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
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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
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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.
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I want to be clear about the intent of this patch, since copyright can
102
be a little controversial.
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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.
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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
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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
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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
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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
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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
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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
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``bzr help`` to document the options for the command - the command
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docstring does not need to document them. Finally, the '_see_also'
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attribute on a command can be used to reference other related help topics.
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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
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new instances. That is to say, they can be used a lot like class objects,
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but they shouldn't be *named* like classes:
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> I think that things named FooBar should create instances of FooBar when
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> called. Its plain confusing for them to do otherwise. When we have
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> something that is going to be used as a class - that is, checked for via
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> isinstance or other such idioms, them I would call it foo_class, so that
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> 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.
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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.
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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
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the same syntax as regular python imports. So to import a few modules in a
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from bzrlib.lazy_import import lazy_import
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lazy_import(globals(), """
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revision as _mod_revision,
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import bzrlib.transport
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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
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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), you need to use a negative
448
./bzr selftest '^(?!.*blackbox)'
279
451
Errors and exceptions
280
452
=====================
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.
454
Errors are handled through Python exceptions.
456
We broadly classify errors as either being either internal or not,
457
depending on whether ``user_error`` is set or not. If we think it's our
458
fault, we show a backtrace, an invitation to report the bug, and possibly
459
other details. This is the default for errors that aren't specifically
460
recognized as being caused by a user error. Otherwise we show a briefer
461
message, unless -Derror was given.
463
Many errors originate as "environmental errors" which are raised by Python
464
or builtin libraries -- for example IOError. These are treated as being
465
our fault, unless they're caught in a particular tight scope where we know
466
that they indicate a user errors. For example if the repository format
467
is not found, the user probably gave the wrong path or URL. But if one of
468
the files inside the repository is not found, then it's our fault --
469
either there's a bug in bzr, or something complicated has gone wrong in
470
the environment that means one internal file was deleted.
472
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
473
to be added near the place where they are used.
475
Exceptions are formatted for the user by conversion to a string
476
(eventually calling their ``__str__`` method.) As a convenience the
477
``._fmt`` member can be used as a template which will be mapped to the
478
error's instance dict.
480
New exception classes should be defined when callers might want to catch
481
that exception specifically, or when it needs a substantially different
484
Exception strings should start with a capital letter and should not have a
485
final fullstop. If long, they may contain newlines to break the text.
294
495
indexes into the branch's revision history.
501
The ``Transport`` layer handles access to local or remote directories.
502
Each Transport object acts like a logical connection to a particular
503
directory, and it allows various operations on files within it. You can
504
*clone* a transport to get a new Transport connected to a subdirectory or
507
Transports are not used for access to the working tree. At present
508
working trees are always local and they are accessed through the regular
509
Python file io mechanisms.
514
Transports work in URLs. Take note that URLs are by definition only
515
ASCII - the decision of how to encode a Unicode string into a URL must be
516
taken at a higher level, typically in the Store. (Note that Stores also
517
escape filenames which cannot be safely stored on all filesystems, but
518
this is a different level.)
520
The main reason for this is that it's not possible to safely roundtrip a
521
URL into Unicode and then back into the same URL. The URL standard
522
gives a way to represent non-ASCII bytes in ASCII (as %-escapes), but
523
doesn't say how those bytes represent non-ASCII characters. (They're not
524
guaranteed to be UTF-8 -- that is common but doesn't happen everywhere.)
526
For example if the user enters the url ``http://example/%e0`` there's no
527
way to tell whether that character represents "latin small letter a with
528
grave" in iso-8859-1, or "latin small letter r with acute" in iso-8859-2
529
or malformed UTF-8. So we can't convert their URL to Unicode reliably.
531
Equally problematic if we're given a url-like string containing non-ascii
532
characters (such as the accented a) we can't be sure how to convert that
533
to the correct URL, because we don't know what encoding the server expects
534
for those characters. (Although this is not totally reliable we might still
535
accept these and assume they should be put into UTF-8.)
537
A similar edge case is that the url ``http://foo/sweet%2Fsour`` contains
538
one directory component whose name is "sweet/sour". The escaped slash is
539
not a directory separator. If we try to convert URLs to regular Unicode
540
paths this information will be lost.
542
This implies that Transports must natively deal with URLs; for simplicity
543
they *only* deal with URLs and conversion of other strings to URLs is done
544
elsewhere. Information they return, such as from ``list_dir``, is also in
545
the form of URL components.
548
Unicode and Encoding Support
549
============================
551
This section discusses various techniques that Bazaar uses to handle
552
characters that are outside the ASCII set.
557
When a ``Command`` object is created, it is given a member variable
558
accessible by ``self.outf``. This is a file-like object, which is bound to
559
``sys.stdout``, and should be used to write information to the screen,
560
rather than directly writing to ``sys.stdout`` or calling ``print``.
561
This file has the ability to translate Unicode objects into the correct
562
representation, based on the console encoding. Also, the class attribute
563
``encoding_type`` will effect how unprintable characters will be
564
handled. This parameter can take one of 3 values:
567
Unprintable characters will be represented with a suitable replacement
568
marker (typically '?'), and no exception will be raised. This is for
569
any command which generates text for the user to review, rather than
570
for automated processing.
571
For example: ``bzr log`` should not fail if one of the entries has text
572
that cannot be displayed.
575
Attempting to print an unprintable character will cause a UnicodeError.
576
This is for commands that are intended more as scripting support, rather
577
than plain user review.
578
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
579
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
580
printed a filename with a '?', the wrong file could be deleted. (At the
581
very least, the correct file would not be deleted). An error is used to
582
indicate that the requested action could not be performed.
585
Do not attempt to automatically convert Unicode strings. This is used
586
for commands that must handle conversion themselves.
587
For example: ``bzr diff`` needs to translate Unicode paths, but should
588
not change the exact text of the contents of the files.
591
``bzrlib.urlutils.unescape_for_display``
592
----------------------------------------
594
Because Transports work in URLs (as defined earlier), printing the raw URL
595
to the user is usually less than optimal. Characters outside the standard
596
set are printed as escapes, rather than the real character, and local
597
paths would be printed as ``file://`` urls. The function
598
``unescape_for_display`` attempts to unescape a URL, such that anything
599
that cannot be printed in the current encoding stays an escaped URL, but
600
valid characters are generated where possible.
606
The ``bzrlib.osutils`` module has many useful helper functions, including
607
some more portable variants of functions in the standard library.
609
In particular, don't use ``shutil.rmtree`` unless it's acceptable for it
610
to fail on Windows if some files are readonly or still open elsewhere.
611
Use ``bzrlib.osutils.rmtree`` instead.
297
614
Merge/review process
298
615
====================
300
617
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
618
bazaar@lists.canonical.com list with a patch, bzr changeset, or link to a
302
619
branch. Please put '[patch]' in the subject so we can pick them out, and
303
620
include some text explaining the change. Remember to put an update to the NEWS
304
621
file in your diff, if it makes any changes visible to users or plugin
added
removed
HACKING
