Merge lp:~jelmer/bzr/lazy-registries into lp:bzr

[Jelmer Vernooij]

Allow lazy registration in registries without loading the registry itself.

Allow lazy registration of entries in registries.

This allows plugins to significantly reduce the amount of code they have to import.

For example, in bzr-git, bzr-svn and bzr-hg this means we can drop imports of:

* bzrlib.directory_service
* bzrlib.send
* bzrlib.diff
* bzrlib.foreign
* bzrlib.help_topics

In e.g. bzr-search we can drop bzrlib.smart.request and bzrlib.log

In bzr-xmloutput, bzrlib.log

Etc.

[Vincent Ladeuil (vila)]

Nice one.

I think I'm not comfortable with two specifics points:

- you've added a feature to Registry, I think it would be clearer to create
  a new class instead,

- the way it works is magical for people that don't know how lazy loading
  works, a few comments or docstrings should address that.

565 +RegistryEntry = collections.namedtuple('RegistryEntry', 'objgetter info help')

Good addition but Worth a docstring.

583 + if module is not None and member_name is not None:

This is the line that conflates two classes into a single one for a benefit
that is not clear to me.

688 +# Lazily registered registries. Maps (module, registry_name, name,
689 +# entry_module, entry_name) -> (objgetter, info, help)
690 +_lazy_registries = {}

This is where you should explain part of the magic.

712 + obj_getter = _LazyObjectGetter(entry_module, entry_name)
713 + registry_dict[key] = RegistryEntry(obj_getter, info, help)

And this is the othe place where the magic takes place (truth is there is
yet another place where the magic occurs but it won't appear that magical if
you use a different class). Someone not knowing about lazy loading and
obj_getter is likely to be completely lost ;)

review: Needs Fixing

[Jelmer Vernooij (jelmer)]

Am 29/03/12 10:27, schrieb Vincent Ladeuil:
> Review: Needs Fixing
>
> Nice one.
>
> I think I'm not comfortable with two specifics points:
>
> - you've added a feature to Registry, I think it would be clearer to create
> a new class instead,
If we add a new class, then that means that any users of registries
would either have to stick with the old implementation *or* be converted
to the new one. Adding it to the current class just allows us to update
the sites and then plugins can use either the lazy registration or
non-lazy registration as they see fit. We wouldn't have to immediately
update all plugins, their existing calls would still just work.
>
> - the way it works is magical for people that don't know how lazy loading
> works, a few comments or docstrings should address that.
>
> 565 +RegistryEntry = collections.namedtuple('RegistryEntry', 'objgetter info help')
>
> Good addition but Worth a docstring.
Fixed.
>
> 583 + if module is not None and member_name is not None:
>
> This is the line that conflates two classes into a single one for a benefit
> that is not clear to me.
If module is not set, then the Registry() object only allows for direct
registration (i.e. importing the object itself and calling
install_named_hook or install_lazy_named_hook on it). If
module/member_name is set, then it also supports install_lazy_hook() *in
addition* to the other methods.

I've added a bit of documentation to the Registry docstring.

>
> 688 +# Lazily registered registries. Maps (module, registry_name, name,
> 689 +# entry_module, entry_name) -> (objgetter, info, help)
> 690 +_lazy_registries = {}
>
> This is where you should explain part of the magic.
>
> 712 + obj_getter = _LazyObjectGetter(entry_module, entry_name)
> 713 + registry_dict[key] = RegistryEntry(obj_getter, info, help)
>
> And this is the othe place where the magic takes place (truth is there is
> yet another place where the magic occurs but it won't appear that magical if
> you use a different class). Someone not knowing about lazy loading and
> obj_getter is likely to be completely lost ;)
I've updated the comments.

Cheers,

Jelmer

[Vincent Ladeuil (vila)]

> If we add a new class, then that means that any users of registries would
> either have to stick with the old implementation *or* be converted to the
> new one.

Hmm. That's true.

On the other hand it means we will never have a clean cut nor a clean
implementation because plugins have no incentive to use the new one, no
deprecation warning here, no nothing.

Not worth blocking this one but I'm always a bit worried when we add more
cruft without a clear path to get rid of it :-/

review: Approve

[Jelmer Vernooij (jelmer)]

sent to pqm by email

[Jelmer Vernooij (jelmer)]

sent to pqm by email

[Jelmer Vernooij (jelmer)]

sent to pqm by email

[Jelmer Vernooij (jelmer)]

sent to pqm by email

[Jelmer Vernooij (jelmer)]

sent to pqm by email

[John A Meinel (jameinel)]

sent to pqm by email

[John A Meinel (jameinel)]

sent to pqm by email

[Martin Packman (gz)]

What is the failure PQM was giving on this branch?

=== modified file 'bzrlib/branch.py'
--- bzrlib/branch.py	2012-03-29 12:27:52 +0000
+++ bzrlib/branch.py	2012-03-31 14:09:30 +0000
@@ -2325,8 +2325,10 @@
 class BranchFormatRegistry(controldir.ControlComponentFormatRegistry):
     """Branch format registry."""
 
-    def __init__(self, other_registry=None):
-        super(BranchFormatRegistry, self).__init__(other_registry)
+    def __init__(self, module_name=None, member_name=None,
+            other_registry=None):
+        super(BranchFormatRegistry, self).__init__(module_name, member_name,
+            other_registry)
         self._default_format = None
 
     def set_default(self, format):
@@ -2336,7 +2338,8 @@
         return self._default_format
 
 
-network_format_registry = registry.FormatRegistry()
+network_format_registry = registry.FormatRegistry("bzrlib.branch",
+    "network_format_registry")
 """Registry of formats indexed by their network name.
 
