291
269
<http://starship.python.net/crew/mwh/bzrlibapi/>.
293
271
See also the `Bazaar Architectural Overview
294
<http://doc.bazaar.canonical.com/developers/overview.html>`_.
272
<http://doc.bazaar-vcs.org/developers/overview.html>`_.
275
The Code Review Process
276
#######################
278
All code changes coming in to Bazaar are reviewed by someone else.
279
Normally changes by core contributors are reviewed by one other core
280
developer, and changes from other people are reviewed by two core
281
developers. Use intelligent discretion if the patch is trivial.
283
Good reviews do take time. They also regularly require a solid
284
understanding of the overall code base. In practice, this means a small
285
number of people often have a large review burden - with knowledge comes
286
responsibility. No one likes their merge requests sitting in a queue going
287
nowhere, so reviewing sooner rather than later is strongly encouraged.
296
Please put a "cover letter" on your merge request explaining:
298
* the reason **why** you're making this change
300
* **how** this change achieves this purpose
302
* anything else you may have fixed in passing
304
* anything significant that you thought of doing, such as a more
305
extensive fix or a different approach, but didn't or couldn't do now
307
A good cover letter makes reviewers' lives easier because they can decide
308
from the letter whether they agree with the purpose and approach, and then
309
assess whether the patch actually does what the cover letter says.
310
Explaining any "drive-by fixes" or roads not taken may also avoid queries
311
from the reviewer. All in all this should give faster and better reviews.
312
Sometimes writing the cover letter helps the submitter realize something
313
else they need to do. The size of the cover letter should be proportional
314
to the size and complexity of the patch.
317
Reviewing proposed changes
318
==========================
320
Anyone is welcome to review code, and reply to the thread with their
323
The simplest way to review a proposed change is to just read the patch on
324
the list or in Bundle Buggy. For more complex changes it may be useful
325
to make a new working tree or branch from trunk, and merge the proposed
326
change into it, so you can experiment with the code or look at a wider
329
There are three main requirements for code to get in:
331
* Doesn't reduce test coverage: if it adds new methods or commands,
332
there should be tests for them. There is a good test framework
333
and plenty of examples to crib from, but if you are having trouble
334
working out how to test something feel free to post a draft patch
337
* Doesn't reduce design clarity, such as by entangling objects
338
we're trying to separate. This is mostly something the more
339
experienced reviewers need to help check.
341
* Improves bugs, features, speed, or code simplicity.
343
Code that goes in should not degrade any of these aspects. Patches are
344
welcome that only cleanup the code without changing the external
345
behaviour. The core developers take care to keep the code quality high
346
and understandable while recognising that perfect is sometimes the enemy
349
It is easy for reviews to make people notice other things which should be
350
fixed but those things should not hold up the original fix being accepted.
351
New things can easily be recorded in the Bug Tracker instead.
353
It's normally much easier to review several smaller patches than one large
354
one. You might want to use ``bzr-loom`` to maintain threads of related
355
work, or submit a preparatory patch that will make your "real" change
359
Checklist for reviewers
360
=======================
362
* Do you understand what the code's doing and why?
364
* Will it perform reasonably for large inputs, both in memory size and
365
run time? Are there some scenarios where performance should be
368
* Is it tested, and are the tests at the right level? Are there both
369
blackbox (command-line level) and API-oriented tests?
371
* If this change will be visible to end users or API users, is it
372
appropriately documented in NEWS?
374
* Does it meet the coding standards below?
376
* If it changes the user-visible behaviour, does it update the help
377
strings and user documentation?
379
* If it adds a new major concept or standard practice, does it update the
380
developer documentation?
382
* (your ideas here...)
388
From May 2009 on, we prefer people to propose code reviews through
391
* <https://launchpad.net/+tour/code-review>
393
* <https://help.launchpad.net/Code/Review>
395
Anyone can propose or comment on a merge proposal just by creating a
398
There are two ways to create a new merge proposal: through the web
399
interface or by email.
