~bzr-pqm/bzr/bzr.dev

============================

guidelines for modifying bzr

============================

* New functionality should have test cases.  Preferably write the

  test before writing the code.

  In general, you can test at either the command-line level or the

  internal API level.  Choose whichever is appropriate: if adding a

  new command, or a new command option, then call through run_bzr().

  It is not necessary to do both.

* Before fixing a bug, write a test case so that it does not regress.

* Exceptions should be defined inside bzrlib.errors, so that we can

  see the whole tree at a glance.

* Imports should be done at the top-level of the file, unless there is

  a strong reason to have them lazily loaded when a particular

  function runs.  Import statements have a cost, so try to make sure

  they don't run inside hot functions.

* Please write PEP-8__ compliant code.  

  One often-missed requirement is that the first line of docstrings

  should be a self-contained one-sentence summary.

__ http://www.python.org/peps/pep-0008.html

* Module names should always be given fully-qualified,

  i.e. ``bzrlib.hashcache`` not just ``hashcache``.

Documentation

=============

If you change the behaviour of a command, please update its docstring

in bzrlib/commands.py.  This is displayed by the 'bzr help' command.

If you make a user-visible change, please add a note to the NEWS file.

The description should be written to make sense to someone who's just

a user of bzr, not a developer: new functions or classes shouldn't be

mentioned, but new commands, changes in behaviour or fixed nontrivial

bugs should be listed.  See the existing entries for an idea of what

should be done.

Writing output

==============

(The strategy described here is what we want to get to, but it's not

consistently followed in the code at the moment.)

bzrlib is intended to be a generically reusable library.  It shouldn't

write messages to stdout or stderr, because some programs that use it

might want to display that information through a GUI or some other

mechanism.

We can distinguish two types of output from the library:

 1. Structured data representing the progress or result of an

    operation.  For example, for a commit command this will be a list

    of the modified files and the finally committed revision number

    and id.

    These should be exposed either through the return code or by calls

    to a callback parameter.

    A special case of this is progress indicators for long-lived

    operations, where the caller should pass a ProgressBar object.

 2. Unstructured log/debug messages, mostly for the benefit of the

    developers or users trying to debug problems.  This should always

    be sent through ``bzrlib.trace`` and Python ``logging``, so that

    it can be redirected by the client.

The distinction between the two is a bit subjective, but in general if

there is any chance that a library would want to see something as

structured data, we should make it so.

The policy about how output is presented in the text-mode client

should be only in the command-line tool.