 The network name for a branch format is an identifier that can be used when
@@ -2344,7 +2347,8 @@
 BranchFormat.network_name() for more detail.
 """
 
-format_registry = BranchFormatRegistry(network_format_registry)
+format_registry = BranchFormatRegistry("bzrlib.branch", "format_registry",
+    network_format_registry)
 
 
 # formats which have no format string are not discoverable
 
=== modified file 'bzrlib/bugtracker.py'
--- bzrlib/bugtracker.py	2011-12-18 12:46:49 +0000
+++ bzrlib/bugtracker.py	2012-03-31 14:09:30 +0000
@@ -174,7 +174,7 @@
         return _bugs_help
 
 
-tracker_registry = TrackerRegistry()
+tracker_registry = TrackerRegistry("bzrlib.bugtracker", "tracker_registry")
 """Registry of bug trackers."""
 
 
 
=== modified file 'bzrlib/bzrdir.py'
--- bzrlib/bzrdir.py	2012-03-29 12:27:52 +0000
+++ bzrlib/bzrdir.py	2012-03-31 14:09:30 +0000
@@ -1226,7 +1226,8 @@
 class BzrProber(controldir.Prober):
     """Prober for formats that use a .bzr/ control directory."""
 
-    formats = registry.FormatRegistry(controldir.network_format_registry)
+    formats = registry.FormatRegistry("bzrlib.bzrdir", "BzrProber.formats",
+        controldir.network_format_registry)
     """The known .bzr formats."""
 
     @classmethod
 
=== modified file 'bzrlib/chk_map.py'
--- bzrlib/chk_map.py	2011-12-19 13:23:58 +0000
+++ bzrlib/chk_map.py	2012-03-31 14:09:30 +0000
@@ -99,7 +99,8 @@
     return '\x00'.join(key)
 
 
-search_key_registry = registry.Registry()
+search_key_registry = registry.Registry("bzrlib.chk_map",
+    "search_key_registry")
 search_key_registry.register('plain', _search_key_plain)
 
 
 
=== modified file 'bzrlib/commands.py'
--- bzrlib/commands.py	2012-03-13 17:25:29 +0000
+++ bzrlib/commands.py	2012-03-31 14:09:30 +0000
@@ -75,8 +75,8 @@
         about the builtin they're decorating.
     """
 
-    def __init__(self):
-        registry.Registry.__init__(self)
+    def __init__(self, module_name=None, member_name=None):
+        registry.Registry.__init__(self, module_name, member_name)
         self.overridden_registry = None
         # map from aliases to the real command that implements the name
         self._alias_dict = {}
@@ -1300,4 +1300,5 @@
         for key, provider in self.iteritems():
             yield provider
 
-command_providers_registry = ProvidersRegistry()
+command_providers_registry = ProvidersRegistry("bzrlib.commands",
+    "command_providers_registry")
 
=== modified file 'bzrlib/config.py'
--- bzrlib/config.py	2012-03-29 12:27:52 +0000
+++ bzrlib/config.py	2012-03-31 14:09:30 +0000
@@ -2098,7 +2098,8 @@
             info=fallback, override_existing=override_existing)
 
 
-credential_store_registry = CredentialStoreRegistry()
+credential_store_registry = CredentialStoreRegistry("bzrlib.config",
+    "credential_store_registry")
 
 
 class CredentialStore(object):
@@ -2574,7 +2575,7 @@
         return the_help
 
 
-option_registry = OptionRegistry()
+option_registry = OptionRegistry("bzrlib.config", "option_registry")
 
 
 # Registered options in lexicographical order
@@ -4176,9 +4177,11 @@
 # The registered object should be a callable receiving a test instance
 # parameter (inheriting from tests.TestCaseWithTransport) and returning a Store
 # object.
-test_store_builder_registry = registry.Registry()
+test_store_builder_registry = registry.Registry("bzrlib.config",
+    "test_store_builder_registry")
 
 # The registered object should be a callable receiving a test instance
 # parameter (inheriting from tests.TestCaseWithTransport) and returning a Stack
 # object.
-test_stack_builder_registry = registry.Registry()
+test_stack_builder_registry = registry.Registry("bzrlib.config",
+     "test_stack_builder_registry")
 
=== modified file 'bzrlib/conflicts.py'
--- bzrlib/conflicts.py	2012-01-16 14:45:48 +0000
+++ bzrlib/conflicts.py	2012-03-31 14:09:30 +0000
@@ -78,8 +78,8 @@
                 self.outf.write(unicode(conflict) + '\n')
 
 
-resolve_action_registry = registry.Registry()
-
+resolve_action_registry = registry.Registry("bzrlib.conflicts",
+    "resolve_action_registry")
 
 resolve_action_registry.register(
     'done', 'done', 'Marks the conflict as resolved.')
 
=== modified file 'bzrlib/controldir.py'
--- bzrlib/controldir.py	2012-02-14 17:22:37 +0000
+++ bzrlib/controldir.py	2012-03-31 14:09:30 +0000
@@ -904,8 +904,10 @@
 class ControlComponentFormatRegistry(registry.FormatRegistry):
     """A registry for control components (branch, workingtree, repository)."""
 
