also send mail directly if you prefer; see the help.
361
From <https://code.launchpad.net/bzr/+activereviews> you can see all
362
currently active reviews, and choose one to comment on. This page also
363
shows proposals that are now approved and should be merged by someone with
367
Reviews through Bundle Buggy
368
============================
370
The Bundle Buggy tool used up to May 2009 is still available as a review
373
Sending patches for review
374
--------------------------
376
If you'd like to propose a change, please post to the
377
bazaar@lists.canonical.com list with a bundle, patch, or link to a
378
branch. Put ``[PATCH]`` or ``[MERGE]`` in the subject so Bundle Buggy
379
can pick it out, and explain the change in the email message text.
380
Remember to update the NEWS file as part of your change if it makes any
381
changes visible to users or plugin developers. Please include a diff
382
against mainline if you're giving a link to a branch.
384
You can generate a merge request like this::
386
bzr send -o bug-1234.patch
388
A ``.patch`` extension is recommended instead of .bundle as many mail clients
389
will send the latter as a binary file.
391
``bzr send`` can also send mail directly if you prefer; see the help.
393
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
394
want it to be merged. If you want comments from developers rather than
395
to be merged, you can put ``[RFC]`` in the subject line.
397
If this change addresses a bug, please put the bug number in the subject
398
line too, in the form ``[#1]`` so that Bundle Buggy can recognize it.
400
If the change is intended for a particular release mark that in the
401
subject too, e.g. ``[1.6]``.
402
Anyone can "vote" on the mailing list by expressing an opinion. Core
403
developers can also vote using Bundle Buggy. Here are the voting codes and
406
:approve: Reviewer wants this submission merged.
407
:tweak: Reviewer wants this submission merged with small changes. (No
409
:abstain: Reviewer does not intend to vote on this patch.
410
:resubmit: Please make changes and resubmit for review.
411
:reject: Reviewer doesn't want this kind of change merged.
412
:comment: Not really a vote. Reviewer just wants to comment, for now.
414
If a change gets two approvals from core reviewers, and no rejections,
415
then it's OK to come in. Any of the core developers can bring it into the
416
bzr.dev trunk and backport it to maintenance branches if required. The
417
Release Manager will merge the change into the branch for a pending
418
release, if any. As a guideline, core developers usually merge their own
419
changes and volunteer to merge other contributions if they were the second
420
reviewer to agree to a change.
422
To track the progress of proposed changes, use Bundle Buggy. See
423
http://bundlebuggy.aaronbentley.com/help for a link to all the
424
outstanding merge requests together with an explanation of the columns.
425
Bundle Buggy will also mail you a link to track just your change.
427
Coding Style Guidelines
428
#######################
433
``hasattr`` should not be used because it swallows exceptions including
434
``KeyboardInterrupt``. Instead, say something like ::
436
if getattr(thing, 'name', None) is None
442
Please write PEP-8__ compliant code.
444
__ http://www.python.org/peps/pep-0008.html
446
One often-missed requirement is that the first line of docstrings
447
should be a self-contained one-sentence summary.
449
We use 4 space indents for blocks, and never use tab characters. (In vim,
452
Trailing white space should be avoided, but is allowed.
453
You should however not make lots of unrelated white space changes.
455
Unix style newlines (LF) are used.
457
Each file must have a newline at the end of it.
459
Lines should be no more than 79 characters if at all possible.
460
Lines that continue a long statement may be indented in either of
463
within the parenthesis or other character that opens the block, e.g.::
469
or indented by four spaces::
475
The first is considered clearer by some people; however it can be a bit
476
harder to maintain (e.g. when the method name changes), and it does not
477
work well if the relevant parenthesis is already far to the right. Avoid
480
self.legbone.kneebone.shinbone.toebone.shake_it(one,
486
self.legbone.kneebone.shinbone.toebone.shake_it(one,
492
self.legbone.kneebone.shinbone.toebone.shake_it(
495
For long lists, we like to add a trailing comma and put the closing
496
character on the following line. This makes it easier to add new items in
499
from bzrlib.goo import (
505
There should be spaces between function paramaters, but not between the
506
keyword name and the value::
508
call(1, 3, cheese=quark)
512
;(defface my-invalid-face
513
; '((t (:background "Red" :underline t)))
514
; "Face used to highlight invalid constructs or other uglyties"
517
(defun my-python-mode-hook ()
518
;; setup preferred indentation style.
