1
============================
2
guidelines for modifying bzr
3
============================
5
* New functionality should have test cases. Preferably write the
6
test before writing the code.
8
In general, you can test at either the command-line level or the
9
internal API level. Choose whichever is appropriate: if adding a
10
new command, or a new command option, then call through run_bzr().
11
It is not necessary to do both.
13
* Before fixing a bug, write a test case so that it does not regress.
15
* Exceptions should be defined inside bzrlib.errors, so that we can
16
see the whole tree at a glance.
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/>.
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.
212
Sending patches for review
213
==========================
215
If you'd like to propose a change, please post to the
216
bazaar@lists.canonical.com list with a bundle, patch, or link to a
217
branch. Put ``[PATCH]`` or ``[MERGE]`` in the subject so Bundle Buggy
218
can pick it out, and explain the change in the email message text.
219
Remember to update the NEWS file as part of your change if it makes any
220
changes visible to users or plugin developers. Please include a diff
221
against mainline if you're giving a link to a branch.
223
You can generate a merge request like this::
225
bzr send -o bug-1234.patch
227
A ``.patch`` extension is recommended instead of .bundle as many mail clients
228
will send the latter as a binary file.
230
``bzr send`` can also send mail directly if you prefer; see the help.
232
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
233
want it to be merged. If you want comments from developers rather than
234
to be merged, you can put ``[RFC]`` in the subject line.
236
If this change addresses a bug, please put the bug number in the subject
237
line too, in the form ``[#1]`` so that Bundle Buggy can recognize it.
239
If the change is intended for a particular release mark that in the
240
subject too, e.g. ``[1.6]``.
246
Please put a "cover letter" on your merge request explaining:
248
* the reason **why** you're making this change
250
* **how** this change achieves this purpose
252
* anything else you may have fixed in passing
254
* anything significant that you thought of doing, such as a more
255
extensive fix or a different approach, but didn't or couldn't do now
257
A good cover letter makes reviewers' lives easier because they can decide
258
from the letter whether they agree with the purpose and approach, and then
259
assess whether the patch actually does what the cover letter says.
260
Explaining any "drive-by fixes" or roads not taken may also avoid queries
261
from the reviewer. All in all this should give faster and better reviews.
262
Sometimes writing the cover letter helps the submitter realize something
263
else they need to do. The size of the cover letter should be proportional
264
to the size and complexity of the patch.
267
Reviewing proposed changes
268
==========================
270
Anyone is welcome to review code, and reply to the thread with their
273
The simplest way to review a proposed change is to just read the patch on
274
the list or in Bundle Buggy. For more complex changes it may be useful
275
to make a new working tree or branch from trunk, and merge the proposed
276
change into it, so you can experiment with the code or look at a wider
279
There are three main requirements for code to get in:
281
* Doesn't reduce test coverage: if it adds new methods or commands,
282
there should be tests for them. There is a good test framework
283
and plenty of examples to crib from, but if you are having trouble
284
working out how to test something feel free to post a draft patch
287
* Doesn't reduce design clarity, such as by entangling objects
288
we're trying to separate. This is mostly something the more
289
experienced reviewers need to help check.
291
* Improves bugs, features, speed, or code simplicity.
293
Code that goes in should not degrade any of these aspects. Patches are
294
welcome that only cleanup the code without changing the external
295
behaviour. The core developers take care to keep the code quality high
296
and understandable while recognising that perfect is sometimes the enemy
299
It is easy for reviews to make people notice other things which should be
300
fixed but those things should not hold up the original fix being accepted.
301
New things can easily be recorded in the Bug Tracker instead.
303
It's normally much easier to review several smaller patches than one large
304
one. You might want to use ``bzr-loom`` to maintain threads of related
305
work, or submit a preparatory patch that will make your "real" change
309
Checklist for reviewers
310
=======================
312
* Do you understand what the code's doing and why?
314
* Will it perform reasonably for large inputs, both in memory size and
315
run time? Are there some scenarios where performance should be
318
* Is it tested, and are the tests at the right level? Are there both
319
blackbox (command-line level) and API-oriented tests?
321
* If this change will be visible to end users or API users, is it
322
appropriately documented in NEWS?
324
* Does it meet the coding standards below?
326
* If it changes the user-visible behaviour, does it update the help
327
strings and user documentation?
329
* If it adds a new major concept or standard practice, does it update the
330
developer documentation?
332
* (your ideas here...)
335
Bundle Buggy and review outcomes
336
================================
338
Anyone can "vote" on the mailing list by expressing an opinion. Core
339
developers can also vote using Bundle Buggy. Here are the voting codes and
342
:approve: Reviewer wants this submission merged.
343
:tweak: Reviewer wants this submission merged with small changes. (No
345
:abstain: Reviewer does not intend to vote on this patch.
346
:resubmit: Please make changes and resubmit for review.
347
:reject: Reviewer doesn't want this kind of change merged.
348
:comment: Not really a vote. Reviewer just wants to comment, for now.