-    def __init__(self, other_registry=None):
-        super(ControlComponentFormatRegistry, self).__init__(other_registry)
+    def __init__(self, module_name=None, member_name=None,
+            other_registry=None):
+        super(ControlComponentFormatRegistry, self).__init__(module_name,
+            member_name, other_registry)
         self._extra_formats = []
 
     def register(self, format):
@@ -1290,11 +1292,11 @@
     e.g. BzrDirMeta1 with weave repository.  Also, it's more user-oriented.
     """
 
-    def __init__(self):
+    def __init__(self, module_name=None, member_name=None):
         """Create a ControlDirFormatRegistry."""
         self._aliases = set()
         self._registration_order = list()
-        super(ControlDirFormatRegistry, self).__init__()
+        super(ControlDirFormatRegistry, self).__init__(module_name, member_name)
 
     def aliases(self):
         """Return a set of the format names which are aliases."""
@@ -1449,9 +1451,11 @@
 # Please register new formats after old formats so that formats
 # appear in chronological order and format descriptions can build
 # on previous ones.
-format_registry = ControlDirFormatRegistry()
+format_registry = ControlDirFormatRegistry("bzrlib.controldir",
+    "format_registry")
 
-network_format_registry = registry.FormatRegistry()
+network_format_registry = registry.FormatRegistry("bzrlib.controldir",
+    "network_format_registry")
 """Registry of formats indexed by their network name.
 
 The network name for a ControlDirFormat is an identifier that can be used when
 
=== modified file 'bzrlib/diff.py'
--- bzrlib/diff.py	2011-12-18 12:46:49 +0000
+++ bzrlib/diff.py	2012-03-31 14:09:30 +0000
@@ -1039,5 +1039,5 @@
             raise errors.NoDiffFound(error_path)
 
 
-format_registry = Registry()
+format_registry = Registry("bzrlib.diff", "format_registry")
 format_registry.register('default', DiffTree)
 
=== modified file 'bzrlib/directory_service.py'
--- bzrlib/directory_service.py	2012-03-21 13:22:09 +0000
+++ bzrlib/directory_service.py	2012-03-31 14:09:30 +0000
@@ -65,7 +65,8 @@
         service, name = match
         return service().look_up(name, url)
 
-directories = DirectoryServiceRegistry()
+directories = DirectoryServiceRegistry("bzrlib.directory_service",
+    "directories")
 
 class AliasDirectory(object):
     """Directory lookup for locations associated with a branch.
@@ -74,7 +75,8 @@
     supported.  On error, a subclass of DirectoryLookupFailure will be raised.
     """
 
-    branch_aliases = registry.Registry()
+    branch_aliases = registry.Registry("bzrlib.directory_service",
+            "AliasDirectory.branch_aliases")
     branch_aliases.register('parent', lambda b: b.get_parent(),
         help="The parent of this branch.")
     branch_aliases.register('submit', lambda b: b.get_submit_branch(),
 
=== modified file 'bzrlib/filters/__init__.py'
--- bzrlib/filters/__init__.py	2012-03-29 14:54:16 +0000
+++ bzrlib/filters/__init__.py	2012-03-31 14:09:30 +0000
@@ -191,7 +191,9 @@
 
 
 # The registry of filter stacks indexed by name.
-filter_stacks_registry = registry.Registry()
+# See register_filter_stack_map for details on the registered values.
+filter_stacks_registry = registry.Registry(
+    "bzrlib.filters", "filter_stacks_registry")
 
 
 # Cache of preferences -> stack
 
=== modified file 'bzrlib/foreign.py'
--- bzrlib/foreign.py	2012-01-18 14:09:19 +0000
+++ bzrlib/foreign.py	2012-03-31 14:09:30 +0000
@@ -188,7 +188,8 @@
         return foreign_vcs.mapping_registry.revision_id_bzr_to_foreign(revid)
 
 
-foreign_vcs_registry = ForeignVcsRegistry()
+foreign_vcs_registry = ForeignVcsRegistry("bzrlib.foreign",
+    "foreign_vcs_registry")
 
 
 class ForeignRepository(Repository):
 
=== modified file 'bzrlib/help_topics/__init__.py'
--- bzrlib/help_topics/__init__.py	2012-03-15 15:36:12 +0000
+++ bzrlib/help_topics/__init__.py	2012-03-31 14:09:30 +0000
@@ -118,7 +118,7 @@
         return result
 
 
-topic_registry = HelpTopicRegistry()
+topic_registry = HelpTopicRegistry("bzrlib.help_topics", "topic_registry")
 
 
 #----------------------------------------------------
 
=== modified file 'bzrlib/hooks.py'
--- bzrlib/hooks.py	2012-03-14 08:34:10 +0000
+++ bzrlib/hooks.py	2012-03-31 14:09:30 +0000
@@ -90,7 +90,7 @@
         'MergeDirectiveHooks'),
     )
 
-known_hooks = KnownHooksRegistry()
+known_hooks = KnownHooksRegistry("bzrlib.hooks", "known_hooks")
 for (_hook_module, _hook_attribute, _hook_class) in _builtin_known_hooks:
     known_hooks.register_lazy_hook(_hook_module, _hook_attribute, _hook_class)
 del _builtin_known_hooks, _hook_module, _hook_attribute, _hook_class
 
=== modified file 'bzrlib/log.py'
--- bzrlib/log.py	2012-03-14 11:30:42 +0000
+++ bzrlib/log.py	2012-03-31 14:09:30 +0000
@@ -1789,7 +1789,8 @@
         return self.get(c.get('log_format'))
 
 
-log_formatter_registry = LogFormatterRegistry()
+log_formatter_registry = LogFormatterRegistry("bzrlib.log",
+    "log_formatter_registry")
 
 
 log_formatter_registry.register('short', ShortLogFormatter,
@@ -1834,7 +1835,7 @@
     return [rev.committer]
 
 
-author_list_registry = registry.Registry()
+author_list_registry = registry.Registry("bzrlib.log", "author_list_registry")
 
 author_list_registry.register('all', author_list_all,
                               'All authors')
@@ -2100,7 +2101,8 @@
         return None
 
