7
(The current version of this document is available in the file ``HACKING``
8
in the source tree, or at http://doc.bazaar-vcs.org/bzr.dev/hacking.html)
14
Exploring the Bazaar Platform
15
=============================
17
Before making changes, it's a good idea to explore the work already
18
done by others. Perhaps the new feature or improvement you're looking
19
for is available in another plug-in already? If you find a bug,
20
perhaps someone else has already fixed it?
22
To answer these questions and more, take a moment to explore the
23
overall Bazaar Platform. Here are some links to browse:
25
* The Plugins page on the Wiki - http://bazaar-vcs.org/BzrPlugins
27
* The Bazaar product family on Launchpad - https://launchpad.net/bazaar
29
* Bug Tracker for the core product - https://bugs.launchpad.net/bzr/
31
* Blueprint Tracker for the core product - https://blueprints.launchpad.net/bzr/
33
If nothing else, perhaps you'll find inspiration in how other developers
34
have solved their challenges.
37
Planning and Discussing Changes
38
===============================
40
There is a very active community around Bazaar. Mostly we meet on IRC
41
(#bzr on irc.freenode.net) and on the mailing list. To join the Bazaar
42
community, see http://bazaar-vcs.org/BzrSupport.
44
If you are planning to make a change, it's a very good idea to mention it
45
on the IRC channel and/or on the mailing list. There are many advantages
46
to involving the community before you spend much time on a change.
49
* you get to build on the wisdom on others, saving time
51
* if others can direct you to similar code, it minimises the work to be done
53
* it assists everyone in coordinating direction, priorities and effort.
55
In summary, maximising the input from others typically minimises the
56
total effort required to get your changes merged. The community is
57
friendly, helpful and always keen to welcome newcomers.
60
Bazaar Development in a Nutshell
61
================================
63
Looking for a 10 minute introduction to submitting a change?
64
See http://bazaar-vcs.org/BzrGivingBack.
66
TODO: Merge that Wiki page into this document.
69
Understanding the Development Process
70
=====================================
72
The development team follows many best-practices including:
74
* a public roadmap and planning process in which anyone can participate
76
* time based milestones everyone can work towards and plan around
78
* extensive code review and feedback to contributors
80
* complete and rigorous test coverage on any code contributed
82
* automated validation that all tests still pass before code is merged
83
into the main code branch.
85
The key tools we use to enable these practices are:
87
* Launchpad - https://launchpad.net/
89
* Bazaar - http://bazaar-vcs.org/
91
* Bundle Buggy - http://bundlebuggy.aaronbentley.com/
93
* Patch Queue Manager - https://launchpad.net/pqm/
95
For further information, see http://bazaar-vcs.org/BzrDevelopment.
98
A Closer Look at the Merge & Review Process
99
===========================================
101
If you'd like to propose a change, please post to the
102
bazaar@lists.canonical.com list with a bundle, patch, or link to a
103
branch. Put '[PATCH]' or '[MERGE]' in the subject so Bundle Buggy
104
can pick it out, and explain the change in the email message text.
105
Remember to update the NEWS file as part of your change if it makes any
106
changes visible to users or plugin developers. Please include a diff
107
against mainline if you're giving a link to a branch.
109
You can generate a bundle like this::
111
bzr bundle > mybundle.patch
113
A .patch extension is recommended instead of .bundle as many mail clients
114
will send the latter as a binary file. If a bundle would be too long or your
115
mailer mangles whitespace (e.g. implicitly converts Unix newlines to DOS
116
newlines), use the merge-directive command instead like this::
118
bzr merge-directive http://bazaar-vcs.org http://example.org/my_branch > my_directive.patch
120
See the help for details on the arguments to merge-directive.
122
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
123
want it to be merged. If you want comments from developers rather than
124
to be merged, you can put '[RFC]' in the subject line.
