105
117
For further information, see http://bazaar-vcs.org/BzrDevelopment.
108
A Closer Look at the Merge & Review Process
109
===========================================
122
Preparing a Sandbox for Making Changes to Bazaar
123
================================================
125
Bazaar supports many ways of organising your work. See
126
http://bazaar-vcs.org/SharedRepositoryLayouts for a summary of the
127
popular alternatives.
129
Of course, the best choice for you will depend on numerous factors:
130
the number of changes you may be making, the complexity of the changes, etc.
131
As a starting suggestion though:
133
* create a local copy of the main development branch (bzr.dev) by using
136
bzr branch http://bazaar-vcs.org/bzr/bzr.dev/ bzr.dev
138
* keep your copy of bzr.dev prestine (by not developing in it) and keep
139
it up to date (by using bzr pull)
141
* create a new branch off your local bzr.dev copy for each issue
142
(bug or feature) you are working on.
144
This approach makes it easy to go back and make any required changes
145
after a code review. Resubmitting the change is then simple with no
146
risk of accidentially including edits related to other issues you may
147
be working on. After the changes for an issue are accepted and merged,
148
the associated branch can be deleted or archived as you wish.
151
Navigating the Code Base
152
========================
154
.. Was at <http://bazaar-vcs.org/NewDeveloperIntroduction>
156
Some of the key files in this directory are:
159
The command you run to start Bazaar itself. This script is pretty
160
short and just does some checks then jumps into bzrlib.
163
This file covers a brief introduction to Bazaar and lists some of its
167
Summary of changes in each Bazaar release that can affect users or
171
Installs Bazaar system-wide or to your home directory. To perform
172
development work on Bazaar it is not required to run this file - you
173
can simply run the bzr command from the top level directory of your
174
development copy. Note: That if you run setup.py this will create a
175
'build' directory in your development branch. There's nothing wrong
176
with this but don't be confused by it. The build process puts a copy
177
of the main code base into this build directory, along with some other
178
files. You don't need to go in here for anything discussed in this
182
Possibly the most exciting folder of all, bzrlib holds the main code
183
base. This is where you will go to edit python files and contribute to
187
Holds documentation on a whole range of things on Bazaar from the
188
origination of ideas within the project to information on Bazaar
189
features and use cases. Within this directory there is a subdirectory
190
for each translation into a human language. All the documentation
191
is in the ReStructuredText markup language.
194
Documentation specifically targetted at Bazaar and plugin developers.
195
(Including this document.)
199
Automatically-generated API reference information is available at
200
<http://starship.python.net/crew/mwh/bzrlibapi/>.
202
See also the `Bazaar Architectural Overview <../../developers/overview.html>`_.
205
The Code Review Process
206
#######################
208
All code changes coming in to Bazaar are reviewed by someone else.
209
Normally changes by core contributors are reviewed by one other core
210
developer, and changes from other people are reviewed by two core
211
developers. Use intelligent discretion if the patch is trivial.
213
Good reviews do take time. They also regularly require a solid
214
understanding of the overall code base. In practice, this means a small
215
number of people often have a large review burden - with knowledge comes
216
responsibility. No one like their merge requests sitting in a queue going
217
nowhere, so reviewing sooner rather than later is strongly encouraged.
226
Please put a "cover letter" on your merge request explaining:
228
* the reason **why** you're making this change
230
* **how** this change achieves this purpose
232
* anything else you may have fixed in passing
234
* anything significant that you thought of doing, such as a more
235
extensive fix or a different approach, but didn't or couldn't do now
237
A good cover letter makes reviewers' lives easier because they can decide
238
from the letter whether they agree with the purpose and approach, and then
239
assess whether the patch actually does what the cover letter says.
240
Explaining any "drive-by fixes" or roads not taken may also avoid queries
241
from the reviewer. All in all this should give faster and better reviews.
242
Sometimes writing the cover letter helps the submitter realize something
243
else they need to do. The size of the cover letter should be proportional
244
to the size and complexity of the patch.