 
-properties_handler_registry = registry.Registry()
+properties_handler_registry = registry.Registry("bzrlib.log",
+    "properties_handler_registry")
 
 # Use the properties handlers to print out bug information if available
 def _bugs_properties_handler(revision):
 
=== modified file 'bzrlib/mail_client.py'
--- bzrlib/mail_client.py	2012-02-01 19:55:27 +0000
+++ bzrlib/mail_client.py	2012-03-31 14:09:30 +0000
@@ -33,7 +33,8 @@
     registry
     )
 
-mail_client_registry = registry.Registry()
+mail_client_registry = registry.Registry("bzrlib.mail_client",
+    "mail_client_registry")
 
 
 class MailClient(object):
 
=== modified file 'bzrlib/merge.py'
--- bzrlib/merge.py	2012-03-14 09:30:48 +0000
+++ bzrlib/merge.py	2012-03-31 14:09:30 +0000
@@ -1956,7 +1956,7 @@
     return merger.do_merge()
 
 
-merge_type_registry = registry.Registry()
+merge_type_registry = registry.Registry("bzrlib.merge", "merge_type_registry")
 merge_type_registry.register('diff3', Diff3Merger,
                              "Merge using external diff3.")
 merge_type_registry.register('lca', LCAMerger,
 
=== modified file 'bzrlib/merge_directive.py'
--- bzrlib/merge_directive.py	2012-02-07 00:49:58 +0000
+++ bzrlib/merge_directive.py	2012-03-31 14:09:30 +0000
@@ -674,7 +674,8 @@
         registry.Registry.register(self, format_string, directive)
 
 
-_format_registry = MergeDirectiveFormatRegistry()
+_format_registry = MergeDirectiveFormatRegistry("bzrlib.merge_directive",
+    "_format_registry")
 _format_registry.register(MergeDirective)
 _format_registry.register(MergeDirective2)
 # 0.19 never existed.  It got renamed to 0.90.  But by that point, there were
 
=== modified file 'bzrlib/option.py'
--- bzrlib/option.py	2011-12-18 12:46:49 +0000
+++ bzrlib/option.py	2012-03-31 14:09:30 +0000
@@ -370,7 +370,7 @@
         RegistryOption constructor.  Any other keyword arguments are treated
         as values for the option, and their value is treated as the help.
         """
-        reg = _mod_registry.Registry()
+        reg = _mod_registry.Registry(None, None)
         for name, switch_help in sorted(kwargs.items()):
             name = name.replace('_', '-')
             reg.register(name, name, help=switch_help)
@@ -570,6 +570,6 @@
                type=str,
                help='Display timezone as local, original, or utc.')
 
-diff_writer_registry = _mod_registry.Registry()
+diff_writer_registry = _mod_registry.Registry("bzrlib.option", "diff_writer_registry")
 diff_writer_registry.register('plain', lambda x: x, 'Plaintext diff output.')
 diff_writer_registry.default_key = 'plain'
 
=== modified file 'bzrlib/plugins/launchpad/__init__.py'
--- bzrlib/plugins/launchpad/__init__.py	2012-03-10 19:11:06 +0000
+++ bzrlib/plugins/launchpad/__init__.py	2012-03-31 14:09:30 +0000
@@ -53,8 +53,8 @@
 from bzrlib.commands import (
     plugin_cmds,
     )
-from bzrlib.directory_service import directories
-from bzrlib.help_topics import topic_registry
+from bzrlib.hooks import install_lazy_named_hook
+from bzrlib.registry import register_lazy
 
 for klsname, aliases in [
     ("cmd_register_branch", []),
@@ -68,16 +68,15 @@
 
 
 def _register_directory():
-    directories.register_lazy('lp:', 'bzrlib.plugins.launchpad.lp_directory',
-                              'LaunchpadDirectory',
-                              'Launchpad-based directory service',)
-    directories.register_lazy(
+    register_lazy("bzrlib.directory_service", "directories", 'lp:',
+        'bzrlib.plugins.launchpad.lp_directory', 'LaunchpadDirectory',
+        'Launchpad-based directory service',)
+    register_lazy("bzrlib.directory_service", "directories",
         'debianlp:', 'bzrlib.plugins.launchpad.lp_directory',
         'LaunchpadDirectory',
         'debianlp: shortcut')
-    directories.register_lazy(
-        'ubuntu:', 'bzrlib.plugins.launchpad.lp_directory',
-        'LaunchpadDirectory',
+    register_lazy("bzrlib.directory_service", "directories", 'ubuntu:',
+        'bzrlib.plugins.launchpad.lp_directory', 'LaunchpadDirectory',
         'ubuntu: shortcut')
 
 _register_directory()
@@ -132,7 +131,7 @@
 
 
 def _register_hooks():
-    _mod_branch.Branch.hooks.install_named_hook('open',
+    install_lazy_named_hook("bzrlib.branch", "Branch.hooks", 'open',
         _check_is_up_to_date, 'package-branch-up-to-date')
 
 
@@ -184,8 +183,8 @@
 
 For more information see http://help.launchpad.net/
 """
-topic_registry.register('launchpad',
-    _launchpad_help,
+register_lazy('bzrlib.help_topics', 'topic_registry', 'launchpad',
+    "bzrlib.plugins.launchpad", "_launchpad_help",
     'Using Bazaar with Launchpad.net')
 
 _mod_config.option_registry.register(
 
=== modified file 'bzrlib/plugins/netrc_credential_store/__init__.py'
--- bzrlib/plugins/netrc_credential_store/__init__.py	2011-12-18 12:46:49 +0000
+++ bzrlib/plugins/netrc_credential_store/__init__.py	2012-03-31 14:09:30 +0000
@@ -25,6 +25,7 @@
     config,
     lazy_import,
     )
+from bzrlib.registry import register_lazy
 
 lazy_import.lazy_import(globals(), """
 import errno
@@ -62,7 +63,7 @@
         return password
 
