Exploring the Bazaar Platform

Before making changes, it’s a good idea to explore the work already done by others. Perhaps the new feature or improvement you’re looking for is available in another plug-in already? If you find a bug, perhaps someone else has already fixed it?

To answer these questions and more, take a moment to explore the overall Bazaar Platform. Here are some links to browse:

• The Plugins page on the Wiki - http://bazaar-vcs.org/BzrPlugins
• The Bazaar product family on Launchpad - https://launchpad.net/bazaar
• Bug Tracker for the core product - https://bugs.launchpad.net/bzr/
• Blueprint Tracker for the core product - https://blueprints.launchpad.net/bzr/

If nothing else, perhaps you’ll find inspiration in how other developers have solved their challenges.

Finding Something To Do

Ad-hoc performance work can also be done. One useful tool is the ‘evil’ debug flag. For instance running bzr -Devil commit -m "test" will log a backtrace to the bzr log file for every method call which triggers a slow or non-scalable part of the bzr library. So checking that a given command with -Devil has no backtraces logged to the log file is a good way to find problem function calls that might be nested deep in the code base.

Planning and Discussing Changes

There is a very active community around Bazaar. Mostly we meet on IRC (#bzr on irc.freenode.net) and on the mailing list. To join the Bazaar community, see http://bazaar-vcs.org/BzrSupport.

If you are planning to make a change, it’s a very good idea to mention it on the IRC channel and/or on the mailing list. There are many advantages to involving the community before you spend much time on a change. These include:

• you get to build on the wisdom of others, saving time
• if others can direct you to similar code, it minimises the work to be done
• it assists everyone in coordinating direction, priorities and effort.

In summary, maximising the input from others typically minimises the total effort required to get your changes merged. The community is friendly, helpful and always keen to welcome newcomers.

Bazaar Development in a Nutshell

One of the fun things about working on a version control system like Bazaar is that the users have a high level of proficiency in contributing back into the tool. Consider the following very brief introduction to contributing back to Bazaar. More detailed instructions are in the following sections.

$ bzr init-repo ~/bzr
$ cd ~/bzr
$ bzr branch http://bazaar-vcs.org/bzr/bzr.dev/ bzr.dev

$ bzr branch bzr.dev 123456-my-bugfix

$ bzr push lp:~your_lp_username/bzr/meaningful_name_here

Understanding the Development Process

The development team follows many practices including:

• a public roadmap and planning process in which anyone can participate
• time based milestones everyone can work towards and plan around
• extensive code review and feedback to contributors
• complete and rigorous test coverage on any code contributed
• automated validation that all tests still pass before code is merged into the main code branch.

The key tools we use to enable these practices are:

• Launchpad - https://launchpad.net/
• Bazaar - http://bazaar-vcs.org/
• Bundle Buggy - http://bundlebuggy.aaronbentley.com/
• Patch Queue Manager - https://launchpad.net/pqm/

For further information, see http://bazaar-vcs.org/BzrDevelopment.

Preparing a Sandbox for Making Changes to Bazaar

Bazaar supports many ways of organising your work. See http://bazaar-vcs.org/SharedRepositoryLayouts for a summary of the popular alternatives.

Of course, the best choice for you will depend on numerous factors: the number of changes you may be making, the complexity of the changes, etc. As a starting suggestion though:

• create a local copy of the main development branch (bzr.dev) by using this command:

  bzr branch http://bazaar-vcs.org/bzr/bzr.dev/ bzr.dev

• keep your copy of bzr.dev pristine (by not developing in it) and keep it up to date (by using bzr pull)

• create a new branch off your local bzr.dev copy for each issue (bug or feature) you are working on.

This approach makes it easy to go back and make any required changes after a code review. Resubmitting the change is then simple with no risk of accidentally including edits related to other issues you may be working on. After the changes for an issue are accepted and merged, the associated branch can be deleted or archived as you wish.