247
Reviewing proposed changes
248
==========================
250
Anyone is welcome to review code, and reply to the thread with their
253
The simplest way to review a proposed change is to just read the patch on
254
the list or in Bundle Buggy. For more complex changes it may be useful
255
to make a new working tree or branch from trunk, and merge the proposed
256
change into it, so you can experiment with the code or look at a wider
259
There are three main requirements for code to get in:
261
* Doesn't reduce test coverage: if it adds new methods or commands,
262
there should be tests for them. There is a good test framework
263
and plenty of examples to crib from, but if you are having trouble
264
working out how to test something feel free to post a draft patch
267
* Doesn't reduce design clarity, such as by entangling objects
268
we're trying to separate. This is mostly something the more
269
experienced reviewers need to help check.
271
* Improves bugs, features, speed, or code simplicity.
273
Code that goes in should not degrade any of these aspects. Patches are
274
welcome that only cleanup the code without changing the external
275
behaviour. The core developers take care to keep the code quality high
276
and understandable while recognising that perfect is sometimes the enemy
279
It is easy for reviews to make people notice other things which should be
280
fixed but those things should not hold up the original fix being accepted.
281
New things can easily be recorded in the Bug Tracker instead.
283
It's normally much easier to review several smaller patches than one large
284
one. You might want to use ``bzr-loom`` to maintain threads of related
285
work, or submit a preparatory patch that will make your "real" change
289
Checklist for reviewers
290
=======================
292
* Do you understand what the code's doing and why?
294
* Will it perform reasonably for large inputs, both in memory size and
295
run time? Are there some scenarios where performance should be
298
* Is it tested, and are the tests at the right level? Are there both
299
blackbox (command-line level) and API-oriented tests?
301
* If this change will be visible to end users or API users, is it
302
appropriately documented in NEWS?
304
* Does it meet the coding standards below?
306
* If it changes the user-visible behaviour, does it update the help
307
strings and user documentation?
309
* If it adds a new major concept or standard practice, does it update the
310
developer documentation?
312
* (your ideas here...)
318
From May 2009 on, we prefer people to propose code reviews through
321
* <https://launchpad.net/+tour/code-review>
323
* <https://help.launchpad.net/Code/Review>
325
Anyone can propose or comment on a merge propsal just by creating a
328
There are two ways to create a new merge proposal: through the web
329
interface or by email.
332
Proposing a merge through the web
333
---------------------------------
335
To create the propsal through the web: push your branch to Launchpad, eg::
337
bzr push lp:~mbp/bzr/doc
339
then go to the branch's web page, which in this case would be
340
<https://code.launchpad.net/~mbp/bzr/doc>. You can automate that by just
345
You can then click "Propose for merging into another branch", and enter a
346
cover letter into the web form. Typically you'll want to merge into
347
``~bzr/bzr/trunk`` which will be the default; you might also want to
348
nominate merging into a release branch for a bug fix. There is the option
349
to specify a specific reviewer or type of review, and you shouldn't
350
normally change those.
352
Submitting the form takes you to the new page about the merge proposal
353
containing the diff of the changes, comments by interested people, and
354
controls to comment or vote on the change.
356
Proposing a merge by mail
357
-------------------------
359
To propose a merge by mail, send a bundle to ``merge@code.launchpad.net``.
361
You can generate a merge request like this::
363
bzr send -o bug-1234.diff
365
``bzr send`` can also send mail directly if you prefer; see the help.
370
From <https://code.launchpad.net/bzr/+activereviews> you can see all
371
currently active reviews, and choose one to comment on. This page also
372
shows proposals that are now approved and should be merged by someone with
376
Reviews through Bundle Buggy
377
============================
379
The Bundle Buggy tool used up to May 2009 is still available as a review
382
Sending patches for review
383
--------------------------
111
385
If you'd like to propose a change, please post to the
112
386
bazaar@lists.canonical.com list with a bundle, patch, or link to a
113
branch. Put '[PATCH]' or '[MERGE]' in the subject so Bundle Buggy
387
branch. Put ``[PATCH]`` or ``[MERGE]`` in the subject so Bundle Buggy
114
388
can pick it out, and explain the change in the email message text.
