ZCML directives without zope.security support
=============================================

This tests run without zope.security available:

  >>> from zope.component.zcml import check_security_support
  >>> check_security_support()
  Traceback (most recent call last):
  ...
  ConfigurationError: security proxied components are not supported because zope.security is not available

Components may be registered using the registration API exposed by
``zope.component`` (provideAdapter, provideUtility, etc.).  They may
also be registered using configuration files.  The common way to do
that is by using ZCML (Zope Configuration Markup Language), an XML
spelling of component registration.

In ZCML, each XML element is a *directive*.  There are different
top-level directives that let us register components.  We will
introduce them one by one here.

This helper will let us easily execute ZCML snippets:

  >>> from cStringIO import StringIO
  >>> from zope.configuration.xmlconfig import xmlconfig
  >>> def runSnippet(snippet):
  ...     template = """\
  ...     <configure xmlns='http://namespaces.zope.org/zope'
  ...                i18n_domain="zope">
  ...     %s
  ...     </configure>"""
  ...     xmlconfig(StringIO(template % snippet))

adapter
-------

Adapters play a key role in the Component Architecture.  In ZCML, they
are registered with the <adapter /> directive.

  >>> from zope.component.testfiles.adapter import A1, A2, A3, Handler
  >>> from zope.component.testfiles.adapter import I1, I2, I3, IS
  >>> from zope.component.testfiles.components import IContent, Content, Comp, comp

Before we register the first test adapter, we can verify that adapter
lookup doesn't work yet:

  >>> from zope.component.tests import clearZCML
  >>> clearZCML()
  >>> from zope.component.testfiles.components import IApp
  >>> IApp(Content(), None) is None
  True

Then we register the adapter and see that the lookup works:

  >>> runSnippet('''
  ...   <adapter
  ...       factory="zope.component.testfiles.components.Comp"
  ...       provides="zope.component.testfiles.components.IApp"
  ...       for="zope.component.testfiles.components.IContent"
  ...       />''')

  >>> IApp(Content()).__class__
  <class 'zope.component.testfiles.components.Comp'>

It is also possible to give adapters names.  Then the combination of
required interface, provided interface and name makes the adapter
lookup unique.  The name is supplied using the ``name`` argument to
the <adapter /> directive:

  >>> from zope.component.tests import clearZCML
  >>> clearZCML()
  >>> import zope.component
  >>> zope.component.queryAdapter(Content(), IApp, 'test') is None
  True

  >>> runSnippet('''
  ...   <adapter
  ...       factory="zope.component.testfiles.components.Comp"
  ...       provides="zope.component.testfiles.components.IApp"
  ...       for="zope.component.testfiles.components.IContent"
  ...       name="test"
  ...       />''')

  >>> zope.component.getAdapter(Content(), IApp, 'test').__class__
  <class 'zope.component.testfiles.components.Comp'>

