~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
1638.1.1 by Robert Collins
Update HACKING to reflect current test writing policy.
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  internal API level.  See Writing Tests below for more detail.
974.1.26 by aaron.bentley at utoronto
merged mbp@sourcefrog.net-20050817233101-0939da1cf91f2472
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1185.33.48 by Martin Pool
Hacking notes on TDD
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* Try to practice Test-Driven Development.  before fixing a bug, write a
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  test case so that it does not regress.  Similarly for adding a new
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  feature: write a test case for a small version of the new feature before
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  starting on the code itself.  Check the test fails on the old code, then
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  add the feature or fix and check it passes.
974.1.26 by aaron.bentley at utoronto
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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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1185.33.48 by Martin Pool
Hacking notes on TDD
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* Commands should return non-zero when they encounter circumstances that
1476 by Robert Collins
Merge now has a retcode of 1 when conflicts occur. (Robert Collins)
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  the user should really pay attention to - which includes trivial shell
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  pipelines.
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1185.34.1 by Jelmer Vernooij
Fix a couple of typo's
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  Recommended values are 
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Merge now has a retcode of 1 when conflicts occur. (Robert Collins)
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    0- OK, 
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    1- Conflicts in merge-like operations, or changes are present in
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       diff-like operations. 
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    2- Unrepresentable diff changes (i.e. binary files that we cannot show 
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       a diff of).
1185.34.1 by Jelmer Vernooij
Fix a couple of typo's
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    3- An error or exception has occurred.
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Merge now has a retcode of 1 when conflicts occur. (Robert Collins)
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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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1534.2.4 by Robert Collins
Update NEWS and HACKING for the symbol_versioning module.
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We have a commitment to 6 months API stability - any supported symbol in a
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release of bzr MUST NOT be altered in any way that would result in
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breaking existing code that uses it. That means that method names,
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parameter ordering, parameter names, variable and attribute names etc must
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not be changed without leaving a 'deprecated forwarder' behind. This even
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applies to modules and classes.
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If you wish to change the behaviour of a supported API in an incompatible
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way, you need to change its name as well. For instance, if I add a optional keyword
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parameter to branch.commit - that's fine. On the other hand, if I add a
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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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When renaming such supported API's, be sure to leave a deprecated_method (or
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_function or ...) behind which forwards to the new API. See the
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bzrlib.symbol_versioning module for decorators that take care of the
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details for you - such as updating the docstring, and issuing a warning
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when the old api is used.
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For unsupported API's, it does not hurt to follow this discipline, but its
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not required. Minimally though, please try to rename things so that
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callers will at least get an AttributeError rather than weird results.
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1393.1.54 by Martin Pool
- more hacking notes on evolving interfaces
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1534.3.1 by Robert Collins
* bzrlib.osutils.safe_unicode now exists to provide parameter coercion
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Standard parameter types
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------------------------
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There are some common requirements in the library: some parameters need to be
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unicode safe, some need byte strings, and so on. At the moment we have
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only codified one specific pattern: Parameters that need to be unicode
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should be check via 'bzrlib.osutils.safe_unicode'. This will coerce the
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input into unicode in a consistent fashion, allowing trivial strings to be
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used for programmer convenience, but not performing unpredictably in the
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presence of different locales.
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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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1185.33.2 by Martin Pool
How to maintain the NEWS file
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NEWS file
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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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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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1185.33.2 by Martin Pool
How to maintain the NEWS file
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Within each release, entries in the news file should have the most
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user-visible changes first.  So the order should be approximately:
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 * changes to existing behaviour - the highest priority because the 
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   user's existing knowledge is incorrect
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 * new features - should be brought to their attention
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 * bug fixes - may be of interest if the bug was affecting them, and
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   should include the bug number if any
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 * major documentation changes
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 * changes to internal interfaces
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People who made significant contributions to each change are listed in
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parenthesis.  This can include reporting bugs (particularly with good
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details or reproduction recipes), submitting patches, etc.
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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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1185.16.85 by mbp at sourcefrog
- rules for using destructors
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Destructors
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-----------
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1185.16.150 by Martin Pool
Improved description of python exception policies
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Python destructors (``__del__``) work differently to those of other
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languages.  In particular, bear in mind that destructors may be called
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immediately when the object apparently becomes unreferenced, or at some
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later time, or possibly never at all.  Therefore we have restrictions on
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what can be done inside them.
1185.16.85 by mbp at sourcefrog
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 0. Never use a __del__ method without asking Martin/Robert first.
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 1. Never rely on a ``__del__`` method running.  If there is code that
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    must run, do it from a ``finally`` block instead.
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 2. Never ``import`` from inside a ``__del__`` method, or you may crash the
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    interpreter!!
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 3. In some places we raise a warning from the destructor if the object
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    has not been cleaned up or closed.  This is considered OK: the warning
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    may not catch every case but it's still useful sometimes.
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- 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.
1092.1.22 by Robert Collins
update hacking with some test foo
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1418 by Robert Collins
merge martins latest
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1092.1.22 by Robert Collins
update hacking with some test foo
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Writing tests
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=============
1638.1.1 by Robert Collins
Update HACKING to reflect current test writing policy.
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In general tests should be placed in a file named test_FOO.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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1638.1.1 by Robert Collins
Update HACKING to reflect current test writing policy.
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For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
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See bzrlib/selftest/test_sampler.py for a template test script.
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Tests can be written for the UI or for individual areas of the library.
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Choose whichever is appropriate: if adding a new command, or a new command 
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option, then you should be writing a UI test.  If you are both adding UI
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functionality and library functionality, you will want to write tests for 
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both the UI and the core behaviours.  We call UI tests 'blackbox' tests
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and they are found in bzrlib/tests/blackbox/*.py. 
