1
============================
2
Guidelines for modifying bzr
3
============================
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)
7
(The current version of this document is available in the file
8
``doc/developers/HACKING.txt`` in the source tree, or at
9
http://doc.bazaar-vcs.org/bzr.dev/developers/HACKING.html)
15
Exploring the Bazaar Platform
16
=============================
18
Before making changes, it's a good idea to explore the work already
19
done by others. Perhaps the new feature or improvement you're looking
20
for is available in another plug-in already? If you find a bug,
21
perhaps someone else has already fixed it?
23
To answer these questions and more, take a moment to explore the
24
overall Bazaar Platform. Here are some links to browse:
26
* The Plugins page on the Wiki - http://bazaar-vcs.org/BzrPlugins
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* The Bazaar product family on Launchpad - https://launchpad.net/bazaar
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* Bug Tracker for the core product - https://bugs.launchpad.net/bzr/
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* Blueprint Tracker for the core product - https://blueprints.launchpad.net/bzr/
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If nothing else, perhaps you'll find inspiration in how other developers
35
have solved their challenges.
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Planning and Discussing Changes
39
===============================
41
There is a very active community around Bazaar. Mostly we meet on IRC
42
(#bzr on irc.freenode.net) and on the mailing list. To join the Bazaar
43
community, see http://bazaar-vcs.org/BzrSupport.
45
If you are planning to make a change, it's a very good idea to mention it
46
on the IRC channel and/or on the mailing list. There are many advantages
47
to involving the community before you spend much time on a change.
50
* you get to build on the wisdom on others, saving time
52
* if others can direct you to similar code, it minimises the work to be done
54
* it assists everyone in coordinating direction, priorities and effort.
56
In summary, maximising the input from others typically minimises the
57
total effort required to get your changes merged. The community is
58
friendly, helpful and always keen to welcome newcomers.
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Bazaar Development in a Nutshell
62
================================
64
Looking for a 10 minute introduction to submitting a change?
65
See http://bazaar-vcs.org/BzrGivingBack.
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TODO: Merge that Wiki page into this document.
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Understanding the Development Process
71
=====================================
73
The development team follows many best-practices including:
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* a public roadmap and planning process in which anyone can participate
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* time based milestones everyone can work towards and plan around
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* extensive code review and feedback to contributors
81
* complete and rigorous test coverage on any code contributed
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* automated validation that all tests still pass before code is merged
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into the main code branch.
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The key tools we use to enable these practices are:
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* Launchpad - https://launchpad.net/
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* Bazaar - http://bazaar-vcs.org/
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* Bundle Buggy - http://bundlebuggy.aaronbentley.com/
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* Patch Queue Manager - https://launchpad.net/pqm/
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For further information, see http://bazaar-vcs.org/BzrDevelopment.
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A Closer Look at the Merge & Review Process
100
===========================================
102
If you'd like to propose a change, please post to the
103
bazaar@lists.canonical.com list with a bundle, patch, or link to a
104
branch. Put '[PATCH]' or '[MERGE]' in the subject so Bundle Buggy
105
can pick it out, and explain the change in the email message text.
106
Remember to update the NEWS file as part of your change if it makes any
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changes visible to users or plugin developers. Please include a diff
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against mainline if you're giving a link to a branch.
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You can generate a bundle like this::
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bzr bundle > mybundle.patch
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A .patch extension is recommended instead of .bundle as many mail clients
115
will send the latter as a binary file. If a bundle would be too long or your
116
mailer mangles whitespace (e.g. implicitly converts Unix newlines to DOS
117
newlines), use the merge-directive command instead like this::
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bzr merge-directive http://bazaar-vcs.org http://example.org/my_branch > my_directive.patch
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See the help for details on the arguments to merge-directive.
123
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
124
want it to be merged. If you want comments from developers rather than
125
to be merged, you can put '[RFC]' in the subject line.
127
Anyone is welcome to review code. There are broadly three gates for
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* Doesn't reduce test coverage: if it adds new methods or commands,
131
there should be tests for them. There is a good test framework
132
and plenty of examples to crib from, but if you are having trouble
133
working out how to test something feel free to post a draft patch
136
* Doesn't reduce design clarity, such as by entangling objects
137
we're trying to separate. This is mostly something the more
138
experienced reviewers need to help check.
140
* Improves bugs, features, speed, or code simplicity.
142
Code that goes in should pass all three. The core developers take care
143
to keep the code quality high and understandable while recognising that
144
perfect is sometimes the enemy of good. (It is easy for reviews to make
145
people notice other things which should be fixed but those things should
146
not hold up the original fix being accepted. New things can easily be
147
recorded in the Bug Tracker instead.)
