~bzr-pqm/bzr/bzr.dev

974.1.26 by aaron.bentley at utoronto
merged mbp@sourcefrog.net-20050817233101-0939da1cf91f2472
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1393.1.53 by Martin Pool
- notes from coding-convention discussion
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Guidelines for modifying bzr
974.1.26 by aaron.bentley at utoronto
merged mbp@sourcefrog.net-20050817233101-0939da1cf91f2472
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============================
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1393.1.53 by Martin Pool
- notes from coding-convention discussion
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.. contents::
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(The current version of this document is available in the file ``HACKING``
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in the source tree, or at http://bazaar-ng.org/hacking.html)
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Overall
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=======
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974.1.26 by aaron.bentley at utoronto
merged mbp@sourcefrog.net-20050817233101-0939da1cf91f2472
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* New functionality should have test cases.  Preferably write the
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  test before writing the code.
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  In general, you can test at either the command-line level or the
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  internal API level.  Choose whichever is appropriate: if adding a
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  new command, or a new command option, then call through run_bzr().
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  It is not necessary to do both. Tests that test the command line level
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  are appropriate for checking the UI behaves well - bug fixes and
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  core improvements should be tested closer to the code that is doing the
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  work. Command line level tests should be placed in 'blackbox.py'.
974.1.26 by aaron.bentley at utoronto
merged mbp@sourcefrog.net-20050817233101-0939da1cf91f2472
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* Before fixing a bug, write a test case so that it does not regress.
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* Exceptions should be defined inside bzrlib.errors, so that we can
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  see the whole tree at a glance.
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* Imports should be done at the top-level of the file, unless there is
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  a strong reason to have them lazily loaded when a particular
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  function runs.  Import statements have a cost, so try to make sure
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  they don't run inside hot functions.
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* Module names should always be given fully-qualified,
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  i.e. ``bzrlib.hashcache`` not just ``hashcache``.
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1393.1.54 by Martin Pool
- more hacking notes on evolving interfaces
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Evolving interfaces
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-------------------
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If you change the behaviour of an API in an incompatible way, please
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be sure to change its name as well. For instance, if I add a keyword
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parameter to branch.commit - that's fine. On the other hand, if I add
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a keyword parameter to branch.commit which is a *required* transaction
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object, I should rename the api - i.e. to 'branch.commit_transaction'.
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This will prevent users of the old api getting surprising results. 
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Instead, they will get an Attribute error as the api is missing, and
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will know to update their code. If in doubt, just ask on #bzr.
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974.1.26 by aaron.bentley at utoronto
merged mbp@sourcefrog.net-20050817233101-0939da1cf91f2472
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Documentation
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=============
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If you change the behaviour of a command, please update its docstring
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in bzrlib/commands.py.  This is displayed by the 'bzr help' command.
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If you make a user-visible change, please add a note to the NEWS file.
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The description should be written to make sense to someone who's just
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a user of bzr, not a developer: new functions or classes shouldn't be
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mentioned, but new commands, changes in behaviour or fixed nontrivial
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bugs should be listed.  See the existing entries for an idea of what
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should be done.
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- notes on how output is written
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1393.1.53 by Martin Pool
- notes from coding-convention discussion
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API documentation
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-----------------
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Functions, methods, classes and modules should have docstrings
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describing how they are used. 
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The first line of the docstring should be a self-contained sentence.
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For the special case of Command classes, this acts as the user-visible
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documentation shown by the help command.
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The docstrings should be formatted as reStructuredText_ (like this
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document), suitable for processing using the epydoc_ tool into HTML
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documentation.
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.. _reStructuredText: http://docutils.sourceforge.net/rst.html
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.. _epydoc: http://epydoc.sourceforge.net/
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Coding style
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============
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Please write PEP-8__ compliant code.  
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One often-missed requirement is that the first line of docstrings
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should be a self-contained one-sentence summary.
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__ http://www.python.org/peps/pep-0008.html
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Naming
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------
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Functions, methods or members that are in some sense "private" are given
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a leading underscore prefix.  This is just a hint that code outside the
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implementation should probably not use that interface.
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We prefer class names to be concatenated capital words (``TestCase``)
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and variables, methods and functions to be lowercase words joined by
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underscores (``revision_id``, ``get_revision``).
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For the purposes of naming some names are treated as single compound
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words: "filename", "revno".
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Consider naming classes as nouns and functions/methods as verbs.
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Standard names
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--------------
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``revision_id`` not ``rev_id`` or ``revid``
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Functions that transform one thing to another should be named ``x_to_y``
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(not ``x2y`` as occurs in some old code.)
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1098 by Martin Pool
- notes on how output is written
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Writing output
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==============
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(The strategy described here is what we want to get to, but it's not
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consistently followed in the code at the moment.)
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bzrlib is intended to be a generically reusable library.  It shouldn't
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write messages to stdout or stderr, because some programs that use it
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might want to display that information through a GUI or some other
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mechanism.
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We can distinguish two types of output from the library:
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 1. Structured data representing the progress or result of an
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    operation.  For example, for a commit command this will be a list
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    of the modified files and the finally committed revision number
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    and id.
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    These should be exposed either through the return code or by calls
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    to a callback parameter.
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    A special case of this is progress indicators for long-lived
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    operations, where the caller should pass a ProgressBar object.
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 2. Unstructured log/debug messages, mostly for the benefit of the
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    developers or users trying to debug problems.  This should always
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    be sent through ``bzrlib.trace`` and Python ``logging``, so that
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    it can be redirected by the client.
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The distinction between the two is a bit subjective, but in general if
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there is any chance that a library would want to see something as
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structured data, we should make it so.
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The policy about how output is presented in the text-mode client
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should be only in the command-line tool.
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1418 by Robert Collins
merge martins latest
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1092.1.22 by Robert Collins
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Writing tests
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=============
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In general tests should be placed in a file named testFOO.py where 
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FOO is the logical thing under test. That file should be placed in the
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tests subdirectory under the package being tested.
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1417.1.1 by Robert Collins
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For example, tests for merge3 in bzrlib belong in bzrlib/tests/testmerge3.py.
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add sample test
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See bzrlib/selftest/testsampler.py for a template test script.
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1393.1.61 by Martin Pool
doc
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1092.1.22 by Robert Collins
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Running tests
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=============
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Currently, bzr selftest is used to invoke tests.
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You can provide a pattern argument to run a subset. For example, 
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to run just the whitebox tests, run::
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  bzr selftest -v whitebox
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Errors and exceptions
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=====================
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[write me]
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1393.1.53 by Martin Pool
- notes from coding-convention discussion
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Jargon
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======
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revno
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    Integer identifier for a revision on the main line of a branch.
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    Revision 0 is always the null revision; others are 1-based
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    indexes into the branch's revision history.