519
(setq fill-column 79)
520
(setq indent-tabs-mode nil) ; no tabs, never, I will not repeat
521
; (font-lock-add-keywords 'python-mode
522
; '(("^\\s *\t" . 'my-invalid-face) ; Leading tabs
523
; ("[ \t]+$" . 'my-invalid-face) ; Trailing spaces
524
; ("^[ \t]+$" . 'my-invalid-face)); Spaces only
528
(add-hook 'python-mode-hook 'my-python-mode-hook)
530
The lines beginning with ';' are comments. They can be activated
531
if one want to have a strong notice of some tab/space usage
7
(The current version of this document is available in the file ``HACKING``
8
in the source tree, or at http://bazaar-ng.org/hacking.html)
13
* New functionality should have test cases. Preferably write the
14
test before writing the code.
16
In general, you can test at either the command-line level or the
17
internal API level. Choose whichever is appropriate: if adding a
18
new command, or a new command option, then call through run_bzr().
19
It is not necessary to do both. Tests that test the command line level
20
are appropriate for checking the UI behaves well - bug fixes and
21
core improvements should be tested closer to the code that is doing the
22
work. Command line level tests should be placed in 'blackbox.py'.
24
* Before fixing a bug, write a test case so that it does not regress.
26
* Exceptions should be defined inside bzrlib.errors, so that we can
27
see the whole tree at a glance.
538
29
* Imports should be done at the top-level of the file, unless there is
539
30
a strong reason to have them lazily loaded when a particular
600
152
may not catch every case but it's still useful sometimes.
606
In some places we have variables which point to callables that construct
607
new instances. That is to say, they can be used a lot like class objects,
608
but they shouldn't be *named* like classes:
610
> I think that things named FooBar should create instances of FooBar when
611
> called. Its plain confusing for them to do otherwise. When we have
612
> something that is going to be used as a class - that is, checked for via
613
> isinstance or other such idioms, them I would call it foo_class, so that
614
> it is clear that a callable is not sufficient. If it is only used as a
615
> factory, then yes, foo_factory is what I would use.
621
Several places in Bazaar use (or will use) a registry, which is a
622
mapping from names to objects or classes. The registry allows for
623
loading in registered code only when it's needed, and keeping
624
associated information such as a help string or description.
627
InterObject and multiple dispatch
628
=================================
630
The ``InterObject`` provides for two-way `multiple dispatch`__: matching
631
up for example a source and destination repository to find the right way
632
to transfer data between them.
634
.. __: http://en.wikipedia.org/wiki/Multiple_dispatch
636
There is a subclass ``InterObject`` classes for each type of object that is
637
dispatched this way, e.g. ``InterRepository``. Calling ``.get()`` on this
638
class will return an ``InterObject`` instance providing the best match for
639
those parameters, and this instance then has methods for operations
642
inter = InterRepository.get(source_repo, target_repo)
643
inter.fetch(revision_id)
645
``InterRepository`` also acts as a registry-like object for its
646
subclasses, and they can be added through ``.register_optimizer``. The
647
right one to run is selected by asking each class, in reverse order of
648
registration, whether it ``.is_compatible`` with the relevant objects.
653
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
654
delay importing modules until they are actually used. ``lazy_import`` uses
655
the same syntax as regular python imports. So to import a few modules in a
658
from bzrlib.lazy_import import lazy_import
659
lazy_import(globals(), """
668
revision as _mod_revision,
670
import bzrlib.transport
674
At this point, all of these exist as a ``ImportReplacer`` object, ready to
675
be imported once a member is accessed. Also, when importing a module into
676
the local namespace, which is likely to clash with variable names, it is
677
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
678
the variable is a module, and these object should be hidden anyway, since
679
they shouldn't be imported into other namespaces.
681
While it is possible for ``lazy_import()`` to import members of a module
682
when using the ``from module import member`` syntax, it is recommended to
683
only use that syntax to load sub modules ``from module import submodule``.
684
This is because variables and classes can frequently be used without
685
needing a sub-member for example::
687
lazy_import(globals(), """
688
from module import MyClass
692
return isinstance(x, MyClass)
694
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
695
object, rather than the real class.
697
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
698
Because the replacer only knows about the original name, it is unable to
699
replace other variables. The ``ImportReplacer`` class will raise an
700
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
701
happened. But it requires accessing a member more than once from the new
702
variable, so some bugs are not detected right away.
708
The null revision is the ancestor of all revisions. Its revno is 0, its
709
revision-id is ``null:``, and its tree is the empty tree. When referring
710
to the null revision, please use ``bzrlib.revision.NULL_REVISION``. Old
711
code sometimes uses ``None`` for the null revision, but this practice is
715
Object string representations
716
=============================
718
Python prints objects using their ``__repr__`` method when they are
719
written to logs, exception tracebacks, or the debugger. We want
720
objects to have useful representations to help in determining what went
723
If you add a new class you should generally add a ``__repr__`` method
724
unless there is an adequate method in a parent class. There should be a
727
Representations should typically look like Python constructor syntax, but
728
they don't need to include every value in the object and they don't need
729
to be able to actually execute. They're to be read by humans, not
730
machines. Don't hardcode the classname in the format, so that we get the
731
correct value if the method is inherited by a subclass. If you're
732
printing attributes of the object, including strings, you should normally
733
use ``%r`` syntax (to call their repr in turn).