149
Anyone can "vote" on the mailing list. Core developers can also vote using
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Bundle Buggy. Here are the voting codes and their explanations.
152
:approve: Reviewer wants this submission merged.
153
:tweak: Reviewer wants this submission merged with small changes. (No
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:abstain: Reviewer does not intend to vote on this patch.
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:resubmit: Please make changes and resubmit for review.
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:reject: Reviewer doesn't want this kind of change merged.
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:comment: Not really a vote. Reviewer just wants to comment, for now.
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If a change gets two approvals from core reviewers, and no rejections,
161
then it's OK to come in. Any of the core developers can bring it into the
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bzr.dev trunk and backport it to maintenance branches if required. The
163
Release Manager will merge the change into the branch for a pending
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release, if any. As a guideline, core developers usually merge their own
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changes and volunteer to merge other contributions if they were the second
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reviewer to agree to a change.
168
To track the progress of proposed changes, use Bundle Buggy. See
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http://bundlebuggy.aaronbentley.com/help for a link to all the
170
outstanding merge requests together with an explanation of the columns.
171
Bundle Buggy will also mail you a link to track just your change.
174
Preparing a Sandbox for Making Changes to Bazaar
175
================================================
177
Bazaar supports many ways of organising your work. See
178
http://bazaar-vcs.org/SharedRepositoryLayouts for a summary of the
179
popular alternatives.
181
Of course, the best choice for you will depend on numerous factors:
182
the number of changes you may be making, the complexity of the changes, etc.
183
As a starting suggestion though:
185
* create a local copy of the main development branch (bzr.dev) by using
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bzr branch http://bazaar-vcs.org/bzr/bzr.dev/ bzr.dev
190
* keep your copy of bzr.dev prestine (by not developing in it) and keep
191
it up to date (by using bzr pull)
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* create a new branch off your local bzr.dev copy for each issue
194
(bug or feature) you are working on.
196
This approach makes it easy to go back and make any required changes
197
after a code review. Resubmitting the change is then simple with no
198
risk of accidentially including edits related to other issues you may
199
be working on. After the changes for an issue are accepted and merged,
200
the associated branch can be deleted or archived as you wish.
203
Navigating the Code Base
204
========================
206
TODO: List and describe in one line the purpose of each directory
207
inside an installation of bzr.
209
TODO: Refer to a central location holding an up to date copy of the API
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documentation generated by epydoc, e.g. something like
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http://starship.python.net/crew/mwh/bzrlibapi/bzrlib.html.
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The Importance of Testing
218
=========================
220
Reliability is a critical success factor for any Version Control System.
221
We want Bazaar to be highly reliable across multiple platforms while
222
evolving over time to meet the needs of its community.
224
In a nutshell, this is want we expect and encourage:
13
226
* New functionality should have test cases. Preferably write the
14
227
test before writing the code.
16
229
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'.
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internal API level. See Writing tests below for more detail.
24
* Try to practice Test-Driven Development. before fixing a bug, write a
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* Try to practice Test-Driven Development: before fixing a bug, write a
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233
test case so that it does not regress. Similarly for adding a new
26
234
feature: write a test case for a small version of the new feature before
27
235
starting on the code itself. Check the test fails on the old code, then
28
236
add the feature or fix and check it passes.
30
* Exceptions should be defined inside bzrlib.errors, so that we can
31
see the whole tree at a glance.
238
By doing these things, the Bazaar team gets increased confidence that
239
changes do what they claim to do, whether provided by the core team or
240
by community members. Equally importantly, we can be surer that changes
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down the track do not break new features or bug fixes that you are
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As of May 2007, Bazaar ships with a test suite containing over 6000 tests
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and growing. We are proud of it and want to remain so. As community
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members, we all benefit from it. Would you trust version control on
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your project to a product *without* a test suite like Bazaar has?
250
Running the Test Suite
251
======================
253
Currently, bzr selftest is used to invoke tests.
254
You can provide a pattern argument to run a subset. For example,
255
to run just the blackbox tests, run::
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./bzr selftest -v blackbox
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To skip a particular test (or set of tests), use the --exclude option
260
(shorthand -x) like so::
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./bzr selftest -v -x blackbox
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To ensure that all tests are being run and succeeding, you can use the
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--strict option which will fail if there are any missing features or known
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./bzr selftest --strict
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To list tests without running them, use the --list-only option like so::
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./bzr selftest --list-only
274
This option can be combined with other selftest options (like -x) and
275
filter patterns to understand their effect.