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When writing blackbox tests please honour the following conventions:
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 1. Place the tests for the command 'name' in
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    bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
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    to locate the test script for a faulty command.
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 2. Use the 'self.run_bzr("name")' utility function to invoke the command
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    rather than running bzr in a subprocess or invoking the
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    cmd_object.run() method directly. This is a lot faster than
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    subprocesses and generates the same logging output as running it in a
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    subprocess (which invoking the method directly does not).
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 3. Only test the one command in a single test script. Use the bzrlib 
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    library when setting up tests and when evaluating the side-effects of
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    the command. We do this so that the library api has continual pressure
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    on it to be as functional as the command line in a simple manner, and
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    to isolate knock-on effects throughout the blackbox test suite when a
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    command changes it name or signature. Ideally only the tests for a
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    given command are affected when a given command is changed.
1393.1.61 by Martin Pool
doc
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1092.1.22 by Robert Collins
update hacking with some test foo
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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, 
1638.1.1 by Robert Collins
Update HACKING to reflect current test writing policy.
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to run just the blackbox tests, run::
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doc
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  ./bzr selftest -v blackbox
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doc
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Errors and exceptions
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=====================
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1185.16.61 by mbp at sourcefrog
- start introducing hct error classes
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Errors are handled through Python exceptions.  They can represent user
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errors, environmental errors or program bugs.  Sometimes we can't be sure
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at the time it's raised which case applies.  See bzrlib/errors.py for 
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details on the error-handling practices.
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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.
1185.16.85 by mbp at sourcefrog
- rules for using destructors
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1185.33.98 by Martin Pool
Add notes on merge/review process.
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1684.1.3 by Martin Pool
(HACKING) some notes on handling unicode & urls for transports
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Transport
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=========
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The ``Transport`` layer handles access to local or remote directories.
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Each Transport object acts like a logical connection to a particular
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directory, and it allows various operations on files within it.  You can
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*clone* a transport to get a new Transport connected to a subdirectory or
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parent directory.
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Transports are not used for access to the working tree.  At present
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working trees are always local and they are accessed through the regular
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Python file io mechanisms.
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filenames vs URLs
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-----------------
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Transports work in URLs.  Take note that URLs are by definition only
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ASCII - the decision of how to encode a Unicode string into a URL must be
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taken at a higher level, typically in the Store.  (Note that Stores also
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escape filenames which cannot be safely stored on all filesystems, but
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this is a different level.)
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The main reason for this is that it's not possible to safely roundtrip a
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URL into Unicode and then back into the same URL.  The URL standard
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gives a way to represent non-ASCII bytes in ASCII (as %-escapes), but
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doesn't say how those bytes represent non-ASCII characters.  (They're not
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guaranteed to be UTF-8 -- that is common but doesn't happen everywhere.)
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For example if the user enters the url ``http://example/%e0`` there's no
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way to tell whether that character represents "latin small letter a with
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grave" in iso-8859-1, or "latin small letter r with acute" in iso-8859-2
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or malformed UTF-8.  So we can't convert their URL to Unicode reliably.
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Equally problematic if we're given a url-like string containing non-ascii
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characters (such as the accented a) we can't be sure how to convert that
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to the correct URL, because we don't know what encoding the server expects
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for those characters.  (Although this is not totally reliable we might still
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accept these and assume they should be put into UTF-8.)
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A similar edge case is that the url ``http://foo/sweet%2Fsour" contains
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one directory component whose name is "sweet/sour".  The escaped slash is
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not a directory separator.  If we try to convert URLs to regular Unicode
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paths this information will be lost.
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This implies that Transports must natively deal with URLs; for simplicity
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they *only* deal with URLs and conversion of other strings to URLs is done
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elsewhere.  Information they return, such as from ``list_dir``, is also in
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the form of URL components.
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1185.33.98 by Martin Pool
Add notes on merge/review process.
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Merge/review process
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====================
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If you'd like to propose a change, please post to the
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bazaar-ng@lists.canonical.com list with a patch, bzr changeset, or link to a
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branch.  Please put '[patch]' in the subject so we can pick them out, and
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include some text explaining the change.  Remember to put an update to the NEWS
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file in your diff, if it makes any changes visible to users or plugin
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developers.  Please include a diff against mainline if you're giving a link to
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a branch.
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Please indicate if you think the code is ready to merge, or if it's just a
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draft or for discussion.  If you want comments from many developers rather than
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to be merged, you can put '[rfc]' in the subject lines.
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Anyone is welcome to review code.  There are broadly three gates for
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code to get in:
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 * Doesn't reduce test coverage: if it adds new methods or commands,
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   there should be tests for them.  There is a good test framework
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   and plenty of examples to crib from, but if you are having trouble
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   working out how to test something feel free to post a draft patch
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   and ask for help.
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 * Doesn't reduce design clarity, such as by entangling objects
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   we're trying to separate.  This is mostly something the more
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   experienced reviewers need to help check.
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 * Improves bugs, features, speed, or code simplicity.
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Code that goes in should pass all three.
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If you read a patch please reply and say so.  We can use a numeric scale
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of -1, -0, +0, +1, meaning respectively "really don't want it in current
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form", "somewhat uncomfortable", "ok with me", and "please put it in".
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Anyone can "vote".   (It's not really voting, just a terse expression.)
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If something gets say two +1 votes from core reviewers, and no
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vetos, then it's OK to come in.  Any of the core developers can bring it
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into their integration branch, which I'll merge regularly.  (If you do
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so, please reply and say so.)
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:: vim:tw=74:ai