735
Try to avoid the representation becoming more than one or two lines long.
736
(But balance this against including useful information, and simplicity of
739
Because repr methods are often called when something has already gone
740
wrong, they should be written somewhat more defensively than most code.
741
The object may be half-initialized or in some other way in an illegal
742
state. The repr method shouldn't raise an exception, or it may hide the
743
(probably more useful) underlying exception.
748
return '%s(%r)' % (self.__class__.__name__,
755
A bare ``except`` statement will catch all exceptions, including ones that
756
really should terminate the program such as ``MemoryError`` and
757
``KeyboardInterrupt``. They should rarely be used unless the exception is
758
later re-raised. Even then, think about whether catching just
759
``Exception`` (which excludes system errors in Python2.5 and later) would
766
All code should be exercised by the test suite. See `Guide to Testing
767
Bazaar <../../developers/testing.html>`_ for detailed information about writing tests.
776
We have a commitment to 6 months API stability - any supported symbol in a
777
release of bzr MUST NOT be altered in any way that would result in
778
breaking existing code that uses it. That means that method names,
779
parameter ordering, parameter names, variable and attribute names etc must
780
not be changed without leaving a 'deprecated forwarder' behind. This even
781
applies to modules and classes.
783
If you wish to change the behaviour of a supported API in an incompatible
784
way, you need to change its name as well. For instance, if I add an optional keyword
785
parameter to branch.commit - that's fine. On the other hand, if I add a
786
keyword parameter to branch.commit which is a *required* transaction
787
object, I should rename the API - i.e. to 'branch.commit_transaction'.
789
When renaming such supported API's, be sure to leave a deprecated_method (or
790
_function or ...) behind which forwards to the new API. See the
791
bzrlib.symbol_versioning module for decorators that take care of the
792
details for you - such as updating the docstring, and issuing a warning
793
when the old api is used.
795
For unsupported API's, it does not hurt to follow this discipline, but it's
796
not required. Minimally though, please try to rename things so that
797
callers will at least get an AttributeError rather than weird results.
800
Deprecation decorators
801
----------------------
803
``bzrlib.symbol_versioning`` provides decorators that can be attached to
804
methods, functions, and other interfaces to indicate that they should no
805
longer be used. For example::
807
@deprecated_method(deprecated_in((0, 1, 4)))
809
return self._new_foo()
811
To deprecate a static method you must call ``deprecated_function``
812
(**not** method), after the staticmethod call::
815
@deprecated_function(deprecated_in((0, 1, 4)))
816
def create_repository(base, shared=False, format=None):
818
When you deprecate an API, you should not just delete its tests, because
819
then we might introduce bugs in them. If the API is still present at all,
820
it should still work. The basic approach is to use
821
``TestCase.applyDeprecated`` which in one step checks that the API gives
822
the expected deprecation message, and also returns the real result from
823
the method, so that tests can keep running.
825
Deprecation warnings will be suppressed for final releases, but not for
826
development versions or release candidates, or when running ``bzr
827
selftest``. This gives developers information about whether their code is
828
using deprecated functions, but avoids confusing users about things they
835
Processing Command Lines
836
------------------------
838
bzrlib has a standard framework for parsing command lines and calling
839
processing routines associated with various commands. See builtins.py
840
for numerous examples.
843
Standard Parameter Types
844
------------------------
846
There are some common requirements in the library: some parameters need to be
847
unicode safe, some need byte strings, and so on. At the moment we have
848
only codified one specific pattern: Parameters that need to be unicode
849
should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
850
input into unicode in a consistent fashion, allowing trivial strings to be
851
used for programmer convenience, but not performing unpredictably in the
852
presence of different locales.
858
158
(The strategy described here is what we want to get to, but it's not
889
189
should be only in the command-line tool.
892
Progress and Activity Indications
893
---------------------------------
895
bzrlib has a way for code to display to the user that stuff is happening
896
during a long operation. There are two particular types: *activity* which
897
means that IO is happening on a Transport, and *progress* which means that
898
higher-level application work is occurring. Both are drawn together by
901
Transport objects are responsible for calling `report_transport_activity`
904
Progress uses a model/view pattern: application code acts on a
905
`ProgressTask` object, which notifies the UI when it needs to be
906
displayed. Progress tasks form a stack. To create a new progress task on
907
top of the stack, call `bzrlib.ui.ui_factory.nested_progress_bar()`, then
908
call `update()` on the returned ProgressTask. It can be updated with just
909
a text description, with a numeric count, or with a numeric count and
910
expected total count. If an expected total count is provided the view
911
can show the progress moving along towards the expected total.