281
In general tests should be placed in a file named test_FOO.py where
282
FOO is the logical thing under test. That file should be placed in the
283
tests subdirectory under the package being tested.
285
For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
286
See bzrlib/tests/test_sampler.py for a template test script.
288
Tests can be written for the UI or for individual areas of the library.
289
Choose whichever is appropriate: if adding a new command, or a new command
290
option, then you should be writing a UI test. If you are both adding UI
291
functionality and library functionality, you will want to write tests for
292
both the UI and the core behaviours. We call UI tests 'blackbox' tests
293
and they are found in ``bzrlib/tests/blackbox/*.py``.
295
When writing blackbox tests please honour the following conventions:
297
1. Place the tests for the command 'name' in
298
bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
299
to locate the test script for a faulty command.
301
2. Use the 'self.run_bzr("name")' utility function to invoke the command
302
rather than running bzr in a subprocess or invoking the
303
cmd_object.run() method directly. This is a lot faster than
304
subprocesses and generates the same logging output as running it in a
305
subprocess (which invoking the method directly does not).
307
3. Only test the one command in a single test script. Use the bzrlib
308
library when setting up tests and when evaluating the side-effects of
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the command. We do this so that the library api has continual pressure
310
on it to be as functional as the command line in a simple manner, and
311
to isolate knock-on effects throughout the blackbox test suite when a
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command changes its name or signature. Ideally only the tests for a
313
given command are affected when a given command is changed.
315
4. If you have a test which does actually require running bzr in a
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subprocess you can use ``run_bzr_subprocess``. By default the spawned
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process will not load plugins unless ``--allow-plugins`` is supplied.
323
We make selective use of doctests__. In general they should provide
324
*examples* within the API documentation which can incidentally be tested. We
325
don't try to test every important case using doctests -- regular Python
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tests are generally a better solution.
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Most of these are in ``bzrlib/doc/api``. More additions are welcome.
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__ http://docs.python.org/lib/module-doctest.html
333
Skipping tests and test requirements
334
------------------------------------
336
In our enhancements to unittest we allow for some addition results beyond
337
just success or failure.
339
If a test can't be run, it can say that it's skipped. This is typically
340
used in parameterized tests - for example if a transport doesn't support
341
setting permissions, we'll skip the tests that relating to that. ::
344
return self.branch_format.initialize(repo.bzrdir)
345
except errors.UninitializableFormat:
346
raise tests.TestSkipped('Uninitializable branch format')
348
Raising TestSkipped is a good idea when you want to make it clear that the
349
test was not run, rather than just returning which makes it look as if it
352
A subtly different case is a test that should run, but can't run in the
353
current environment. This covers tests that can only run in particular
354
operating systems or locales, or that depend on external libraries. Here
355
we want to inform the user that they didn't get full test coverage, but
356
they possibly could if they installed more libraries. These are expressed
357
as a dependency on a feature so we can summarise them, and so that the
358
test for the feature is done only once. (For historical reasons, as of
359
May 2007 many cases that should depend on features currently raise
360
TestSkipped.) The typical use is::
362
class TestStrace(TestCaseWithTransport):
364
_test_needs_features = [StraceFeature]
366
which means all tests in this class need the feature. The feature itself
367
should provide a ``_probe`` method which is called once to determine if
374
Known failures are when a test exists but we know it currently doesn't
375
work, allowing the test suite to still pass. These should be used with
376
care, we don't want a proliferation of quietly broken tests. It might be
377
appropriate to use them if you've committed a test for a bug but not the
378
fix for it, or if something works on Unix but not on Windows.
381
Testing exceptions and errors
382
-----------------------------
384
It's important to test handling of errors and exceptions. Because this
385
code is often not hit in ad-hoc testing it can often have hidden bugs --
386
it's particularly common to get NameError because the exception code
387
references a variable that has since been renamed.
389
.. TODO: Something about how to provoke errors in the right way?
391
In general we want to test errors at two levels:
393
1. A test in ``test_errors.py`` checking that when the exception object is
394
constructed with known parameters it produces an expected string form.
395
This guards against mistakes in writing the format string, or in the
396
``str`` representations of its parameters. There should be one for
397
each exception class.
399
2. Tests that when an api is called in a particular situation, it raises
400
an error of the expected class. You should typically use
401
``assertRaises``, which in the Bazaar test suite returns the exception
402
object to allow you to examine its parameters.
404
In some cases blackbox tests will also want to check error reporting. But
405
it can be difficult to provoke every error through the commandline
406
interface, so those tests are only done as needed -- eg in response to a
407
particular bug or if the error is reported in an unusual way(?) Blackbox
408
tests should mostly be testing how the command-line interface works, so
409
should only test errors if there is something particular to the cli in how
410
they're displayed or handled.