402
Proposing a merge through the web
403
---------------------------------
405
To create the proposal through the web, first push your branch to Launchpad.
406
For example, a branch dealing with documentation belonging to the Launchpad
407
User mbp could be pushed as ::
409
bzr push lp:~mbp/bzr/doc
411
Then go to the branch's web page, which in this case would be
412
<https://code.launchpad.net/~mbp/bzr/doc>. You can simplify this step by just
417
You can then click "Propose for merging into another branch", and enter your
418
cover letter (see above) into the web form. Typically you'll want to merge
419
into ``~bzr/bzr/trunk`` which will be the default; you might also want to
420
nominate merging into a release branch for a bug fix. There is the option to
421
specify a specific reviewer or type of review, and you shouldn't normally
424
Submitting the form takes you to the new page about the merge proposal
425
containing the diff of the changes, comments by interested people, and
426
controls to comment or vote on the change.
428
Proposing a merge by mail
429
-------------------------
431
To propose a merge by mail, send a bundle to ``merge@code.launchpad.net``.
433
You can generate a merge request like this::
435
bzr send -o bug-1234.diff
437
``bzr send`` can also send mail directly if you prefer; see the help.
442
From <https://code.launchpad.net/bzr/+activereviews> you can see all
443
currently active reviews, and choose one to comment on. This page also
444
shows proposals that are now approved and should be merged by someone with
448
Reviews through Bundle Buggy
449
============================
451
The Bundle Buggy tool used up to May 2009 is still available as a review
454
Sending patches for review
455
--------------------------
457
If you'd like to propose a change, please post to the
458
bazaar@lists.canonical.com list with a bundle, patch, or link to a
459
branch. Put ``[PATCH]`` or ``[MERGE]`` in the subject so Bundle Buggy
460
can pick it out, and explain the change in the email message text.
461
Remember to update the NEWS file as part of your change if it makes any
462
changes visible to users or plugin developers. Please include a diff
463
against mainline if you're giving a link to a branch.
465
You can generate a merge request like this::
467
bzr send -o bug-1234.patch
469
A ``.patch`` extension is recommended instead of .bundle as many mail clients
470
will send the latter as a binary file.
472
``bzr send`` can also send mail directly if you prefer; see the help.
474
Please do **NOT** put [PATCH] or [MERGE] in the subject line if you don't
475
want it to be merged. If you want comments from developers rather than
476
to be merged, you can put ``[RFC]`` in the subject line.
478
If this change addresses a bug, please put the bug number in the subject
479
line too, in the form ``[#1]`` so that Bundle Buggy can recognize it.
481
If the change is intended for a particular release mark that in the
482
subject too, e.g. ``[1.6]``.
483
Anyone can "vote" on the mailing list by expressing an opinion. Core
484
developers can also vote using Bundle Buggy. Here are the voting codes and
487
:approve: Reviewer wants this submission merged.
488
:tweak: Reviewer wants this submission merged with small changes. (No
490
:abstain: Reviewer does not intend to vote on this patch.
491
:resubmit: Please make changes and resubmit for review.
492
:reject: Reviewer doesn't want this kind of change merged.
493
:comment: Not really a vote. Reviewer just wants to comment, for now.
495
If a change gets two approvals from core reviewers, and no rejections,
496
then it's OK to come in. Any of the core developers can bring it into the
497
bzr.dev trunk and backport it to maintenance branches if required. The
498
Release Manager will merge the change into the branch for a pending
499
release, if any. As a guideline, core developers usually merge their own
500
changes and volunteer to merge other contributions if they were the second
501
reviewer to agree to a change.
503
To track the progress of proposed changes, use Bundle Buggy. See
504
http://bundlebuggy.aaronbentley.com/help for a link to all the
505
outstanding merge requests together with an explanation of the columns.
506
Bundle Buggy will also mail you a link to track just your change.
