73
61
Bazaar Development in a Nutshell
74
62
================================
76
.. was from http://wiki.bazaar.canonical.com/BzrGivingBack
78
One of the fun things about working on a version control system like Bazaar is
79
that the users have a high level of proficiency in contributing back into
80
the tool. Consider the following very brief introduction to contributing back
81
to Bazaar. More detailed instructions are in the following sections.
86
First, get a local copy of the development mainline (See `Why make a local
92
$ bzr branch lp:bzr bzr.dev
94
Now make your own branch::
96
$ bzr branch bzr.dev 123456-my-bugfix
98
This will give you a branch called "123456-my-bugfix" that you can work on
99
and commit in. Here, you can study the code, make a fix or a new feature.
100
Feel free to commit early and often (after all, it's your branch!).
102
Documentation improvements are an easy place to get started giving back to the
103
Bazaar project. The documentation is in the `doc/` subdirectory of the Bazaar
106
When you are done, make sure that you commit your last set of changes as well!
107
Once you are happy with your changes, ask for them to be merged, as described
110
Making a Merge Proposal
111
-----------------------
113
The Bazaar developers use Launchpad to further enable a truly distributed
114
style of development. Anyone can propose a branch for merging into the Bazaar
115
trunk. To start this process, you need to push your branch to Launchpad. To
116
do this, you will need a Launchpad account and user name, e.g.
117
`your_lp_username`. You can push your branch to Launchpad directly from
120
$ bzr push lp:~<your_lp_username>/bzr/meaningful_name_here
122
After you have pushed your branch, you will need to propose it for merging to
123
the Bazaar trunk. Go to
124
<https://launchpad.net/~<your_lp_username>/bzr/meaningful_name_here> and choose
125
"Propose for merging into another branch". Select "lp:bzr" to hand
126
your changes off to the Bazaar developers for review and merging.
128
Alternatively, after pushing you can use the ``lp-propose`` command to
129
create the merge proposal.
131
Using a meaningful name for your branch will help you and the reviewer(s)
132
better track the submission. Use a very succint description of your submission
133
and prefix it with bug number if needed (lp:~mbp/bzr/484558-merge-directory
134
for example). Alternatively, you can suffix with the bug number
135
(lp:~jameinel/bzr/export-file-511987).
141
Please put a "cover letter" on your merge request explaining:
143
* the reason **why** you're making this change
145
* **how** this change achieves this purpose
147
* anything else you may have fixed in passing
149
* anything significant that you thought of doing, such as a more
150
extensive fix or a different approach, but didn't or couldn't do now
152
A good cover letter makes reviewers' lives easier because they can decide
153
from the letter whether they agree with the purpose and approach, and then
154
assess whether the patch actually does what the cover letter says.
155
Explaining any "drive-by fixes" or roads not taken may also avoid queries
156
from the reviewer. All in all this should give faster and better reviews.
157
Sometimes writing the cover letter helps the submitter realize something
158
else they need to do. The size of the cover letter should be proportional
159
to the size and complexity of the patch.
162
Why make a local copy of bzr.dev?
163
---------------------------------
165
Making a local mirror of bzr.dev is not strictly necessary, but it means
167
- You can use that copy of bzr.dev as your main bzr executable, and keep it
168
up-to-date using ``bzr pull``.
169
- Certain operations are faster, and can be done when offline. For example:
172
- ``bzr diff -r ancestor:...``
175
- When it's time to create your next branch, it's more convenient. When you
176
have further contributions to make, you should do them in their own branch::
179
$ bzr branch bzr.dev additional_fixes
180
$ cd additional_fixes # hack, hack, hack
64
Looking for a 10 minute introduction to submitting a change?
65
See http://bazaar-vcs.org/BzrGivingBack.
67
TODO: Merge that Wiki page into this document.
184
70
Understanding the Development Process
185
71
=====================================
187
The development team follows many practices including:
73
The development team follows many best-practices including:
189
75
* a public roadmap and planning process in which anyone can participate
202
88
* Launchpad - https://launchpad.net/
204
* Bazaar - http://bazaar.canonical.com/
90
* Bazaar - http://bazaar-vcs.org/
92
* Bundle Buggy - http://bundlebuggy.aaronbentley.com/
206
94
* Patch Queue Manager - https://launchpad.net/pqm/
208
For further information, see <http://wiki.bazaar.canonical.com/BzrDevelopment>.
96
For further information, see http://bazaar-vcs.org/BzrDevelopment.
99
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
107
changes visible to users or plugin developers. Please include a diff
108
against mainline if you're giving a link to a branch.
110
You can generate a bundle like this::
112
bzr bundle > mybundle.patch
114
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::
119
bzr merge-directive http://bazaar-vcs.org http://example.org/my_branch > my_directive.patch
121
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
130
* 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
150
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
155
:abstain: Reviewer does not intend to vote on this patch.
