254
278
Holds documentation on a whole range of things on Bazaar from the
255
279
origination of ideas within the project to information on Bazaar
256
280
features and use cases. Within this directory there is a subdirectory
257
for each translation into a human language. All the documentation
281
for each translation into a human language. All the documentation
258
282
is in the ReStructuredText markup language.
261
285
Documentation specifically targeted at Bazaar and plugin developers.
262
286
(Including this document.)
266
Automatically-generated API reference information is available at
267
<http://starship.python.net/crew/mwh/bzrlibapi/>.
269
See also the `Bazaar Architectural Overview <../../developers/overview.html>`_.
272
The Code Review Process
273
#######################
275
All code changes coming in to Bazaar are reviewed by someone else.
276
Normally changes by core contributors are reviewed by one other core
277
developer, and changes from other people are reviewed by two core
278
developers. Use intelligent discretion if the patch is trivial.
280
Good reviews do take time. They also regularly require a solid
281
understanding of the overall code base. In practice, this means a small
282
number of people often have a large review burden - with knowledge comes
283
responsibility. No one likes their merge requests sitting in a queue going
284
nowhere, so reviewing sooner rather than later is strongly encouraged.
293
Please put a "cover letter" on your merge request explaining:
295
* the reason **why** you're making this change
297
* **how** this change achieves this purpose
299
* anything else you may have fixed in passing
301
* anything significant that you thought of doing, such as a more
302
extensive fix or a different approach, but didn't or couldn't do now
304
A good cover letter makes reviewers' lives easier because they can decide
305
from the letter whether they agree with the purpose and approach, and then
306
assess whether the patch actually does what the cover letter says.
307
Explaining any "drive-by fixes" or roads not taken may also avoid queries
308
from the reviewer. All in all this should give faster and better reviews.
309
Sometimes writing the cover letter helps the submitter realize something
310
else they need to do. The size of the cover letter should be proportional
311
to the size and complexity of the patch.
314
Reviewing proposed changes
315
==========================
317
Anyone is welcome to review code, and reply to the thread with their
320
The simplest way to review a proposed change is to just read the patch on
321
the list or in Bundle Buggy. For more complex changes it may be useful
322
to make a new working tree or branch from trunk, and merge the proposed
323
change into it, so you can experiment with the code or look at a wider
326
There are three main requirements for code to get in:
328
* Doesn't reduce test coverage: if it adds new methods or commands,
329
there should be tests for them. There is a good test framework
330
and plenty of examples to crib from, but if you are having trouble
331
working out how to test something feel free to post a draft patch
334
* Doesn't reduce design clarity, such as by entangling objects
335
we're trying to separate. This is mostly something the more
336
experienced reviewers need to help check.
338
* Improves bugs, features, speed, or code simplicity.
340
Code that goes in should not degrade any of these aspects. Patches are
341
welcome that only cleanup the code without changing the external
342
behaviour. The core developers take care to keep the code quality high
343
and understandable while recognising that perfect is sometimes the enemy
346
It is easy for reviews to make people notice other things which should be
347
fixed but those things should not hold up the original fix being accepted.
348
New things can easily be recorded in the Bug Tracker instead.
350
It's normally much easier to review several smaller patches than one large
351
one. You might want to use ``bzr-loom`` to maintain threads of related
352
work, or submit a preparatory patch that will make your "real" change
356
Checklist for reviewers
357
=======================
359
* Do you understand what the code's doing and why?
361
* Will it perform reasonably for large inputs, both in memory size and
362
run time? Are there some scenarios where performance should be
365
* Is it tested, and are the tests at the right level? Are there both
366
blackbox (command-line level) and API-oriented tests?
368
* If this change will be visible to end users or API users, is it
369
appropriately documented in NEWS?
371
* Does it meet the coding standards below?
373
* If it changes the user-visible behaviour, does it update the help
374
strings and user documentation?
376
* If it adds a new major concept or standard practice, does it update the
377
developer documentation?