 
-config.credential_store_registry.register_lazy(
+register_lazy("bzrlib.config", "credential_store_registry",
     'netrc', __name__, 'NetrcCredentialStore', help=__doc__)
 
 
 
=== modified file 'bzrlib/plugins/po_merge/__init__.py'
--- bzrlib/plugins/po_merge/__init__.py	2011-12-20 22:09:13 +0000
+++ bzrlib/plugins/po_merge/__init__.py	2012-03-31 14:09:30 +0000
@@ -54,15 +54,15 @@
 """
 
 from bzrlib import (
-    config,
     # Since we are a built-in plugin we share the bzrlib version
     version_info,
     )
 from bzrlib.hooks import install_lazy_named_hook
+from bzrlib.registry import register_lazy
 
 
 def register_lazy_option(key, member):
-    config.option_registry.register_lazy(
+    register_lazy("bzrlib.config", "option_registry",
         key, 'bzrlib.plugins.po_merge.po_merge', member)
 
 
 
=== modified file 'bzrlib/plugins/weave_fmt/__init__.py'
--- bzrlib/plugins/weave_fmt/__init__.py	2011-12-18 12:46:49 +0000
+++ bzrlib/plugins/weave_fmt/__init__.py	2012-03-31 14:09:30 +0000
@@ -28,9 +28,9 @@
     branch as _mod_branch,
     controldir,
     repository as _mod_repository,
-    serializer,
     workingtree as _mod_workingtree,
     )
+from bzrlib.registry import register_lazy
 from bzrlib.bzrdir import (
     BzrProber,
     register_metadir,
@@ -114,8 +114,8 @@
     'bzrlib.plugins.weave_fmt.workingtree',
     'WorkingTreeFormat2')
 
-serializer.format_registry.register_lazy('4', 'bzrlib.plugins.weave_fmt.xml4',
-    'serializer_v4')
+register_lazy("bzrlib.serializer", "format_registry", '4',
+    'bzrlib.plugins.weave_fmt.xml4', 'serializer_v4')
 
 def load_tests(basic_tests, module, loader):
     testmod_names = [
 
=== modified file 'bzrlib/registry.py'
--- bzrlib/registry.py	2011-12-19 13:23:58 +0000
+++ bzrlib/registry.py	2012-03-31 14:09:30 +0000
@@ -18,6 +18,8 @@
 
 from __future__ import absolute_import
 
+import collections
+
 from bzrlib.pyutils import get_named_object
 
 
@@ -81,6 +83,16 @@
             self._module_name, self._member_name, self._imported)
 
 
+"""\
+Entry in a registry
+
+:ivar objgetter: _ObjectGetter instance which can provide the actual object
+:ivar info: Info object (registry-dependent)
+:ivar help: Help string
+"""
+RegistryEntry = collections.namedtuple('RegistryEntry', 'objgetter info help')
+
+
 class Registry(object):
     """A class that registers objects to a name.
 
@@ -97,13 +109,23 @@
     will return the entry for the default key.
     """
 
-    def __init__(self):
-        """Create a new Registry."""
+    def __init__(self, module=None, member_name=None):
+        """Create a new Registry.
+
+        :param module: Optional module registry is present in. Used
+            for lazy registration.
+        :param member_name: Optional member_name of registry in module. Used
+            for lazy registration.
+
+        If module and member_name aren't specified, then lazy registration is
+        not supported.
+        """
         self._default_key = None
         # Map from key => (is_lazy, info)
-        self._dict = {}
-        self._help_dict = {}
-        self._info_dict = {}
+        if module is not None and member_name is not None:
+            self._dict = _lazy_registries.setdefault((module, member_name), {})
+        else:
+            self._dict = {}
 
     def register(self, key, obj, help=None, info=None,
                  override_existing=False):
@@ -125,8 +147,7 @@
         if not override_existing:
             if key in self._dict:
                 raise KeyError('Key %r already registered' % key)
-        self._dict[key] = _ObjectGetter(obj)
-        self._add_help_and_info(key, help=help, info=info)
+        self._dict[key] = RegistryEntry(_ObjectGetter(obj), info, help)
 
     def register_lazy(self, key, module_name, member_name,
                       help=None, info=None,
@@ -149,13 +170,8 @@
         if not override_existing:
             if key in self._dict:
                 raise KeyError('Key %r already registered' % key)
-        self._dict[key] = _LazyObjectGetter(module_name, member_name)
-        self._add_help_and_info(key, help=help, info=info)
-
-    def _add_help_and_info(self, key, help=None, info=None):
-        """Add the help and information about this key"""
-        self._help_dict[key] = help
-        self._info_dict[key] = info
+        self._dict[key] = RegistryEntry(
+            _LazyObjectGetter(module_name, member_name), info, help)
 
     def get(self, key=None):
         """Return the object register()'ed to the given key.
@@ -174,7 +190,7 @@
         :raises AttributeError: If registered lazily, and the module does not
             contain the registered member.
         """
-        return self._dict[self._get_key_or_default(key)].get_obj()
+        return self._dict[self._get_key_or_default(key)].objgetter.get_obj()
 
     def _get_module(self, key):
         """Return the module the object will be or was loaded from.
@@ -182,7 +198,7 @@
         :param key: The key to obtain the module for.
         :return: The name of the module
         """
-        return self._dict[key].get_module()
+        return self._dict[key].objgetter.get_module()
 