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Essential Domain Classes
414
########################
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Introducing the Object Model
417
============================
419
The core domain objects within the bazaar model are:
429
Transports are explained below. See http://bazaar-vcs.org/Classes/
430
for an introduction to the other key classes.
435
The ``Transport`` layer handles access to local or remote directories.
436
Each Transport object acts like a logical connection to a particular
437
directory, and it allows various operations on files within it. You can
438
*clone* a transport to get a new Transport connected to a subdirectory or
441
Transports are not used for access to the working tree. At present
442
working trees are always local and they are accessed through the regular
443
Python file io mechanisms.
448
Transports work in URLs. Take note that URLs are by definition only
449
ASCII - the decision of how to encode a Unicode string into a URL must be
450
taken at a higher level, typically in the Store. (Note that Stores also
451
escape filenames which cannot be safely stored on all filesystems, but
452
this is a different level.)
454
The main reason for this is that it's not possible to safely roundtrip a
455
URL into Unicode and then back into the same URL. The URL standard
456
gives a way to represent non-ASCII bytes in ASCII (as %-escapes), but
457
doesn't say how those bytes represent non-ASCII characters. (They're not
458
guaranteed to be UTF-8 -- that is common but doesn't happen everywhere.)
460
For example if the user enters the url ``http://example/%e0`` there's no
461
way to tell whether that character represents "latin small letter a with
462
grave" in iso-8859-1, or "latin small letter r with acute" in iso-8859-2
463
or malformed UTF-8. So we can't convert their URL to Unicode reliably.
465
Equally problematic if we're given a url-like string containing non-ascii
466
characters (such as the accented a) we can't be sure how to convert that
467
to the correct URL, because we don't know what encoding the server expects
468
for those characters. (Although this is not totally reliable we might still
469
accept these and assume they should be put into UTF-8.)
471
A similar edge case is that the url ``http://foo/sweet%2Fsour`` contains
472
one directory component whose name is "sweet/sour". The escaped slash is
473
not a directory separator. If we try to convert URLs to regular Unicode
474
paths this information will be lost.
476
This implies that Transports must natively deal with URLs; for simplicity
477
they *only* deal with URLs and conversion of other strings to URLs is done
478
elsewhere. Information they return, such as from ``list_dir``, is also in
479
the form of URL components.
488
We have a commitment to 6 months API stability - any supported symbol in a
489
release of bzr MUST NOT be altered in any way that would result in
490
breaking existing code that uses it. That means that method names,
491
parameter ordering, parameter names, variable and attribute names etc must
492
not be changed without leaving a 'deprecated forwarder' behind. This even
493
applies to modules and classes.
495
If you wish to change the behaviour of a supported API in an incompatible
496
way, you need to change its name as well. For instance, if I add an optional keyword
497
parameter to branch.commit - that's fine. On the other hand, if I add a
498
keyword parameter to branch.commit which is a *required* transaction
499
object, I should rename the API - i.e. to 'branch.commit_transaction'.
501
When renaming such supported API's, be sure to leave a deprecated_method (or
502
_function or ...) behind which forwards to the new API. See the
503
bzrlib.symbol_versioning module for decorators that take care of the
504
details for you - such as updating the docstring, and issuing a warning
505
when the old api is used.
507
For unsupported API's, it does not hurt to follow this discipline, but it's
508
not required. Minimally though, please try to rename things so that
509
callers will at least get an AttributeError rather than weird results.
512
Coding Style Guidelines
513
=======================
515
Please write PEP-8__ compliant code.
517
One often-missed requirement is that the first line of docstrings
518
should be a self-contained one-sentence summary.
520
__ http://www.python.org/peps/pep-0008.html
33
526
* Imports should be done at the top-level of the file, unless there is
34
527
a strong reason to have them lazily loaded when a particular
174
586
may not catch every case but it's still useful sometimes.
592
In some places we have variables which point to callables that construct
593
new instances. That is to say, they can be used a lot like class objects,
594
but they shouldn't be *named* like classes:
596
> I think that things named FooBar should create instances of FooBar when
597
> called. Its plain confusing for them to do otherwise. When we have
598
> something that is going to be used as a class - that is, checked for via
599
> isinstance or other such idioms, them I would call it foo_class, so that
600
> it is clear that a callable is not sufficient. If it is only used as a
601
> factory, then yes, foo_factory is what I would use.
607
Several places in Bazaar use (or will use) a registry, which is a
608
mapping from names to objects or classes. The registry allows for
609
loading in registered code only when it's needed, and keeping
610
associated information such as a help string or description.