508
Coding Style Guidelines
509
#######################
514
``hasattr`` should not be used because it swallows exceptions including
515
``KeyboardInterrupt``. Instead, say something like ::
517
if getattr(thing, 'name', None) is None
523
Please write PEP-8__ compliant code.
525
__ http://www.python.org/peps/pep-0008.html
527
One often-missed requirement is that the first line of docstrings
528
should be a self-contained one-sentence summary.
530
We use 4 space indents for blocks, and never use tab characters. (In vim,
533
Trailing white space should be avoided, but is allowed.
534
You should however not make lots of unrelated white space changes.
536
Unix style newlines (LF) are used.
538
Each file must have a newline at the end of it.
540
Lines should be no more than 79 characters if at all possible.
541
Lines that continue a long statement may be indented in either of
544
within the parenthesis or other character that opens the block, e.g.::
550
or indented by four spaces::
556
The first is considered clearer by some people; however it can be a bit
557
harder to maintain (e.g. when the method name changes), and it does not
558
work well if the relevant parenthesis is already far to the right. Avoid
561
self.legbone.kneebone.shinbone.toebone.shake_it(one,
567
self.legbone.kneebone.shinbone.toebone.shake_it(one,
573
self.legbone.kneebone.shinbone.toebone.shake_it(
576
For long lists, we like to add a trailing comma and put the closing
577
character on the following line. This makes it easier to add new items in
580
from bzrlib.goo import (
586
There should be spaces between function parameters, but not between the
587
keyword name and the value::
589
call(1, 3, cheese=quark)
593
;(defface my-invalid-face
594
; '((t (:background "Red" :underline t)))
595
; "Face used to highlight invalid constructs or other uglyties"
598
(defun my-python-mode-hook ()
599
;; setup preferred indentation style.
600
(setq fill-column 79)
601
(setq indent-tabs-mode nil) ; no tabs, never, I will not repeat
602
; (font-lock-add-keywords 'python-mode
603
; '(("^\\s *\t" . 'my-invalid-face) ; Leading tabs
604
; ("[ \t]+$" . 'my-invalid-face) ; Trailing spaces
605
; ("^[ \t]+$" . 'my-invalid-face)); Spaces only
609
(add-hook 'python-mode-hook 'my-python-mode-hook)
611
The lines beginning with ';' are comments. They can be activated
612
if one want to have a strong notice of some tab/space usage
619
* Imports should be done at the top-level of the file, unless there is
620
a strong reason to have them lazily loaded when a particular
621
function runs. Import statements have a cost, so try to make sure
622
they don't run inside hot functions.
624
* Module names should always be given fully-qualified,
625
i.e. ``bzrlib.hashcache`` not just ``hashcache``.
631
Functions, methods or members that are relatively private are given
632
a leading underscore prefix. Names without a leading underscore are
633
public not just across modules but to programmers using bzrlib as an
636
We prefer class names to be concatenated capital words (``TestCase``)
637
and variables, methods and functions to be lowercase words joined by
638
underscores (``revision_id``, ``get_revision``).
640
For the purposes of naming some names are treated as single compound
641
words: "filename", "revno".
643
Consider naming classes as nouns and functions/methods as verbs.
645
Try to avoid using abbreviations in names, because there can be
646
inconsistency if other people use the full name.
652
``revision_id`` not ``rev_id`` or ``revid``
654
Functions that transform one thing to another should be named ``x_to_y``
655
(not ``x2y`` as occurs in some old code.)
661
Python destructors (``__del__``) work differently to those of other
662
languages. In particular, bear in mind that destructors may be called
663
immediately when the object apparently becomes unreferenced, or at some
664
later time, or possibly never at all. Therefore we have restrictions on
665
what can be done inside them.
667
0. If you think you need to use a ``__del__`` method ask another
668
developer for alternatives. If you do need to use one, explain
671
1. Never rely on a ``__del__`` method running. If there is code that
672
must run, do it from a ``finally`` block instead.