115
389
Remember to update the NEWS file as part of your change if it makes any
116
390
changes visible to users or plugin developers. Please include a diff
117
391
against mainline if you're giving a link to a branch.
119
You can generate a bundle like this::
393
You can generate a merge request like this::
121
bzr bundle > mybundle.patch
395
bzr send -o bug-1234.patch
123
A .patch extension is recommended instead of .bundle as many mail clients
124
will send the latter as a binary file. If a bundle would be too long or your
125
mailer mangles whitespace (e.g. implicitly converts Unix newlines to DOS
126
newlines), use the merge-directive command instead like this::
128
bzr merge-directive http://bazaar-vcs.org http://example.org/my_branch > my_directive.patch
130
See the help for details on the arguments to merge-directive.
397
A ``.patch`` extension is recommended instead of .bundle as many mail clients
398
will send the latter as a binary file.
400
``bzr send`` can also send mail directly if you prefer; see the help.
132
402
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
133
403
want it to be merged. If you want comments from developers rather than
134
to be merged, you can put '[RFC]' in the subject line.
136
Anyone is welcome to review code. There are broadly three gates for
139
* Doesn't reduce test coverage: if it adds new methods or commands,
140
there should be tests for them. There is a good test framework
141
and plenty of examples to crib from, but if you are having trouble
142
working out how to test something feel free to post a draft patch
145
* Doesn't reduce design clarity, such as by entangling objects
146
we're trying to separate. This is mostly something the more
147
experienced reviewers need to help check.
149
* Improves bugs, features, speed, or code simplicity.
151
Code that goes in should pass all three. The core developers take care
152
to keep the code quality high and understandable while recognising that
153
perfect is sometimes the enemy of good. (It is easy for reviews to make
154
people notice other things which should be fixed but those things should
155
not hold up the original fix being accepted. New things can easily be
156
recorded in the Bug Tracker instead.)
158
Anyone can "vote" on the mailing list. Core developers can also vote using
159
Bundle Buggy. Here are the voting codes and their explanations.
404
to be merged, you can put ``[RFC]`` in the subject line.
406
If this change addresses a bug, please put the bug number in the subject
407
line too, in the form ``[#1]`` so that Bundle Buggy can recognize it.
409
If the change is intended for a particular release mark that in the
410
subject too, e.g. ``[1.6]``.
411
Anyone can "vote" on the mailing list by expressing an opinion. Core
412
developers can also vote using Bundle Buggy. Here are the voting codes and
161
415
:approve: Reviewer wants this submission merged.
162
416
:tweak: Reviewer wants this submission merged with small changes. (No
179
433
outstanding merge requests together with an explanation of the columns.
180
434
Bundle Buggy will also mail you a link to track just your change.
183
Preparing a Sandbox for Making Changes to Bazaar
184
================================================
186
Bazaar supports many ways of organising your work. See
187
http://bazaar-vcs.org/SharedRepositoryLayouts for a summary of the
188
popular alternatives.
190
Of course, the best choice for you will depend on numerous factors:
191
the number of changes you may be making, the complexity of the changes, etc.
192
As a starting suggestion though:
194
* create a local copy of the main development branch (bzr.dev) by using
197
bzr branch http://bazaar-vcs.org/bzr/bzr.dev/ bzr.dev
199
* keep your copy of bzr.dev prestine (by not developing in it) and keep
200
it up to date (by using bzr pull)
202
* create a new branch off your local bzr.dev copy for each issue
203
(bug or feature) you are working on.
205
This approach makes it easy to go back and make any required changes
206
after a code review. Resubmitting the change is then simple with no
207
risk of accidentially including edits related to other issues you may
208
be working on. After the changes for an issue are accepted and merged,
209
the associated branch can be deleted or archived as you wish.
212
Navigating the Code Base
213
========================
215
TODO: List and describe in one line the purpose of each directory
216
inside an installation of bzr.
218
TODO: Refer to a central location holding an up to date copy of the API
219
documentation generated by epydoc, e.g. something like
220
http://starship.python.net/crew/mwh/bzrlibapi/bzrlib.html.