126
Anyone is welcome to review code. There are broadly three gates for
129
* Doesn't reduce test coverage: if it adds new methods or commands,
130
there should be tests for them. There is a good test framework
131
and plenty of examples to crib from, but if you are having trouble
132
working out how to test something feel free to post a draft patch
135
* Doesn't reduce design clarity, such as by entangling objects
136
we're trying to separate. This is mostly something the more
137
experienced reviewers need to help check.
139
* Improves bugs, features, speed, or code simplicity.
141
Code that goes in should pass all three. The core developers take care
142
to keep the code quality high and understandable while recognising that
143
perfect is sometimes the enemy of good. (It is easy for reviews to make
144
people notice other things which should be fixed but those things should
145
not hold up the original fix being accepted. New things can easily be
146
recorded in the Bug Tracker instead.)
148
Anyone can "vote" on the mailing list. Core developers can also vote using
149
Bundle Buggy. Here are the voting codes and their explanations.
151
-1 really don't want it in current form
152
-0 somewhat uncomfortable
153
+0 comfortable but resubmission after changes requested
154
+1 conditional good to go after some minor changes
157
+1 conditional is used as a way to avoid another submit/review cycle for
158
patches that need small changes.
160
If a change gets two +1 votes from core reviewers, and no
161
vetos, then it's OK to come in. Any of the core developers can bring it
162
into the bzr.dev trunk and backport it to maintenance branches if required.
163
The 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.
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
188
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)
193
* 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
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 list tests without running them, use the --list-only option like so::
266
./bzr selftest --list-only
268
This option can be combined with other selftest options (like -x) and
269
filter patterns to understand their effect.
275
In general tests should be placed in a file named test_FOO.py where
276
FOO is the logical thing under test. That file should be placed in the
277
tests subdirectory under the package being tested.
279
For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
280
See bzrlib/tests/test_sampler.py for a template test script.
282
Tests can be written for the UI or for individual areas of the library.
283
Choose whichever is appropriate: if adding a new command, or a new command
284
option, then you should be writing a UI test. If you are both adding UI
285
functionality and library functionality, you will want to write tests for
286
both the UI and the core behaviours. We call UI tests 'blackbox' tests
287
and they are found in ``bzrlib/tests/blackbox/*.py``.
289
When writing blackbox tests please honour the following conventions:
291
1. Place the tests for the command 'name' in
292
bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
293
to locate the test script for a faulty command.
295
2. Use the 'self.run_bzr("name")' utility function to invoke the command
296
rather than running bzr in a subprocess or invoking the
297
cmd_object.run() method directly. This is a lot faster than
298
subprocesses and generates the same logging output as running it in a
299
subprocess (which invoking the method directly does not).
301
3. Only test the one command in a single test script. Use the bzrlib
302
library when setting up tests and when evaluating the side-effects of
303
the command. We do this so that the library api has continual pressure
304
on it to be as functional as the command line in a simple manner, and
305
to isolate knock-on effects throughout the blackbox test suite when a
306
command changes its name or signature. Ideally only the tests for a
307
given command are affected when a given command is changed.
309
4. If you have a test which does actually require running bzr in a
310
subprocess you can use ``run_bzr_subprocess``. By default the spawned
311
process will not load plugins unless ``--allow-plugins`` is supplied.
317
We make selective use of doctests__. In general they should provide
318
*examples* within the API documentation which can incidentally be tested. We
319
don't try to test every important case using doctests -- regular Python
320
tests are generally a better solution.
322
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
324
__ http://docs.python.org/lib/module-doctest.html
327
Skipping tests and test requirements
328
------------------------------------
330
In our enhancements to unittest we allow for some addition results beyond
331
just success or failure.
