1
============================
2
Guidelines for modifying bzr
3
============================
7
(The current version of this document is available in the file ``HACKING``
8
in the source tree, or at http://bazaar-ng.org/hacking.html)
13
* New functionality should have test cases. Preferably write the
14
test before writing the code.
16
In general, you can test at either the command-line level or the
17
internal API level. Choose whichever is appropriate: if adding a
18
new command, or a new command option, then call through run_bzr().
19
It is not necessary to do both. Tests that test the command line level
20
are appropriate for checking the UI behaves well - bug fixes and
21
core improvements should be tested closer to the code that is doing the
22
work. Command line level tests should be placed in 'blackbox.py'.
24
* Before fixing a bug, write a test case so that it does not regress.
26
* Exceptions should be defined inside bzrlib.errors, so that we can
27
see the whole tree at a glance.
29
* Imports should be done at the top-level of the file, unless there is
30
a strong reason to have them lazily loaded when a particular
31
function runs. Import statements have a cost, so try to make sure
32
they don't run inside hot functions.
34
* Module names should always be given fully-qualified,
35
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
37
* Commands should return Non-Zero when they encounter circumstances that
38
the user should really pay attention to - which includes trivial shell
41
Recommanded values are
43
1- Conflicts in merge-like operations, or changes are present in
45
2- Unrepresentable diff changes (i.e. binary files that we cannot show
47
3- An error or exception has occured.
52
If you change the behaviour of an API in an incompatible way, please
53
be sure to change its name as well. For instance, if I add a keyword
54
parameter to branch.commit - that's fine. On the other hand, if I add
55
a keyword parameter to branch.commit which is a *required* transaction
56
object, I should rename the api - i.e. to 'branch.commit_transaction'.
58
This will prevent users of the old api getting surprising results.
59
Instead, they will get an Attribute error as the api is missing, and
60
will know to update their code. If in doubt, just ask on #bzr.
65
If you change the behaviour of a command, please update its docstring
66
in bzrlib/commands.py. This is displayed by the 'bzr help' command.
68
If you make a user-visible change, please add a note to the NEWS file.
69
The description should be written to make sense to someone who's just
70
a user of bzr, not a developer: new functions or classes shouldn't be
71
mentioned, but new commands, changes in behaviour or fixed nontrivial
72
bugs should be listed. See the existing entries for an idea of what
79
Functions, methods, classes and modules should have docstrings
80
describing how they are used.
82
The first line of the docstring should be a self-contained sentence.
84
For the special case of Command classes, this acts as the user-visible
85
documentation shown by the help command.
87
The docstrings should be formatted as reStructuredText_ (like this
88
document), suitable for processing using the epydoc_ tool into HTML
91
.. _reStructuredText: http://docutils.sourceforge.net/rst.html
92
.. _epydoc: http://epydoc.sourceforge.net/
99
Please write PEP-8__ compliant code.
101
One often-missed requirement is that the first line of docstrings
102
should be a self-contained one-sentence summary.
104
__ http://www.python.org/peps/pep-0008.html
111
Functions, methods or members that are in some sense "private" are given
112
a leading underscore prefix. This is just a hint that code outside the
113
implementation should probably not use that interface.
115
We prefer class names to be concatenated capital words (``TestCase``)
116
and variables, methods and functions to be lowercase words joined by
117
underscores (``revision_id``, ``get_revision``).
119
For the purposes of naming some names are treated as single compound
120
words: "filename", "revno".
122
Consider naming classes as nouns and functions/methods as verbs.
128
``revision_id`` not ``rev_id`` or ``revid``
130
Functions that transform one thing to another should be named ``x_to_y``
131
(not ``x2y`` as occurs in some old code.)
137
Python destructors (``__del__``) work rather differently from in other
138
languages. In particular, bear in mind that destructors may not be called
139
immediately when the object apparently becomes unreferenced, and that
140
there are tight restrictions on what can be done inside them.
142
0. Never use a __del__ method without asking Martin/Robert first.
144
1. Never rely on a ``__del__`` method running. If there is code that
145
must run, do it from a ``finally`` block instead.
147
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
150
3. In some places we raise a warning from the destructor if the object
151
has not been cleaned up or closed. This is considered OK: the warning
152
may not catch every case but it's still useful sometimes.
158
(The strategy described here is what we want to get to, but it's not
159
consistently followed in the code at the moment.)
161
bzrlib is intended to be a generically reusable library. It shouldn't
162
write messages to stdout or stderr, because some programs that use it
163
might want to display that information through a GUI or some other
166
We can distinguish two types of output from the library:
168
1. Structured data representing the progress or result of an
169
operation. For example, for a commit command this will be a list
170
of the modified files and the finally committed revision number
173
These should be exposed either through the return code or by calls
174
to a callback parameter.
176
A special case of this is progress indicators for long-lived
177
operations, where the caller should pass a ProgressBar object.
179
2. Unstructured log/debug messages, mostly for the benefit of the
180
developers or users trying to debug problems. This should always
181
be sent through ``bzrlib.trace`` and Python ``logging``, so that
182
it can be redirected by the client.
184
The distinction between the two is a bit subjective, but in general if
185
there is any chance that a library would want to see something as
186
structured data, we should make it so.
188
The policy about how output is presented in the text-mode client
189
should be only in the command-line tool.
194
In general tests should be placed in a file named testFOO.py where
195
FOO is the logical thing under test. That file should be placed in the
196
tests subdirectory under the package being tested.
198
For example, tests for merge3 in bzrlib belong in bzrlib/tests/testmerge3.py.
199
See bzrlib/selftest/testsampler.py for a template test script.
204
Currently, bzr selftest is used to invoke tests.
205
You can provide a pattern argument to run a subset. For example,
206
to run just the whitebox tests, run::
208
bzr selftest -v whitebox
211
Errors and exceptions
212
=====================
214
Errors are handled through Python exceptions. They can represent user
215
errors, environmental errors or program bugs. Sometimes we can't be sure
216
at the time it's raised which case applies. See bzrlib/errors.py for
217
details on the error-handling practices.
224
Integer identifier for a revision on the main line of a branch.
225
Revision 0 is always the null revision; others are 1-based
226
indexes into the branch's revision history.
added
removed
HACKING