379
* (your ideas here...)
385
From May 2009 on, we prefer people to propose code reviews through
388
* <https://launchpad.net/+tour/code-review>
390
* <https://help.launchpad.net/Code/Review>
392
Anyone can propose or comment on a merge proposal just by creating a
395
There are two ways to create a new merge proposal: through the web
396
interface or by email.
399
Proposing a merge through the web
400
---------------------------------
402
To create the proposal through the web, first push your branch to Launchpad.
403
For example, a branch dealing with documentation belonging to the Launchpad
404
User mbp could be pushed as ::
406
bzr push lp:~mbp/bzr/doc
408
Then go to the branch's web page, which in this case would be
409
<https://code.launchpad.net/~mbp/bzr/doc>. You can simplify this step by just
414
You can then click "Propose for merging into another branch", and enter your
415
cover letter (see above) into the web form. Typically you'll want to merge
416
into ``~bzr/bzr/trunk`` which will be the default; you might also want to
417
nominate merging into a release branch for a bug fix. There is the option to
418
specify a specific reviewer or type of review, and you shouldn't normally
421
Submitting the form takes you to the new page about the merge proposal
422
containing the diff of the changes, comments by interested people, and
423
controls to comment or vote on the change.
425
Proposing a merge by mail
426
-------------------------
428
To propose a merge by mail, send a bundle to ``merge@code.launchpad.net``.
430
You can generate a merge request like this::
432
bzr send -o bug-1234.diff
434
``bzr send`` can also send mail directly if you prefer; see the help.
439
From <https://code.launchpad.net/bzr/+activereviews> you can see all
440
currently active reviews, and choose one to comment on. This page also
441
shows proposals that are now approved and should be merged by someone with
445
Reviews through Bundle Buggy
446
============================
448
The Bundle Buggy tool used up to May 2009 is still available as a review
451
Sending patches for review
452
--------------------------
454
If you'd like to propose a change, please post to the
455
bazaar@lists.canonical.com list with a bundle, patch, or link to a
456
branch. Put ``[PATCH]`` or ``[MERGE]`` in the subject so Bundle Buggy
457
can pick it out, and explain the change in the email message text.
458
Remember to update the NEWS file as part of your change if it makes any
459
changes visible to users or plugin developers. Please include a diff
460
against mainline if you're giving a link to a branch.
462
You can generate a merge request like this::
464
bzr send -o bug-1234.patch
466
A ``.patch`` extension is recommended instead of .bundle as many mail clients
467
will send the latter as a binary file.
469
``bzr send`` can also send mail directly if you prefer; see the help.
471
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
472
want it to be merged. If you want comments from developers rather than
473
to be merged, you can put ``[RFC]`` in the subject line.
475
If this change addresses a bug, please put the bug number in the subject
476
line too, in the form ``[#1]`` so that Bundle Buggy can recognize it.
478
If the change is intended for a particular release mark that in the
479
subject too, e.g. ``[1.6]``.
480
Anyone can "vote" on the mailing list by expressing an opinion. Core
481
developers can also vote using Bundle Buggy. Here are the voting codes and
484
:approve: Reviewer wants this submission merged.
485
:tweak: Reviewer wants this submission merged with small changes. (No
487
:abstain: Reviewer does not intend to vote on this patch.
488
:resubmit: Please make changes and resubmit for review.
489
:reject: Reviewer doesn't want this kind of change merged.
490
:comment: Not really a vote. Reviewer just wants to comment, for now.
492
If a change gets two approvals from core reviewers, and no rejections,
493
then it's OK to come in. Any of the core developers can bring it into the
494
bzr.dev trunk and backport it to maintenance branches if required. The
495
Release Manager will merge the change into the branch for a pending
496
release, if any. As a guideline, core developers usually merge their own
497
changes and volunteer to merge other contributions if they were the second
498
reviewer to agree to a change.