616
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
617
delay importing modules until they are actually used. ``lazy_import`` uses
618
the same syntax as regular python imports. So to import a few modules in a
621
from bzrlib.lazy_import import lazy_import
622
lazy_import(globals(), """
631
revision as _mod_revision,
633
import bzrlib.transport
637
At this point, all of these exist as a ``ImportReplacer`` object, ready to
638
be imported once a member is accessed. Also, when importing a module into
639
the local namespace, which is likely to clash with variable names, it is
640
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
641
the variable is a module, and these object should be hidden anyway, since
642
they shouldn't be imported into other namespaces.
645
Modules versus Members
646
~~~~~~~~~~~~~~~~~~~~~~
648
While it is possible for ``lazy_import()`` to import members of a module
649
when using the ``from module import member`` syntax, it is recommended to
650
only use that syntax to load sub modules ``from module import submodule``.
651
This is because variables and classes can frequently be used without
652
needing a sub-member for example::
654
lazy_import(globals(), """
655
from module import MyClass
659
return isinstance(x, MyClass)
661
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
662
object, rather than the real class.
665
Passing to Other Variables
666
~~~~~~~~~~~~~~~~~~~~~~~~~~
668
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
669
Because the replacer only knows about the original name, it is unable to
670
replace other variables. The ``ImportReplacer`` class will raise an
671
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
672
happened. But it requires accessing a member more than once from the new
673
variable, so some bugs are not detected right away.
679
The null revision is the ancestor of all revisions. Its revno is 0, its
680
revision-id is ``null:``, and its tree is the empty tree. When referring
681
to the null revision, please use ``bzrlib.revision.NULL_REVISION``. Old
682
code sometimes uses ``None`` for the null revision, but this practice is
689
Processing Command Lines
690
------------------------
692
bzrlib has a standard framework for parsing command lines and calling
693
processing routines associated with various commands. See builtins.py
694
for numerous examples.
697
Standard Parameter Types
698
------------------------
700
There are some common requirements in the library: some parameters need to be
701
unicode safe, some need byte strings, and so on. At the moment we have
702
only codified one specific pattern: Parameters that need to be unicode
703
should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
704
input into unicode in a consistent fashion, allowing trivial strings to be
705
used for programmer convenience, but not performing unpredictably in the
706
presence of different locales.
180
712
(The strategy described here is what we want to get to, but it's not
211
743
should be only in the command-line tool.
750
Bazaar has online help for various topics through ``bzr help COMMAND`` or
751
equivalently ``bzr command -h``. We also have help on command options,
752
and on other help topics. (See ``help_topics.py``.)
754
As for python docstrings, the first paragraph should be a single-sentence
755
synopsis of the command.
757
The help for options should be one or more proper sentences, starting with
758
a capital letter and finishing with a full stop (period).
760
All help messages and documentation should have two spaces between
216
In general tests should be placed in a file named testFOO.py where
767
In general tests should be placed in a file named test_FOO.py where
217
768
FOO is the logical thing under test. That file should be placed in the
218
769
tests subdirectory under the package being tested.
220
For example, tests for merge3 in bzrlib belong in bzrlib/tests/testmerge3.py.
221
See bzrlib/selftest/testsampler.py for a template test script.
771
For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
772
See bzrlib/tests/test_sampler.py for a template test script.
774
Tests can be written for the UI or for individual areas of the library.
775
Choose whichever is appropriate: if adding a new command, or a new command
776
option, then you should be writing a UI test. If you are both adding UI
777
functionality and library functionality, you will want to write tests for
778
both the UI and the core behaviours. We call UI tests 'blackbox' tests
779
and they are found in ``bzrlib/tests/blackbox/*.py``.
781
When writing blackbox tests please honour the following conventions:
783
1. Place the tests for the command 'name' in
784
bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
785
to locate the test script for a faulty command.
787
2. Use the 'self.run_bzr("name")' utility function to invoke the command
788
rather than running bzr in a subprocess or invoking the
789
cmd_object.run() method directly. This is a lot faster than
790
subprocesses and generates the same logging output as running it in a
791
subprocess (which invoking the method directly does not).
793
3. Only test the one command in a single test script. Use the bzrlib
794
library when setting up tests and when evaluating the side-effects of
795
the command. We do this so that the library api has continual pressure
796
on it to be as functional as the command line in a simple manner, and
797
to isolate knock-on effects throughout the blackbox test suite when a
798
command changes its name or signature. Ideally only the tests for a
799
given command are affected when a given command is changed.