333
If a test can't be run, it can say that it's skipped. This is typically
334
used in parameterized tests - for example if a transport doesn't support
335
setting permissions, we'll skip the tests that relating to that. ::
338
return self.branch_format.initialize(repo.bzrdir)
339
except errors.UninitializableFormat:
340
raise tests.TestSkipped('Uninitializable branch format')
342
Raising TestSkipped is a good idea when you want to make it clear that the
343
test was not run, rather than just returning which makes it look as if it
346
A subtly different case is a test that should run, but can't run in the
347
current environment. This covers tests that can only run in particular
348
operating systems or locales, or that depend on external libraries. Here
349
we want to inform the user that they didn't get full test coverage, but
350
they possibly could if they installed more libraries. These are expressed
351
as a dependency on a feature so we can summarise them, and so that the
352
test for the feature is done only once. (For historical reasons, as of
353
May 2007 many cases that should depend on features currently raise
354
TestSkipped.) The typical use is::
356
class TestStrace(TestCaseWithTransport):
358
_test_needs_features = [StraceFeature]
360
which means all tests in this class need the feature. The feature itself
361
should provide a ``_probe`` method which is called once to determine if
368
Known failures are when a test exists but we know it currently doesn't
369
work, allowing the test suite to still pass. These should be used with
370
care, we don't want a proliferation of quietly broken tests. It might be
371
appropriate to use them if you've committed a test for a bug but not the
372
fix for it, or if something works on Unix but not on Windows.
376
Essential Domain Classes
377
########################
379
Introducing the Object Model
380
============================
382
The core domain objects within the bazaar model are:
392
Transports are explained below. See http://bazaar-vcs.org/Classes/
393
for an introduction to the other key classes.
398
The ``Transport`` layer handles access to local or remote directories.
399
Each Transport object acts like a logical connection to a particular
400
directory, and it allows various operations on files within it. You can
401
*clone* a transport to get a new Transport connected to a subdirectory or
404
Transports are not used for access to the working tree. At present
405
working trees are always local and they are accessed through the regular
406
Python file io mechanisms.
411
Transports work in URLs. Take note that URLs are by definition only
412
ASCII - the decision of how to encode a Unicode string into a URL must be
413
taken at a higher level, typically in the Store. (Note that Stores also
414
escape filenames which cannot be safely stored on all filesystems, but
415
this is a different level.)
417
The main reason for this is that it's not possible to safely roundtrip a
418
URL into Unicode and then back into the same URL. The URL standard
419
gives a way to represent non-ASCII bytes in ASCII (as %-escapes), but
420
doesn't say how those bytes represent non-ASCII characters. (They're not
421
guaranteed to be UTF-8 -- that is common but doesn't happen everywhere.)
423
For example if the user enters the url ``http://example/%e0`` there's no
424
way to tell whether that character represents "latin small letter a with
425
grave" in iso-8859-1, or "latin small letter r with acute" in iso-8859-2
426
or malformed UTF-8. So we can't convert their URL to Unicode reliably.
428
Equally problematic if we're given a url-like string containing non-ascii
429
characters (such as the accented a) we can't be sure how to convert that
430
to the correct URL, because we don't know what encoding the server expects
431
for those characters. (Although this is not totally reliable we might still
432
accept these and assume they should be put into UTF-8.)
434
A similar edge case is that the url ``http://foo/sweet%2Fsour`` contains
435
one directory component whose name is "sweet/sour". The escaped slash is
436
not a directory separator. If we try to convert URLs to regular Unicode
437
paths this information will be lost.
439
This implies that Transports must natively deal with URLs; for simplicity
440
they *only* deal with URLs and conversion of other strings to URLs is done
441
elsewhere. Information they return, such as from ``list_dir``, is also in
442
the form of URL components.
451
We have a commitment to 6 months API stability - any supported symbol in a
452
release of bzr MUST NOT be altered in any way that would result in
453
breaking existing code that uses it. That means that method names,
454
parameter ordering, parameter names, variable and attribute names etc must
455
not be changed without leaving a 'deprecated forwarder' behind. This even
456
applies to modules and classes.
