1
1
============================
2
Guidelines for modifying bzr
2
guidelines for modifying bzr
3
3
============================
7
(The current version of this document is available in the file ``HACKING``
8
in the source tree, or at http://bazaar-ng.org/hacking.html)
13
5
* New functionality should have test cases. Preferably write the
14
6
test before writing the code.
16
8
In general, you can test at either the command-line level or the
17
9
internal API level. Choose whichever is appropriate: if adding a
18
10
new command, or a new command option, then call through run_bzr().
19
It is not necessary to do both. Tests that test the command line level
20
are appropriate for checking the UI behaves well - bug fixes and
21
core improvements should be tested closer to the code that is doing the
22
work. Command line level tests should be placed in 'blackbox.py'.
11
It is not necessary to do both.
24
* Try to practice Test-Driven Development. before fixing a bug, write a
25
test case so that it does not regress. Similarly for adding a new
26
feature: write a test case for a small version of the new feature before
27
starting on the code itself. Check the test fails on the old code, then
28
add the feature or fix and check it passes.
13
* Before fixing a bug, write a test case so that it does not regress.
30
15
* Exceptions should be defined inside bzrlib.errors, so that we can
31
16
see the whole tree at a glance.
35
20
function runs. Import statements have a cost, so try to make sure
36
21
they don't run inside hot functions.
23
* Please write PEP-8__ compliant code.
25
__ http://www.python.org/peps/pep-0008.html
38
27
* Module names should always be given fully-qualified,
39
28
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
41
* Commands should return non-zero when they encounter circumstances that
42
the user should really pay attention to - which includes trivial shell
45
Recommended values are
47
1- Conflicts in merge-like operations, or changes are present in
49
2- Unrepresentable diff changes (i.e. binary files that we cannot show
51
3- An error or exception has occurred.
56
We have a commitment to 6 months API stability - any supported symbol in a
57
release of bzr MUST NOT be altered in any way that would result in
58
breaking existing code that uses it. That means that method names,
59
parameter ordering, parameter names, variable and attribute names etc must
60
not be changed without leaving a 'deprecated forwarder' behind. This even
61
applies to modules and classes.
63
If you wish to change the behaviour of a supported API in an incompatible
64
way, you need to change its name as well. For instance, if I add a optional keyword
65
parameter to branch.commit - that's fine. On the other hand, if I add a
66
keyword parameter to branch.commit which is a *required* transaction
67
object, I should rename the API - i.e. to 'branch.commit_transaction'.
69
When renaming such supported API's, be sure to leave a deprecated_method (or
70
_function or ...) behind which forwards to the new API. See the
71
bzrlib.symbol_versioning module for decorators that take care of the
72
details for you - such as updating the docstring, and issuing a warning
73
when the old api is used.
75
For unsupported API's, it does not hurt to follow this discipline, but its
76
not required. Minimally though, please try to rename things so that
77
callers will at least get an AttributeError rather than weird results.
80
Standard parameter types
81
------------------------
83
There are some common requirements in the library: some parameters need to be
84
unicode safe, some need byte strings, and so on. At the moment we have
85
only codified one specific pattern: Parameters that need to be unicode
86
should be check via 'bzrlib.osutils.safe_unicode'. This will coerce the
87
input into unicode in a consistent fashion, allowing trivial strings to be
88
used for programmer convenience, but not performing unpredictably in the
89
presence of different locales.
94
35
If you change the behaviour of a command, please update its docstring
95
36
in bzrlib/commands.py. This is displayed by the 'bzr help' command.
100
38
If you make a user-visible change, please add a note to the NEWS file.
101
39
The description should be written to make sense to someone who's just
102
40
a user of bzr, not a developer: new functions or classes shouldn't be
103
41
mentioned, but new commands, changes in behaviour or fixed nontrivial
104
42
bugs should be listed. See the existing entries for an idea of what
107
Within each release, entries in the news file should have the most
108
user-visible changes first. So the order should be approximately:
110
* changes to existing behaviour - the highest priority because the
111
user's existing knowledge is incorrect
112
* new features - should be brought to their attention
113
* bug fixes - may be of interest if the bug was affecting them, and
114
should include the bug number if any
115
* major documentation changes
116
* changes to internal interfaces
118
People who made significant contributions to each change are listed in
119
parenthesis. This can include reporting bugs (particularly with good
120
details or reproduction recipes), submitting patches, etc.
125
Functions, methods, classes and modules should have docstrings
126
describing how they are used.
128
The first line of the docstring should be a self-contained sentence.
130
For the special case of Command classes, this acts as the user-visible
131
documentation shown by the help command.
133
The docstrings should be formatted as reStructuredText_ (like this
134
document), suitable for processing using the epydoc_ tool into HTML
137
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
138
.. _epydoc: http://epydoc.sourceforge.net/
145
Please write PEP-8__ compliant code.
147
One often-missed requirement is that the first line of docstrings
148
should be a self-contained one-sentence summary.