350
If a change gets two approvals from core reviewers, and no rejections,
351
then it's OK to come in. Any of the core developers can bring it into the
352
bzr.dev trunk and backport it to maintenance branches if required. The
353
Release Manager will merge the change into the branch for a pending
354
release, if any. As a guideline, core developers usually merge their own
355
changes and volunteer to merge other contributions if they were the second
356
reviewer to agree to a change.
358
To track the progress of proposed changes, use Bundle Buggy. See
359
http://bundlebuggy.aaronbentley.com/help for a link to all the
360
outstanding merge requests together with an explanation of the columns.
361
Bundle Buggy will also mail you a link to track just your change.
363
Coding Style Guidelines
364
#######################
369
``hasattr`` should not be used because it swallows exceptions including
370
``KeyboardInterrupt``. Instead, say something like ::
372
if getattr(thing, 'name', None) is None
378
Please write PEP-8__ compliant code.
380
__ http://www.python.org/peps/pep-0008.html
382
One often-missed requirement is that the first line of docstrings
383
should be a self-contained one-sentence summary.
385
We use 4 space indents for blocks, and never use tab characters. (In vim,
388
No trailing white space is allowed.
390
Unix style newlines (LF) are used.
392
Each file must have a newline at the end of it.
394
Lines should be no more than 79 characters if at all possible.
395
Lines that continue a long statement may be indented in either of
398
within the parenthesis or other character that opens the block, e.g.::
404
or indented by four spaces::
410
The first is considered clearer by some people; however it can be a bit
411
harder to maintain (e.g. when the method name changes), and it does not
412
work well if the relevant parenthesis is already far to the right. Avoid
415
self.legbone.kneebone.shinbone.toebone.shake_it(one,
421
self.legbone.kneebone.shinbone.toebone.shake_it(one,
427
self.legbone.kneebone.shinbone.toebone.shake_it(
430
For long lists, we like to add a trailing comma and put the closing
431
character on the following line. This makes it easier to add new items in
434
from bzrlib.goo import (
440
There should be spaces between function paramaters, but not between the
441
keyword name and the value::
443
call(1, 3, cheese=quark)
447
;(defface my-invalid-face
448
; '((t (:background "Red" :underline t)))
449
; "Face used to highlight invalid constructs or other uglyties"
452
(defun my-python-mode-hook ()
453
;; setup preferred indentation style.
454
(setq fill-column 79)
455
(setq indent-tabs-mode nil) ; no tabs, never, I will not repeat
456
; (font-lock-add-keywords 'python-mode
457
; '(("^\\s *\t" . 'my-invalid-face) ; Leading tabs
458
; ("[ \t]+$" . 'my-invalid-face) ; Trailing spaces
459
; ("^[ \t]+$" . 'my-invalid-face)); Spaces only
463
(add-hook 'python-mode-hook 'my-python-mode-hook)
465
The lines beginning with ';' are comments. They can be activated
466
if one want to have a strong notice of some tab/space usage
18
473
* Imports should be done at the top-level of the file, unless there is
19
474
a strong reason to have them lazily loaded when a particular
20
475
function runs. Import statements have a cost, so try to make sure
21
476
they don't run inside hot functions.
23
* Please write PEP-8__ compliant code.
25
One often-missed requirement is that the first line of docstrings
26
should be a self-contained one-sentence summary.
28
__ http://www.python.org/peps/pep-0008.html
30
478
* Module names should always be given fully-qualified,
31
479
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
38
If you change the behaviour of a command, please update its docstring
39
in bzrlib/commands.py. This is displayed by the 'bzr help' command.
41
If you make a user-visible change, please add a note to the NEWS file.
42
The description should be written to make sense to someone who's just
43
a user of bzr, not a developer: new functions or classes shouldn't be
44
mentioned, but new commands, changes in behaviour or fixed nontrivial
45
bugs should be listed. See the existing entries for an idea of what
485
Functions, methods or members that are "private" to bzrlib are given
486
a leading underscore prefix. Names without a leading underscore are
487
public not just across modules but to programmers using bzrlib as an
488
API. As a consequence, a leading underscore is appropriate for names
489
exposed across modules but that are not to be exposed to bzrlib API
492
We prefer class names to be concatenated capital words (``TestCase``)
493
and variables, methods and functions to be lowercase words joined by
494
underscores (``revision_id``, ``get_revision``).
496
For the purposes of naming some names are treated as single compound
497
words: "filename", "revno".
499
Consider naming classes as nouns and functions/methods as verbs.
501
Try to avoid using abbreviations in names, because there can be
502
inconsistency if other people use the full name.
508
``revision_id`` not ``rev_id`` or ``revid``
510
Functions that transform one thing to another should be named ``x_to_y``
511
(not ``x2y`` as occurs in some old code.)
517
Python destructors (``__del__``) work differently to those of other
518
languages. In particular, bear in mind that destructors may be called
519
immediately when the object apparently becomes unreferenced, or at some
520
later time, or possibly never at all. Therefore we have restrictions on
521
what can be done inside them.