913
The user should call `finish` on the `ProgressTask` when the logical
914
operation has finished, so it can be removed from the stack.
916
Progress tasks have a complex relatioship with generators: it's a very
917
good place to use them, but because python2.4 does not allow ``finally``
918
blocks in generators it's hard to clean them up properly. In this case
919
it's probably better to have the code calling the generator allocate a
920
progress task for its use and then call `finalize` when it's done, which
921
will close it if it was not already closed. The generator should also
922
finish the progress task when it exits, because it may otherwise be a long
923
time until the finally block runs.
929
Bazaar has online help for various topics through ``bzr help COMMAND`` or
930
equivalently ``bzr command -h``. We also have help on command options,
931
and on other help topics. (See ``help_topics.py``.)
933
As for python docstrings, the first paragraph should be a single-sentence
934
synopsis of the command.
936
The help for options should be one or more proper sentences, starting with
937
a capital letter and finishing with a full stop (period).
939
All help messages and documentation should have two spaces between
943
Handling Errors and Exceptions
944
==============================
946
Commands should return non-zero when they encounter circumstances that
947
the user should really pay attention to - which includes trivial shell
950
Recommended values are:
953
1. Conflicts in merge-like operations, or changes are present in
954
diff-like operations.
955
2. Unrepresentable diff changes (i.e. binary files that we cannot show
957
3. An error or exception has occurred.
958
4. An internal error occurred (one that shows a traceback.)
960
Errors are handled through Python exceptions. Exceptions should be defined
961
inside bzrlib.errors, so that we can see the whole tree at a glance.
963
We broadly classify errors as either being either internal or not,
964
depending on whether ``internal_error`` is set or not. If we think it's our
965
fault, we show a backtrace, an invitation to report the bug, and possibly
966
other details. This is the default for errors that aren't specifically
967
recognized as being caused by a user error. Otherwise we show a briefer
968
message, unless -Derror was given.
970
Many errors originate as "environmental errors" which are raised by Python
971
or builtin libraries -- for example IOError. These are treated as being
972
our fault, unless they're caught in a particular tight scope where we know
973
that they indicate a user errors. For example if the repository format
974
is not found, the user probably gave the wrong path or URL. But if one of
975
the files inside the repository is not found, then it's our fault --
976
either there's a bug in bzr, or something complicated has gone wrong in
977
the environment that means one internal file was deleted.
979
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
980
to be added near the place where they are used.
982
Exceptions are formatted for the user by conversion to a string
983
(eventually calling their ``__str__`` method.) As a convenience the
984
``._fmt`` member can be used as a template which will be mapped to the
985
error's instance dict.
987
New exception classes should be defined when callers might want to catch
988
that exception specifically, or when it needs a substantially different
991
#. If it is something that a caller can recover from, a custom exception
994
#. If it is a data consistency issue, using a builtin like
995
``ValueError``/``TypeError`` is reasonable.
997
#. If it is a programmer error (using an api incorrectly)
998
``AssertionError`` is reasonable.
1000
#. Otherwise, use ``BzrError`` or ``InternalBzrError``.
1002
Exception strings should start with a capital letter and should not have a
1003
final fullstop. If long, they may contain newlines to break the text.
1009
Do not use the Python ``assert`` statement, either in tests or elsewhere.
1010
A source test checks that it is not used. It is ok to explicitly raise
1015
* It makes the behaviour vary depending on whether bzr is run with -O
1016
or not, therefore giving a chance for bugs that occur in one case or
1017
the other, several of which have already occurred: assertions with
1018
side effects, code which can't continue unless the assertion passes,
1019
cases where we should give the user a proper message rather than an
1021
* It's not that much shorter than an explicit if/raise.
1022
* It tends to lead to fuzzy thinking about whether the check is
1023
actually needed or not, and whether it's an internal error or not
1024
* It tends to cause look-before-you-leap patterns.
1025
* It's unsafe if the check is needed to protect the integrity of the
1027
* It tends to give poor messages since the developer can get by with
1028
no explanatory text at all.
1029
* We can't rely on people always running with -O in normal use, so we
1030
can't use it for tests that are actually expensive.
1031
* Expensive checks that help developers are better turned on from the
1032
test suite or a -D flag.
1033
* If used instead of ``self.assert*()`` in tests it makes them falsely pass with -O.
1039
When you change bzrlib, please update the relevant documentation for the
1040
change you made: Changes to commands should update their help, and
1041
possibly end user tutorials; changes to the core library should be
1042
reflected in API documentation.
1047
If you make a user-visible change, please add a note to the NEWS file.