Navigating the Code Base

Some of the key files in this directory are:

bzr

The command you run to start Bazaar itself. This script is pretty short and just does some checks then jumps into bzrlib.

README

This file covers a brief introduction to Bazaar and lists some of its key features.

NEWS

Summary of changes in each Bazaar release that can affect users or plugin developers.

setup.py

Installs Bazaar system-wide or to your home directory. To perform development work on Bazaar it is not required to run this file - you can simply run the bzr command from the top level directory of your development copy. Note: That if you run setup.py this will create a ‘build’ directory in your development branch. There’s nothing wrong with this but don’t be confused by it. The build process puts a copy of the main code base into this build directory, along with some other files. You don’t need to go in here for anything discussed in this guide.

bzrlib

Possibly the most exciting folder of all, bzrlib holds the main code base. This is where you will go to edit python files and contribute to Bazaar.

doc

Holds documentation on a whole range of things on Bazaar from the origination of ideas within the project to information on Bazaar features and use cases. Within this directory there is a subdirectory for each translation into a human language. All the documentation is in the ReStructuredText markup language.

doc/developers

Documentation specifically targeted at Bazaar and plugin developers. (Including this document.)

Automatically-generated API reference information is available at <http://starship.python.net/crew/mwh/bzrlibapi/>.

See also the Bazaar Architectural Overview.

Review cover letters

Please put a “cover letter” on your merge request explaining:

• the reason why you’re making this change
• how this change achieves this purpose
• anything else you may have fixed in passing
• anything significant that you thought of doing, such as a more extensive fix or a different approach, but didn’t or couldn’t do now

A good cover letter makes reviewers’ lives easier because they can decide from the letter whether they agree with the purpose and approach, and then assess whether the patch actually does what the cover letter says. Explaining any “drive-by fixes” or roads not taken may also avoid queries from the reviewer. All in all this should give faster and better reviews. Sometimes writing the cover letter helps the submitter realize something else they need to do. The size of the cover letter should be proportional to the size and complexity of the patch.

Reviewing proposed changes

Anyone is welcome to review code, and reply to the thread with their opinion or comments.

The simplest way to review a proposed change is to just read the patch on the list or in Bundle Buggy. For more complex changes it may be useful to make a new working tree or branch from trunk, and merge the proposed change into it, so you can experiment with the code or look at a wider context.

There are three main requirements for code to get in:

• Doesn’t reduce test coverage: if it adds new methods or commands, there should be tests for them. There is a good test framework and plenty of examples to crib from, but if you are having trouble working out how to test something feel free to post a draft patch and ask for help.
• Doesn’t reduce design clarity, such as by entangling objects we’re trying to separate. This is mostly something the more experienced reviewers need to help check.
• Improves bugs, features, speed, or code simplicity.

Code that goes in should not degrade any of these aspects. Patches are welcome that only cleanup the code without changing the external behaviour. The core developers take care to keep the code quality high and understandable while recognising that perfect is sometimes the enemy of good.

It is easy for reviews to make people notice other things which should be fixed but those things should not hold up the original fix being accepted. New things can easily be recorded in the Bug Tracker instead.

It’s normally much easier to review several smaller patches than one large one. You might want to use bzr-loom to maintain threads of related work, or submit a preparatory patch that will make your “real” change easier.

Checklist for reviewers

• Do you understand what the code’s doing and why?
• Will it perform reasonably for large inputs, both in memory size and run time? Are there some scenarios where performance should be measured?
• Is it tested, and are the tests at the right level? Are there both blackbox (command-line level) and API-oriented tests?
• If this change will be visible to end users or API users, is it appropriately documented in NEWS?
• Does it meet the coding standards below?
• If it changes the user-visible behaviour, does it update the help strings and user documentation?
• If it adds a new major concept or standard practice, does it update the developer documentation?
• (your ideas here...)

Reviews on Launchpad

From May 2009 on, we prefer people to propose code reviews through Launchpad.