Adapter factories
~~~~~~~~~~~~~~~~~

It is possible to supply more than one adapter factory.  In this case,
during adapter lookup each factory will be called and the return value
will be given to the next factory.  The return value of the last
factory is returned as the result of the adapter lookup.  For examle:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <adapter
  ...       factory="zope.component.testfiles.adapter.A1
  ...                zope.component.testfiles.adapter.A2
  ...                zope.component.testfiles.adapter.A3"
  ...       provides="zope.component.testfiles.components.IApp"
  ...       for="zope.component.testfiles.components.IContent"
  ...       />''')

The resulting adapter is an A3, around an A2, around an A1, around the
adapted object:

  >>> content = Content()
  >>> a3 = IApp(content)
  >>> a3.__class__ is A3
  True

  >>> a2 = a3.context[0]
  >>> a2.__class__ is A2
  True

  >>> a1 = a2.context[0]
  >>> a1.__class__ is A1
  True

  >>> a1.context[0] is content
  True

Of course, if no factory is provided at all, we will get an error:

  >>> runSnippet('''
  ...   <adapter
  ...       factory=""
  ...       provides="zope.component.testfiles.components.IApp"
  ...       for="zope.component.testfiles.components.IContent"
  ...       />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-8.8
      ValueError: No factory specified

Declaring ``for`` and ``provides`` in Python
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The <adapter /> directive can figure out from the in-line Python
declaration (using ``zope.component.adapts()`` or
``zope.component.adapter()`` as well as ``zope.interface.implements``)
what the adapter should be registered for and what it provides::

  >>> clearZCML()
  >>> IApp(Content(), None) is None
  True

  >>> runSnippet('''
  ...   <adapter factory="zope.component.testfiles.components.Comp" />''')

  >>> IApp(Content()).__class__
  <class 'zope.component.testfiles.components.Comp'>

Of course, if the adapter has no ``implements()`` declaration, ZCML
can't figure out what it provides:

  >>> runSnippet('''
  ...   <adapter
  ...       factory="zope.component.testfiles.adapter.A4"
  ...       for="zope.component.testfiles.components.IContent"
  ...       />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-7.8
      TypeError: Missing 'provides' attribute

On the other hand, if the factory implements more than one interface,
ZCML can't figure out what it should provide either:

  >>> runSnippet('''
  ...   <adapter
  ...       factory="zope.component.testfiles.adapter.A5"
  ...       for="zope.component.testfiles.components.IContent"
  ...       />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-7.8
      TypeError: Missing 'provides' attribute

A not so common edge case is registering adapters directly for
classes, not for interfaces.  For example:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <adapter
  ...       for="zope.component.testfiles.components.Content"
  ...       provides="zope.component.testfiles.adapter.I1"
  ...       factory="zope.component.testfiles.adapter.A1"
  ...       />''')

  >>> content = Content()
  >>> a1 = zope.component.getAdapter(content, I1, '')
  >>> isinstance(a1, A1)
  True

This time, any object providing ``IContent`` won't work if it's not an
instance of the ``Content`` class:

  >>> import zope.interface
  >>> class MyContent:
  ...     zope.interface.implements(IContent)
  >>> zope.component.getAdapter(MyContent(), I1, '')  # doctest: +ELLIPSIS
  Traceback (most recent call last):
    ...
  ComponentLookupError: ...

Multi-adapters
~~~~~~~~~~~~~~

Conventional adapters adapt one object to provide another interface.
Multi-adapters adapt several objects at once:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <adapter
  ...       for="zope.component.testfiles.components.IContent
  ...            zope.component.testfiles.adapter.I1
  ...            zope.component.testfiles.adapter.I2"
  ...       provides="zope.component.testfiles.adapter.I3"
  ...       factory="zope.component.testfiles.adapter.A3"
  ...       />''')

  >>> content = Content()
  >>> a1 = A1()
  >>> a2 = A2()
  >>> a3 = zope.component.queryMultiAdapter((content, a1, a2), I3)
  >>> a3.__class__ is A3
  True
  >>> a3.context == (content, a1, a2)
  True

You can even adapt an empty list of objects (we call this a
null-adapter):

  >>> clearZCML()
  >>> runSnippet('''
  ...   <adapter
  ...       for=""
  ...       provides="zope.component.testfiles.adapter.I3"
  ...       factory="zope.component.testfiles.adapter.A3"
  ...       />''')

  >>> a3 = zope.component.queryMultiAdapter((), I3)
  >>> a3.__class__ is A3
  True
  >>> a3.context == ()
  True

Even with multi-adapters, ZCML can figure out the ``for`` and
``provides`` parameters from the Python declarations:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <adapter factory="zope.component.testfiles.adapter.A3" />''')

  >>> a3 = zope.component.queryMultiAdapter((content, a1, a2), I3)
  >>> a3.__class__ is A3
  True
  >>> a3.context == (content, a1, a2)
  True

Chained factories are not supported for multi-adapters, though:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <adapter
  ...       for="zope.component.testfiles.components.IContent
  ...            zope.component.testfiles.adapter.I1
  ...            zope.component.testfiles.adapter.I2"
  ...       provides="zope.component.testfiles.components.IApp"
  ...       factory="zope.component.testfiles.adapter.A1
  ...                zope.component.testfiles.adapter.A2"
  ...       />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-11.8
      ValueError: Can't use multiple factories and multiple for

And neither for null-adapters:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <adapter
  ...       for=""
  ...       provides="zope.component.testfiles.components.IApp"
  ...       factory="zope.component.testfiles.adapter.A1
  ...                zope.component.testfiles.adapter.A2"
  ...       />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-9.8
      ValueError: Can't use multiple factories and multiple for

subscriber
----------

With the <subscriber /> directive you can register subscription
adapters or event subscribers with the adapter registry.  Consider
this very typical example of a <subscriber /> directive:
 