     def get_prefix(self, fullname):
         """Return an object whose key is a prefix of the supplied value.
@@ -206,14 +222,14 @@
 
     def get_help(self, key=None):
         """Get the help text associated with the given key"""
-        the_help = self._help_dict[self._get_key_or_default(key)]
+        the_help = self._dict[self._get_key_or_default(key)].help
         if callable(the_help):
             return the_help(self, key)
         return the_help
 
     def get_info(self, key=None):
         """Get the extra information associated with the given key"""
-        return self._info_dict[self._get_key_or_default(key)]
+        return self._dict[self._get_key_or_default(key)].info
 
     def remove(self, key):
         """Remove a registered entry.
@@ -230,14 +246,14 @@
         return sorted(self._dict.keys())
 
     def iteritems(self):
-        for key, getter in self._dict.iteritems():
-            yield key, getter.get_obj()
+        for key, entry in self._dict.iteritems():
+            yield key, entry.objgetter.get_obj()
 
     def items(self):
         # We should not use the iteritems() implementation below (see bug
         # #430510)
-        return sorted([(key, getter.get_obj())
-                       for key, getter in self._dict.items()])
+        return sorted([(key, entry.objgetter.get_obj())
+                       for key, entry in self._dict.items()])
 
     def _set_default_key(self, key):
         if not self._dict.has_key(key):
@@ -256,8 +272,9 @@
 class FormatRegistry(Registry):
     """Registry specialised for handling formats."""
 
-    def __init__(self, other_registry=None):
-        Registry.__init__(self)
+    def __init__(self, module_name=None, member_name=None,
+            other_registry=None):
+        Registry.__init__(self, module_name, member_name)
         self._other_registry = other_registry
 
     def register(self, key, obj, help=None, info=None,
@@ -289,3 +306,42 @@
         if callable(r):
             r = r()
         return r
+
+
+# Lazily registered registries.
+# Maps (module, registry_member_name) -> registry_dict
+#
+# A registry dict maps a key to a RegistryEntry
+#
+# A Registry is associated with either its own private dictionary or
+# a dictionary based in _lazy_registries, if a module name and member name
+# were specified during its creation.
+#
+# The internal registry dictionaries live here so entries can be added
+# without having to load the actual registry.
+_lazy_registries = {}
+
+
+def register_lazy(registry_module, registry_name, key, entry_module,
+        entry_name, help=None, info=None, override_existing=False):
+    """Lazily register an entry in a registry that's not yet loaded.
+
+    :param registry_module: Name of the module in which the registry lives
+    :param registry_name: Python name of the registry
+    :param key: Key of the entry in the registry
+    :param entry_module: Module name for the entry
+    :param entry_name: Python name of the entry
+    :param info: Optional info object
+    :param help: Optional help description
+    :param override_existing: Whether to allow overriding existing
+        entries
+    """
+    # Find the internal registry dict for the specified registry.
+    registry_dict = _lazy_registries.setdefault(
+        (registry_module, registry_name), {})
+    if not override_existing:
+        if key in registry_dict:
+            raise KeyError('Key %r already registered' % key)
+    obj_getter = _LazyObjectGetter(entry_module, entry_name)
+    # Add the entry to the registry dict.
+    registry_dict[key] = RegistryEntry(obj_getter, info, help)
 
=== modified file 'bzrlib/remote.py'
--- bzrlib/remote.py	2012-03-14 14:17:48 +0000
+++ bzrlib/remote.py	2012-03-31 14:09:30 +0000
@@ -4139,8 +4139,9 @@
         tar.extract(tarinfo, to_dir)
 
 
-error_translators = registry.Registry()
-no_context_error_translators = registry.Registry()
+error_translators = registry.Registry("bzrlib.remote", "error_translators")
+no_context_error_translators = registry.Registry("bzrlib.remote",
+    "no_context_error_translators")
 
 
 def _translate_error(err, **context):
 
=== modified file 'bzrlib/repository.py'
--- bzrlib/repository.py	2012-03-29 12:27:52 +0000
+++ bzrlib/repository.py	2012-03-31 14:09:30 +0000
@@ -1324,7 +1324,8 @@
         return controldir.format_registry.make_bzrdir('default').repository_format
 
 
-network_format_registry = registry.FormatRegistry()
+network_format_registry = registry.FormatRegistry("bzrlib.repository",
+    "network_format_registry")
 """Registry of formats indexed by their network name.
 
 The network name for a repository format is an identifier that can be used when
@@ -1333,7 +1334,8 @@
 """
 
 
-format_registry = RepositoryFormatRegistry(network_format_registry)
+format_registry = RepositoryFormatRegistry("bzrlib.repository",
+    "format_registry", network_format_registry)
 """Registry of formats, indexed by their BzrDirMetaFormat format string.
 
 This can contain either format instances themselves, or classes/factories that
 
=== modified file 'bzrlib/revisionspec.py'
--- bzrlib/revisionspec.py	2011-12-19 10:58:39 +0000
+++ bzrlib/revisionspec.py	2012-03-31 14:09:30 +0000
@@ -992,7 +992,7 @@
 RevisionSpec_dwim.append_possible_revspec(RevisionSpec_date)
 RevisionSpec_dwim.append_possible_revspec(RevisionSpec_branch)
 
-revspec_registry = registry.Registry()
+revspec_registry = registry.Registry("bzrlib.revisionspec", "revspec_registry")
 def _register_revspec(revspec):
     revspec_registry.register(revspec.prefix, revspec)
 
 
=== modified file 'bzrlib/send.py'
--- bzrlib/send.py	2012-02-01 19:18:09 +0000
+++ bzrlib/send.py	2012-03-31 14:09:30 +0000
@@ -35,7 +35,7 @@
     )
 