500
To track the progress of proposed changes, use Bundle Buggy. See
501
http://bundlebuggy.aaronbentley.com/help for a link to all the
502
outstanding merge requests together with an explanation of the columns.
503
Bundle Buggy will also mail you a link to track just your change.
505
Coding Style Guidelines
506
#######################
511
``hasattr`` should not be used because it swallows exceptions including
512
``KeyboardInterrupt``. Instead, say something like ::
514
if getattr(thing, 'name', None) is None
520
Please write PEP-8__ compliant code.
522
__ http://www.python.org/peps/pep-0008.html
524
One often-missed requirement is that the first line of docstrings
525
should be a self-contained one-sentence summary.
527
We use 4 space indents for blocks, and never use tab characters. (In vim,
530
Trailing white space should be avoided, but is allowed.
531
You should however not make lots of unrelated white space changes.
533
Unix style newlines (LF) are used.
535
Each file must have a newline at the end of it.
537
Lines should be no more than 79 characters if at all possible.
538
Lines that continue a long statement may be indented in either of
541
within the parenthesis or other character that opens the block, e.g.::
547
or indented by four spaces::
553
The first is considered clearer by some people; however it can be a bit
554
harder to maintain (e.g. when the method name changes), and it does not
555
work well if the relevant parenthesis is already far to the right. Avoid
558
self.legbone.kneebone.shinbone.toebone.shake_it(one,
564
self.legbone.kneebone.shinbone.toebone.shake_it(one,
570
self.legbone.kneebone.shinbone.toebone.shake_it(
573
For long lists, we like to add a trailing comma and put the closing
574
character on the following line. This makes it easier to add new items in
577
from bzrlib.goo import (
583
There should be spaces between function parameters, but not between the
584
keyword name and the value::
586
call(1, 3, cheese=quark)
590
;(defface my-invalid-face
591
; '((t (:background "Red" :underline t)))
592
; "Face used to highlight invalid constructs or other uglyties"
595
(defun my-python-mode-hook ()
596
;; setup preferred indentation style.
597
(setq fill-column 79)
598
(setq indent-tabs-mode nil) ; no tabs, never, I will not repeat
599
; (font-lock-add-keywords 'python-mode
600
; '(("^\\s *\t" . 'my-invalid-face) ; Leading tabs
601
; ("[ \t]+$" . 'my-invalid-face) ; Trailing spaces
602
; ("^[ \t]+$" . 'my-invalid-face)); Spaces only
606
(add-hook 'python-mode-hook 'my-python-mode-hook)
608
The lines beginning with ';' are comments. They can be activated
609
if one want to have a strong notice of some tab/space usage
616
* Imports should be done at the top-level of the file, unless there is
617
a strong reason to have them lazily loaded when a particular
618
function runs. Import statements have a cost, so try to make sure
619
they don't run inside hot functions.
621
* Module names should always be given fully-qualified,
622
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
628
Functions, methods or members that are "private" to bzrlib are given
629
a leading underscore prefix. Names without a leading underscore are
630
public not just across modules but to programmers using bzrlib as an
631
API. As a consequence, a leading underscore is appropriate for names
632
exposed across modules but that are not to be exposed to bzrlib API
635
We prefer class names to be concatenated capital words (``TestCase``)
636
and variables, methods and functions to be lowercase words joined by
637
underscores (``revision_id``, ``get_revision``).
639
For the purposes of naming some names are treated as single compound
640
words: "filename", "revno".
642
Consider naming classes as nouns and functions/methods as verbs.
644
Try to avoid using abbreviations in names, because there can be
645
inconsistency if other people use the full name.
651
``revision_id`` not ``rev_id`` or ``revid``
653
Functions that transform one thing to another should be named ``x_to_y``
654
(not ``x2y`` as occurs in some old code.)
660
Python destructors (``__del__``) work differently to those of other
661
languages. In particular, bear in mind that destructors may be called
662
immediately when the object apparently becomes unreferenced, or at some
663
later time, or possibly never at all. Therefore we have restrictions on
664
what can be done inside them.