1048
The description should be written to make sense to someone who's just
1049
a user of bzr, not a developer: new functions or classes shouldn't be
1050
mentioned, but new commands, changes in behaviour or fixed nontrivial
1051
bugs should be listed. See the existing entries for an idea of what
1054
Within each release, entries in the news file should have the most
1055
user-visible changes first. So the order should be approximately:
1057
* changes to existing behaviour - the highest priority because the
1058
user's existing knowledge is incorrect
1059
* new features - should be brought to their attention
1060
* bug fixes - may be of interest if the bug was affecting them, and
1061
should include the bug number if any
1062
* major documentation changes
1063
* changes to internal interfaces
1065
People who made significant contributions to each change are listed in
1066
parenthesis. This can include reporting bugs (particularly with good
1067
details or reproduction recipes), submitting patches, etc.
1072
The docstring of a command is used by ``bzr help`` to generate help output
1073
for the command. The list 'takes_options' attribute on a command is used by
1074
``bzr help`` to document the options for the command - the command
1075
docstring does not need to document them. Finally, the '_see_also'
1076
attribute on a command can be used to reference other related help topics.
1081
Functions, methods, classes and modules should have docstrings
1082
describing how they are used.
1084
The first line of the docstring should be a self-contained sentence.
1086
For the special case of Command classes, this acts as the user-visible
1087
documentation shown by the help command.
1089
The docstrings should be formatted as reStructuredText_ (like this
1090
document), suitable for processing using the epydoc_ tool into HTML
1093
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
1094
.. _epydoc: http://epydoc.sourceforge.net/
1103
The copyright policy for bzr was recently made clear in this email (edited
1104
for grammatical correctness)::
1106
The attached patch cleans up the copyright and license statements in
1107
the bzr source. It also adds tests to help us remember to add them
1108
with the correct text.
1110
We had the problem that lots of our files were "Copyright Canonical
1111
Development Ltd" which is not a real company, and some other variations
1112
on this theme. Also, some files were missing the GPL statements.
1114
I want to be clear about the intent of this patch, since copyright can
1115
be a little controversial.
1117
1) The big motivation for this is not to shut out the community, but
1118
just to clean up all of the invalid copyright statements.
1120
2) It has been the general policy for bzr that we want a single
1121
copyright holder for all of the core code. This is following the model
1122
set by the FSF, which makes it easier to update the code to a new
1123
license in case problems are encountered. (For example, if we want to
1124
upgrade the project universally to GPL v3 it is much simpler if there is
1125
a single copyright holder). It also makes it clearer if copyright is
1126
ever debated, there is a single holder, which makes it easier to defend
1127
in court, etc. (I think the FSF position is that if you assign them
1128
copyright, they can defend it in court rather than you needing to, and
1129
I'm sure Canonical would do the same).
1130
As such, Canonical has requested copyright assignments from all of the
1133
3) If someone wants to add code and not attribute it to Canonical, there
1134
is a specific list of files that are excluded from this check. And the
1135
test failure indicates where that is, and how to update it.
1137
4) If anyone feels that I changed a copyright statement incorrectly, just
1138
let me know, and I'll be happy to correct it. Whenever you have large
1139
mechanical changes like this, it is possible to make some mistakes.
1141
Just to reiterate, this is a community project, and it is meant to stay
1142
that way. Core bzr code is copyright Canonical for legal reasons, and
1143
the tests are just there to help us maintain that.
1146
Miscellaneous Topics
1147
####################
1152
Bazaar has a few facilities to help debug problems by going into pdb_, the
1155
.. _pdb: http://docs.python.org/lib/debugger-commands.html
1157
If the ``BZR_PDB`` environment variable is set
1158
then bzr will go into pdb post-mortem mode when an unhandled exception
1161
If you send a SIGQUIT signal to bzr, which can be done by pressing
1162
Ctrl-\\ on Unix, bzr will go into the debugger immediately. You can
1163
continue execution by typing ``c``. This can be disabled if necessary
1164
by setting the environment variable ``BZR_SIGQUIT_PDB=0``.
1170
Bazaar accepts some global options starting with ``-D`` such as
1171
``-Dhpss``. These set a value in `bzrlib.debug.debug_flags`, and
1172
typically cause more information to be written to the trace file. Most
1173
`mutter` calls should be guarded by a check of those flags so that we
1174
don't write out too much information if it's not needed.
1176
Debug flags may have effects other than just emitting trace messages.
1178
Run ``bzr help global-options`` to see them all.
1180
These flags may also be set as a comma-separated list in the
1181
``debug_flags`` option in e.g. ``~/.bazaar/bazaar.conf``. (Note that it
1182
must be in this global file, not in the branch or location configuration,
1183
because it's currently only loaded at startup time.) For instance you may
1184
want to always record hpss traces and to see full error tracebacks::
1186
debug_flags = hpss, error
194
In general tests should be placed in a file named testFOO.py where
195
FOO is the logical thing under test. That file should be placed in the
196
tests subdirectory under the package being tested.
