78
78
There are some common requirements in the library: some parameters need to be
79
79
unicode safe, some need byte strings, and so on. At the moment we have
80
80
only codified one specific pattern: Parameters that need to be unicode
81
should be check via 'bzrlib.osutils.safe_unicode'. This will coerce the
81
should be checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
82
82
input into unicode in a consistent fashion, allowing trivial strings to be
83
83
used for programmer convenience, but not performing unpredictably in the
84
84
presence of different locales.
90
The copyright policy for bzr was recently made clear in this email (edited
91
for grammatical correctness)::
93
The attached patch cleans up the copyright and license statements in
94
the bzr source. It also adds tests to help us remember to add them
95
with the correct text.
97
We had the problem that lots of our files were "Copyright Canonical
98
Development Ltd" which is not a real company, and some other variations
99
on this theme. Also, some files were missing the GPL statements.
101
I want to be clear about the intent of this patch, since copyright can
102
be a little controversial.
104
1) The big motivation for this is not to shut out the community, but
105
just to clean up all of the invalid copyright statements.
107
2) It has been the general policy for bzr that we want a single
108
copyright holder for all of the core code. This is following the model
109
set by the FSF, which makes it easier to update the code to a new
110
license in case problems are encountered. (For example, if we want to
111
upgrade the project universally to GPL v3 it is much simpler if there is
112
a single copyright holder). It also makes it clearer if copyright is
113
ever debated, there is a single holder, which makes it easier to defend
114
in court, etc. (I think the FSF position is that if you assign them
115
copyright, they can defend it in court rather than you needing to, and
116
I'm sure Canonical would do the same).
117
As such, Canonical has requested copyright assignments from all of the
120
3) If someone wants to add code and not attribute it to Canonical, there
121
is a specific list of files that are excluded from this check. And the
122
test failure indicates where that is, and how to update it.
124
4) If anyone feels that I changed a copyright statement incorrectly, just
125
let me know, and I'll be happy to correct it. Whenever you have large
126
mechanical changes like this, it is possible to make some mistakes.
128
Just to reiterate, this is a community project, and it is meant to stay
129
that way. Core bzr code is copyright Canonical for legal reasons, and
130
the tests are just there to help us maintain that.
89
If you change the behaviour of a command, please update its docstring
90
in bzrlib/commands.py. This is displayed by the 'bzr help' command.
136
When you change bzrlib, please update the relevant documentation for the
137
change you made: Changes to commands should update their help, and
138
possibly end user tutorials; changes to the core library should be
139
reflected in API documentation.
144
The docstring of a command is used by ``bzr help`` to generate help output
145
for the command. The list 'takes_options' attribute on a command is used by
146
``bzr help`` to document the options for the command - the command
147
docstring does not need to document them. Finally, the '_see_also'
148
attribute on a command can be used to reference other related help topics.
194
255
may not catch every case but it's still useful sometimes.
261
In some places we have variables which point to callables that construct
262
new instances. That is to say, they can be used a lot like class objects,
263
but they shouldn't be *named* like classes:
265
> I think that things named FooBar should create instances of FooBar when
266
> called. Its plain confusing for them to do otherwise. When we have
267
> something that is going to be used as a class - that is, checked for via
268
> isinstance or other such idioms, them I would call it foo_class, so that
269
> it is clear that a callable is not sufficient. If it is only used as a
270
> factory, then yes, foo_factory is what I would use.
276
Several places in Bazaar use (or will use) a registry, which is a
277
mapping from names to objects or classes. The registry allows for
278
loading in registered code only when it's needed, and keeping
279
associated information such as a help string or description.
285
To make startup time faster, we use the ``bzrlib.lazy_import`` module to
286
delay importing modules until they are actually used. ``lazy_import`` uses
287
the same syntax as regular python imports. So to import a few modules in a
290
from bzrlib.lazy_import import lazy_import
291
lazy_import(globals(), """
300
revision as _mod_revision,
302
import bzrlib.transport
306
At this point, all of these exist as a ``ImportReplacer`` object, ready to
307
be imported once a member is accessed. Also, when importing a module into
308
the local namespace, which is likely to clash with variable names, it is
309
recommended to prefix it as ``_mod_<module>``. This makes it clearer that
310
the variable is a module, and these object should be hidden anyway, since
311
they shouldn't be imported into other namespaces.
314
Modules versus Members
315
~~~~~~~~~~~~~~~~~~~~~~
317
While it is possible for ``lazy_import()`` to import members of a module
318
when using the ``from module import member`` syntax, it is recommended to
319
only use that syntax to load sub modules ``from module import submodule``.
320
This is because variables and classes can frequently be used without
321
needing a sub-member for example::
323
lazy_import(globals(), """
324
from module import MyClass
328
return isinstance(x, MyClass)
330
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
331
object, rather than the real class.