150
__ http://www.python.org/peps/pep-0008.html
157
Functions, methods or members that are in some sense "private" are given
158
a leading underscore prefix. This is just a hint that code outside the
159
implementation should probably not use that interface.
161
We prefer class names to be concatenated capital words (``TestCase``)
162
and variables, methods and functions to be lowercase words joined by
163
underscores (``revision_id``, ``get_revision``).
165
For the purposes of naming some names are treated as single compound
166
words: "filename", "revno".
168
Consider naming classes as nouns and functions/methods as verbs.
174
``revision_id`` not ``rev_id`` or ``revid``
176
Functions that transform one thing to another should be named ``x_to_y``
177
(not ``x2y`` as occurs in some old code.)
183
Python destructors (``__del__``) work differently to those of other
184
languages. In particular, bear in mind that destructors may be called
185
immediately when the object apparently becomes unreferenced, or at some
186
later time, or possibly never at all. Therefore we have restrictions on
187
what can be done inside them.
189
0. Never use a __del__ method without asking Martin/Robert first.
191
1. Never rely on a ``__del__`` method running. If there is code that
192
must run, do it from a ``finally`` block instead.
194
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
197
3. In some places we raise a warning from the destructor if the object
198
has not been cleaned up or closed. This is considered OK: the warning
199
may not catch every case but it's still useful sometimes.
205
(The strategy described here is what we want to get to, but it's not
206
consistently followed in the code at the moment.)
208
bzrlib is intended to be a generically reusable library. It shouldn't
209
write messages to stdout or stderr, because some programs that use it
210
might want to display that information through a GUI or some other
213
We can distinguish two types of output from the library:
215
1. Structured data representing the progress or result of an
216
operation. For example, for a commit command this will be a list
217
of the modified files and the finally committed revision number
220
These should be exposed either through the return code or by calls
221
to a callback parameter.
223
A special case of this is progress indicators for long-lived
224
operations, where the caller should pass a ProgressBar object.
226
2. Unstructured log/debug messages, mostly for the benefit of the
227
developers or users trying to debug problems. This should always
228
be sent through ``bzrlib.trace`` and Python ``logging``, so that
229
it can be redirected by the client.
231
The distinction between the two is a bit subjective, but in general if
232
there is any chance that a library would want to see something as
233
structured data, we should make it so.
235
The policy about how output is presented in the text-mode client
236
should be only in the command-line tool.
241
In general tests should be placed in a file named testFOO.py where
242
FOO is the logical thing under test. That file should be placed in the
243
tests subdirectory under the package being tested.
245
For example, tests for merge3 in bzrlib belong in bzrlib/tests/testmerge3.py.
246
See bzrlib/selftest/testsampler.py for a template test script.
251
Currently, bzr selftest is used to invoke tests.
252
You can provide a pattern argument to run a subset. For example,
253
to run just the whitebox tests, run::
255
bzr selftest -v whitebox
258
Errors and exceptions
259
=====================
261
Errors are handled through Python exceptions. They can represent user
262
errors, environmental errors or program bugs. Sometimes we can't be sure
263
at the time it's raised which case applies. See bzrlib/errors.py for
264
details on the error-handling practices.
271
Integer identifier for a revision on the main line of a branch.
272
Revision 0 is always the null revision; others are 1-based
273
indexes into the branch's revision history.
279
If you'd like to propose a change, please post to the
280
bazaar-ng@lists.canonical.com list with a patch, bzr changeset, or link to a
281
branch. Please put '[patch]' in the subject so we can pick them out, and
282
include some text explaining the change. Remember to put an update to the NEWS
283
file in your diff, if it makes any changes visible to users or plugin
284
developers. Please include a diff against mainline if you're giving a link to
287
Please indicate if you think the code is ready to merge, or if it's just a
288
draft or for discussion. If you want comments from many developers rather than
289
to be merged, you can put '[rfc]' in the subject lines.
291
Anyone is welcome to review code. There are broadly three gates for
294
* Doesn't reduce test coverage: if it adds new methods or commands,
295
there should be tests for them. There is a good test framework
296
and plenty of examples to crib from, but if you are having trouble
297
working out how to test something feel free to post a draft patch
300
* Doesn't reduce design clarity, such as by entangling objects
301
we're trying to separate. This is mostly something the more
302
experienced reviewers need to help check.
304
* Improves bugs, features, speed, or code simplicity.
306
Code that goes in should pass all three.
308
If you read a patch please reply and say so. We can use a numeric scale
309
of -1, -0, +0, +1, meaning respectively "really don't want it in current
310
form", "somewhat uncomfortable", "ok with me", and "please put it in".
311
Anyone can "vote". (It's not really voting, just a terse expression.)
313
If something gets say two +1 votes from core reviewers, and no
314
vetos, then it's OK to come in. Any of the core developers can bring it
315
into their integration branch, which I'll merge regularly. (If you do
316
so, please reply and say so.)
added
removed
HACKING