198
For example, tests for merge3 in bzrlib belong in bzrlib/tests/testmerge3.py.
199
See bzrlib/selftest/testsampler.py for a template test script.
204
Currently, bzr selftest is used to invoke tests.
205
You can provide a pattern argument to run a subset. For example,
206
to run just the whitebox tests, run::
208
bzr selftest -v whitebox
211
Errors and exceptions
212
=====================
214
Errors are handled through Python exceptions. They can represent user
215
errors, environmental errors or program bugs. Sometimes we can't be sure
216
at the time it's raised which case applies. See bzrlib/errors.py for
217
details on the error-handling practices.
1194
225
Revision 0 is always the null revision; others are 1-based
1195
226
indexes into the branch's revision history.
1198
Unicode and Encoding Support
1199
============================
1201
This section discusses various techniques that Bazaar uses to handle
1202
characters that are outside the ASCII set.
1207
When a ``Command`` object is created, it is given a member variable
1208
accessible by ``self.outf``. This is a file-like object, which is bound to
1209
``sys.stdout``, and should be used to write information to the screen,
1210
rather than directly writing to ``sys.stdout`` or calling ``print``.
1211
This file has the ability to translate Unicode objects into the correct
1212
representation, based on the console encoding. Also, the class attribute
1213
``encoding_type`` will effect how unprintable characters will be
1214
handled. This parameter can take one of 3 values:
1217
Unprintable characters will be represented with a suitable replacement
1218
marker (typically '?'), and no exception will be raised. This is for
1219
any command which generates text for the user to review, rather than
1220
for automated processing.
1221
For example: ``bzr log`` should not fail if one of the entries has text
1222
that cannot be displayed.
1225
Attempting to print an unprintable character will cause a UnicodeError.
1226
This is for commands that are intended more as scripting support, rather
1227
than plain user review.
1228
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
1229
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
1230
printed a filename with a '?', the wrong file could be deleted. (At the
1231
very least, the correct file would not be deleted). An error is used to
1232
indicate that the requested action could not be performed.
1235
Do not attempt to automatically convert Unicode strings. This is used
1236
for commands that must handle conversion themselves.
1237
For example: ``bzr diff`` needs to translate Unicode paths, but should
1238
not change the exact text of the contents of the files.
1241
``bzrlib.urlutils.unescape_for_display``
1242
----------------------------------------
1244
Because Transports work in URLs (as defined earlier), printing the raw URL
1245
to the user is usually less than optimal. Characters outside the standard
1246
set are printed as escapes, rather than the real character, and local
1247
paths would be printed as ``file://`` urls. The function
1248
``unescape_for_display`` attempts to unescape a URL, such that anything
1249
that cannot be printed in the current encoding stays an escaped URL, but
1250
valid characters are generated where possible.
1256
The ``bzrlib.osutils`` module has many useful helper functions, including
1257
some more portable variants of functions in the standard library.
1259
In particular, don't use ``shutil.rmtree`` unless it's acceptable for it
1260
to fail on Windows if some files are readonly or still open elsewhere.
1261
Use ``bzrlib.osutils.rmtree`` instead.
1267
We write some extensions in C using pyrex. We design these to work in
1270
* User with no C compiler
1271
* User with C compiler
1274
The recommended way to install bzr is to have a C compiler so that the
1275
extensions can be built, but if no C compiler is present, the pure python
1276
versions we supply will work, though more slowly.
1278
For developers we recommend that pyrex be installed, so that the C
1279
extensions can be changed if needed.
1281
For the C extensions, the extension module should always match the
1282
original python one in all respects (modulo speed). This should be
1283
maintained over time.
1285
To create an extension, add rules to setup.py for building it with pyrex,
1286
and with distutils. Now start with an empty .pyx file. At the top add
1287
"include 'yourmodule.py'". This will import the contents of foo.py into this
1288
file at build time - remember that only one module will be loaded at
1289
runtime. Now you can subclass classes, or replace functions, and only your
1290
changes need to be present in the .pyx file.
1292
Note that pyrex does not support all 2.4 programming idioms, so some
1293
syntax changes may be required. I.e.
1295
- 'from foo import (bar, gam)' needs to change to not use the brackets.
1296
- 'import foo.bar as bar' needs to be 'import foo.bar; bar = foo.bar'
1298
If the changes are too dramatic, consider
1299
maintaining the python code twice - once in the .pyx, and once in the .py,
1300
and no longer including the .py file.