• <https://launchpad.net/+tour/code-review>
• <https://help.launchpad.net/Code/Review>

Anyone can propose or comment on a merge proposal just by creating a Launchpad account.

There are two ways to create a new merge proposal: through the web interface or by email.

bzr push lp:~mbp/bzr/doc

bzr lp-open

bzr send -o bug-1234.diff

Reviews through Bundle Buggy

The Bundle Buggy tool used up to May 2009 is still available as a review mechanism.

bzr send -o bug-1234.patch

hasattr and getattr

hasattr should not be used because it swallows exceptions including KeyboardInterrupt. Instead, say something like

if getattr(thing, 'name', None) is None

Code layout

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.

We use 4 space indents for blocks, and never use tab characters. (In vim, set expandtab.)

Trailing white space should be avoided, but is allowed. You should however not make lots of unrelated white space changes.

Unix style newlines (LF) are used.

Each file must have a newline at the end of it.

Lines should be no more than 79 characters if at all possible. Lines that continue a long statement may be indented in either of two ways:

within the parenthesis or other character that opens the block, e.g.:

my_long_method(arg1,
               arg2,
               arg3)

or indented by four spaces:

my_long_method(arg1,
    arg2,
    arg3)

The first is considered clearer by some people; however it can be a bit harder to maintain (e.g. when the method name changes), and it does not work well if the relevant parenthesis is already far to the right. Avoid this:

self.legbone.kneebone.shinbone.toebone.shake_it(one,
                                                two,
                                                three)

but rather

self.legbone.kneebone.shinbone.toebone.shake_it(one,
    two,
    three)

or

self.legbone.kneebone.shinbone.toebone.shake_it(
    one, two, three)

For long lists, we like to add a trailing comma and put the closing character on the following line. This makes it easier to add new items in future:

from bzrlib.goo import (
    jam,
    jelly,
    marmalade,
    )

There should be spaces between function parameters, but not between the keyword name and the value:

call(1, 3, cheese=quark)

In emacs:

;(defface my-invalid-face
;  '((t (:background "Red" :underline t)))
;  "Face used to highlight invalid constructs or other uglyties"
;  )

(defun my-python-mode-hook ()
 ;; setup preferred indentation style.
 (setq fill-column 79)
 (setq indent-tabs-mode nil) ; no tabs, never, I will not repeat
;  (font-lock-add-keywords 'python-mode
;                         '(("^\\s *\t" . 'my-invalid-face) ; Leading tabs
;                            ("[ \t]+$" . 'my-invalid-face)  ; Trailing spaces
;                            ("^[ \t]+$" . 'my-invalid-face)); Spaces only
;                          )
 )

(add-hook 'python-mode-hook 'my-python-mode-hook)

The lines beginning with ‘;’ are comments. They can be activated if one want to have a strong notice of some tab/space usage violations.

Module Imports

• 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.
• Module names should always be given fully-qualified, i.e. bzrlib.hashcache not just hashcache.

Naming

Functions, methods or members that are relatively private are given a leading underscore prefix. Names without a leading underscore are public not just across modules but to programmers using bzrlib as an API.

We prefer class names to be concatenated capital words (TestCase) and variables, methods and functions to be lowercase words joined by underscores (revision_id, get_revision).

For the purposes of naming some names are treated as single compound words: “filename”, “revno”.

Consider naming classes as nouns and functions/methods as verbs.

Try to avoid using abbreviations in names, because there can be inconsistency if other people use the full name.

Standard Names

revision_id not rev_id or revid

Functions that transform one thing to another should be named x_to_y (not x2y as occurs in some old code.)

Destructors

Python destructors (__del__) work differently to those of other languages. In particular, bear in mind that destructors may be called immediately when the object apparently becomes unreferenced, or at some later time, or possibly never at all. Therefore we have restrictions on what can be done inside them.