666
0. If you think you need to use a ``__del__`` method ask another
667
developer for alternatives. If you do need to use one, explain
670
1. Never rely on a ``__del__`` method running. If there is code that
671
must run, do it from a ``finally`` block instead.
673
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
676
3. In some places we raise a warning from the destructor if the object
677
has not been cleaned up or closed. This is considered OK: the warning
678
may not catch every case but it's still useful sometimes.
684
In some places we have variables which point to callables that construct
685
new instances. That is to say, they can be used a lot like class objects,
686
but they shouldn't be *named* like classes:
688
> I think that things named FooBar should create instances of FooBar when
689
> called. Its plain confusing for them to do otherwise. When we have
690
> something that is going to be used as a class - that is, checked for via
691
> isinstance or other such idioms, them I would call it foo_class, so that
692
> it is clear that a callable is not sufficient. If it is only used as a
693
> factory, then yes, foo_factory is what I would use.
699
Several places in Bazaar use (or will use) a registry, which is a
700
mapping from names to objects or classes. The registry allows for
701
loading in registered code only when it's needed, and keeping
702
associated information such as a help string or description.
705
InterObject and multiple dispatch
706
=================================
708
The ``InterObject`` provides for two-way `multiple dispatch`__: matching
709
up for example a source and destination repository to find the right way
710
to transfer data between them.
712
.. __: http://en.wikipedia.org/wiki/Multiple_dispatch
714
There is a subclass ``InterObject`` classes for each type of object that is
715
dispatched this way, e.g. ``InterRepository``. Calling ``.get()`` on this
716
class will return an ``InterObject`` instance providing the best match for
717
those parameters, and this instance then has methods for operations
720
inter = InterRepository.get(source_repo, target_repo)
721
inter.fetch(revision_id)
723
``InterRepository`` also acts as a registry-like object for its
724
subclasses, and they can be added through ``.register_optimizer``. The
725
right one to run is selected by asking each class, in reverse order of
726
registration, whether it ``.is_compatible`` with the relevant objects.
731
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
732
delay importing modules until they are actually used. ``lazy_import`` uses
733
the same syntax as regular python imports. So to import a few modules in a
736
from bzrlib.lazy_import import lazy_import
737
lazy_import(globals(), """
746
revision as _mod_revision,
748
import bzrlib.transport
752
At this point, all of these exist as a ``ImportReplacer`` object, ready to
753
be imported once a member is accessed. Also, when importing a module into
754
the local namespace, which is likely to clash with variable names, it is
755
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
756
the variable is a module, and these object should be hidden anyway, since
757
they shouldn't be imported into other namespaces.
759
While it is possible for ``lazy_import()`` to import members of a module
760
when using the ``from module import member`` syntax, it is recommended to
761
only use that syntax to load sub modules ``from module import submodule``.
762
This is because variables and classes can frequently be used without
763
needing a sub-member for example::
765
lazy_import(globals(), """
766
from module import MyClass
770
return isinstance(x, MyClass)
772
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
773
object, rather than the real class.
775
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
776
Because the replacer only knows about the original name, it is unable to
777
replace other variables. The ``ImportReplacer`` class will raise an
778
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
779
happened. But it requires accessing a member more than once from the new
780
variable, so some bugs are not detected right away.
786
The null revision is the ancestor of all revisions. Its revno is 0, its
787
revision-id is ``null:``, and its tree is the empty tree. When referring
788
to the null revision, please use ``bzrlib.revision.NULL_REVISION``. Old
789
code sometimes uses ``None`` for the null revision, but this practice is
793
Object string representations
794
=============================
796
Python prints objects using their ``__repr__`` method when they are
797
written to logs, exception tracebacks, or the debugger. We want
798
objects to have useful representations to help in determining what went
801
If you add a new class you should generally add a ``__repr__`` method
802
unless there is an adequate method in a parent class. There should be a
805
Representations should typically look like Python constructor syntax, but
806
they don't need to include every value in the object and they don't need
807
to be able to actually execute. They're to be read by humans, not
808
machines. Don't hardcode the classname in the format, so that we get the
809
correct value if the method is inherited by a subclass. If you're
810
printing attributes of the object, including strings, you should normally
811
use ``%r`` syntax (to call their repr in turn).