458
If you wish to change the behaviour of a supported API in an incompatible
459
way, you need to change its name as well. For instance, if I add an optional keyword
460
parameter to branch.commit - that's fine. On the other hand, if I add a
461
keyword parameter to branch.commit which is a *required* transaction
462
object, I should rename the API - i.e. to 'branch.commit_transaction'.
464
When renaming such supported API's, be sure to leave a deprecated_method (or
465
_function or ...) behind which forwards to the new API. See the
466
bzrlib.symbol_versioning module for decorators that take care of the
467
details for you - such as updating the docstring, and issuing a warning
468
when the old api is used.
470
For unsupported API's, it does not hurt to follow this discipline, but it's
471
not required. Minimally though, please try to rename things so that
472
callers will at least get an AttributeError rather than weird results.
475
Coding Style Guidelines
476
=======================
478
Please write PEP-8__ compliant code.
480
One often-missed requirement is that the first line of docstrings
481
should be a self-contained one-sentence summary.
483
__ http://www.python.org/peps/pep-0008.html
489
* Imports should be done at the top-level of the file, unless there is
490
a strong reason to have them lazily loaded when a particular
491
function runs. Import statements have a cost, so try to make sure
492
they don't run inside hot functions.
494
* Module names should always be given fully-qualified,
495
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
501
Functions, methods or members that are in some sense "private" are given
502
a leading underscore prefix. This is just a hint that code outside the
503
implementation should probably not use that interface.
505
We prefer class names to be concatenated capital words (``TestCase``)
506
and variables, methods and functions to be lowercase words joined by
507
underscores (``revision_id``, ``get_revision``).
509
For the purposes of naming some names are treated as single compound
510
words: "filename", "revno".
512
Consider naming classes as nouns and functions/methods as verbs.
514
Try to avoid using abbreviations in names, because there can be
515
inconsistency if other people use the full name.
521
``revision_id`` not ``rev_id`` or ``revid``
523
Functions that transform one thing to another should be named ``x_to_y``
524
(not ``x2y`` as occurs in some old code.)
530
Python destructors (``__del__``) work differently to those of other
531
languages. In particular, bear in mind that destructors may be called
532
immediately when the object apparently becomes unreferenced, or at some
533
later time, or possibly never at all. Therefore we have restrictions on
534
what can be done inside them.
536
0. Never use a __del__ method without asking Martin/Robert first.
538
1. Never rely on a ``__del__`` method running. If there is code that
539
must run, do it from a ``finally`` block instead.
541
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
544
3. In some places we raise a warning from the destructor if the object
545
has not been cleaned up or closed. This is considered OK: the warning
546
may not catch every case but it's still useful sometimes.
552
In some places we have variables which point to callables that construct
553
new instances. That is to say, they can be used a lot like class objects,
554
but they shouldn't be *named* like classes:
556
> I think that things named FooBar should create instances of FooBar when
557
> called. Its plain confusing for them to do otherwise. When we have
558
> something that is going to be used as a class - that is, checked for via
559
> isinstance or other such idioms, them I would call it foo_class, so that
560
> it is clear that a callable is not sufficient. If it is only used as a
561
> factory, then yes, foo_factory is what I would use.
567
Several places in Bazaar use (or will use) a registry, which is a
568
mapping from names to objects or classes. The registry allows for
569
loading in registered code only when it's needed, and keeping
570
associated information such as a help string or description.
576
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
577
delay importing modules until they are actually used. ``lazy_import`` uses
578
the same syntax as regular python imports. So to import a few modules in a
581
from bzrlib.lazy_import import lazy_import
582
lazy_import(globals(), """
591
revision as _mod_revision,
593
import bzrlib.transport
597
At this point, all of these exist as a ``ImportReplacer`` object, ready to
598
be imported once a member is accessed. Also, when importing a module into
599
the local namespace, which is likely to clash with variable names, it is
600
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
601
the variable is a module, and these object should be hidden anyway, since
602
they shouldn't be imported into other namespaces.