0. If you think you need to use a __del__ method ask another developer for alternatives. If you do need to use one, explain why in a comment.
1. Never rely on a __del__ method running. If there is code that must run, do it from a finally block instead.
2. Never import from inside a __del__ method, or you may crash the interpreter!!
3. In some places we raise a warning from the destructor if the object has not been cleaned up or closed. This is considered OK: the warning may not catch every case but it’s still useful sometimes.

Cleanup methods

Often when something has failed later code, including cleanups invoked from finally blocks, will fail too. These secondary failures are generally uninteresting compared to the original exception. So use the only_raises decorator (from bzrlib.decorators) for methods that are typically called in finally blocks, such as unlock methods. For example, @only_raises(LockNotHeld, LockBroken). All errors that are unlikely to be a knock-on failure from a previous failure should be allowed.

Factories

In some places we have variables which point to callables that construct new instances. That is to say, they can be used a lot like class objects, but they shouldn’t be named like classes:

> I think that things named FooBar should create instances of FooBar when
> called. Its plain confusing for them to do otherwise. When we have
> something that is going to be used as a class - that is, checked for via
> isinstance or other such idioms, them I would call it foo_class, so that
> it is clear that a callable is not sufficient. If it is only used as a
> factory, then yes, foo_factory is what I would use.

Registries

Several places in Bazaar use (or will use) a registry, which is a mapping from names to objects or classes. The registry allows for loading in registered code only when it’s needed, and keeping associated information such as a help string or description.

InterObject and multiple dispatch

The InterObject provides for two-way multiple dispatch: matching up for example a source and destination repository to find the right way to transfer data between them.

There is a subclass InterObject classes for each type of object that is dispatched this way, e.g. InterRepository. Calling .get() on this class will return an InterObject instance providing the best match for those parameters, and this instance then has methods for operations between the objects.

inter = InterRepository.get(source_repo, target_repo)
inter.fetch(revision_id)

InterRepository also acts as a registry-like object for its subclasses, and they can be added through .register_optimizer. The right one to run is selected by asking each class, in reverse order of registration, whether it .is_compatible with the relevant objects.

Lazy Imports

To make startup time faster, we use the bzrlib.lazy_import module to delay importing modules until they are actually used. lazy_import uses the same syntax as regular python imports. So to import a few modules in a lazy fashion do:

from bzrlib.lazy_import import lazy_import
lazy_import(globals(), """
import os
import subprocess
import sys
import time

from bzrlib import (
   errors,
   transport,
   revision as _mod_revision,
   )
import bzrlib.transport
import bzrlib.xml5
""")

At this point, all of these exist as a ImportReplacer object, ready to be imported once a member is accessed. Also, when importing a module into the local namespace, which is likely to clash with variable names, it is recommended to prefix it as _mod_<module>. This makes it clearer that the variable is a module, and these object should be hidden anyway, since they shouldn’t be imported into other namespaces.

While it is possible for lazy_import() to import members of a module when using the from module import member syntax, it is recommended to only use that syntax to load sub modules from module import submodule. This is because variables and classes can frequently be used without needing a sub-member for example:

lazy_import(globals(), """
from module import MyClass
""")

def test(x):
    return isinstance(x, MyClass)

This will incorrectly fail, because MyClass is a ImportReplacer object, rather than the real class.

It also is incorrect to assign ImportReplacer objects to other variables. Because the replacer only knows about the original name, it is unable to replace other variables. The ImportReplacer class will raise an IllegalUseOfScopeReplacer exception if it can figure out that this happened. But it requires accessing a member more than once from the new variable, so some bugs are not detected right away.

The Null revision

The null revision is the ancestor of all revisions. Its revno is 0, its revision-id is null:, and its tree is the empty tree. When referring to the null revision, please use bzrlib.revision.NULL_REVISION. Old code sometimes uses None for the null revision, but this practice is being phased out.

Object string representations

Python prints objects using their __repr__ method when they are written to logs, exception tracebacks, or the debugger. We want objects to have useful representations to help in determining what went wrong.

If you add a new class you should generally add a __repr__ method unless there is an adequate method in a parent class. There should be a test for the repr.