523
0. If you think you need to use a ``__del__`` method ask another
524
developer for alternatives. If you do need to use one, explain
527
1. Never rely on a ``__del__`` method running. If there is code that
528
must run, do it from a ``finally`` block instead.
530
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
533
3. In some places we raise a warning from the destructor if the object
534
has not been cleaned up or closed. This is considered OK: the warning
535
may not catch every case but it's still useful sometimes.
541
In some places we have variables which point to callables that construct
542
new instances. That is to say, they can be used a lot like class objects,
543
but they shouldn't be *named* like classes:
545
> I think that things named FooBar should create instances of FooBar when
546
> called. Its plain confusing for them to do otherwise. When we have
547
> something that is going to be used as a class - that is, checked for via
548
> isinstance or other such idioms, them I would call it foo_class, so that
549
> it is clear that a callable is not sufficient. If it is only used as a
550
> factory, then yes, foo_factory is what I would use.
556
Several places in Bazaar use (or will use) a registry, which is a
557
mapping from names to objects or classes. The registry allows for
558
loading in registered code only when it's needed, and keeping
559
associated information such as a help string or description.
562
InterObject and multiple dispatch
563
=================================
565
The ``InterObject`` provides for two-way `multiple dispatch`__: matching
566
up for example a source and destination repository to find the right way
567
to transfer data between them.
569
.. __: http://en.wikipedia.org/wiki/Multiple_dispatch
571
There is a subclass ``InterObject`` classes for each type of object that is
572
dispatched this way, e.g. ``InterRepository``. Calling ``.get()`` on this
573
class will return an ``InterObject`` instance providing the best match for
574
those parameters, and this instance then has methods for operations
577
inter = InterRepository.get(source_repo, target_repo)
578
inter.fetch(revision_id)
580
``InterRepository`` also acts as a registry-like object for its
581
subclasses, and they can be added through ``.register_optimizer``. The
582
right one to run is selected by asking each class, in reverse order of
583
registration, whether it ``.is_compatible`` with the relevant objects.
588
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
589
delay importing modules until they are actually used. ``lazy_import`` uses
590
the same syntax as regular python imports. So to import a few modules in a
593
from bzrlib.lazy_import import lazy_import
594
lazy_import(globals(), """
603
revision as _mod_revision,
605
import bzrlib.transport
609
At this point, all of these exist as a ``ImportReplacer`` object, ready to
610
be imported once a member is accessed. Also, when importing a module into
611
the local namespace, which is likely to clash with variable names, it is
612
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
613
the variable is a module, and these object should be hidden anyway, since
614
they shouldn't be imported into other namespaces.
616
While it is possible for ``lazy_import()`` to import members of a module
617
when using the ``from module import member`` syntax, it is recommended to
618
only use that syntax to load sub modules ``from module import submodule``.
619
This is because variables and classes can frequently be used without
620
needing a sub-member for example::
622
lazy_import(globals(), """
623
from module import MyClass
627
return isinstance(x, MyClass)
629
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
630
object, rather than the real class.
632
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
633
Because the replacer only knows about the original name, it is unable to
634
replace other variables. The ``ImportReplacer`` class will raise an
635
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
636
happened. But it requires accessing a member more than once from the new
637
variable, so some bugs are not detected right away.
643
The null revision is the ancestor of all revisions. Its revno is 0, its
644
revision-id is ``null:``, and its tree is the empty tree. When referring
645
to the null revision, please use ``bzrlib.revision.NULL_REVISION``. Old
646
code sometimes uses ``None`` for the null revision, but this practice is
650
Object string representations
651
=============================
653
Python prints objects using their ``__repr__`` method when they are
654
written to logs, exception tracebacks, or the debugger. We want
655
objects to have useful representations to help in determining what went
658
If you add a new class you should generally add a ``__repr__`` method
659
unless there is an adequate method in a parent class. There should be a
662
Representations should typically look like Python constructor syntax, but
663
they don't need to include every value in the object and they don't need
664
to be able to actually execute. They're to be read by humans, not
665
machines. Don't hardcode the classname in the format, so that we get the
666
correct value if the method is inherited by a subclass. If you're
667
printing attributes of the object, including strings, you should normally
668
use ``%r`` syntax (to call their repr in turn).
670
Try to avoid the representation becoming more than one or two lines long.
671
(But balance this against including useful information, and simplicity of
674
Because repr methods are often called when something has already gone
675
wrong, they should be written somewhat more defensively than most code.
676
The object may be half-initialized or in some other way in an illegal
677
state. The repr method shouldn't raise an exception, or it may hide the
678
(probably more useful) underlying exception.
683
return '%s(%r)' % (self.__class__.__name__,
690
A bare ``except`` statement will catch all exceptions, including ones that
691
really should terminate the program such as ``MemoryError`` and
692
``KeyboardInterrupt``. They should rarely be used unless the exception is
693
later re-raised. Even then, think about whether catching just
694
``Exception`` (which excludes system errors in Python2.5 and later) would
701
All code should be exercised by the test suite. See `Guide to Testing
702
Bazaar <testing.html>`_ for detailed information about writing tests.