156
:resubmit: Please make changes and resubmit for review.
157
:reject: Reviewer doesn't want this kind of change merged.
158
:comment: Not really a vote. Reviewer just wants to comment, for now.
160
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
162
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
164
release, if any. As a guideline, core developers usually merge their own
165
changes and volunteer to merge other contributions if they were the second
166
reviewer to agree to a change.
168
To track the progress of proposed changes, use Bundle Buggy. See
169
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.
213
174
Preparing a Sandbox for Making Changes to Bazaar
214
175
================================================
216
177
Bazaar supports many ways of organising your work. See
217
http://wiki.bazaar.canonical.com/SharedRepositoryLayouts for a summary of the
178
http://bazaar-vcs.org/SharedRepositoryLayouts for a summary of the
218
179
popular alternatives.
220
181
Of course, the best choice for you will depend on numerous factors:
242
203
Navigating the Code Base
243
204
========================
245
.. Was at <http://wiki.bazaar.canonical.com/NewDeveloperIntroduction>
247
Some of the key files in this directory are:
250
The command you run to start Bazaar itself. This script is pretty
251
short and just does some checks then jumps into bzrlib.
254
This file covers a brief introduction to Bazaar and lists some of its
258
Installs Bazaar system-wide or to your home directory. To perform
259
development work on Bazaar it is not required to run this file - you
260
can simply run the bzr command from the top level directory of your
261
development copy. Note: That if you run setup.py this will create a
262
'build' directory in your development branch. There's nothing wrong
263
with this but don't be confused by it. The build process puts a copy
264
of the main code base into this build directory, along with some other
265
files. You don't need to go in here for anything discussed in this
269
Possibly the most exciting folder of all, bzrlib holds the main code
270
base. This is where you will go to edit python files and contribute to
274
Holds documentation on a whole range of things on Bazaar from the
275
origination of ideas within the project to information on Bazaar
276
features and use cases. Within this directory there is a subdirectory
277
for each translation into a human language. All the documentation
278
is in the ReStructuredText markup language.
281
Documentation specifically targeted at Bazaar and plugin developers.
282
(Including this document.)
284
doc/en/release-notes/
286
Detailed changes in each Bazaar release (there is one file by series:
287
bzr-2.3.txt, bzr-2.4.txt, etc) that can affect users or plugin
292
High-level summaries of changes in each Bazaar release (there is one
293
file by series: whats-new-in-2.3.txt, whats-new-in-2.4.txt, etc).
296
Automatically-generated API reference information is available at
297
<http://starship.python.net/crew/mwh/bzrlibapi/>.
299
See also the `Bazaar Architectural Overview
300
<http://doc.bazaar.canonical.com/developers/overview.html>`_.
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
210
documentation generated by epydoc, e.g. something like
211
http://starship.python.net/crew/mwh/bzrlibapi/bzrlib.html.
217
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:
226
* New functionality should have test cases. Preferably write the
227
test before writing the code.
229
In general, you can test at either the command-line level or the
230
internal API level. See Writing tests below for more detail.
232
* Try to practice Test-Driven Development: before fixing a bug, write a
233
test case so that it does not regress. Similarly for adding a new
234
feature: write a test case for a small version of the new feature before
235
starting on the code itself. Check the test fails on the old code, then
236
add the feature or fix and check it passes.
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
241
down the track do not break new features or bug fixes that you are
244
As of May 2007, Bazaar ships with a test suite containing over 6000 tests
245
and growing. We are proud of it and want to remain so. As community
246
members, we all benefit from it. Would you trust version control on
247
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::
257
./bzr selftest -v blackbox
259
To skip a particular test (or set of tests), use the --exclude option
260
(shorthand -x) like so::
262
./bzr selftest -v -x blackbox
264
To ensure that all tests are being run and succeeding, you can use the
265
--strict option which will fail if there are any missing features or known
268
./bzr selftest --strict
270
To list tests without running them, use the --list-only option like so::
272
./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
309
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
312
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
316
subprocess you can use ``run_bzr_subprocess``. By default the spawned
317
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
326
tests are generally a better solution.
328
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
330
__ 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.
413
Essential Domain Classes
414
########################
416
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.
317
496
way, you need to change its name as well. For instance, if I add an optional keyword
318
497
parameter to branch.commit - that's fine. On the other hand, if I add a
319
498
keyword parameter to branch.commit which is a *required* transaction
320
object, I should rename the API - i.e. to 'branch.commit_transaction'.
322
(Actually, that may break code that provides a new implementation of
323
``commit`` and doesn't expect to receive the parameter.)