 
-format_registry = registry.Registry()
+format_registry = registry.Registry("bzrlib.send", "format_registry")
 
 
 def send(target_branch, revision, public_branch, remember,
 
=== modified file 'bzrlib/serializer.py'
--- bzrlib/serializer.py	2011-12-19 13:23:58 +0000
+++ bzrlib/serializer.py	2012-03-31 14:09:30 +0000
@@ -92,7 +92,7 @@
     """Registry for serializer objects"""
 
 
-format_registry = SerializerRegistry()
+format_registry = SerializerRegistry("bzrlib.serializer", "format_registry")
 format_registry.register_lazy('5', 'bzrlib.xml5', 'serializer_v5')
 format_registry.register_lazy('6', 'bzrlib.xml6', 'serializer_v6')
 format_registry.register_lazy('7', 'bzrlib.xml7', 'serializer_v7')
 
=== modified file 'bzrlib/smart/request.py'
--- bzrlib/smart/request.py	2012-02-23 23:26:35 +0000
+++ bzrlib/smart/request.py	2012-03-31 14:09:30 +0000
@@ -521,7 +521,7 @@
 #   mutate  State is updated in a way that replaying that request results in a
 #           different state. For example 'append' writes more bytes to a given
 #           file. If append succeeds, it moves the file pointer.
-request_handlers = registry.Registry()
+request_handlers = registry.Registry("bzrlib.smart.request", "request_handlers")
 request_handlers.register_lazy(
     'append', 'bzrlib.smart.vfs', 'AppendRequest', info='mutate')
 request_handlers.register_lazy(
 
=== modified file 'bzrlib/tag.py'
--- bzrlib/tag.py	2011-12-19 13:23:58 +0000
+++ bzrlib/tag.py	2012-03-31 14:09:30 +0000
@@ -421,7 +421,7 @@
     tags.sort(key=lambda x: timestamps[x[1]])
 
 
-tag_sort_methods = Registry()
+tag_sort_methods = Registry("bzrlib.tag", "tag_sort_methods")
 tag_sort_methods.register("natural", sort_natural,
     'Sort numeric substrings as numbers. (default)')
 tag_sort_methods.register("alpha", sort_alpha, 'Sort tags lexicographically.')
 
=== modified file 'bzrlib/tests/__init__.py'
--- bzrlib/tests/__init__.py	2012-03-13 09:07:18 +0000
+++ bzrlib/tests/__init__.py	2012-03-31 14:09:30 +0000
@@ -3328,7 +3328,7 @@
 
 
 # A registry where get() returns a suite decorator.
-parallel_registry = registry.Registry()
+parallel_registry = registry.Registry("bzrlib.tests", "parallel_registry")
 
 
 def fork_decorator(suite):
@@ -3884,7 +3884,8 @@
         return '.'.join(parts)
 
 
-test_prefix_alias_registry = TestPrefixAliasRegistry()
+test_prefix_alias_registry = TestPrefixAliasRegistry("bzrlib.tests",
+    "test_prefix_alias_registry")
 """Registry of test prefix aliases."""
 
 
 
=== modified file 'bzrlib/tests/test_foreign.py'
--- bzrlib/tests/test_foreign.py	2012-02-23 19:45:15 +0000
+++ bzrlib/tests/test_foreign.py	2012-03-31 14:09:30 +0000
@@ -76,7 +76,7 @@
     """
 
     def __init__(self):
-        self.mapping_registry = DummyForeignVcsMappingRegistry()
+        self.mapping_registry = DummyForeignVcsMappingRegistry(None, None)
         self.mapping_registry.register("v1", DummyForeignVcsMapping(self),
                                        "Version 1")
         self.abbreviation = "dummy"
 
=== modified file 'bzrlib/tests/test_registry.py'
--- bzrlib/tests/test_registry.py	2012-01-25 21:13:15 +0000
+++ bzrlib/tests/test_registry.py	2012-03-31 14:09:30 +0000
@@ -22,6 +22,7 @@
 from bzrlib import (
     branch,
     osutils,
+    pyutils,
     registry,
     tests,
     )
@@ -238,7 +239,7 @@
         # We peek under the covers because the alternative is to use lazy
         # registration and create a module that can reference our test registry
         # it's too much work for such a corner case -- vila 090916
-        self.registry._dict['hacky'] = InvasiveGetter(None)
+        self.registry._dict['hacky'] = registry.RegistryEntry(InvasiveGetter(None), None, None)
 
     def _iter_them(self, iter_func_name):
         iter_func = getattr(self.registry, iter_func_name, None)
@@ -354,3 +355,41 @@
         a_registry.register("obj", AThing())
         self.assertEquals("bzrlib.tests.test_registry",
             a_registry._get_module("obj"))
+
+
+
+class TestLazyRegistry(tests.TestCase):
+    """Test bzrlib.registry.register_lazy."""
+
+    def test_valid_lazy_registries(self):
+        # Make sure that all the registered lazy hooks are referring to existing
+        # hook points which allow lazy registration.
+        for key, registry_dict in registry._lazy_registries.iteritems():
+            (module_name, member_name) = key
+            obj = pyutils.get_named_object(module_name, member_name)
+            self.assertIsInstance(obj, registry.Registry)
+            self.assertIsInstance(registry_dict, dict)
+            self.assertIs(obj._dict, registry_dict)
+
+    def test_register_lazy(self):
+        # A lazily registered entry shows up if the registry is later created
+        registry.register_lazy("bzrlib.tests.test_registry", "SomeRegistry",
+                "myname", "bzrlib.tests.test_registry", "TestLazyRegistry",
+                help="HELLUP!", info="Informatief")
+        a_registry = registry.Registry("bzrlib.tests.test_registry", "SomeRegistry")
+        self.addCleanup(registry._lazy_registries.__delitem__,
+            ("bzrlib.tests.test_registry", "SomeRegistry"))
+        self.assertEquals([("myname", TestLazyRegistry)], a_registry.items())
+
+    def test_register_lazy_dupe(self):
+        # Two registry entries can't be registered with the same name
+        registry.register_lazy("bzrlib.tests.test_registry", "SomeRegistry",
+                "myname", "bzrlib.tests.test_registry", "TestLazyRegistry")
+        self.addCleanup(registry._lazy_registries.__delitem__,
+            ("bzrlib.tests.test_registry", "SomeRegistry"))
+        self.assertRaises(KeyError,
+            registry.register_lazy, "bzrlib.tests.test_registry", "SomeRegistry",
+                "myname", "bzrlib.tests.test_registry", "TestLazyRegistry")
+        registry.register_lazy("bzrlib.tests.test_registry", "SomeRegistry",
+            "myname", "bzrlib.tests.test_registry", "TestLazyRegistry",
+            override_existing=True)
 