605
Modules versus Members
606
~~~~~~~~~~~~~~~~~~~~~~
608
While it is possible for ``lazy_import()`` to import members of a module
609
when using the ``from module import member`` syntax, it is recommended to
610
only use that syntax to load sub modules ``from module import submodule``.
611
This is because variables and classes can frequently be used without
612
needing a sub-member for example::
614
lazy_import(globals(), """
615
from module import MyClass
619
return isinstance(x, MyClass)
621
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
622
object, rather than the real class.
625
Passing to Other Variables
626
~~~~~~~~~~~~~~~~~~~~~~~~~~
628
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
629
Because the replacer only knows about the original name, it is unable to
630
replace other variables. The ``ImportReplacer`` class will raise an
631
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
632
happened. But it requires accessing a member more than once from the new
633
variable, so some bugs are not detected right away.
639
Processing Command Lines
640
------------------------
642
bzrlib has a standard framework for parsing command lines and calling
643
processing routines associated with various commands. See builtins.py
644
for numerous examples.
647
Standard Parameter Types
648
------------------------
650
There are some common requirements in the library: some parameters need to be
651
unicode safe, some need byte strings, and so on. At the moment we have
652
only codified one specific pattern: Parameters that need to be unicode
653
should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
654
input into unicode in a consistent fashion, allowing trivial strings to be
655
used for programmer convenience, but not performing unpredictably in the
656
presence of different locales.
662
(The strategy described here is what we want to get to, but it's not
663
consistently followed in the code at the moment.)
665
bzrlib is intended to be a generically reusable library. It shouldn't
666
write messages to stdout or stderr, because some programs that use it
667
might want to display that information through a GUI or some other
670
We can distinguish two types of output from the library:
672
1. Structured data representing the progress or result of an
673
operation. For example, for a commit command this will be a list
674
of the modified files and the finally committed revision number
677
These should be exposed either through the return code or by calls
678
to a callback parameter.
680
A special case of this is progress indicators for long-lived
681
operations, where the caller should pass a ProgressBar object.
683
2. Unstructured log/debug messages, mostly for the benefit of the
684
developers or users trying to debug problems. This should always
685
be sent through ``bzrlib.trace`` and Python ``logging``, so that
686
it can be redirected by the client.
688
The distinction between the two is a bit subjective, but in general if
689
there is any chance that a library would want to see something as
690
structured data, we should make it so.
692
The policy about how output is presented in the text-mode client
693
should be only in the command-line tool.
699
In general tests should be placed in a file named test_FOO.py where
700
FOO is the logical thing under test. That file should be placed in the
701
tests subdirectory under the package being tested.
703
For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
704
See bzrlib/tests/test_sampler.py for a template test script.
706
Tests can be written for the UI or for individual areas of the library.
707
Choose whichever is appropriate: if adding a new command, or a new command
708
option, then you should be writing a UI test. If you are both adding UI
709
functionality and library functionality, you will want to write tests for
710
both the UI and the core behaviours. We call UI tests 'blackbox' tests
711
and they are found in ``bzrlib/tests/blackbox/*.py``.
713
When writing blackbox tests please honour the following conventions:
715
1. Place the tests for the command 'name' in
716
bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
717
to locate the test script for a faulty command.
719
2. Use the 'self.run_bzr("name")' utility function to invoke the command
720
rather than running bzr in a subprocess or invoking the
721
cmd_object.run() method directly. This is a lot faster than
722
subprocesses and generates the same logging output as running it in a
723
subprocess (which invoking the method directly does not).
725
3. Only test the one command in a single test script. Use the bzrlib
726
library when setting up tests and when evaluating the side-effects of
727
the command. We do this so that the library api has continual pressure
728
on it to be as functional as the command line in a simple manner, and
729
to isolate knock-on effects throughout the blackbox test suite when a
730
command changes its name or signature. Ideally only the tests for a
731
given command are affected when a given command is changed.
733
4. If you have a test which does actually require running bzr in a
734
subprocess you can use ``run_bzr_subprocess``. By default the spawned
735
process will not load plugins unless ``--allow-plugins`` is supplied.