813
Try to avoid the representation becoming more than one or two lines long.
814
(But balance this against including useful information, and simplicity of
817
Because repr methods are often called when something has already gone
818
wrong, they should be written somewhat more defensively than most code.
819
The object may be half-initialized or in some other way in an illegal
820
state. The repr method shouldn't raise an exception, or it may hide the
821
(probably more useful) underlying exception.
826
return '%s(%r)' % (self.__class__.__name__,
833
A bare ``except`` statement will catch all exceptions, including ones that
834
really should terminate the program such as ``MemoryError`` and
835
``KeyboardInterrupt``. They should rarely be used unless the exception is
836
later re-raised. Even then, think about whether catching just
837
``Exception`` (which excludes system errors in Python2.5 and later) would
844
All code should be exercised by the test suite. See `Guide to Testing
845
Bazaar <../../developers/testing.html>`_ for detailed information about writing tests.
290
Automatically-generated API reference information is available at
291
<http://starship.python.net/crew/mwh/bzrlibapi/>.
293
See also the `Bazaar Architectural Overview
294
<http://doc.bazaar.canonical.com/developers/overview.html>`_.
1446
885
how to set it up and configure it.
1455
Of the many workflows supported by Bazaar, the one adopted for Bazaar
1456
development itself is known as "Decentralized with automatic gatekeeper".
1457
To repeat the explanation of this given on
1458
http://bazaar-vcs.org/Workflows:
1461
In this workflow, each developer has their own branch or
1462
branches, plus read-only access to the mainline. A software gatekeeper
1463
(e.g. PQM) has commit rights to the main branch. When a developer wants
1464
their work merged, they request the gatekeeper to merge it. The gatekeeper
1465
does a merge, a compile, and runs the test suite. If the code passes, it
1466
is merged into the mainline.
1468
In a nutshell, here's the overall submission process:
1470
#. get your work ready (including review except for trivial changes)
1471
#. push to a public location
1472
#. ask PQM to merge from that location
1475
At present, PQM always takes the changes to merge from a branch
1476
at a URL that can be read by it. For Bazaar, that means a public,
1477
typically http, URL.
1479
As a result, the following things are needed to use PQM for submissions:
1481
#. A publicly available web server
1482
#. Your OpenPGP key registered with PQM (contact RobertCollins for this)
1483
#. The PQM plugin installed and configured (not strictly required but
1484
highly recommended).
1487
Selecting a Public Branch Location
1488
----------------------------------
1490
If you don't have your own web server running, branches can always be
1491
pushed to Launchpad. Here's the process for doing that:
1493
Depending on your location throughout the world and the size of your
1494
repository though, it is often quicker to use an alternative public
1495
location to Launchpad, particularly if you can set up your own repo and
1496
push into that. By using an existing repo, push only needs to send the
1497
changes, instead of the complete repository every time. Note that it is
1498
easy to register branches in other locations with Launchpad so no benefits
1499
are lost by going this way.
1502
For Canonical staff, http://people.ubuntu.com/~<user>/ is one
1503
suggestion for public http branches. Contact your manager for information
1504
on accessing this system if required.
1506
It should also be noted that best practice in this area is subject to
1507
change as things evolve. For example, once the Bazaar smart server on
1508
Launchpad supports server-side branching, the performance situation will
1509
be very different to what it is now (Jun 2007).