334
Passing to other variables
335
~~~~~~~~~~~~~~~~~~~~~~~~~~
337
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
338
Because the replacer only knows about the original name, it is unable to
339
replace other variables. The ``ImportReplacer`` class will raise an
340
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
341
happened. But it requires accessing a member more than once from the new
342
variable, so some bugs are not detected right away.
264
413
the command. We do this so that the library api has continual pressure
265
414
on it to be as functional as the command line in a simple manner, and
266
415
to isolate knock-on effects throughout the blackbox test suite when a
267
command changes it name or signature. Ideally only the tests for a
416
command changes its name or signature. Ideally only the tests for a
268
417
given command are affected when a given command is changed.
419
4. If you have a test which does actually require running bzr in a
420
subprocess you can use ``run_bzr_subprocess``. By default the spawned
421
process will not load plugins unless ``--allow-plugins`` is supplied.
427
We make selective use of doctests__. In general they should provide
428
*examples* within the API documentation which can incidentally be tested. We
429
don't try to test every important case using doctests -- regular Python
430
tests are generally a better solution.
432
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
434
__ http://docs.python.org/lib/module-doctest.html
272
439
Currently, bzr selftest is used to invoke tests.
276
443
./bzr selftest -v blackbox
445
To skip a particular test (or set of tests), use the --exclude option
446
(shorthand -x) like so::
448
./bzr selftest -v -x blackbox
450
To list tests without running them, use the --list-only option like so::
452
./bzr selftest --list-only
454
This option can be combined with other selftest options (like -x) and
455
filter patterns to understand their effect.
279
458
Errors and exceptions
280
459
=====================
282
Errors are handled through Python exceptions. They can represent user
283
errors, environmental errors or program bugs. Sometimes we can't be sure
284
at the time it's raised which case applies. See bzrlib/errors.py for
285
details on the error-handling practices.
461
Errors are handled through Python exceptions.
463
We broadly classify errors as either being either internal or not,
464
depending on whether ``user_error`` is set or not. If we think it's our
465
fault, we show a backtrace, an invitation to report the bug, and possibly
466
other details. This is the default for errors that aren't specifically
467
recognized as being caused by a user error. Otherwise we show a briefer
468
message, unless -Derror was given.
470
Many errors originate as "environmental errors" which are raised by Python
471
or builtin libraries -- for example IOError. These are treated as being
472
our fault, unless they're caught in a particular tight scope where we know
473
that they indicate a user errors. For example if the repository format
474
is not found, the user probably gave the wrong path or URL. But if one of
475
the files inside the repository is not found, then it's our fault --
476
either there's a bug in bzr, or something complicated has gone wrong in
477
the environment that means one internal file was deleted.
479
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
480
to be added near the place where they are used.
482
Exceptions are formatted for the user by conversion to a string
483
(eventually calling their ``__str__`` method.) As a convenience the
484
``._fmt`` member can be used as a template which will be mapped to the
485
error's instance dict.
487
New exception classes should be defined when callers might want to catch
488
that exception specifically, or when it needs a substantially different
491
Exception strings should start with a capital letter and should not have a
492
final fullstop. If long, they may contain newlines to break the text.
499
Bazaar has a few facilities to help debug problems by going into pdb_, the
502
.. _pdb: http://docs.python.org/lib/debugger-commands.html
504
If the ``BZR_PDB`` environment variable is set
505
then bzr will go into pdb post-mortem mode when an unhandled exception
508
If you send a SIGQUIT signal to bzr, which can be done by pressing C-\ on Unix,
509
bzr will go into the debugger immediately. You can continue execution by
510
typing ``c``. This can be disabled if necessary by setting the
511
environment variable ``BZR_SIGQUIT_PDB=0``.
294
521
indexes into the branch's revision history.
527
The ``Transport`` layer handles access to local or remote directories.
528
Each Transport object acts like a logical connection to a particular
529
directory, and it allows various operations on files within it. You can
530
*clone* a transport to get a new Transport connected to a subdirectory or
533
Transports are not used for access to the working tree. At present
534
working trees are always local and they are accessed through the regular
535
Python file io mechanisms.
540
Transports work in URLs. Take note that URLs are by definition only
541
ASCII - the decision of how to encode a Unicode string into a URL must be
542
taken at a higher level, typically in the Store. (Note that Stores also
543
escape filenames which cannot be safely stored on all filesystems, but
544
this is a different level.)
546
The main reason for this is that it's not possible to safely roundtrip a
547
URL into Unicode and then back into the same URL. The URL standard
548
gives a way to represent non-ASCII bytes in ASCII (as %-escapes), but
549
doesn't say how those bytes represent non-ASCII characters. (They're not
550
guaranteed to be UTF-8 -- that is common but doesn't happen everywhere.)
552
For example if the user enters the url ``http://example/%e0`` there's no
553
way to tell whether that character represents "latin small letter a with
554
grave" in iso-8859-1, or "latin small letter r with acute" in iso-8859-2
555
or malformed UTF-8. So we can't convert their URL to Unicode reliably.