226
The Importance of Testing
227
=========================
229
Reliability is a critical success factor for any Version Control System.
230
We want Bazaar to be highly reliable across multiple platforms while
231
evolving over time to meet the needs of its community.
233
In a nutshell, this is want we expect and encourage:
235
* New functionality should have test cases. Preferably write the
236
test before writing the code.
238
In general, you can test at either the command-line level or the
239
internal API level. See Writing tests below for more detail.
241
* Try to practice Test-Driven Development: before fixing a bug, write a
242
test case so that it does not regress. Similarly for adding a new
243
feature: write a test case for a small version of the new feature before
244
starting on the code itself. Check the test fails on the old code, then
245
add the feature or fix and check it passes.
247
By doing these things, the Bazaar team gets increased confidence that
248
changes do what they claim to do, whether provided by the core team or
249
by community members. Equally importantly, we can be surer that changes
250
down the track do not break new features or bug fixes that you are
253
As of May 2008, Bazaar ships with a test suite containing over 12000 tests
254
and growing. We are proud of it and want to remain so. As community
255
members, we all benefit from it. Would you trust version control on
256
your project to a product *without* a test suite like Bazaar has?
259
Running the Test Suite
260
======================
262
Currently, bzr selftest is used to invoke tests.
263
You can provide a pattern argument to run a subset. For example,
264
to run just the blackbox tests, run::
266
./bzr selftest -v blackbox
268
To skip a particular test (or set of tests), use the --exclude option
269
(shorthand -x) like so::
271
./bzr selftest -v -x blackbox
273
To ensure that all tests are being run and succeeding, you can use the
274
--strict option which will fail if there are any missing features or known
277
./bzr selftest --strict
279
To list tests without running them, use the --list-only option like so::
281
./bzr selftest --list-only
283
This option can be combined with other selftest options (like -x) and
284
filter patterns to understand their effect.
286
Once you understand how to create a list of tests, you can use the --load-list
287
option to run only a restricted set of tests that you kept in a file, one test
288
id by line. Keep in mind that this will never be sufficient to validate your
289
modifications, you still need to run the full test suite for that, but using it
290
can help in some cases (like running only the failed tests for some time)::
292
./bzr selftest -- load-list my_failing_tests
294
This option can also be combined with other selftest options, including
295
patterns. It has some drawbacks though, the list can become out of date pretty
296
quick when doing Test Driven Development.
298
To address this concern, there is another way to run a restricted set of tests:
299
the --starting-with option will run only the tests whose name starts with the
300
specified string. It will also avoid loading the other tests and as a
301
consequence starts running your tests quicker::
303
./bzr selftest --starting-with bzrlib.blackbox
305
This option can be combined with all the other selftest options including
306
--load-list. The later is rarely used but allows to run a subset of a list of
307
failing tests for example.
309
Test suite debug flags
310
----------------------
312
Similar to the global ``-Dfoo`` debug options, bzr selftest accepts
313
``-E=foo`` debug flags. These flags are:
315
:allow_debug: do *not* clear the global debug flags when running a test.
316
This can provide useful logging to help debug test failures when used
317
with e.g. ``bzr -Dhpss selftest -E=allow_debug``
323
In general tests should be placed in a file named test_FOO.py where
324
FOO is the logical thing under test. That file should be placed in the
325
tests subdirectory under the package being tested.
327
For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
328
See bzrlib/tests/test_sampler.py for a template test script.
330
Tests can be written for the UI or for individual areas of the library.
331
Choose whichever is appropriate: if adding a new command, or a new command
332
option, then you should be writing a UI test. If you are both adding UI
333
functionality and library functionality, you will want to write tests for
334
both the UI and the core behaviours. We call UI tests 'blackbox' tests
335
and they are found in ``bzrlib/tests/blackbox/*.py``.
337
When writing blackbox tests please honour the following conventions:
339
1. Place the tests for the command 'name' in
340
bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
341
to locate the test script for a faulty command.