711
We have a commitment to 6 months API stability - any supported symbol in a
712
release of bzr MUST NOT be altered in any way that would result in
713
breaking existing code that uses it. That means that method names,
714
parameter ordering, parameter names, variable and attribute names etc must
715
not be changed without leaving a 'deprecated forwarder' behind. This even
716
applies to modules and classes.
718
If you wish to change the behaviour of a supported API in an incompatible
719
way, you need to change its name as well. For instance, if I add an optional keyword
720
parameter to branch.commit - that's fine. On the other hand, if I add a
721
keyword parameter to branch.commit which is a *required* transaction
722
object, I should rename the API - i.e. to 'branch.commit_transaction'.
724
When renaming such supported API's, be sure to leave a deprecated_method (or
725
_function or ...) behind which forwards to the new API. See the
726
bzrlib.symbol_versioning module for decorators that take care of the
727
details for you - such as updating the docstring, and issuing a warning
728
when the old api is used.
730
For unsupported API's, it does not hurt to follow this discipline, but it's
731
not required. Minimally though, please try to rename things so that
732
callers will at least get an AttributeError rather than weird results.
735
Deprecation decorators
736
----------------------
738
``bzrlib.symbol_versioning`` provides decorators that can be attached to
739
methods, functions, and other interfaces to indicate that they should no
740
longer be used. For example::
742
@deprecated_method(deprecated_in((0, 1, 4)))
744
return self._new_foo()
746
To deprecate a static method you must call ``deprecated_function``
747
(**not** method), after the staticmethod call::
750
@deprecated_function(deprecated_in((0, 1, 4)))
751
def create_repository(base, shared=False, format=None):
753
When you deprecate an API, you should not just delete its tests, because
754
then we might introduce bugs in them. If the API is still present at all,
755
it should still work. The basic approach is to use
756
``TestCase.applyDeprecated`` which in one step checks that the API gives
757
the expected deprecation message, and also returns the real result from
758
the method, so that tests can keep running.
760
Deprecation warnings will be suppressed for final releases, but not for
761
development versions or release candidates, or when running ``bzr
762
selftest``. This gives developers information about whether their code is
763
using deprecated functions, but avoids confusing users about things they
770
Processing Command Lines
771
------------------------
773
bzrlib has a standard framework for parsing command lines and calling
774
processing routines associated with various commands. See builtins.py
775
for numerous examples.
778
Standard Parameter Types
779
------------------------
781
There are some common requirements in the library: some parameters need to be
782
unicode safe, some need byte strings, and so on. At the moment we have
783
only codified one specific pattern: Parameters that need to be unicode
784
should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
785
input into unicode in a consistent fashion, allowing trivial strings to be
786
used for programmer convenience, but not performing unpredictably in the
787
presence of different locales.
53
793
(The strategy described here is what we want to get to, but it's not
83
823
The policy about how output is presented in the text-mode client
84
824
should be only in the command-line tool.
88
In general tests should be placed in a file named test_FOO.py where
89
FOO is the logical thing under test. That file should be placed in the
90
tests subdirectory under the package being tested.
92
For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
96
Currently, bzr selftest is used to invoke tests.
97
You can provide a pattern argument to run a subset. For example,
98
to run just the whitebox tests, run bzr selftest --pattern .*whitebox.*
831
Bazaar has online help for various topics through ``bzr help COMMAND`` or
832
equivalently ``bzr command -h``. We also have help on command options,
833
and on other help topics. (See ``help_topics.py``.)
835
As for python docstrings, the first paragraph should be a single-sentence
836
synopsis of the command.
838
The help for options should be one or more proper sentences, starting with
839
a capital letter and finishing with a full stop (period).
841
All help messages and documentation should have two spaces between
845
Handling Errors and Exceptions
846
==============================
848
Commands should return non-zero when they encounter circumstances that
849
the user should really pay attention to - which includes trivial shell
852
Recommended values are:
855
1. Conflicts in merge-like operations, or changes are present in
856
diff-like operations.
857
2. Unrepresentable diff changes (i.e. binary files that we cannot show
859
3. An error or exception has occurred.
860
4. An internal error occurred (one that shows a traceback.)
862
Errors are handled through Python exceptions. Exceptions should be defined
863
inside bzrlib.errors, so that we can see the whole tree at a glance.
865
We broadly classify errors as either being either internal or not,
866
depending on whether ``internal_error`` is set or not. If we think it's our
867
fault, we show a backtrace, an invitation to report the bug, and possibly
868
other details. This is the default for errors that aren't specifically
869
recognized as being caused by a user error. Otherwise we show a briefer
870
message, unless -Derror was given.
872
Many errors originate as "environmental errors" which are raised by Python
873
or builtin libraries -- for example IOError. These are treated as being
874
our fault, unless they're caught in a particular tight scope where we know
875
that they indicate a user errors. For example if the repository format
876
is not found, the user probably gave the wrong path or URL. But if one of
877
the files inside the repository is not found, then it's our fault --
878
either there's a bug in bzr, or something complicated has gone wrong in
879
the environment that means one internal file was deleted.