1303
Making Installers for OS Windows
1304
================================
1305
To build a win32 installer, see the instructions on the wiki page:
1306
http://bazaar-vcs.org/BzrWin32Installer
1309
Core Developer Tasks
1310
####################
1315
What is a Core Developer?
1316
-------------------------
1318
While everyone in the Bazaar community is welcome and encouraged to
1319
propose and submit changes, a smaller team is reponsible for pulling those
1320
changes together into a cohesive whole. In addition to the general developer
1321
stuff covered above, "core" developers have responsibility for:
1324
* reviewing blueprints
1326
* managing releases (see the `Releasing Bazaar <../../developers/releasing.html>`_)
1329
Removing barriers to community participation is a key reason for adopting
1330
distributed VCS technology. While DVCS removes many technical barriers,
1331
a small number of social barriers are often necessary instead.
1332
By documenting how the above things are done, we hope to
1333
encourage more people to participate in these activities, keeping the
1334
differences between core and non-core contributors to a minimum.
1337
Communicating and Coordinating
1338
------------------------------
1340
While it has many advantages, one of the challenges of distributed
1341
development is keeping everyone else aware of what you're working on.
1342
There are numerous ways to do this:
1344
#. Assign bugs to yourself in Launchpad
1345
#. Mention it on the mailing list
1346
#. Mention it on IRC
1348
As well as the email notifcations that occur when merge requests are sent
1349
and reviewed, you can keep others informed of where you're spending your
1350
energy by emailing the **bazaar-commits** list implicitly. To do this,
1351
install and configure the Email plugin. One way to do this is add these
1352
configuration settings to your central configuration file (e.g.
1353
``~/.bazaar/bazaar.conf`` on Linux)::
1356
email = Joe Smith <joe.smith@internode.on.net>
1357
smtp_server = mail.internode.on.net:25
1359
Then add these lines for the relevant branches in ``locations.conf``::
1361
post_commit_to = bazaar-commits@lists.canonical.com
1362
post_commit_mailer = smtplib
1364
While attending a sprint, RobertCollins' Dbus plugin is useful for the
1365
same reason. See the documentation within the plugin for information on
1366
how to set it up and configure it.
1375
Of the many workflows supported by Bazaar, the one adopted for Bazaar
1376
development itself is known as "Decentralized with automatic gatekeeper".
1377
To repeat the explanation of this given on
1378
http://bazaar-vcs.org/Workflows:
1381
In this workflow, each developer has their own branch or
1382
branches, plus read-only access to the mainline. A software gatekeeper
1383
(e.g. PQM) has commit rights to the main branch. When a developer wants
1384
their work merged, they request the gatekeeper to merge it. The gatekeeper
1385
does a merge, a compile, and runs the test suite. If the code passes, it
1386
is merged into the mainline.
1388
In a nutshell, here's the overall submission process:
1390
#. get your work ready (including review except for trivial changes)
1391
#. push to a public location
1392
#. ask PQM to merge from that location
1395
At present, PQM always takes the changes to merge from a branch
1396
at a URL that can be read by it. For Bazaar, that means a public,
1397
typically http, URL.
1399
As a result, the following things are needed to use PQM for submissions:
1401
#. A publicly available web server
1402
#. Your OpenPGP key registered with PQM (contact RobertCollins for this)
1403
#. The PQM plugin installed and configured (not strictly required but
1404
highly recommended).
1407
Selecting a Public Branch Location
1408
----------------------------------
1410
If you don't have your own web server running, branches can always be
1411
pushed to Launchpad. Here's the process for doing that:
1413
Depending on your location throughout the world and the size of your
1414
repository though, it is often quicker to use an alternative public
1415
location to Launchpad, particularly if you can set up your own repo and
1416
push into that. By using an existing repo, push only needs to send the
1417
changes, instead of the complete repository every time. Note that it is
1418
easy to register branches in other locations with Launchpad so no benefits
1419
are lost by going this way.
1422
For Canonical staff, http://people.ubuntu.com/~<user>/ is one
1423
suggestion for public http branches. Contact your manager for information
1424
on accessing this system if required.
1426
It should also be noted that best practice in this area is subject to
1427
change as things evolve. For example, once the Bazaar smart server on
1428
Launchpad supports server-side branching, the performance situation will
1429
be very different to what it is now (Jun 2007).
1432
Configuring the PQM Plug-In
1433
---------------------------
1435
While not strictly required, the PQM plugin automates a few things and
1436
reduces the chance of error. Before looking at the plugin, it helps to
1437
understand a little more how PQM operates. Basically, PQM requires an
1438
email indicating what you want it to do. The email typically looks like
1441
star-merge source-branch target-branch
1445
star-merge http://bzr.arbash-meinel.com/branches/bzr/jam-integration http://bazaar-vcs.org/bzr/bzr.dev
1447
Note that the command needs to be on one line. The subject of the email
1448
will be used for the commit message. The email also needs to be ``gpg``
1449
signed with a key that PQM accepts.