801
4. If you have a test which does actually require running bzr in a
802
subprocess you can use ``run_bzr_subprocess``. By default the spawned
803
process will not load plugins unless ``--allow-plugins`` is supplied.
809
We have a rich collection of tools to support writing tests. Please use
810
them in preference to ad-hoc solutions as they provide portability and
811
performance benefits.
816
The ``TreeBuilder`` interface allows the construction of arbitrary trees
817
with a declarative interface. A sample session might look like::
819
tree = self.make_branch_and_tree('path')
820
builder = TreeBuilder()
821
builder.start_tree(tree)
822
builder.build(['foo', "bar/", "bar/file"])
823
tree.commit('commit the tree')
824
builder.finish_tree()
826
Please see bzrlib.treebuilder for more details.
831
The ``BranchBuilder`` interface allows the creation of test branches in a
832
quick and easy manner. A sample session::
834
builder = BranchBuilder(self.get_transport().clone('relpath'))
835
builder.build_commit()
836
builder.build_commit()
837
builder.build_commit()
838
branch = builder.get_branch()
840
Please see bzrlib.branchbuilder for more details.
845
We make selective use of doctests__. In general they should provide
846
*examples* within the API documentation which can incidentally be tested. We
847
don't try to test every important case using doctests -- regular Python
848
tests are generally a better solution.
850
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
852
__ http://docs.python.org/lib/module-doctest.html
226
857
Currently, bzr selftest is used to invoke tests.
227
858
You can provide a pattern argument to run a subset. For example,
228
to run just the whitebox tests, run::
230
bzr selftest -v whitebox
233
Errors and exceptions
234
=====================
236
Errors are handled through Python exceptions. They can represent user
237
errors, environmental errors or program bugs. Sometimes we can't be sure
238
at the time it's raised which case applies. See bzrlib/errors.py for
239
details on the error-handling practices.
859
to run just the blackbox tests, run::
861
./bzr selftest -v blackbox
863
To skip a particular test (or set of tests), use the --exclude option
864
(shorthand -x) like so::
866
./bzr selftest -v -x blackbox
868
To list tests without running them, use the --list-only option like so::
870
./bzr selftest --list-only
872
This option can be combined with other selftest options (like -x) and
873
filter patterns to understand their effect.
876
Handling Errors and Exceptions
877
==============================
879
Commands should return non-zero when they encounter circumstances that
880
the user should really pay attention to - which includes trivial shell
883
Recommended values are:
886
1. Conflicts in merge-like operations, or changes are present in
887
diff-like operations.
888
2. Unrepresentable diff changes (i.e. binary files that we cannot show
890
3. An error or exception has occurred.
892
Errors are handled through Python exceptions. Exceptions should be defined
893
inside bzrlib.errors, so that we can see the whole tree at a glance.
895
We broadly classify errors as either being either internal or not,
896
depending on whether ``internal_error`` is set or not. If we think it's our
897
fault, we show a backtrace, an invitation to report the bug, and possibly
898
other details. This is the default for errors that aren't specifically
899
recognized as being caused by a user error. Otherwise we show a briefer
900
message, unless -Derror was given.
902
Many errors originate as "environmental errors" which are raised by Python
903
or builtin libraries -- for example IOError. These are treated as being
904
our fault, unless they're caught in a particular tight scope where we know
905
that they indicate a user errors. For example if the repository format
906
is not found, the user probably gave the wrong path or URL. But if one of
907
the files inside the repository is not found, then it's our fault --
908
either there's a bug in bzr, or something complicated has gone wrong in
909
the environment that means one internal file was deleted.
911
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
912
to be added near the place where they are used.
914
Exceptions are formatted for the user by conversion to a string
915
(eventually calling their ``__str__`` method.) As a convenience the
916
``._fmt`` member can be used as a template which will be mapped to the
917
error's instance dict.
919
New exception classes should be defined when callers might want to catch
920
that exception specifically, or when it needs a substantially different
923
Exception strings should start with a capital letter and should not have a
924
final fullstop. If long, they may contain newlines to break the text.
930
When you change bzrlib, please update the relevant documentation for the
931
change you made: Changes to commands should update their help, and
932
possibly end user tutorials; changes to the core library should be
933
reflected in API documentation.
938
If you make a user-visible change, please add a note to the NEWS file.