741
We have a rich collection of tools to support writing tests. Please use
742
them in preference to ad-hoc solutions as they provide portability and
743
performance benefits.
748
The ``TreeBuilder`` interface allows the construction of arbitrary trees
749
with a declarative interface. A sample session might look like::
751
tree = self.make_branch_and_tree('path')
752
builder = TreeBuilder()
753
builder.start_tree(tree)
754
builder.build(['foo', "bar/", "bar/file"])
755
tree.commit('commit the tree')
756
builder.finish_tree()
758
Please see bzrlib.treebuilder for more details.
763
The ``BranchBuilder`` interface allows the creation of test branches in a
764
quick and easy manner. A sample session::
766
builder = BranchBuilder(self.get_transport().clone('relpath'))
767
builder.build_commit()
768
builder.build_commit()
769
builder.build_commit()
770
branch = builder.get_branch()
772
Please see bzrlib.branchbuilder for more details.
777
We make selective use of doctests__. In general they should provide
778
*examples* within the API documentation which can incidentally be tested. We
779
don't try to test every important case using doctests -- regular Python
780
tests are generally a better solution.
782
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
784
__ http://docs.python.org/lib/module-doctest.html
789
Currently, bzr selftest is used to invoke tests.
790
You can provide a pattern argument to run a subset. For example,
791
to run just the blackbox tests, run::
793
./bzr selftest -v blackbox
795
To skip a particular test (or set of tests), use the --exclude option
796
(shorthand -x) like so::
798
./bzr selftest -v -x blackbox
800
To list tests without running them, use the --list-only option like so::
802
./bzr selftest --list-only
804
This option can be combined with other selftest options (like -x) and
805
filter patterns to understand their effect.
808
Handling Errors and Exceptions
809
==============================
811
Commands should return non-zero when they encounter circumstances that
812
the user should really pay attention to - which includes trivial shell
815
Recommended values are:
818
1. Conflicts in merge-like operations, or changes are present in
819
diff-like operations.
820
2. Unrepresentable diff changes (i.e. binary files that we cannot show
822
3. An error or exception has occurred.
824
Errors are handled through Python exceptions. Exceptions should be defined
825
inside bzrlib.errors, so that we can see the whole tree at a glance.
827
We broadly classify errors as either being either internal or not,
828
depending on whether ``internal_error`` is set or not. If we think it's our
829
fault, we show a backtrace, an invitation to report the bug, and possibly
830
other details. This is the default for errors that aren't specifically
831
recognized as being caused by a user error. Otherwise we show a briefer
832
message, unless -Derror was given.
834
Many errors originate as "environmental errors" which are raised by Python
835
or builtin libraries -- for example IOError. These are treated as being
836
our fault, unless they're caught in a particular tight scope where we know
837
that they indicate a user errors. For example if the repository format
838
is not found, the user probably gave the wrong path or URL. But if one of
839
the files inside the repository is not found, then it's our fault --
840
either there's a bug in bzr, or something complicated has gone wrong in
841
the environment that means one internal file was deleted.
843
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
844
to be added near the place where they are used.
846
Exceptions are formatted for the user by conversion to a string
847
(eventually calling their ``__str__`` method.) As a convenience the
848
``._fmt`` member can be used as a template which will be mapped to the
849
error's instance dict.
851
New exception classes should be defined when callers might want to catch
852
that exception specifically, or when it needs a substantially different
855
Exception strings should start with a capital letter and should not have a
856
final fullstop. If long, they may contain newlines to break the text.
862
When you change bzrlib, please update the relevant documentation for the
863
change you made: Changes to commands should update their help, and
864
possibly end user tutorials; changes to the core library should be
865
reflected in API documentation.
870
If you make a user-visible change, please add a note to the NEWS file.