881
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
882
to be added near the place where they are used.
884
Exceptions are formatted for the user by conversion to a string
885
(eventually calling their ``__str__`` method.) As a convenience the
886
``._fmt`` member can be used as a template which will be mapped to the
887
error's instance dict.
889
New exception classes should be defined when callers might want to catch
890
that exception specifically, or when it needs a substantially different
893
#. If it is something that a caller can recover from, a custom exception
896
#. If it is a data consistency issue, using a builtin like
897
``ValueError``/``TypeError`` is reasonable.
899
#. If it is a programmer error (using an api incorrectly)
900
``AssertionError`` is reasonable.
902
#. Otherwise, use ``BzrError`` or ``InternalBzrError``.
904
Exception strings should start with a capital letter and should not have a
905
final fullstop. If long, they may contain newlines to break the text.
911
Do not use the Python ``assert`` statement, either in tests or elsewhere.
912
A source test checks that it is not used. It is ok to explicitly raise
917
* It makes the behaviour vary depending on whether bzr is run with -O
918
or not, therefore giving a chance for bugs that occur in one case or
919
the other, several of which have already occurred: assertions with
920
side effects, code which can't continue unless the assertion passes,
921
cases where we should give the user a proper message rather than an
923
* It's not that much shorter than an explicit if/raise.
924
* It tends to lead to fuzzy thinking about whether the check is
925
actually needed or not, and whether it's an internal error or not
926
* It tends to cause look-before-you-leap patterns.
927
* It's unsafe if the check is needed to protect the integrity of the
929
* It tends to give poor messages since the developer can get by with
930
no explanatory text at all.
931
* We can't rely on people always running with -O in normal use, so we
932
can't use it for tests that are actually expensive.
933
* Expensive checks that help developers are better turned on from the
934
test suite or a -D flag.
935
* If used instead of ``self.assert*()`` in tests it makes them falsely pass with -O.
941
When you change bzrlib, please update the relevant documentation for the
942
change you made: Changes to commands should update their help, and
943
possibly end user tutorials; changes to the core library should be
944
reflected in API documentation.
949
If you make a user-visible change, please add a note to the NEWS file.
950
The description should be written to make sense to someone who's just
951
a user of bzr, not a developer: new functions or classes shouldn't be
952
mentioned, but new commands, changes in behaviour or fixed nontrivial
953
bugs should be listed. See the existing entries for an idea of what
956
Within each release, entries in the news file should have the most
957
user-visible changes first. So the order should be approximately:
959
* changes to existing behaviour - the highest priority because the
960
user's existing knowledge is incorrect
961
* new features - should be brought to their attention
962
* bug fixes - may be of interest if the bug was affecting them, and
963
should include the bug number if any
964
* major documentation changes
965
* changes to internal interfaces
967
People who made significant contributions to each change are listed in
968
parenthesis. This can include reporting bugs (particularly with good
969
details or reproduction recipes), submitting patches, etc.
974
The docstring of a command is used by ``bzr help`` to generate help output
975
for the command. The list 'takes_options' attribute on a command is used by
976
``bzr help`` to document the options for the command - the command
977
docstring does not need to document them. Finally, the '_see_also'
978
attribute on a command can be used to reference other related help topics.
983
Functions, methods, classes and modules should have docstrings
984
describing how they are used.
986
The first line of the docstring should be a self-contained sentence.
988
For the special case of Command classes, this acts as the user-visible
989
documentation shown by the help command.
991
The docstrings should be formatted as reStructuredText_ (like this
992
document), suitable for processing using the epydoc_ tool into HTML
995
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
996
.. _epydoc: http://epydoc.sourceforge.net/
1005
The copyright policy for bzr was recently made clear in this email (edited
1006
for grammatical correctness)::
1008
The attached patch cleans up the copyright and license statements in
1009
the bzr source. It also adds tests to help us remember to add them
1010
with the correct text.
1012
We had the problem that lots of our files were "Copyright Canonical
1013
Development Ltd" which is not a real company, and some other variations
1014
on this theme. Also, some files were missing the GPL statements.
1016
I want to be clear about the intent of this patch, since copyright can
1017
be a little controversial.
1019
1) The big motivation for this is not to shut out the community, but
1020
just to clean up all of the invalid copyright statements.
1022
2) It has been the general policy for bzr that we want a single
1023
copyright holder for all of the core code. This is following the model
1024
set by the FSF, which makes it easier to update the code to a new
1025
license in case problems are encountered. (For example, if we want to
1026
upgrade the project universally to GPL v3 it is much simpler if there is
1027
a single copyright holder). It also makes it clearer if copyright is
1028
ever debated, there is a single holder, which makes it easier to defend
1029
in court, etc. (I think the FSF position is that if you assign them
1030
copyright, they can defend it in court rather than you needing to, and
1031
I'm sure Canonical would do the same).