Representations should typically look like Python constructor syntax, but they don’t need to include every value in the object and they don’t need to be able to actually execute. They’re to be read by humans, not machines. Don’t hardcode the classname in the format, so that we get the correct value if the method is inherited by a subclass. If you’re printing attributes of the object, including strings, you should normally use %r syntax (to call their repr in turn).

Try to avoid the representation becoming more than one or two lines long. (But balance this against including useful information, and simplicity of implementation.)

Because repr methods are often called when something has already gone wrong, they should be written somewhat more defensively than most code. The object may be half-initialized or in some other way in an illegal state. The repr method shouldn’t raise an exception, or it may hide the (probably more useful) underlying exception.

Example:

def __repr__(self):
    return '%s(%r)' % (self.__class__.__name__,
                       self._transport)

Exception handling

A bare except statement will catch all exceptions, including ones that really should terminate the program such as MemoryError and KeyboardInterrupt. They should rarely be used unless the exception is later re-raised. Even then, think about whether catching just Exception (which excludes system errors in Python2.5 and later) would be better.

Test coverage

All code should be exercised by the test suite. See the Bazaar Testing Guide for detailed information about writing tests.

Evolving Interfaces

We don’t change APIs in stable branches: any supported symbol in a stable release of bzr must not be altered in any way that would result in breaking existing code that uses it. That means that method names, parameter ordering, parameter names, variable and attribute names etc must not be changed without leaving a ‘deprecated forwarder’ behind. This even applies to modules and classes.

If you wish to change the behaviour of a supported API in an incompatible way, you need to change its name as well. For instance, if I add an optional keyword parameter to branch.commit - that’s fine. On the other hand, if I add a keyword parameter to branch.commit which is a required transaction object, I should rename the API - i.e. to ‘branch.commit_transaction’.

(Actually, that may break code that provides a new implementation of commit and doesn’t expect to receive the parameter.)

When renaming such supported API’s, be sure to leave a deprecated_method (or _function or ...) behind which forwards to the new API. See the bzrlib.symbol_versioning module for decorators that take care of the details for you - such as updating the docstring, and issuing a warning when the old API is used.

For unsupported API’s, it does not hurt to follow this discipline, but it’s not required. Minimally though, please try to rename things so that callers will at least get an AttributeError rather than weird results.

@deprecated_method(deprecated_in((0, 1, 4)))
def foo(self):
     return self._new_foo()

@staticmethod
@deprecated_function(deprecated_in((0, 1, 4)))
def create_repository(base, shared=False, format=None):

Getting Input

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.

Displaying help

Bazaar has online help for various topics through bzr help COMMAND or equivalently bzr command -h. We also have help on command options, and on other help topics. (See help_topics.py.)

As for python docstrings, the first paragraph should be a single-sentence synopsis of the command.

The help for options should be one or more proper sentences, starting with a capital letter and finishing with a full stop (period).

All help messages and documentation should have two spaces between sentences.

Handling Errors and Exceptions

Commands should return non-zero when they encounter circumstances that the user should really pay attention to - which includes trivial shell pipelines.

Recommended values are:

0. OK.
1. Conflicts in merge-like operations, or changes are present in diff-like operations.
2. Unrepresentable diff changes (i.e. binary files that we cannot show a diff of).
3. An error or exception has occurred.
4. An internal error occurred (one that shows a traceback.)

Errors are handled through Python exceptions. Exceptions should be defined inside bzrlib.errors, so that we can see the whole tree at a glance.

We broadly classify errors as either being either internal or not, depending on whether internal_error is set or not. If we think it’s our fault, we show a backtrace, an invitation to report the bug, and possibly other details. This is the default for errors that aren’t specifically recognized as being caused by a user error. Otherwise we show a briefer message, unless -Derror was given.