  >>> clearZCML()
  >>> runSnippet('''
  ...   <subscriber
  ...       provides="zope.component.testfiles.adapter.IS"
  ...       factory="zope.component.testfiles.adapter.A3"
  ...       for="zope.component.testfiles.components.IContent
  ...            zope.component.testfiles.adapter.I1"
  ...       />''')

  >>> content = Content()
  >>> a1 = A1()

  >>> subscribers = zope.component.subscribers((content, a1), IS)
  >>> a3 = subscribers[0]
  >>> a3.__class__ is A3
  True
  >>> a3.context == (content, a1)
  True

Note how ZCML provides some additional information when registering
components, such as the ZCML filename and line numbers:

  >>> sm = zope.component.getSiteManager()
  >>> doc = [reg.info for reg in sm.registeredSubscriptionAdapters()
  ...        if reg.provided is IS][0]
  >>> print doc
  File "<string>", line 4.2-9.8
    Could not read source.

The "fun" behind subscription adapters/subscribers is that when
several ones are declared for the same for/provides, they are all
found.  With regular adapters, the most specific one (and in doubt the
one registered last) wins.  Consider these two subscribers:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <subscriber
  ...       provides="zope.component.testfiles.adapter.IS"
  ...       factory="zope.component.testfiles.adapter.A3"
  ...       for="zope.component.testfiles.components.IContent
  ...            zope.component.testfiles.adapter.I1"
  ...       />
  ...   <subscriber
  ...       provides="zope.component.testfiles.adapter.IS"
  ...       factory="zope.component.testfiles.adapter.A2"
  ...       for="zope.component.testfiles.components.IContent
  ...            zope.component.testfiles.adapter.I1"
  ...       />''')

  >>> subscribers = zope.component.subscribers((content, a1), IS)
  >>> len(subscribers)
  2
  >>> sorted([a.__class__.__name__ for a in subscribers])
  ['A2', 'A3']

Declaring ``for`` and ``provides`` in Python
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Like the <adapter /> directive, the <subscriber /> directive can
figure out from the in-line Python declaration (using
``zope.component.adapts()`` or ``zope.component.adapter()``) what the
subscriber should be registered for:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <subscriber
  ...       provides="zope.component.testfiles.adapter.IS"
  ...       factory="zope.component.testfiles.adapter.A3"
  ...       />''')

  >>> content = Content()
  >>> a2 = A2()
  >>> subscribers = zope.component.subscribers((content, a1, a2), IS)

  >>> a3 = subscribers[0]
  >>> a3.__class__ is A3
  True
  >>> a3.context == (content, a1, a2)
  True

In the same way the directive can figure out what a subscriber
provides:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <subscriber handler="zope.component.testfiles.adapter.A3" />''')

  >>> sm = zope.component.getSiteManager()
  >>> a3 = sm.adapters.subscriptions((IContent, I1, I2), None)[0]
  >>> a3 is A3
  True

A not so common edge case is declaring subscribers directly for
classes, not for interfaces.  For example:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <subscriber
  ...       for="zope.component.testfiles.components.Content"
  ...       provides="zope.component.testfiles.adapter.I1"
  ...       factory="zope.component.testfiles.adapter.A1"
  ...       />''')

  >>> subs = list(zope.component.subscribers((Content(),), I1))
  >>> isinstance(subs[0], A1)
  True

This time, any object providing ``IContent`` won't work if it's not an
instance of the ``Content`` class:

  >>> list(zope.component.subscribers((MyContent(),), I1))
  []

Event subscriber (handlers)
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sometimes, subscribers don't need to be adapters that actually provide
anything.  It's enough that a callable is called for a certain event.

  >>> clearZCML()
  >>> runSnippet('''
  ...   <subscriber
  ...       for="zope.component.testfiles.components.IContent
  ...            zope.component.testfiles.adapter.I1"
  ...       handler="zope.component.testfiles.adapter.Handler"
  ...       />''')

In this case, simply getting the subscribers is enough to invoke them:

  >>> list(zope.component.subscribers((content, a1), None))
  []
  >>> content.args == ((a1,),)
  True


utility
-------

Apart from adapters (and subscription adapters), the Component
Architecture knows a second kind of component: utilities.  They are
registered using the <utility /> directive.