343
2. Use the 'self.run_bzr("name")' utility function to invoke the command
344
rather than running bzr in a subprocess or invoking the
345
cmd_object.run() method directly. This is a lot faster than
346
subprocesses and generates the same logging output as running it in a
347
subprocess (which invoking the method directly does not).
349
3. Only test the one command in a single test script. Use the bzrlib
350
library when setting up tests and when evaluating the side-effects of
351
the command. We do this so that the library api has continual pressure
352
on it to be as functional as the command line in a simple manner, and
353
to isolate knock-on effects throughout the blackbox test suite when a
354
command changes its name or signature. Ideally only the tests for a
355
given command are affected when a given command is changed.
357
4. If you have a test which does actually require running bzr in a
358
subprocess you can use ``run_bzr_subprocess``. By default the spawned
359
process will not load plugins unless ``--allow-plugins`` is supplied.
365
We make selective use of doctests__. In general they should provide
366
*examples* within the API documentation which can incidentally be tested. We
367
don't try to test every important case using doctests -- regular Python
368
tests are generally a better solution.
370
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
372
__ http://docs.python.org/lib/module-doctest.html
375
Skipping tests and test requirements
376
------------------------------------
378
In our enhancements to unittest we allow for some addition results beyond
379
just success or failure.
381
If a test can't be run, it can say that it's skipped. This is typically
382
used in parameterized tests - for example if a transport doesn't support
383
setting permissions, we'll skip the tests that relating to that. ::
386
return self.branch_format.initialize(repo.bzrdir)
387
except errors.UninitializableFormat:
388
raise tests.TestSkipped('Uninitializable branch format')
390
Raising TestSkipped is a good idea when you want to make it clear that the
391
test was not run, rather than just returning which makes it look as if it
394
Several different cases are distinguished:
397
Generic skip; the only type that was present up to bzr 0.18.
400
The test doesn't apply to the parameters with which it was run.
401
This is typically used when the test is being applied to all
402
implementations of an interface, but some aspects of the interface
403
are optional and not present in particular concrete
404
implementations. (Some tests that should raise this currently
405
either silently return or raise TestSkipped.) Another option is
406
to use more precise parameterization to avoid generating the test
410
**(Not implemented yet)**
411
The test can't be run because of an inherent limitation of the
412
environment, such as not having symlinks or not supporting
416
The test can't be run because a dependency (typically a Python
417
library) is not available in the test environment. These
418
are in general things that the person running the test could fix
419
by installing the library. It's OK if some of these occur when
420
an end user runs the tests or if we're specifically testing in a
421
limited environment, but a full test should never see them.
424
The test exists but is known to fail, for example because the
425
code to fix it hasn't been run yet. Raising this allows
426
you to distinguish these failures from the ones that are not
427
expected to fail. This could be conditionally raised if something
428
is broken on some platforms but not on others.
430
We plan to support three modes for running the test suite to control the
431
interpretation of these results. Strict mode is for use in situations
432
like merges to the mainline and releases where we want to make sure that
433
everything that can be tested has been tested. Lax mode is for use by
434
developers who want to temporarily tolerate some known failures. The
435
default behaviour is obtained by ``bzr selftest`` with no options, and
436
also (if possible) by running under another unittest harness.
438
======================= ======= ======= ========
439
result strict default lax
440
======================= ======= ======= ========
441
TestSkipped pass pass pass
442
TestNotApplicable pass pass pass
443
TestPlatformLimit pass pass pass
444
TestDependencyMissing fail pass pass
445
KnownFailure fail pass pass
446
======================= ======= ======= ========
449
Test feature dependencies
450
-------------------------
452
Rather than manually checking the environment in each test, a test class
453
can declare its dependence on some test features. The feature objects are
454
checked only once for each run of the whole test suite.
456
For historical reasons, as of May 2007 many cases that should depend on
457
features currently raise TestSkipped.)
461
class TestStrace(TestCaseWithTransport):
463
_test_needs_features = [StraceFeature]
465
This means all tests in this class need the feature. The feature itself
466
should provide a ``_probe`` method which is called once to determine if
469
These should generally be equivalent to either TestDependencyMissing or
470
sometimes TestPlatformLimit.