Many errors originate as “environmental errors” which are raised by Python or builtin libraries – for example IOError. These are treated as being our fault, unless they’re caught in a particular tight scope where we know that they indicate a user errors. For example if the repository format is not found, the user probably gave the wrong path or URL. But if one of the files inside the repository is not found, then it’s our fault – either there’s a bug in bzr, or something complicated has gone wrong in the environment that means one internal file was deleted.

Many errors are defined in bzrlib/errors.py but it’s OK for new errors to be added near the place where they are used.

Exceptions are formatted for the user by conversion to a string (eventually calling their __str__ method.) As a convenience the ._fmt member can be used as a template which will be mapped to the error’s instance dict.

New exception classes should be defined when callers might want to catch that exception specifically, or when it needs a substantially different format string.

1. If it is something that a caller can recover from, a custom exception is reasonable.
2. If it is a data consistency issue, using a builtin like ValueError/TypeError is reasonable.
3. If it is a programmer error (using an api incorrectly) AssertionError is reasonable.
4. Otherwise, use BzrError or InternalBzrError.

Exception strings should start with a capital letter and should not have a final fullstop. If long, they may contain newlines to break the text.

Assertions

Do not use the Python assert statement, either in tests or elsewhere. A source test checks that it is not used. It is ok to explicitly raise AssertionError.

Rationale:

• It makes the behaviour vary depending on whether bzr is run with -O or not, therefore giving a chance for bugs that occur in one case or the other, several of which have already occurred: assertions with side effects, code which can’t continue unless the assertion passes, cases where we should give the user a proper message rather than an assertion failure.
• It’s not that much shorter than an explicit if/raise.
• It tends to lead to fuzzy thinking about whether the check is actually needed or not, and whether it’s an internal error or not
• It tends to cause look-before-you-leap patterns.
• It’s unsafe if the check is needed to protect the integrity of the user’s data.
• It tends to give poor messages since the developer can get by with no explanatory text at all.
• We can’t rely on people always running with -O in normal use, so we can’t use it for tests that are actually expensive.
• Expensive checks that help developers are better turned on from the test suite or a -D flag.
• If used instead of self.assert*() in tests it makes them falsely pass with -O.

Documenting Changes

When you change bzrlib, please update the relevant documentation for the change you made: Changes to commands should update their help, and possibly end user tutorials; changes to the core library should be reflected in API documentation.

General Guidelines

The attached patch cleans up the copyright and license statements in
the bzr source. It also adds tests to help us remember to add them
with the correct text.

We had the problem that lots of our files were "Copyright Canonical
Development Ltd" which is not a real company, and some other variations
on this theme. Also, some files were missing the GPL statements.

I want to be clear about the intent of this patch, since copyright can
be a little controversial.

1) The big motivation for this is not to shut out the community, but
just to clean up all of the invalid copyright statements.

2) It has been the general policy for bzr that we want a single
copyright holder for all of the core code. This is following the model
set by the FSF, which makes it easier to update the code to a new
license in case problems are encountered. (For example, if we want to
upgrade the project universally to GPL v3 it is much simpler if there is
a single copyright holder). It also makes it clearer if copyright is
ever debated, there is a single holder, which makes it easier to defend
in court, etc. (I think the FSF position is that if you assign them
copyright, they can defend it in court rather than you needing to, and
I'm sure Canonical would do the same).
As such, Canonical has requested copyright assignments from all of the
major contributers.

3) If someone wants to add code and not attribute it to Canonical, there
is a specific list of files that are excluded from this check. And the
test failure indicates where that is, and how to update it.

4) If anyone feels that I changed a copyright statement incorrectly, just
let me know, and I'll be happy to correct it. Whenever you have large
mechanical changes like this, it is possible to make some mistakes.

Just to reiterate, this is a community project, and it is meant to stay
that way. Core bzr code is copyright Canonical for legal reasons, and
the tests are just there to help us maintain that.

Debugging

Bazaar has a few facilities to help debug problems by going into pdb, the Python debugger.

If the BZR_PDB environment variable is set then bzr will go into pdb post-mortem mode when an unhandled exception occurs.