Before we register the first test utility, we can verify that utility
lookup doesn't work yet:

  >>> clearZCML()
  >>> zope.component.queryUtility(IApp) is None
  True

Then we register the utility:

  >>> runSnippet('''
  ...   <utility
  ...       component="zope.component.testfiles.components.comp"
  ...       provides="zope.component.testfiles.components.IApp"
  ...       />''')
  >>> zope.component.getUtility(IApp) is comp
  True

Like adapters, utilities can also have names.  There can be more than
one utility registered for a certain interface, as long as they each
have a different name.

First, we make sure that there's no utility yet:

  >>> clearZCML()
  >>> zope.component.queryUtility(IApp, 'test') is None
  True

Then we register it:

  >>> runSnippet('''
  ...   <utility
  ...       component="zope.component.testfiles.components.comp"
  ...       provides="zope.component.testfiles.components.IApp"
  ...       name="test"
  ...       />''')
  >>> zope.component.getUtility(IApp, 'test') is comp
  True

Utilities can also be registered from a factory.  In this case, the
ZCML handler calls the factory (without any arguments) and registers
the returned value as a utility.  Typically, you'd pass a class for
the factory:

  >>> clearZCML()
  >>> zope.component.queryUtility(IApp) is None
  True

  >>> runSnippet('''
  ...   <utility
  ...       factory="zope.component.testfiles.components.Comp"
  ...       provides="zope.component.testfiles.components.IApp"
  ...       />''')
  >>> zope.component.getUtility(IApp).__class__ is Comp
  True

Declaring ``provides`` in Python
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Like other directives, <utility /> can also figure out which interface
a utility provides from the Python declaration:

  >>> clearZCML()
  >>> zope.component.queryUtility(IApp) is None
  True

  >>> runSnippet('''
  ...   <utility component="zope.component.testfiles.components.comp" />''')
  >>> zope.component.getUtility(IApp) is comp
  True

It won't work if the component that is to be registered doesn't
provide anything:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <utility component="zope.component.testfiles.adapter.a4" />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-4.61
      TypeError: Missing 'provides' attribute

Or if more than one interface is provided (then the ZCML directive
handler doesn't know under which the utility should be registered):

  >>> clearZCML()
  >>> runSnippet('''
  ...   <utility component="zope.component.testfiles.adapter.a5" />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-4.61
      TypeError: Missing 'provides' attribute

We can repeat the same drill for utility factories:

  >>> clearZCML()
  >>> runSnippet('''
  ...   <utility factory="zope.component.testfiles.components.Comp" />''')
  >>> zope.component.getUtility(IApp).__class__ is Comp
  True

  >>> runSnippet('''
  ...   <utility factory="zope.component.testfiles.adapter.A4" />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-4.59
      TypeError: Missing 'provides' attribute

  >>> clearZCML()
  >>> runSnippet('''
  ...   <utility factory="zope.component.testfiles.adapter.A5" />''')
  Traceback (most recent call last):
    ...
  ZopeXMLConfigurationError: File "<string>", line 4.2-4.59
      TypeError: Missing 'provides' attribute

interface
---------

The <interface /> directive lets us register an interface.  Interfaces
are registered as named utilities.  We therefore needn't go though all
the lookup details again, it is sufficient to see whether the
directive handler emits the right actions.

First we provide a stub configuration context:

  >>> import re, pprint
  >>> atre = re.compile(' at [0-9a-fA-Fx]+')
  >>> class Context(object):
  ...    actions = ()
  ...    def action(self, discriminator, callable, args):
  ...        self.actions += ((discriminator, callable, args), )
  ...    def __repr__(self):
  ...        stream = StringIO()
  ...        pprinter = pprint.PrettyPrinter(stream=stream, width=60)
  ...        pprinter.pprint(self.actions)
  ...        r = stream.getvalue()
  ...        return (''.join(atre.split(r))).strip()
  >>> context = Context()

Then we provide a test interface that we'd like to register:

  >>> from zope.interface import Interface
  >>> class I(Interface):
  ...     pass

It doesn't yet provide ``ITestType``:

  >>> from zope.component.tests import ITestType
  >>> ITestType.providedBy(I)
  False

However, after calling the directive handler...

  >>> from zope.component.zcml import interface
  >>> interface(context, I, ITestType)
  >>> context
  ((None,
    <function provideInterface>,
    ('',
     <InterfaceClass __builtin__.I>,
     <InterfaceClass zope.component.tests.ITestType>)),)

...it does provide ``ITestType``:

  >>> from zope.interface.interfaces import IInterface
  >>> ITestType.extends(IInterface)
  True
  >>> IInterface.providedBy(I)
  True