1032
As such, Canonical has requested copyright assignments from all of the
1035
3) If someone wants to add code and not attribute it to Canonical, there
1036
is a specific list of files that are excluded from this check. And the
1037
test failure indicates where that is, and how to update it.
1039
4) If anyone feels that I changed a copyright statement incorrectly, just
1040
let me know, and I'll be happy to correct it. Whenever you have large
1041
mechanical changes like this, it is possible to make some mistakes.
1043
Just to reiterate, this is a community project, and it is meant to stay
1044
that way. Core bzr code is copyright Canonical for legal reasons, and
1045
the tests are just there to help us maintain that.
1048
Miscellaneous Topics
1049
####################
1054
Bazaar has a few facilities to help debug problems by going into pdb_, the
1057
.. _pdb: http://docs.python.org/lib/debugger-commands.html
1059
If the ``BZR_PDB`` environment variable is set
1060
then bzr will go into pdb post-mortem mode when an unhandled exception
1063
If you send a SIGQUIT signal to bzr, which can be done by pressing
1064
Ctrl-\\ on Unix, bzr will go into the debugger immediately. You can
1065
continue execution by typing ``c``. This can be disabled if necessary
1066
by setting the environment variable ``BZR_SIGQUIT_PDB=0``.
1072
Bazaar accepts some global options starting with ``-D`` such as
1073
``-Dhpss``. These set a value in `bzrlib.debug.debug_flags`, and
1074
typically cause more information to be written to the trace file. Most
1075
`mutter` calls should be guarded by a check of those flags so that we
1076
don't write out too much information if it's not needed.
1078
Debug flags may have effects other than just emitting trace messages.
1080
Run ``bzr help global-options`` to see them all.
1087
Integer identifier for a revision on the main line of a branch.
1088
Revision 0 is always the null revision; others are 1-based
1089
indexes into the branch's revision history.
1092
Unicode and Encoding Support
1093
============================
1095
This section discusses various techniques that Bazaar uses to handle
1096
characters that are outside the ASCII set.
1101
When a ``Command`` object is created, it is given a member variable
1102
accessible by ``self.outf``. This is a file-like object, which is bound to
1103
``sys.stdout``, and should be used to write information to the screen,
1104
rather than directly writing to ``sys.stdout`` or calling ``print``.
1105
This file has the ability to translate Unicode objects into the correct
1106
representation, based on the console encoding. Also, the class attribute
1107
``encoding_type`` will effect how unprintable characters will be
1108
handled. This parameter can take one of 3 values:
1111
Unprintable characters will be represented with a suitable replacement
1112
marker (typically '?'), and no exception will be raised. This is for
1113
any command which generates text for the user to review, rather than
1114
for automated processing.
1115
For example: ``bzr log`` should not fail if one of the entries has text
1116
that cannot be displayed.
1119
Attempting to print an unprintable character will cause a UnicodeError.
1120
This is for commands that are intended more as scripting support, rather
1121
than plain user review.
1122
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
1123
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
1124
printed a filename with a '?', the wrong file could be deleted. (At the
1125
very least, the correct file would not be deleted). An error is used to
1126
indicate that the requested action could not be performed.
1129
Do not attempt to automatically convert Unicode strings. This is used
1130
for commands that must handle conversion themselves.
1131
For example: ``bzr diff`` needs to translate Unicode paths, but should
1132
not change the exact text of the contents of the files.
1135
``bzrlib.urlutils.unescape_for_display``
1136
----------------------------------------
1138
Because Transports work in URLs (as defined earlier), printing the raw URL
1139
to the user is usually less than optimal. Characters outside the standard
1140
set are printed as escapes, rather than the real character, and local
1141
paths would be printed as ``file://`` urls. The function
1142
``unescape_for_display`` attempts to unescape a URL, such that anything
1143
that cannot be printed in the current encoding stays an escaped URL, but
1144
valid characters are generated where possible.
1150
The ``bzrlib.osutils`` module has many useful helper functions, including
1151
some more portable variants of functions in the standard library.
1153
In particular, don't use ``shutil.rmtree`` unless it's acceptable for it
1154
to fail on Windows if some files are readonly or still open elsewhere.
1155
Use ``bzrlib.osutils.rmtree`` instead.
1161
We write some extensions in C using pyrex. We design these to work in
1164
* User with no C compiler
1165
* User with C compiler
1168
The recommended way to install bzr is to have a C compiler so that the
1169
extensions can be built, but if no C compiler is present, the pure python
1170
versions we supply will work, though more slowly.
1172
For developers we recommend that pyrex be installed, so that the C
1173
extensions can be changed if needed.
1175
For the C extensions, the extension module should always match the
1176
original python one in all respects (modulo speed). This should be
1177
maintained over time.
1179
To create an extension, add rules to setup.py for building it with pyrex,
1180
and with distutils. Now start with an empty .pyx file. At the top add
1181
"include 'yourmodule.py'". This will import the contents of foo.py into this
1182
file at build time - remember that only one module will be loaded at
1183
runtime. Now you can subclass classes, or replace functions, and only your
1184
changes need to be present in the .pyx file.