674
2. Never ``import`` from inside a ``__del__`` method, or you may crash the
677
3. In some places we raise a warning from the destructor if the object
678
has not been cleaned up or closed. This is considered OK: the warning
679
may not catch every case but it's still useful sometimes.
685
Often when something has failed later code, including cleanups invoked
686
from ``finally`` blocks, will fail too. These secondary failures are
687
generally uninteresting compared to the original exception. So use the
688
``only_raises`` decorator (from ``bzrlib.decorators``) for methods that
689
are typically called in ``finally`` blocks, such as ``unlock`` methods.
690
For example, ``@only_raises(LockNotHeld, LockBroken)``. All errors that
691
are unlikely to be a knock-on failure from a previous failure should be
698
In some places we have variables which point to callables that construct
699
new instances. That is to say, they can be used a lot like class objects,
700
but they shouldn't be *named* like classes::
702
> I think that things named FooBar should create instances of FooBar when
703
> called. Its plain confusing for them to do otherwise. When we have
704
> something that is going to be used as a class - that is, checked for via
705
> isinstance or other such idioms, them I would call it foo_class, so that
706
> it is clear that a callable is not sufficient. If it is only used as a
707
> factory, then yes, foo_factory is what I would use.
713
Several places in Bazaar use (or will use) a registry, which is a
714
mapping from names to objects or classes. The registry allows for
715
loading in registered code only when it's needed, and keeping
716
associated information such as a help string or description.
719
InterObject and multiple dispatch
720
=================================
722
The ``InterObject`` provides for two-way `multiple dispatch`__: matching
723
up for example a source and destination repository to find the right way
724
to transfer data between them.
726
.. __: http://en.wikipedia.org/wiki/Multiple_dispatch
728
There is a subclass ``InterObject`` classes for each type of object that is
729
dispatched this way, e.g. ``InterRepository``. Calling ``.get()`` on this
730
class will return an ``InterObject`` instance providing the best match for
731
those parameters, and this instance then has methods for operations
736
inter = InterRepository.get(source_repo, target_repo)
737
inter.fetch(revision_id)
739
``InterRepository`` also acts as a registry-like object for its
740
subclasses, and they can be added through ``.register_optimizer``. The
741
right one to run is selected by asking each class, in reverse order of
742
registration, whether it ``.is_compatible`` with the relevant objects.
747
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
748
delay importing modules until they are actually used. ``lazy_import`` uses
749
the same syntax as regular python imports. So to import a few modules in a
752
from bzrlib.lazy_import import lazy_import
753
lazy_import(globals(), """
762
revision as _mod_revision,
764
import bzrlib.transport
768
At this point, all of these exist as a ``ImportReplacer`` object, ready to
769
be imported once a member is accessed. Also, when importing a module into
770
the local namespace, which is likely to clash with variable names, it is
771
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
772
the variable is a module, and these object should be hidden anyway, since
773
they shouldn't be imported into other namespaces.
775
While it is possible for ``lazy_import()`` to import members of a module
776
when using the ``from module import member`` syntax, it is recommended to
777
only use that syntax to load sub modules ``from module import submodule``.
778
This is because variables and classes can frequently be used without
779
needing a sub-member for example::
781
lazy_import(globals(), """
782
from module import MyClass
786
return isinstance(x, MyClass)
788
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
789
object, rather than the real class.
791
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
792
Because the replacer only knows about the original name, it is unable to
793
replace other variables. The ``ImportReplacer`` class will raise an
794
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
795
happened. But it requires accessing a member more than once from the new
796
variable, so some bugs are not detected right away.