557
Equally problematic if we're given a url-like string containing non-ascii
558
characters (such as the accented a) we can't be sure how to convert that
559
to the correct URL, because we don't know what encoding the server expects
560
for those characters. (Although this is not totally reliable we might still
561
accept these and assume they should be put into UTF-8.)
563
A similar edge case is that the url ``http://foo/sweet%2Fsour`` contains
564
one directory component whose name is "sweet/sour". The escaped slash is
565
not a directory separator. If we try to convert URLs to regular Unicode
566
paths this information will be lost.
568
This implies that Transports must natively deal with URLs; for simplicity
569
they *only* deal with URLs and conversion of other strings to URLs is done
570
elsewhere. Information they return, such as from ``list_dir``, is also in
571
the form of URL components.
574
Unicode and Encoding Support
575
============================
577
This section discusses various techniques that Bazaar uses to handle
578
characters that are outside the ASCII set.
583
When a ``Command`` object is created, it is given a member variable
584
accessible by ``self.outf``. This is a file-like object, which is bound to
585
``sys.stdout``, and should be used to write information to the screen,
586
rather than directly writing to ``sys.stdout`` or calling ``print``.
587
This file has the ability to translate Unicode objects into the correct
588
representation, based on the console encoding. Also, the class attribute
589
``encoding_type`` will effect how unprintable characters will be
590
handled. This parameter can take one of 3 values:
593
Unprintable characters will be represented with a suitable replacement
594
marker (typically '?'), and no exception will be raised. This is for
595
any command which generates text for the user to review, rather than
596
for automated processing.
597
For example: ``bzr log`` should not fail if one of the entries has text
598
that cannot be displayed.
601
Attempting to print an unprintable character will cause a UnicodeError.
602
This is for commands that are intended more as scripting support, rather
603
than plain user review.
604
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
605
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
606
printed a filename with a '?', the wrong file could be deleted. (At the
607
very least, the correct file would not be deleted). An error is used to
608
indicate that the requested action could not be performed.
611
Do not attempt to automatically convert Unicode strings. This is used
612
for commands that must handle conversion themselves.
613
For example: ``bzr diff`` needs to translate Unicode paths, but should
614
not change the exact text of the contents of the files.
617
``bzrlib.urlutils.unescape_for_display``
618
----------------------------------------
620
Because Transports work in URLs (as defined earlier), printing the raw URL
621
to the user is usually less than optimal. Characters outside the standard
622
set are printed as escapes, rather than the real character, and local
623
paths would be printed as ``file://`` urls. The function
624
``unescape_for_display`` attempts to unescape a URL, such that anything
625
that cannot be printed in the current encoding stays an escaped URL, but
626
valid characters are generated where possible.
632
The ``bzrlib.osutils`` module has many useful helper functions, including
633
some more portable variants of functions in the standard library.
635
In particular, don't use ``shutil.rmtree`` unless it's acceptable for it
636
to fail on Windows if some files are readonly or still open elsewhere.
637
Use ``bzrlib.osutils.rmtree`` instead.
297
640
Merge/review process
298
641
====================
300
643
If you'd like to propose a change, please post to the
301
bazaar-ng@lists.canonical.com list with a patch, bzr changeset, or link to a
644
bazaar@lists.canonical.com list with a patch, bzr changeset, or link to a
302
645
branch. Please put '[patch]' in the subject so we can pick them out, and
303
646
include some text explaining the change. Remember to put an update to the NEWS
304
647
file in your diff, if it makes any changes visible to users or plugin
337
680
so, please reply and say so.)
686
We write some extensions in C using pyrex. We design these to work in
689
* User with no C compiler
690
* User with C compiler
693
The recommended way to install bzr is to have a C compiler so that the
694
extensions can be built, but if no C compiler is present, the pure python
695
versions we supply will work, though more slowly.
697
For developers we recommend that pyrex be installed, so that the C
698
extensions can be changed if needed.
700
For the C extensions, the extension module should always match the
701
original python one in all respects (modulo speed). This should be
702
maintained over time.
704
To create an extension, add rules to setup.py for building it with pyrex,
705
and with distutils. Now start with an empty .pyx file. At the top add
706
"include 'yourmodule.py'". This will import the contents of foo.py into this
707
file at build time - remember that only one module will be loaded at
708
runtime. Now you can subclass classes, or replace functions, and only your
709
changes need to be present in the .pyx file.
711
Note that pyrex does not support all 2.4 programming idioms, so some
712
syntax changes may be required. I.e.
714
- 'from foo import (bar, gam)' needs to change to not use the brackets.
715
- 'import foo.bar as bar' needs to be 'import foo.bar; bar = foo.bar'
717
If the changes are too dramatic, consider
718
maintaining the python code twice - once in the .pyx, and once in the .py,
719
and no longer including the .py file.
721
Making installers for OS Windows
722
================================
723
To build a win32 installer, see the instructions on the wiki page:
724
http://bazaar-vcs.org/BzrWin32Installer
727
:: vim: ft=rst tw=74 ai
added
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HACKING