1186
Note that pyrex does not support all 2.4 programming idioms, so some
1187
syntax changes may be required. I.e.
1189
- 'from foo import (bar, gam)' needs to change to not use the brackets.
1190
- 'import foo.bar as bar' needs to be 'import foo.bar; bar = foo.bar'
1192
If the changes are too dramatic, consider
1193
maintaining the python code twice - once in the .pyx, and once in the .py,
1194
and no longer including the .py file.
1197
Making Installers for OS Windows
1198
================================
1199
To build a win32 installer, see the instructions on the wiki page:
1200
http://bazaar-vcs.org/BzrWin32Installer
1203
Core Developer Tasks
1204
####################
1209
What is a Core Developer?
1210
-------------------------
1212
While everyone in the Bazaar community is welcome and encouraged to
1213
propose and submit changes, a smaller team is reponsible for pulling those
1214
changes together into a cohesive whole. In addition to the general developer
1215
stuff covered above, "core" developers have responsibility for:
1218
* reviewing blueprints
1220
* managing releases (see the `Releasing Bazaar <../../developers/releasing.html>`_)
1223
Removing barriers to community participation is a key reason for adopting
1224
distributed VCS technology. While DVCS removes many technical barriers,
1225
a small number of social barriers are often necessary instead.
1226
By documenting how the above things are done, we hope to
1227
encourage more people to participate in these activities, keeping the
1228
differences between core and non-core contributors to a minimum.
1231
Communicating and Coordinating
1232
------------------------------
1234
While it has many advantages, one of the challenges of distributed
1235
development is keeping everyone else aware of what you're working on.
1236
There are numerous ways to do this:
1238
#. Assign bugs to yourself in Launchpad
1239
#. Mention it on the mailing list
1240
#. Mention it on IRC
1242
As well as the email notifcations that occur when merge requests are sent
1243
and reviewed, you can keep others informed of where you're spending your
1244
energy by emailing the **bazaar-commits** list implicitly. To do this,
1245
install and configure the Email plugin. One way to do this is add these
1246
configuration settings to your central configuration file (e.g.
1247
``~/.bazaar/bazaar.conf`` on Linux)::
1250
email = Joe Smith <joe.smith@internode.on.net>
1251
smtp_server = mail.internode.on.net:25
1253
Then add these lines for the relevant branches in ``locations.conf``::
1255
post_commit_to = bazaar-commits@lists.canonical.com
1256
post_commit_mailer = smtplib
1258
While attending a sprint, RobertCollins' Dbus plugin is useful for the
1259
same reason. See the documentation within the plugin for information on
1260
how to set it up and configure it.
1269
Of the many workflows supported by Bazaar, the one adopted for Bazaar
1270
development itself is known as "Decentralized with automatic gatekeeper".
1271
To repeat the explanation of this given on
1272
http://bazaar-vcs.org/Workflows:
1275
In this workflow, each developer has their own branch or
1276
branches, plus read-only access to the mainline. A software gatekeeper
1277
(e.g. PQM) has commit rights to the main branch. When a developer wants
1278
their work merged, they request the gatekeeper to merge it. The gatekeeper
1279
does a merge, a compile, and runs the test suite. If the code passes, it
1280
is merged into the mainline.
1282
In a nutshell, here's the overall submission process:
1284
#. get your work ready (including review except for trivial changes)
1285
#. push to a public location
1286
#. ask PQM to merge from that location
1289
At present, PQM always takes the changes to merge from a branch
1290
at a URL that can be read by it. For Bazaar, that means a public,
1291
typically http, URL.
1293
As a result, the following things are needed to use PQM for submissions:
1295
#. A publicly available web server
1296
#. Your OpenPGP key registered with PQM (contact RobertCollins for this)
1297
#. The PQM plugin installed and configured (not strictly required but
1298
highly recommended).
1301
Selecting a Public Branch Location
1302
----------------------------------
1304
If you don't have your own web server running, branches can always be
1305
pushed to Launchpad. Here's the process for doing that:
1307
Depending on your location throughout the world and the size of your
1308
repository though, it is often quicker to use an alternative public
1309
location to Launchpad, particularly if you can set up your own repo and
1310
push into that. By using an existing repo, push only needs to send the
1311
changes, instead of the complete repository every time. Note that it is
1312
easy to register branches in other locations with Launchpad so no benefits
1313
are lost by going this way.
1316
For Canonical staff, http://people.ubuntu.com/~<user>/ is one
1317
suggestion for public http branches. Contact your manager for information
1318
on accessing this system if required.
1320
It should also be noted that best practice in this area is subject to
1321
change as things evolve. For example, once the Bazaar smart server on
1322
Launchpad supports server-side branching, the performance situation will
1323
be very different to what it is now (Jun 2007).