871
The description should be written to make sense to someone who's just
872
a user of bzr, not a developer: new functions or classes shouldn't be
873
mentioned, but new commands, changes in behaviour or fixed nontrivial
874
bugs should be listed. See the existing entries for an idea of what
877
Within each release, entries in the news file should have the most
878
user-visible changes first. So the order should be approximately:
880
* changes to existing behaviour - the highest priority because the
881
user's existing knowledge is incorrect
882
* new features - should be brought to their attention
883
* bug fixes - may be of interest if the bug was affecting them, and
884
should include the bug number if any
885
* major documentation changes
886
* changes to internal interfaces
888
People who made significant contributions to each change are listed in
889
parenthesis. This can include reporting bugs (particularly with good
890
details or reproduction recipes), submitting patches, etc.
895
The docstring of a command is used by ``bzr help`` to generate help output
896
for the command. The list 'takes_options' attribute on a command is used by
897
``bzr help`` to document the options for the command - the command
898
docstring does not need to document them. Finally, the '_see_also'
899
attribute on a command can be used to reference other related help topics.
904
Functions, methods, classes and modules should have docstrings
905
describing how they are used.
907
The first line of the docstring should be a self-contained sentence.
909
For the special case of Command classes, this acts as the user-visible
910
documentation shown by the help command.
912
The docstrings should be formatted as reStructuredText_ (like this
913
document), suitable for processing using the epydoc_ tool into HTML
916
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
917
.. _epydoc: http://epydoc.sourceforge.net/
926
The copyright policy for bzr was recently made clear in this email (edited
927
for grammatical correctness)::
929
The attached patch cleans up the copyright and license statements in
930
the bzr source. It also adds tests to help us remember to add them
931
with the correct text.
933
We had the problem that lots of our files were "Copyright Canonical
934
Development Ltd" which is not a real company, and some other variations
935
on this theme. Also, some files were missing the GPL statements.
937
I want to be clear about the intent of this patch, since copyright can
938
be a little controversial.
940
1) The big motivation for this is not to shut out the community, but
941
just to clean up all of the invalid copyright statements.
943
2) It has been the general policy for bzr that we want a single
944
copyright holder for all of the core code. This is following the model
945
set by the FSF, which makes it easier to update the code to a new
946
license in case problems are encountered. (For example, if we want to
947
upgrade the project universally to GPL v3 it is much simpler if there is
948
a single copyright holder). It also makes it clearer if copyright is
949
ever debated, there is a single holder, which makes it easier to defend
950
in court, etc. (I think the FSF position is that if you assign them
951
copyright, they can defend it in court rather than you needing to, and
952
I'm sure Canonical would do the same).
953
As such, Canonical has requested copyright assignments from all of the
956
3) If someone wants to add code and not attribute it to Canonical, there
957
is a specific list of files that are excluded from this check. And the
958
test failure indicates where that is, and how to update it.
960
4) If anyone feels that I changed a copyright statement incorrectly, just
961
let me know, and I'll be happy to correct it. Whenever you have large
962
mechanical changes like this, it is possible to make some mistakes.
964
Just to reiterate, this is a community project, and it is meant to stay
965
that way. Core bzr code is copyright Canonical for legal reasons, and
966
the tests are just there to help us maintain that.
975
Bazaar has a few facilities to help debug problems by going into pdb_, the
978
.. _pdb: http://docs.python.org/lib/debugger-commands.html
980
If the ``BZR_PDB`` environment variable is set
981
then bzr will go into pdb post-mortem mode when an unhandled exception
984
If you send a SIGQUIT signal to bzr, which can be done by pressing
985
Ctrl-\\ on Unix, bzr will go into the debugger immediately. You can
986
continue execution by typing ``c``. This can be disabled if necessary
987
by setting the environment variable ``BZR_SIGQUIT_PDB=0``.
994
Integer identifier for a revision on the main line of a branch.
995
Revision 0 is always the null revision; others are 1-based
996
indexes into the branch's revision history.