802
The null revision is the ancestor of all revisions. Its revno is 0, its
803
revision-id is ``null:``, and its tree is the empty tree. When referring
804
to the null revision, please use ``bzrlib.revision.NULL_REVISION``. Old
805
code sometimes uses ``None`` for the null revision, but this practice is
809
Object string representations
810
=============================
812
Python prints objects using their ``__repr__`` method when they are
813
written to logs, exception tracebacks, or the debugger. We want
814
objects to have useful representations to help in determining what went
817
If you add a new class you should generally add a ``__repr__`` method
818
unless there is an adequate method in a parent class. There should be a
821
Representations should typically look like Python constructor syntax, but
822
they don't need to include every value in the object and they don't need
823
to be able to actually execute. They're to be read by humans, not
824
machines. Don't hardcode the classname in the format, so that we get the
825
correct value if the method is inherited by a subclass. If you're
826
printing attributes of the object, including strings, you should normally
827
use ``%r`` syntax (to call their repr in turn).
829
Try to avoid the representation becoming more than one or two lines long.
830
(But balance this against including useful information, and simplicity of
833
Because repr methods are often called when something has already gone
834
wrong, they should be written somewhat more defensively than most code.
835
The object may be half-initialized or in some other way in an illegal
836
state. The repr method shouldn't raise an exception, or it may hide the
837
(probably more useful) underlying exception.
842
return '%s(%r)' % (self.__class__.__name__,
849
A bare ``except`` statement will catch all exceptions, including ones that
850
really should terminate the program such as ``MemoryError`` and
851
``KeyboardInterrupt``. They should rarely be used unless the exception is
852
later re-raised. Even then, think about whether catching just
853
``Exception`` (which excludes system errors in Python2.5 and later) would
860
All code should be exercised by the test suite. See the `Bazaar Testing
861
Guide <http://doc.bazaar-vcs.org/developers/testing.html>`_ for detailed
862
information about writing tests.
885
1475
how to set it up and configure it.
1484
Of the many workflows supported by Bazaar, the one adopted for Bazaar
1485
development itself is known as "Decentralized with automatic gatekeeper".
1486
To repeat the explanation of this given on
1487
http://bazaar-vcs.org/Workflows:
1490
In this workflow, each developer has their own branch or
1491
branches, plus read-only access to the mainline. A software gatekeeper
1492
(e.g. PQM) has commit rights to the main branch. When a developer wants
1493
their work merged, they request the gatekeeper to merge it. The gatekeeper
1494
does a merge, a compile, and runs the test suite. If the code passes, it
1495
is merged into the mainline.
1497
In a nutshell, here's the overall submission process:
1499
#. get your work ready (including review except for trivial changes)
1500
#. push to a public location
1501
#. ask PQM to merge from that location
1504
At present, PQM always takes the changes to merge from a branch
1505
at a URL that can be read by it. For Bazaar, that means a public,
1506
typically http, URL.
1508
As a result, the following things are needed to use PQM for submissions:
1510
#. A publicly available web server
1511
#. Your OpenPGP key registered with PQM (contact RobertCollins for this)
1512
#. The PQM plugin installed and configured (not strictly required but
1513
highly recommended).
1516
Selecting a Public Branch Location
1517
----------------------------------
1519
If you don't have your own web server running, branches can always be
1520
pushed to Launchpad. Here's the process for doing that:
1522
Depending on your location throughout the world and the size of your
1523
repository though, it is often quicker to use an alternative public
1524
location to Launchpad, particularly if you can set up your own repo and
1525
push into that. By using an existing repo, push only needs to send the
1526
changes, instead of the complete repository every time. Note that it is
1527
easy to register branches in other locations with Launchpad so no benefits
1528
are lost by going this way.
1531
For Canonical staff, http://people.ubuntu.com/~<user>/ is one
1532
suggestion for public http branches. Contact your manager for information
1533
on accessing this system if required.
1535
It should also be noted that best practice in this area is subject to
1536
change as things evolve. For example, once the Bazaar smart server on
1537
Launchpad supports server-side branching, the performance situation will
1538
be very different to what it is now (Jun 2007).