1326
Configuring the PQM Plug-In
1327
---------------------------
1329
While not strictly required, the PQM plugin automates a few things and
1330
reduces the chance of error. Before looking at the plugin, it helps to
1331
understand a little more how PQM operates. Basically, PQM requires an
1332
email indicating what you want it to do. The email typically looks like
1335
star-merge source-branch target-branch
1339
star-merge http://bzr.arbash-meinel.com/branches/bzr/jam-integration http://bazaar-vcs.org/bzr/bzr.dev
1341
Note that the command needs to be on one line. The subject of the email
1342
will be used for the commit message. The email also needs to be ``gpg``
1343
signed with a key that PQM accepts.
1345
The advantages of using the PQM plugin are:
1347
#. You can use the config policies to make it easy to set up public
1348
branches, so you don't have to ever type the full paths you want to merge
1351
#. It checks to make sure the public branch last revision matches the
1352
local last revision so you are submitting what you think you are.
1354
#. It uses the same public_branch and smtp sending settings as bzr-email,
1355
so if you have one set up, you have the other mostly set up.
1357
#. Thunderbird refuses to not wrap lines, and request lines are usually
1358
pretty long (you have 2 long URLs in there).
1360
Here are sample configuration settings for the PQM plugin. Here are the
1361
lines in bazaar.conf::
1364
email = Joe Smith <joe.smith@internode.on.net>
1365
smtp_server=mail.internode.on.net:25
1367
And here are the lines in ``locations.conf`` (or ``branch.conf`` for
1368
dirstate-tags branches)::
1370
[/home/joe/bzr/my-integration]
1371
push_location = sftp://joe-smith@bazaar.launchpad.net/%7Ejoe-smith/bzr/my-integration/
1372
push_location:policy = norecurse
1373
public_branch = http://bazaar.launchpad.net/~joe-smith/bzr/my-integration/
1374
public_branch:policy = appendpath
1375
pqm_email = Bazaar PQM <pqm@bazaar-vcs.org>
1376
pqm_branch = http://bazaar-vcs.org/bzr/bzr.dev
1378
Note that the push settings will be added by the first ``push`` on
1379
a branch. Indeed the preferred way to generate the lines above is to use
1380
``push`` with an argument, then copy-and-paste the other lines into
1387
Here is one possible recipe once the above environment is set up:
1389
#. pull bzr.dev => my-integration
1390
#. merge patch => my-integration
1391
#. fix up any final merge conflicts (NEWS being the big killer here).
1397
The ``push`` step is not required if ``my-integration`` is a checkout of
1400
Because of defaults, you can type a single message into commit and
1401
pqm-commit will reuse that.
1404
Tracking Change Acceptance
1405
--------------------------
1407
The web interface to PQM is https://pqm.bazaar-vcs.org/. After submitting
1408
a change, you can visit this URL to confirm it was received and placed in
1411
When PQM completes processing a change, an email is sent to you with the
1415
Reviewing Blueprints
1416
====================
1418
Blueprint Tracking Using Launchpad
1419
----------------------------------
1421
New features typically require a fair amount of discussion, design and
1422
debate. For Bazaar, that information is often captured in a so-called
1423
"blueprint" on our Wiki. Overall tracking of blueprints and their status
1424
is done using Launchpad's relevant tracker,
1425
https://blueprints.launchpad.net/bzr/. Once a blueprint for ready for
1426
review, please announce it on the mailing list.
1428
Alternatively, send an email begining with [RFC] with the proposal to the
1429
list. In some cases, you may wish to attach proposed code or a proposed
1430
developer document if that best communicates the idea. Debate can then
1431
proceed using the normal merge review processes.
1434
Recording Blueprint Review Feedback
1435
-----------------------------------
1437
Unlike its Bug Tracker, Launchpad's Blueprint Tracker doesn't currently
1438
(Jun 2007) support a chronological list of comment responses. Review
1439
feedback can either be recorded on the Wiki hosting the blueprints or by
1440
using Launchpad's whiteboard feature.
1449
As the two senior developers, Martin Pool and Robert Collins coordinate
1450
the overall Bazaar product development roadmap. Core developers provide
1451
input and review into this, particularly during sprints. It's totally
1452
expected that community members ought to be working on things that
1453
interest them the most. The roadmap is valuable though because it provides
1454
context for understanding where the product is going as a whole and why.
1457
Using Releases and Milestones in Launchpad
1458
------------------------------------------
1460
TODO ... (Exact policies still under discussion)
1466
Keeping on top of bugs reported is an important part of ongoing release
1467
planning. Everyone in the community is welcome and encouraged to raise
1468
bugs, confirm bugs raised by others, and nominate a priority. Practically
1469
though, a good percentage of bug triage is often done by the core
1470
developers, partially because of their depth of product knowledge.
1472
With respect to bug triage, core developers are encouraged to play an
1473
active role with particular attention to the following tasks:
1475
* keeping the number of unconfirmed bugs low
1476
* ensuring the priorities are generally right (everything as critical - or
1477
medium - is meaningless)
1478
* looking out for regressions and turning those around sooner rather than later.
1481
As well as prioritizing bugs and nominating them against a
1482
target milestone, Launchpad lets core developers offer to mentor others in
1487
vim: ft=rst tw=74 ai
added
removed
doc/developers/HACKING.txt