476
Known failures are when a test exists but we know it currently doesn't
477
work, allowing the test suite to still pass. These should be used with
478
care, we don't want a proliferation of quietly broken tests. It might be
479
appropriate to use them if you've committed a test for a bug but not the
480
fix for it, or if something works on Unix but not on Windows.
483
Testing exceptions and errors
484
-----------------------------
486
It's important to test handling of errors and exceptions. Because this
487
code is often not hit in ad-hoc testing it can often have hidden bugs --
488
it's particularly common to get NameError because the exception code
489
references a variable that has since been renamed.
491
.. TODO: Something about how to provoke errors in the right way?
493
In general we want to test errors at two levels:
495
1. A test in ``test_errors.py`` checking that when the exception object is
496
constructed with known parameters it produces an expected string form.
497
This guards against mistakes in writing the format string, or in the
498
``str`` representations of its parameters. There should be one for
499
each exception class.
501
2. Tests that when an api is called in a particular situation, it raises
502
an error of the expected class. You should typically use
503
``assertRaises``, which in the Bazaar test suite returns the exception
504
object to allow you to examine its parameters.
506
In some cases blackbox tests will also want to check error reporting. But
507
it can be difficult to provoke every error through the commandline
508
interface, so those tests are only done as needed -- eg in response to a
509
particular bug or if the error is reported in an unusual way(?) Blackbox
510
tests should mostly be testing how the command-line interface works, so
511
should only test errors if there is something particular to the cli in how
512
they're displayed or handled.
518
The Python ``warnings`` module is used to indicate a non-fatal code
519
problem. Code that's expected to raise a warning can be tested through
522
The test suite can be run with ``-Werror`` to check no unexpected errors
525
However, warnings should be used with discretion. It's not an appropriate
526
way to give messages to the user, because the warning is normally shown
527
only once per source line that causes the problem. You should also think
528
about whether the warning is serious enought that it should be visible to
529
users who may not be able to fix it.
532
Interface implementation testing and test scenarios
533
---------------------------------------------------
535
There are several cases in Bazaar of multiple implementations of a common
536
conceptual interface. ("Conceptual" because
537
it's not necessary for all the implementations to share a base class,
538
though they often do.) Examples include transports and the working tree,
539
branch and repository classes.
541
In these cases we want to make sure that every implementation correctly
542
fulfils the interface requirements. For example, every Transport should
543
support the ``has()`` and ``get()`` and ``clone()`` methods. We have a
544
sub-suite of tests in ``test_transport_implementations``. (Most
545
per-implementation tests are in submodules of ``bzrlib.tests``, but not
546
the transport tests at the moment.)
548
These tests are repeated for each registered Transport, by generating a
549
new TestCase instance for the cross product of test methods and transport
550
implementations. As each test runs, it has ``transport_class`` and
551
``transport_server`` set to the class it should test. Most tests don't
552
access these directly, but rather use ``self.get_transport`` which returns
553
a transport of the appropriate type.
555
The goal is to run per-implementation only tests that relate to that
556
particular interface. Sometimes we discover a bug elsewhere that happens
557
with only one particular transport. Once it's isolated, we can consider
558
whether a test should be added for that particular implementation,
559
or for all implementations of the interface.
561
The multiplication of tests for different implementations is normally
562
accomplished by overriding the ``test_suite`` function used to load
563
tests from a module. This function typically loads all the tests,
564
then applies a TestProviderAdapter to them, which generates a longer
565
suite containing all the test variations.
571
Some utilities are provided for generating variations of tests. This can
572
be used for per-implementation tests, or other cases where the same test
573
code needs to run several times on different scenarios.
575
The general approach is to define a class that provides test methods,
576
which depend on attributes of the test object being pre-set with the
577
values to which the test should be applied. The test suite should then
578
also provide a list of scenarios in which to run the tests.
580
Typically ``multiply_tests_from_modules`` should be called from the test
581
module's ``test_suite`` function.
