56
56
applies to modules and classes.
58
58
If you wish to change the behaviour of a supported API in an incompatible
59
way, you need to change its name as well. For instance, if I add an optional keyword
59
way, you need to change its name as well. For instance, if I add a optional keyword
60
60
parameter to branch.commit - that's fine. On the other hand, if I add a
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keyword parameter to branch.commit which is a *required* transaction
62
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object, I should rename the API - i.e. to 'branch.commit_transaction'.
67
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details for you - such as updating the docstring, and issuing a warning
68
68
when the old api is used.
70
For unsupported API's, it does not hurt to follow this discipline, but it's
70
For unsupported API's, it does not hurt to follow this discipline, but its
71
71
not required. Minimally though, please try to rename things so that
72
72
callers will at least get an AttributeError rather than weird results.
78
78
There are some common requirements in the library: some parameters need to be
79
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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 checked via ``bzrlib.osutils.safe_unicode``. This will coerce the
81
should be check 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
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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
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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
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.
241
194
may not catch every case but it's still useful sometimes.
247
In some places we have variables which point to callables that construct
248
new instances. That is to say, they can be used a lot like class objects,
249
but they shouldn't be *named* like classes:
251
> I think that things named FooBar should create instances of FooBar when
252
> 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
254
> 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
256
> 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
263
mapping from names to objects or classes. The registry allows for
264
loading in registered code only when it's needed, and keeping
265
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
272
delay importing modules until they are actually used. ``lazy_import`` uses
273
the same syntax as regular python imports. So to import a few modules in a
276
from bzrlib.lazy_import import lazy_import
277
lazy_import(globals(), """
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revision as _mod_revision,
288
import bzrlib.transport
292
At this point, all of these exist as a ``ImportReplacer`` object, ready to
293
be imported once a member is accessed. Also, when importing a module into
294
the local namespace, which is likely to clash with variable names, it is
295
recommended to prefix it as ``_mod_<module>``. This makes it clean that
296
the variable is a module, and these object should be hidden anyway, since
297
they shouldn't be imported into other namespaces.
300
Modules versus Members
301
~~~~~~~~~~~~~~~~~~~~~~
303
While it is possible for ``lazy_import()`` to import members of a module
304
when using the ``from module import member`` syntax, it is recommended to
305
only use that syntax to load sub modules ``from module import submodule``.
306
This is because variables and classes can frequently be used without
307
needing a sub-member for example::
309
lazy_import(globals(), """
310
from module import MyClass
314
return isinstance(x, MyClass)
316
This will incorrectly fail, because ``MyClass`` is a ``ImportReplacer``
317
object, rather than the real class.
320
Passing to other variables
321
~~~~~~~~~~~~~~~~~~~~~~~~~~
323
It also is incorrect to assign ``ImportReplacer`` objects to other variables.
324
Because the replacer only knows about the original name, it is unable to
325
replace other variables. The ``ImportReplacer`` class will raise an
326
``IllegalUseOfScopeReplacer`` exception if it can figure out that this
327
happened. But it requires accessing a member more than once from the new
328
variable, so some bugs are not detected right away.
399
264
the command. We do this so that the library api has continual pressure
400
265
on it to be as functional as the command line in a simple manner, and
401
266
to isolate knock-on effects throughout the blackbox test suite when a
402
command changes its name or signature. Ideally only the tests for a
267
command changes it name or signature. Ideally only the tests for a
403
268
given command are affected when a given command is changed.
405
4. If you have a test which does actually require running bzr in a
406
subprocess you can use ``run_bzr_subprocess``. By default the spawned
407
process will not load plugins unless ``--allow-plugins`` is supplied.
413
We make selective use of doctests__. In general they should provide
414
*examples* within the API documentation which can incidentally be tested. We
415
don't try to test every important case using doctests -- regular Python
416
tests are generally a better solution.
418
Most of these are in ``bzrlib/doc/api``. More additions are welcome.