939
The description should be written to make sense to someone who's just
940
a user of bzr, not a developer: new functions or classes shouldn't be
941
mentioned, but new commands, changes in behaviour or fixed nontrivial
942
bugs should be listed. See the existing entries for an idea of what
945
Within each release, entries in the news file should have the most
946
user-visible changes first. So the order should be approximately:
948
* changes to existing behaviour - the highest priority because the
949
user's existing knowledge is incorrect
950
* new features - should be brought to their attention
951
* bug fixes - may be of interest if the bug was affecting them, and
952
should include the bug number if any
953
* major documentation changes
954
* changes to internal interfaces
956
People who made significant contributions to each change are listed in
957
parenthesis. This can include reporting bugs (particularly with good
958
details or reproduction recipes), submitting patches, etc.
963
The docstring of a command is used by ``bzr help`` to generate help output
964
for the command. The list 'takes_options' attribute on a command is used by
965
``bzr help`` to document the options for the command - the command
966
docstring does not need to document them. Finally, the '_see_also'
967
attribute on a command can be used to reference other related help topics.
972
Functions, methods, classes and modules should have docstrings
973
describing how they are used.
975
The first line of the docstring should be a self-contained sentence.
977
For the special case of Command classes, this acts as the user-visible
978
documentation shown by the help command.
980
The docstrings should be formatted as reStructuredText_ (like this
981
document), suitable for processing using the epydoc_ tool into HTML
984
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
985
.. _epydoc: http://epydoc.sourceforge.net/
994
The copyright policy for bzr was recently made clear in this email (edited
995
for grammatical correctness)::
997
The attached patch cleans up the copyright and license statements in
998
the bzr source. It also adds tests to help us remember to add them
999
with the correct text.
1001
We had the problem that lots of our files were "Copyright Canonical
1002
Development Ltd" which is not a real company, and some other variations
1003
on this theme. Also, some files were missing the GPL statements.
1005
I want to be clear about the intent of this patch, since copyright can
1006
be a little controversial.
1008
1) The big motivation for this is not to shut out the community, but
1009
just to clean up all of the invalid copyright statements.
1011
2) It has been the general policy for bzr that we want a single
1012
copyright holder for all of the core code. This is following the model
1013
set by the FSF, which makes it easier to update the code to a new
1014
license in case problems are encountered. (For example, if we want to
1015
upgrade the project universally to GPL v3 it is much simpler if there is
1016
a single copyright holder). It also makes it clearer if copyright is
1017
ever debated, there is a single holder, which makes it easier to defend
1018
in court, etc. (I think the FSF position is that if you assign them
1019
copyright, they can defend it in court rather than you needing to, and
1020
I'm sure Canonical would do the same).
1021
As such, Canonical has requested copyright assignments from all of the
1024
3) If someone wants to add code and not attribute it to Canonical, there
1025
is a specific list of files that are excluded from this check. And the
1026
test failure indicates where that is, and how to update it.
1028
4) If anyone feels that I changed a copyright statement incorrectly, just
1029
let me know, and I'll be happy to correct it. Whenever you have large
1030
mechanical changes like this, it is possible to make some mistakes.
1032
Just to reiterate, this is a community project, and it is meant to stay
1033
that way. Core bzr code is copyright Canonical for legal reasons, and
1034
the tests are just there to help us maintain that.
1037
Miscellaneous Topics
1038
####################
1043
Bazaar has a few facilities to help debug problems by going into pdb_, the
1046
.. _pdb: http://docs.python.org/lib/debugger-commands.html
1048
If the ``BZR_PDB`` environment variable is set
1049
then bzr will go into pdb post-mortem mode when an unhandled exception
1052
If you send a SIGQUIT signal to bzr, which can be done by pressing
1053
Ctrl-\\ on Unix, bzr will go into the debugger immediately. You can
1054
continue execution by typing ``c``. This can be disabled if necessary
1055
by setting the environment variable ``BZR_SIGQUIT_PDB=0``.
248
1064
indexes into the branch's revision history.
254
If you'd like to propose a change, please post to the
255
bazaar-ng@lists.canonical.com list with a patch, bzr changeset, or link to a
256
branch. Please put '[patch]' in the subject so we can pick them out, and
257
include some text explaining the change. Remember to put an update to the NEWS
258
file in your diff, if it makes any changes visible to users or plugin
259
developers. Please include a diff against mainline if you're giving a link to
262
Please indicate if you think the code is ready to merge, or if it's just a
263
draft or for discussion. If you want comments from many developers rather than
264
to be merged, you can put '[rfc]' in the subject lines.
266
Anyone is welcome to review code. There are broadly three gates for
269
* Doesn't reduce test coverage: if it adds new methods or commands,
270
there should be tests for them. There is a good test framework
271
and plenty of examples to crib from, but if you are having trouble
272
working out how to test something feel free to post a draft patch
275
* Doesn't reduce design clarity, such as by entangling objects
276
we're trying to separate. This is mostly something the more
277
experienced reviewers need to help check.