999
Unicode and Encoding Support
1000
============================
1002
This section discusses various techniques that Bazaar uses to handle
1003
characters that are outside the ASCII set.
1008
When a ``Command`` object is created, it is given a member variable
1009
accessible by ``self.outf``. This is a file-like object, which is bound to
1010
``sys.stdout``, and should be used to write information to the screen,
1011
rather than directly writing to ``sys.stdout`` or calling ``print``.
1012
This file has the ability to translate Unicode objects into the correct
1013
representation, based on the console encoding. Also, the class attribute
1014
``encoding_type`` will effect how unprintable characters will be
1015
handled. This parameter can take one of 3 values:
1018
Unprintable characters will be represented with a suitable replacement
1019
marker (typically '?'), and no exception will be raised. This is for
1020
any command which generates text for the user to review, rather than
1021
for automated processing.
1022
For example: ``bzr log`` should not fail if one of the entries has text
1023
that cannot be displayed.
1026
Attempting to print an unprintable character will cause a UnicodeError.
1027
This is for commands that are intended more as scripting support, rather
1028
than plain user review.
1029
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
1030
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
1031
printed a filename with a '?', the wrong file could be deleted. (At the
1032
very least, the correct file would not be deleted). An error is used to
1033
indicate that the requested action could not be performed.
1036
Do not attempt to automatically convert Unicode strings. This is used
1037
for commands that must handle conversion themselves.
1038
For example: ``bzr diff`` needs to translate Unicode paths, but should
1039
not change the exact text of the contents of the files.
1042
``bzrlib.urlutils.unescape_for_display``
1043
----------------------------------------
1045
Because Transports work in URLs (as defined earlier), printing the raw URL
1046
to the user is usually less than optimal. Characters outside the standard
1047
set are printed as escapes, rather than the real character, and local
1048
paths would be printed as ``file://`` urls. The function
1049
``unescape_for_display`` attempts to unescape a URL, such that anything
1050
that cannot be printed in the current encoding stays an escaped URL, but
1051
valid characters are generated where possible.
1057
The ``bzrlib.osutils`` module has many useful helper functions, including
1058
some more portable variants of functions in the standard library.
1060
In particular, don't use ``shutil.rmtree`` unless it's acceptable for it
1061
to fail on Windows if some files are readonly or still open elsewhere.
1062
Use ``bzrlib.osutils.rmtree`` instead.
1068
We write some extensions in C using pyrex. We design these to work in
1071
* User with no C compiler
1072
* User with C compiler
1075
The recommended way to install bzr is to have a C compiler so that the
1076
extensions can be built, but if no C compiler is present, the pure python
1077
versions we supply will work, though more slowly.
1079
For developers we recommend that pyrex be installed, so that the C
1080
extensions can be changed if needed.
1082
For the C extensions, the extension module should always match the
1083
original python one in all respects (modulo speed). This should be
1084
maintained over time.
1086
To create an extension, add rules to setup.py for building it with pyrex,
1087
and with distutils. Now start with an empty .pyx file. At the top add
1088
"include 'yourmodule.py'". This will import the contents of foo.py into this
1089
file at build time - remember that only one module will be loaded at
1090
runtime. Now you can subclass classes, or replace functions, and only your
1091
changes need to be present in the .pyx file.
1093
Note that pyrex does not support all 2.4 programming idioms, so some
1094
syntax changes may be required. I.e.
1096
- 'from foo import (bar, gam)' needs to change to not use the brackets.
1097
- 'import foo.bar as bar' needs to be 'import foo.bar; bar = foo.bar'
1099
If the changes are too dramatic, consider
1100
maintaining the python code twice - once in the .pyx, and once in the .py,
1101
and no longer including the .py file.
1104
Making Installers for OS Windows
1105
================================
1106
To build a win32 installer, see the instructions on the wiki page:
1107
http://bazaar-vcs.org/BzrWin32Installer
1111
vim: ft=rst tw=74 ai
added
removed
doc/developers/HACKING