If you send a SIGQUIT or SIGBREAK signal to bzr then it will drop into the debugger immediately. SIGQUIT can be generated by pressing Ctrl-\ on Unix. SIGBREAK is generated with Ctrl-Pause on Windows (some laptops have this as Fn-Pause). You can continue execution by typing c. This can be disabled if necessary by setting the environment variable BZR_SIGQUIT_PDB=0.

Debug Flags

Bazaar accepts some global options starting with -D such as -Dhpss. These set a value in bzrlib.debug.debug_flags, and typically cause more information to be written to the trace file. Most mutter calls should be guarded by a check of those flags so that we don’t write out too much information if it’s not needed.

Debug flags may have effects other than just emitting trace messages.

Run bzr help global-options to see them all.

These flags may also be set as a comma-separated list in the debug_flags option in e.g. ~/.bazaar/bazaar.conf. (Note that it must be in this global file, not in the branch or location configuration, because it’s currently only loaded at startup time.) For instance you may want to always record hpss traces and to see full error tracebacks:

debug_flags = hpss, error

Jargon

revno

Integer identifier for a revision on the main line of a branch. Revision 0 is always the null revision; others are 1-based indexes into the branch’s revision history.

Unicode and Encoding Support

This section discusses various techniques that Bazaar uses to handle characters that are outside the ASCII set.

Portability Tips

The bzrlib.osutils module has many useful helper functions, including some more portable variants of functions in the standard library.

In particular, don’t use shutil.rmtree unless it’s acceptable for it to fail on Windows if some files are readonly or still open elsewhere. Use bzrlib.osutils.rmtree instead.

C Extension Modules

We write some extensions in C using pyrex. We design these to work in three scenarios:

• User with no C compiler
• User with C compiler
• Developers

The recommended way to install bzr is to have a C compiler so that the extensions can be built, but if no C compiler is present, the pure python versions we supply will work, though more slowly.

For developers we recommend that pyrex be installed, so that the C extensions can be changed if needed.

For the C extensions, the extension module should always match the original python one in all respects (modulo speed). This should be maintained over time.

To create an extension, add rules to setup.py for building it with pyrex, and with distutils. Now start with an empty .pyx file. At the top add “include ‘yourmodule.py’”. This will import the contents of foo.py into this file at build time - remember that only one module will be loaded at runtime. Now you can subclass classes, or replace functions, and only your changes need to be present in the .pyx file.

Note that pyrex does not support all 2.4 programming idioms, so some syntax changes may be required. I.e.

• ‘from foo import (bar, gam)’ needs to change to not use the brackets.
• ‘import foo.bar as bar’ needs to be ‘import foo.bar; bar = foo.bar’

If the changes are too dramatic, consider maintaining the python code twice - once in the .pyx, and once in the .py, and no longer including the .py file.

Making Installers for OS Windows

To build a win32 installer, see the instructions on the wiki page: http://bazaar-vcs.org/BzrWin32Installer

Overview

[DEFAULT]
email = Joe Smith <[email protected]>
smtp_server = mail.internode.on.net:25

post_commit_to = [email protected]
post_commit_mailer = smtplib

Submitting Changes

star-merge source-branch target-branch

star-merge http://bzr.arbash-meinel.com/branches/bzr/jam-integration http://bazaar-vcs.org/bzr/bzr.dev

[DEFAULT]
email = Joe Smith <[email protected]>
smtp_server=mail.internode.on.net:25

[/home/joe/bzr/my-integration]
push_location = sftp://[email protected]/%7Ejoe-smith/bzr/my-integration/
push_location:policy = norecurse
public_branch = http://bazaar.launchpad.net/~joe-smith/bzr/my-integration/
public_branch:policy = appendpath
pqm_email = Bazaar PQM <[email protected]>
pqm_branch = http://bazaar-vcs.org/bzr/bzr.dev

Reviewing Blueprints

Planning Releases