1512
Configuring the PQM Plug-In
1513
---------------------------
1515
While not strictly required, the PQM plugin automates a few things and
1516
reduces the chance of error. Before looking at the plugin, it helps to
1517
understand a little more how PQM operates. Basically, PQM requires an
1518
email indicating what you want it to do. The email typically looks like
1521
star-merge source-branch target-branch
1525
star-merge http://bzr.arbash-meinel.com/branches/bzr/jam-integration http://bazaar-vcs.org/bzr/bzr.dev
1527
Note that the command needs to be on one line. The subject of the email
1528
will be used for the commit message. The email also needs to be ``gpg``
1529
signed with a key that PQM accepts.
1531
The advantages of using the PQM plugin are:
1533
#. You can use the config policies to make it easy to set up public
1534
branches, so you don't have to ever type the full paths you want to merge
1537
#. It checks to make sure the public branch last revision matches the
1538
local last revision so you are submitting what you think you are.
1540
#. It uses the same public_branch and smtp sending settings as bzr-email,
1541
so if you have one set up, you have the other mostly set up.
1543
#. Thunderbird refuses to not wrap lines, and request lines are usually
1544
pretty long (you have 2 long URLs in there).
1546
Here are sample configuration settings for the PQM plugin. Here are the
1547
lines in bazaar.conf::
1550
email = Joe Smith <joe.smith@internode.on.net>
1551
smtp_server=mail.internode.on.net:25
1553
And here are the lines in ``locations.conf`` (or ``branch.conf`` for
1554
dirstate-tags branches)::
1556
[/home/joe/bzr/my-integration]
1557
push_location = sftp://joe-smith@bazaar.launchpad.net/%7Ejoe-smith/bzr/my-integration/
1558
push_location:policy = norecurse
1559
public_branch = http://bazaar.launchpad.net/~joe-smith/bzr/my-integration/
1560
public_branch:policy = appendpath
1561
pqm_email = Bazaar PQM <pqm@bazaar-vcs.org>
1562
pqm_branch = http://bazaar-vcs.org/bzr/bzr.dev
1564
Note that the push settings will be added by the first ``push`` on
1565
a branch. Indeed the preferred way to generate the lines above is to use
1566
``push`` with an argument, then copy-and-paste the other lines into
1573
Here is one possible recipe once the above environment is set up:
1575
#. pull bzr.dev => my-integration
1576
#. merge patch => my-integration
1577
#. fix up any final merge conflicts (NEWS being the big killer here).
1583
The ``push`` step is not required if ``my-integration`` is a checkout of
1586
Because of defaults, you can type a single message into commit and
1587
pqm-commit will reuse that.
1590
Tracking Change Acceptance
1591
--------------------------
1593
The web interface to PQM is https://pqm.bazaar-vcs.org/. After submitting
1594
a change, you can visit this URL to confirm it was received and placed in
1597
When PQM completes processing a change, an email is sent to you with the
1601
Reviewing Blueprints
1602
====================
1604
Blueprint Tracking Using Launchpad
1605
----------------------------------
1607
New features typically require a fair amount of discussion, design and
1608
debate. For Bazaar, that information is often captured in a so-called
1609
"blueprint" on our Wiki. Overall tracking of blueprints and their status
1610
is done using Launchpad's relevant tracker,
1611
https://blueprints.launchpad.net/bzr/. Once a blueprint for ready for
1612
review, please announce it on the mailing list.
1614
Alternatively, send an email beginning with [RFC] with the proposal to the
1615
list. In some cases, you may wish to attach proposed code or a proposed
1616
developer document if that best communicates the idea. Debate can then
1617
proceed using the normal merge review processes.
1620
Recording Blueprint Review Feedback
1621
-----------------------------------
1623
Unlike its Bug Tracker, Launchpad's Blueprint Tracker doesn't currently
1624
(Jun 2007) support a chronological list of comment responses. Review
1625
feedback can either be recorded on the Wiki hosting the blueprints or by
1626
using Launchpad's whiteboard feature.
1629
889
Planning Releases
1630
890
=================
1633
Using Releases and Milestones in Launchpad
1634
------------------------------------------
1636
TODO ... (Exact policies still under discussion)
added
removed
doc/developers/HACKING.txt