584
Essential Domain Classes
585
########################
587
Introducing the Object Model
588
============================
590
The core domain objects within the bazaar model are:
600
Transports are explained below. See http://bazaar-vcs.org/Classes/
601
for an introduction to the other key classes.
606
The ``Transport`` layer handles access to local or remote directories.
607
Each Transport object acts like a logical connection to a particular
608
directory, and it allows various operations on files within it. You can
609
*clone* a transport to get a new Transport connected to a subdirectory or
612
Transports are not used for access to the working tree. At present
613
working trees are always local and they are accessed through the regular
614
Python file io mechanisms.
619
Transports work in URLs. Take note that URLs are by definition only
620
ASCII - the decision of how to encode a Unicode string into a URL must be
621
taken at a higher level, typically in the Store. (Note that Stores also
622
escape filenames which cannot be safely stored on all filesystems, but
623
this is a different level.)
625
The main reason for this is that it's not possible to safely roundtrip a
626
URL into Unicode and then back into the same URL. The URL standard
627
gives a way to represent non-ASCII bytes in ASCII (as %-escapes), but
628
doesn't say how those bytes represent non-ASCII characters. (They're not
629
guaranteed to be UTF-8 -- that is common but doesn't happen everywhere.)
631
For example if the user enters the url ``http://example/%e0`` there's no
632
way to tell whether that character represents "latin small letter a with
633
grave" in iso-8859-1, or "latin small letter r with acute" in iso-8859-2
634
or malformed UTF-8. So we can't convert their URL to Unicode reliably.
636
Equally problematic if we're given a url-like string containing non-ascii
637
characters (such as the accented a) we can't be sure how to convert that
638
to the correct URL, because we don't know what encoding the server expects
639
for those characters. (Although this is not totally reliable we might still
640
accept these and assume they should be put into UTF-8.)
642
A similar edge case is that the url ``http://foo/sweet%2Fsour`` contains
643
one directory component whose name is "sweet/sour". The escaped slash is
644
not a directory separator. If we try to convert URLs to regular Unicode
645
paths this information will be lost.
647
This implies that Transports must natively deal with URLs; for simplicity
648
they *only* deal with URLs and conversion of other strings to URLs is done
649
elsewhere. Information they return, such as from ``list_dir``, is also in
650
the form of URL components.
659
We have a commitment to 6 months API stability - any supported symbol in a
660
release of bzr MUST NOT be altered in any way that would result in
661
breaking existing code that uses it. That means that method names,
662
parameter ordering, parameter names, variable and attribute names etc must
663
not be changed without leaving a 'deprecated forwarder' behind. This even
664
applies to modules and classes.
666
If you wish to change the behaviour of a supported API in an incompatible
667
way, you need to change its name as well. For instance, if I add an optional keyword
668
parameter to branch.commit - that's fine. On the other hand, if I add a
669
keyword parameter to branch.commit which is a *required* transaction
670
object, I should rename the API - i.e. to 'branch.commit_transaction'.
672
When renaming such supported API's, be sure to leave a deprecated_method (or
673
_function or ...) behind which forwards to the new API. See the
674
bzrlib.symbol_versioning module for decorators that take care of the
675
details for you - such as updating the docstring, and issuing a warning
676
when the old api is used.
678
For unsupported API's, it does not hurt to follow this discipline, but it's
679
not required. Minimally though, please try to rename things so that
680
callers will at least get an AttributeError rather than weird results.
683
Deprecation decorators
684
----------------------
686
``bzrlib.symbol_versioning`` provides decorators that can be attached to
687
methods, functions, and other interfaces to indicate that they should no
690
To deprecate a static method you must call ``deprecated_function``
691
(**not** method), after the staticmethod call::
694
@deprecated_function(zero_ninetyone)
695
def create_repository(base, shared=False, format=None):
697
When you deprecate an API, you should not just delete its tests, because
698
then we might introduce bugs in them. If the API is still present at all,
699
it should still work. The basic approach is to use
700
``TestCase.applyDeprecated`` which in one step checks that the API gives
701
the expected deprecation message, and also returns the real result from
702
the method, so that tests can keep running.