1541
Configuring the PQM Plug-In
1542
---------------------------
1544
While not strictly required, the PQM plugin automates a few things and
1545
reduces the chance of error. Before looking at the plugin, it helps to
1546
understand a little more how PQM operates. Basically, PQM requires an
1547
email indicating what you want it to do. The email typically looks like
1550
star-merge source-branch target-branch
1554
star-merge http://bzr.arbash-meinel.com/branches/bzr/jam-integration http://bazaar-vcs.org/bzr/bzr.dev
1556
Note that the command needs to be on one line. The subject of the email
1557
will be used for the commit message. The email also needs to be ``gpg``
1558
signed with a key that PQM accepts.
1560
The advantages of using the PQM plugin are:
1562
#. You can use the config policies to make it easy to set up public
1563
branches, so you don't have to ever type the full paths you want to merge
1566
#. It checks to make sure the public branch last revision matches the
1567
local last revision so you are submitting what you think you are.
1569
#. It uses the same public_branch and smtp sending settings as bzr-email,
1570
so if you have one set up, you have the other mostly set up.
1572
#. Thunderbird refuses to not wrap lines, and request lines are usually
1573
pretty long (you have 2 long URLs in there).
1575
Here are sample configuration settings for the PQM plugin. Here are the
1576
lines in bazaar.conf::
1579
email = Joe Smith <joe.smith@internode.on.net>
1580
smtp_server=mail.internode.on.net:25
1582
And here are the lines in ``locations.conf`` (or ``branch.conf`` for
1583
dirstate-tags branches)::
1585
[/home/joe/bzr/my-integration]
1586
push_location = sftp://joe-smith@bazaar.launchpad.net/%7Ejoe-smith/bzr/my-integration/
1587
push_location:policy = norecurse
1588
public_branch = http://bazaar.launchpad.net/~joe-smith/bzr/my-integration/
1589
public_branch:policy = appendpath
1590
pqm_email = Bazaar PQM <pqm@bazaar-vcs.org>
1591
pqm_branch = http://bazaar-vcs.org/bzr/bzr.dev
1593
Note that the push settings will be added by the first ``push`` on
1594
a branch. Indeed the preferred way to generate the lines above is to use
1595
``push`` with an argument, then copy-and-paste the other lines into
1602
Here is one possible recipe once the above environment is set up:
1604
#. pull bzr.dev => my-integration
1605
#. merge patch => my-integration
1606
#. fix up any final merge conflicts (NEWS being the big killer here).
1612
The ``push`` step is not required if ``my-integration`` is a checkout of
1615
Because of defaults, you can type a single message into commit and
1616
pqm-commit will reuse that.
1619
Tracking Change Acceptance
1620
--------------------------
1622
The web interface to PQM is https://pqm.bazaar-vcs.org/. After submitting
1623
a change, you can visit this URL to confirm it was received and placed in
1626
When PQM completes processing a change, an email is sent to you with the
1630
Reviewing Blueprints
1631
====================
1633
Blueprint Tracking Using Launchpad
1634
----------------------------------
1636
New features typically require a fair amount of discussion, design and
1637
debate. For Bazaar, that information is often captured in a so-called
1638
"blueprint" on our Wiki. Overall tracking of blueprints and their status
1639
is done using Launchpad's relevant tracker,
1640
https://blueprints.launchpad.net/bzr/. Once a blueprint for ready for
1641
review, please announce it on the mailing list.
1643
Alternatively, send an email beginning with [RFC] with the proposal to the
1644
list. In some cases, you may wish to attach proposed code or a proposed
1645
developer document if that best communicates the idea. Debate can then
1646
proceed using the normal merge review processes.
1649
Recording Blueprint Review Feedback
1650
-----------------------------------
1652
Unlike its Bug Tracker, Launchpad's Blueprint Tracker doesn't currently
1653
(Jun 2007) support a chronological list of comment responses. Review
1654
feedback can either be recorded on the Wiki hosting the blueprints or by
1655
using Launchpad's whiteboard feature.
889
1658
Planning Releases
890
1659
=================
1662
Using Releases and Milestones in Launchpad
1663
------------------------------------------
1665
TODO ... (Exact policies still under discussion)
added
removed
doc/developers/HACKING.txt