=== modified file 'bzrlib/transform.py'
--- bzrlib/transform.py	2012-03-14 10:17:12 +0000
+++ bzrlib/transform.py	2012-03-31 14:09:30 +0000
@@ -1461,7 +1461,7 @@
     raise OrphaningForbidden('never')
 
 
-orphaning_registry = registry.Registry()
+orphaning_registry = registry.Registry("bzrlib.transform", "orphaning_registry")
 orphaning_registry.register(
     'conflict', refuse_orphan,
     'Leave orphans in place and create a conflict on the directory.')
 
=== modified file 'bzrlib/transport/__init__.py'
--- bzrlib/transport/__init__.py	2012-03-13 17:25:29 +0000
+++ bzrlib/transport/__init__.py	2012-03-31 14:09:30 +0000
@@ -123,7 +123,8 @@
         self.register(key, [], help)
 
 
-transport_list_registry = TransportListRegistry()
+transport_list_registry = TransportListRegistry("bzrlib.transport",
+    "transport_list_registry")
 
 
 def register_transport_proto(prefix, help=None, info=None,
@@ -1890,7 +1891,8 @@
                         'HintingSSHTransport')
 
 
-transport_server_registry = registry.Registry()
+transport_server_registry = registry.Registry("bzrlib.transport",
+    "transport_server_registry")
 transport_server_registry.register_lazy('bzr', 'bzrlib.smart.server',
     'serve_bzr', help="The Bazaar smart server protocol over TCP. (default port: 4155)")
 transport_server_registry.default_key = 'bzr'
 
=== modified file 'bzrlib/version_info_formats/__init__.py'
--- bzrlib/version_info_formats/__init__.py	2011-12-30 13:02:27 +0000
+++ bzrlib/version_info_formats/__init__.py	2012-03-31 14:09:30 +0000
@@ -186,8 +186,8 @@
         raise NotImplementedError(VersionInfoBuilder.generate)
 
 
-format_registry = registry.Registry()
-
+format_registry = registry.Registry("bzrlib.version_info_formats",
+    "format_registry")
 
 format_registry.register_lazy(
     'rio',
 
=== modified file 'bzrlib/versionedfile.py'
--- bzrlib/versionedfile.py	2011-12-19 13:23:58 +0000
+++ bzrlib/versionedfile.py	2012-03-31 14:09:30 +0000
@@ -45,7 +45,7 @@
 from bzrlib.textmerge import TextMerge
 
 
-adapter_registry = Registry()
+adapter_registry = Registry("bzrlib.versionedfile", "adapter_registry")
 adapter_registry.register_lazy(('knit-delta-gz', 'fulltext'), 'bzrlib.knit',
     'DeltaPlainToFullText')
 adapter_registry.register_lazy(('knit-ft-gz', 'fulltext'), 'bzrlib.knit',
 
=== modified file 'bzrlib/workingtree.py'
--- bzrlib/workingtree.py	2012-03-29 12:27:52 +0000
+++ bzrlib/workingtree.py	2012-03-31 14:09:30 +0000
@@ -2998,8 +2998,10 @@
 class WorkingTreeFormatRegistry(controldir.ControlComponentFormatRegistry):
     """Registry for working tree formats."""
 
-    def __init__(self, other_registry=None):
-        super(WorkingTreeFormatRegistry, self).__init__(other_registry)
+    def __init__(self, module_name=None, member_name=None,
+            other_registry=None):
+        super(WorkingTreeFormatRegistry, self).__init__(module_name,
+            member_name, other_registry)
         self._default_format = None
         self._default_format_key = None
 
@@ -3021,7 +3023,8 @@
         self._default_format = None
 
 
-format_registry = WorkingTreeFormatRegistry()
+format_registry = WorkingTreeFormatRegistry("bzrlib.workingtree",
+    "format_registry")
 
 
 class WorkingTreeFormat(controldir.ControlComponentFormat):
 
=== modified file 'doc/en/release-notes/bzr-2.6.txt'
--- doc/en/release-notes/bzr-2.6.txt	2012-03-30 02:23:41 +0000
+++ doc/en/release-notes/bzr-2.6.txt	2012-03-31 14:09:30 +0000
@@ -157,6 +157,10 @@
 * New method ``Repository.verify_revision_signatures``.
   (Jelmer Vernooij)
 
+* New function ``bzrlib.registry.register_lazy`` which can
+  register new keys into registries before they are loaded.
+  (Jelmer Vernooij)
+
 * New configuration option class ``RegistryOption`` which is backed
   onto a registry. (Jelmer Vernooij)