279
* Improves bugs, features, speed, or code simplicity.
281
Code that goes in should pass all three.
283
If you read a patch please reply and say so. We can use a numeric scale
284
of -1, -0, +0, +1, meaning respectively "really don't want it in current
285
form", "somewhat uncomfortable", "ok with me", and "please put it in".
286
Anyone can "vote". (It's not really voting, just a terse expression.)
288
If something gets say two +1 votes from core reviewers, and no
289
vetos, then it's OK to come in. Any of the core developers can bring it
290
into their integration branch, which I'll merge regularly. (If you do
291
so, please reply and say so.)
1067
Unicode and Encoding Support
1068
============================
1070
This section discusses various techniques that Bazaar uses to handle
1071
characters that are outside the ASCII set.
1076
When a ``Command`` object is created, it is given a member variable
1077
accessible by ``self.outf``. This is a file-like object, which is bound to
1078
``sys.stdout``, and should be used to write information to the screen,
1079
rather than directly writing to ``sys.stdout`` or calling ``print``.
1080
This file has the ability to translate Unicode objects into the correct
1081
representation, based on the console encoding. Also, the class attribute
1082
``encoding_type`` will effect how unprintable characters will be
1083
handled. This parameter can take one of 3 values:
1086
Unprintable characters will be represented with a suitable replacement
1087
marker (typically '?'), and no exception will be raised. This is for
1088
any command which generates text for the user to review, rather than
1089
for automated processing.
1090
For example: ``bzr log`` should not fail if one of the entries has text
1091
that cannot be displayed.
1094
Attempting to print an unprintable character will cause a UnicodeError.
1095
This is for commands that are intended more as scripting support, rather
1096
than plain user review.
1097
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
1098
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
1099
printed a filename with a '?', the wrong file could be deleted. (At the
1100
very least, the correct file would not be deleted). An error is used to
1101
indicate that the requested action could not be performed.
1104
Do not attempt to automatically convert Unicode strings. This is used
1105
for commands that must handle conversion themselves.
1106
For example: ``bzr diff`` needs to translate Unicode paths, but should
1107
not change the exact text of the contents of the files.
1110
``bzrlib.urlutils.unescape_for_display``
1111
----------------------------------------
1113
Because Transports work in URLs (as defined earlier), printing the raw URL
1114
to the user is usually less than optimal. Characters outside the standard
1115
set are printed as escapes, rather than the real character, and local
1116
paths would be printed as ``file://`` urls. The function
1117
``unescape_for_display`` attempts to unescape a URL, such that anything
1118
that cannot be printed in the current encoding stays an escaped URL, but
1119
valid characters are generated where possible.
1125
The ``bzrlib.osutils`` module has many useful helper functions, including
1126
some more portable variants of functions in the standard library.
1128
In particular, don't use ``shutil.rmtree`` unless it's acceptable for it
1129
to fail on Windows if some files are readonly or still open elsewhere.
1130
Use ``bzrlib.osutils.rmtree`` instead.
1136
We write some extensions in C using pyrex. We design these to work in
1139
* User with no C compiler
1140
* User with C compiler
1143
The recommended way to install bzr is to have a C compiler so that the
1144
extensions can be built, but if no C compiler is present, the pure python
1145
versions we supply will work, though more slowly.
1147
For developers we recommend that pyrex be installed, so that the C
1148
extensions can be changed if needed.
1150
For the C extensions, the extension module should always match the
1151
original python one in all respects (modulo speed). This should be
1152
maintained over time.
1154
To create an extension, add rules to setup.py for building it with pyrex,
1155
and with distutils. Now start with an empty .pyx file. At the top add
1156
"include 'yourmodule.py'". This will import the contents of foo.py into this
1157
file at build time - remember that only one module will be loaded at
1158
runtime. Now you can subclass classes, or replace functions, and only your
1159
changes need to be present in the .pyx file.
1161
Note that pyrex does not support all 2.4 programming idioms, so some
1162
syntax changes may be required. I.e.
1164
- 'from foo import (bar, gam)' needs to change to not use the brackets.
1165
- 'import foo.bar as bar' needs to be 'import foo.bar; bar = foo.bar'
1167
If the changes are too dramatic, consider
1168
maintaining the python code twice - once in the .pyx, and once in the .py,
1169
and no longer including the .py file.
1172
Making Installers for OS Windows
1173
================================
1174
To build a win32 installer, see the instructions on the wiki page:
1175
http://bazaar-vcs.org/BzrWin32Installer
1179
vim: ft=rst tw=74 ai
added
removed
doc/developers/HACKING.txt