499
object, I should rename the API - i.e. to 'branch.commit_transaction'.
325
501
When renaming such supported API's, be sure to leave a deprecated_method (or
326
502
_function or ...) behind which forwards to the new API. See the
327
503
bzrlib.symbol_versioning module for decorators that take care of the
328
504
details for you - such as updating the docstring, and issuing a warning
329
when the old API is used.
505
when the old api is used.
331
507
For unsupported API's, it does not hurt to follow this discipline, but it's
332
508
not required. Minimally though, please try to rename things so that
333
509
callers will at least get an AttributeError rather than weird results.
336
Deprecation decorators
337
----------------------
339
``bzrlib.symbol_versioning`` provides decorators that can be attached to
340
methods, functions, and other interfaces to indicate that they should no
341
longer be used. For example::
343
@deprecated_method(deprecated_in((0, 1, 4)))
345
return self._new_foo()
347
To deprecate a static method you must call ``deprecated_function``
348
(**not** method), after the staticmethod call::
351
@deprecated_function(deprecated_in((0, 1, 4)))
352
def create_repository(base, shared=False, format=None):
354
When you deprecate an API, you should not just delete its tests, because
355
then we might introduce bugs in them. If the API is still present at all,
356
it should still work. The basic approach is to use
357
``TestCase.applyDeprecated`` which in one step checks that the API gives
358
the expected deprecation message, and also returns the real result from
359
the method, so that tests can keep running.
361
Deprecation warnings will be suppressed for final releases, but not for
362
development versions or release candidates, or when running ``bzr
363
selftest``. This gives developers information about whether their code is
364
using deprecated functions, but avoids confusing users about things they
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
526
* Imports should be done at the top-level of the file, unless there is
527
a strong reason to have them lazily loaded when a particular
528
function runs. Import statements have a cost, so try to make sure
529
they don't run inside hot functions.
531
* Module names should always be given fully-qualified,
532
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
538
Functions, methods or members that are "private" to bzrlib are given
539
a leading underscore prefix. Names without a leading underscore are
540
public not just across modules but to programmers using bzrlib as an
541
API. As a consequence, a leading underscore is appropriate for names
542
exposed across modules but that are not to be exposed to bzrlib API
545
We prefer class names to be concatenated capital words (``TestCase``)
546
and variables, methods and functions to be lowercase words joined by
547
underscores (``revision_id``, ``get_revision``).
549
For the purposes of naming some names are treated as single compound
550
words: "filename", "revno".
552
Consider naming classes as nouns and functions/methods as verbs.
554
Try to avoid using abbreviations in names, because there can be
555
inconsistency if other people use the full name.
561
``revision_id`` not ``rev_id`` or ``revid``
563
Functions that transform one thing to another should be named ``x_to_y``
564
(not ``x2y`` as occurs in some old code.)
570
Python destructors (``__del__``) work differently to those of other
571
languages. In particular, bear in mind that destructors may be called
572
immediately when the object apparently becomes unreferenced, or at some
573
later time, or possibly never at all. Therefore we have restrictions on
574
what can be done inside them.
576
0. Never use a __del__ method without asking Martin/Robert first.
578
1. Never rely on a ``__del__`` method running. If there is code that
579
must run, do it from a ``finally`` block instead.
581
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
584
3. In some places we raise a warning from the destructor if the object
585
has not been cleaned up or closed. This is considered OK: the warning
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.
712
(The strategy described here is what we want to get to, but it's not
713
consistently followed in the code at the moment.)
715
bzrlib is intended to be a generically reusable library. It shouldn't
716
write messages to stdout or stderr, because some programs that use it
717
might want to display that information through a GUI or some other
720
We can distinguish two types of output from the library:
722
1. Structured data representing the progress or result of an
723
operation. For example, for a commit command this will be a list
724
of the modified files and the finally committed revision number
727
These should be exposed either through the return code or by calls
728
to a callback parameter.
730
A special case of this is progress indicators for long-lived
731
operations, where the caller should pass a ProgressBar object.
733
2. Unstructured log/debug messages, mostly for the benefit of the
734
developers or users trying to debug problems. This should always
735
be sent through ``bzrlib.trace`` and Python ``logging``, so that
736
it can be redirected by the client.
738
The distinction between the two is a bit subjective, but in general if
739
there is any chance that a library would want to see something as
740
structured data, we should make it so.
742
The policy about how output is presented in the text-mode client
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
767
In general tests should be placed in a file named test_FOO.py where
768
FOO is the logical thing under test. That file should be placed in the
769
tests subdirectory under the package being tested.
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
857
Currently, bzr selftest is used to invoke tests.
858
You can provide a pattern argument to run a subset. For example,
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/
368
988
General Guidelines
added
removed
doc/developers/HACKING.txt