704
436
Coding Style Guidelines
705
=======================
437
#######################
707
439
hasattr and getattr
710
442
``hasattr`` should not be used because it swallows exceptions including
711
443
``KeyboardInterrupt``. Instead, say something like ::
965
721
being phased out.
724
Object string representations
725
=============================
727
Python prints objects using their ``__repr__`` method when they are
728
written to logs, exception tracebacks, or the debugger. We want
729
objects to have useful representations to help in determining what went
732
If you add a new class you should generally add a ``__repr__`` method
733
unless there is an adequate method in a parent class. There should be a
736
Representations should typically look like Python constructor syntax, but
737
they don't need to include every value in the object and they don't need
738
to be able to actually execute. They're to be read by humans, not
739
machines. Don't hardcode the classname in the format, so that we get the
740
correct value if the method is inherited by a subclass. If you're
741
printing attributes of the object, including strings, you should normally
742
use ``%r`` syntax (to call their repr in turn).
744
Try to avoid the representation becoming more than one or two lines long.
745
(But balance this against including useful information, and simplicity of
748
Because repr methods are often called when something has already gone
749
wrong, they should be written somewhat more defensively than most code.
750
The object may be half-initialized or in some other way in an illegal
751
state. The repr method shouldn't raise an exception, or it may hide the
752
(probably more useful) underlying exception.
757
return '%s(%r)' % (self.__class__.__name__,
764
A bare ``except`` statement will catch all exceptions, including ones that
765
really should terminate the program such as ``MemoryError`` and
766
``KeyboardInterrupt``. They should rarely be used unless the exception is
767
later re-raised. Even then, think about whether catching just
768
``Exception`` (which excludes system errors in Python2.5 and later) would
775
All code should be exercised by the test suite. See `Guide to Testing
776
Bazaar <../../developers/testing.html>`_ for detailed information about writing tests.
785
We have a commitment to 6 months API stability - any supported symbol in a
786
release of bzr MUST NOT be altered in any way that would result in
787
breaking existing code that uses it. That means that method names,
788
parameter ordering, parameter names, variable and attribute names etc must
789
not be changed without leaving a 'deprecated forwarder' behind. This even
790
applies to modules and classes.
792
If you wish to change the behaviour of a supported API in an incompatible
793
way, you need to change its name as well. For instance, if I add an optional keyword
794
parameter to branch.commit - that's fine. On the other hand, if I add a
795
keyword parameter to branch.commit which is a *required* transaction
796
object, I should rename the API - i.e. to 'branch.commit_transaction'.
798
When renaming such supported API's, be sure to leave a deprecated_method (or
799
_function or ...) behind which forwards to the new API. See the
800
bzrlib.symbol_versioning module for decorators that take care of the
801
details for you - such as updating the docstring, and issuing a warning
802
when the old api is used.
804
For unsupported API's, it does not hurt to follow this discipline, but it's
805
not required. Minimally though, please try to rename things so that
806
callers will at least get an AttributeError rather than weird results.
809
Deprecation decorators
810
----------------------
812
``bzrlib.symbol_versioning`` provides decorators that can be attached to
813
methods, functions, and other interfaces to indicate that they should no
814
longer be used. For example::
816
@deprecated_method(deprecated_in((0, 1, 4)))
818
return self._new_foo()
820
To deprecate a static method you must call ``deprecated_function``
821
(**not** method), after the staticmethod call::
824
@deprecated_function(deprecated_in((0, 1, 4)))
825
def create_repository(base, shared=False, format=None):
827
When you deprecate an API, you should not just delete its tests, because
828
then we might introduce bugs in them. If the API is still present at all,
829
it should still work. The basic approach is to use
830
``TestCase.applyDeprecated`` which in one step checks that the API gives
831
the expected deprecation message, and also returns the real result from
832
the method, so that tests can keep running.
834
Deprecation warnings will be suppressed for final releases, but not for
835
development versions or release candidates, or when running ``bzr
836
selftest``. This gives developers information about whether their code is
837
using deprecated functions, but avoids confusing users about things they
added
removed
doc/en/developer-guide/HACKING.txt