420
__ http://docs.python.org/lib/module-doctest.html
425
272
Currently, bzr selftest is used to invoke tests.
429
276
./bzr selftest -v blackbox
431
To skip a particular test (or set of tests), you need to use a negative
434
./bzr selftest '^(?!.*blackbox)'
437
279
Errors and exceptions
438
280
=====================
440
Errors are handled through Python exceptions.
442
We broadly classify errors as either being either internal or not,
443
depending on whether ``user_error`` is set or not. If we think it's our
444
fault, we show a backtrace, an invitation to report the bug, and possibly
445
other details. This is the default for errors that aren't specifically
446
recognized as being caused by a user error. Otherwise we show a briefer
447
message, unless -Derror was given.
449
Many errors originate as "environmental errors" which are raised by Python
450
or builtin libraries -- for example IOError. These are treated as being
451
our fault, unless they're caught in a particular tight scope where we know
452
that they indicate a user errors. For example if the repository format
453
is not found, the user probably gave the wrong path or URL. But if one of
454
the files inside the repository is not found, then it's our fault --
455
either there's a bug in bzr, or something complicated has gone wrong in
456
the environment that means one internal file was deleted.
458
Many errors are defined in ``bzrlib/errors.py`` but it's OK for new errors
459
to be added near the place where they are used.
461
Exceptions are formatted for the user by conversion to a string
462
(eventually calling their ``__str__`` method.) As a convenience the
463
``._fmt`` member can be used as a template which will be mapped to the
464
error's instance dict.
466
New exception classes should be defined when callers might want to catch
467
that exception specifically, or when it needs a substantially different
470
Exception strings should start with a capital letter and should not have a
471
final fullstop. If long, they may contain newlines to break the text.
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.
531
344
the form of URL components.
534
Unicode and Encoding Support
535
============================
537
This section discusses various techniques that Bazaar uses to handle
538
characters that are outside the ASCII set.
543
When a ``Command`` object is created, it is given a member variable
544
accessible by ``self.outf``. This is a file-like object, which is bound to
545
``sys.stdout``, and should be used to write information to the screen,
546
rather than directly writing to ``sys.stdout`` or calling ``print``.
547
This file has the ability to translate Unicode objects into the correct
548
representation, based on the console encoding. Also, the class attribute
549
``encoding_type`` will effect how unprintable characters will be
550
handled. This parameter can take one of 3 values:
553
Unprintable characters will be represented with a suitable replacement
554
marker (typically '?'), and no exception will be raised. This is for
555
any command which generates text for the user to review, rather than
556
for automated processing.
557
For example: ``bzr log`` should not fail if one of the entries has text
558
that cannot be displayed.
561
Attempting to print an unprintable character will cause a UnicodeError.
562
This is for commands that are intended more as scripting support, rather
563
than plain user review.
564
For exampl: ``bzr ls`` is designed to be used with shell scripting. One
565
use would be ``bzr ls --null --unknows | xargs -0 rm``. If ``bzr``
566
printed a filename with a '?', the wrong file could be deleted. (At the
567
very least, the correct file would not be deleted). An error is used to
568
indicate that the requested action could not be performed.
571
Do not attempt to automatically convert Unicode strings. This is used
572
for commands that must handle conversion themselves.
573
For example: ``bzr diff`` needs to translate Unicode paths, but should
574
not change the exact text of the contents of the files.
577
``bzrlib.urlutils.unescape_for_display``
578
----------------------------------------
580
Because Transports work in URLs (as defined earlier), printing the raw URL
581
to the user is usually less than optimal. Characters outside the standard
582
set are printed as escapes, rather than the real character, and local
583
paths would be printed as ``file://`` urls. The function
584
``unescape_for_display`` attempts to unescape a URL, such that anything
585
that cannot be printed in the current encoding stays an escaped URL, but
586
valid characters are generated where possible.
589
347
Merge/review process
590
348
====================
added
removed
HACKING