1451
The advantages of using the PQM plugin are:
1453
#. You can use the config policies to make it easy to set up public
1454
branches, so you don't have to ever type the full paths you want to merge
1457
#. It checks to make sure the public branch last revision matches the
1458
local last revision so you are submitting what you think you are.
1460
#. It uses the same public_branch and smtp sending settings as bzr-email,
1461
so if you have one set up, you have the other mostly set up.
1463
#. Thunderbird refuses to not wrap lines, and request lines are usually
1464
pretty long (you have 2 long URLs in there).
1466
Here are sample configuration settings for the PQM plugin. Here are the
1467
lines in bazaar.conf::
1470
email = Joe Smith <joe.smith@internode.on.net>
1471
smtp_server=mail.internode.on.net:25
1473
And here are the lines in ``locations.conf`` (or ``branch.conf`` for
1474
dirstate-tags branches)::
1476
[/home/joe/bzr/my-integration]
1477
push_location = sftp://joe-smith@bazaar.launchpad.net/%7Ejoe-smith/bzr/my-integration/
1478
push_location:policy = norecurse
1479
public_branch = http://bazaar.launchpad.net/~joe-smith/bzr/my-integration/
1480
public_branch:policy = appendpath
1481
pqm_email = Bazaar PQM <pqm@bazaar-vcs.org>
1482
pqm_branch = http://bazaar-vcs.org/bzr/bzr.dev
1484
Note that the push settings will be added by the first ``push`` on
1485
a branch. Indeed the preferred way to generate the lines above is to use
1486
``push`` with an argument, then copy-and-paste the other lines into
1493
Here is one possible recipe once the above environment is set up:
1495
#. pull bzr.dev => my-integration
1496
#. merge patch => my-integration
1497
#. fix up any final merge conflicts (NEWS being the big killer here).
1503
The ``push`` step is not required if ``my-integration`` is a checkout of
1506
Because of defaults, you can type a single message into commit and
1507
pqm-commit will reuse that.
1510
Tracking Change Acceptance
1511
--------------------------
1513
The web interface to PQM is https://pqm.bazaar-vcs.org/. After submitting
1514
a change, you can visit this URL to confirm it was received and placed in
1517
When PQM completes processing a change, an email is sent to you with the
1521
Reviewing Blueprints
1522
====================
1524
Blueprint Tracking Using Launchpad
1525
----------------------------------
1527
New features typically require a fair amount of discussion, design and
1528
debate. For Bazaar, that information is often captured in a so-called
1529
"blueprint" on our Wiki. Overall tracking of blueprints and their status
1530
is done using Launchpad's relevant tracker,
1531
https://blueprints.launchpad.net/bzr/. Once a blueprint for ready for
1532
review, please announce it on the mailing list.
1534
Alternatively, send an email begining with [RFC] with the proposal to the
1535
list. In some cases, you may wish to attach proposed code or a proposed
1536
developer document if that best communicates the idea. Debate can then
1537
proceed using the normal merge review processes.
1540
Recording Blueprint Review Feedback
1541
-----------------------------------
1543
Unlike its Bug Tracker, Launchpad's Blueprint Tracker doesn't currently
1544
(Jun 2007) support a chronological list of comment responses. Review
1545
feedback can either be recorded on the Wiki hosting the blueprints or by
1546
using Launchpad's whiteboard feature.
1555
As the two senior developers, Martin Pool and Robert Collins coordinate
1556
the overall Bazaar product development roadmap. Core developers provide
1557
input and review into this, particularly during sprints. It's totally
1558
expected that community members ought to be working on things that
1559
interest them the most. The roadmap is valuable though because it provides
1560
context for understanding where the product is going as a whole and why.
1563
Using Releases and Milestones in Launchpad
1564
------------------------------------------
1566
TODO ... (Exact policies still under discussion)
1572
Keeping on top of bugs reported is an important part of ongoing release
1573
planning. Everyone in the community is welcome and encouraged to raise
1574
bugs, confirm bugs raised by others, and nominate a priority. Practically
1575
though, a good percentage of bug triage is often done by the core
1576
developers, partially because of their depth of product knowledge.
1578
With respect to bug triage, core developers are encouraged to play an
1579
active role with particular attention to the following tasks:
1581
* keeping the number of unconfirmed bugs low
1582
* ensuring the priorities are generally right (everything as critical - or
1583
medium - is meaningless)
1584
* looking out for regressions and turning those around sooner rather than later.
1587
As well as prioritizing bugs and nominating them against a
1588
target milestone, Launchpad lets core developers offer to mentor others in
1593
vim: ft=rst tw=74 ai
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HACKING
