Merge pull request #198 from zopefoundation/issue197

Ensure that objects that implement no interfaces still have Interface in iro and sro

4 files changed, 60 insertions, 13 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index 961bf72..d6965cb 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,7 +5,12 @@
 5.0.2 (unreleased)
 ==================
 
-- Nothing changed yet.
+- Ensure that objects that implement no interfaces (such as direct
+  subclasses of ``object``) still include ``Interface`` itself in
+  their ``__iro___`` and ``__sro___``. This fixes adapter registry
+  lookups for such objects when the adapter is registered for
+  ``Interface``. See `issue 197
+  <https://github.com/zopefoundation/zope.interface/issues/197>`_.
 
 
 5.0.1 (2020-03-21)
diff --git a/src/zope/interface/declarations.py b/src/zope/interface/declarations.py
index d85dbf4..e84a728 100644
--- a/src/zope/interface/declarations.py
+++ b/src/zope/interface/declarations.py
@@ -180,7 +180,7 @@ class _ImmutableDeclaration(Declaration):
         return iter(())
 
     def extends(self, interface, strict=True):
-        return False
+        return interface is self._ROOT
 
     def get(self, name, default=None):
         return default
diff --git a/src/zope/interface/interface.py b/src/zope/interface/interface.py
index 6a1ca2a..ac55633 100644
--- a/src/zope/interface/interface.py
+++ b/src/zope/interface/interface.py
@@ -1064,3 +1064,9 @@ from zope.interface.declarations import implementedBy
 from zope.interface.declarations import providedBy
 from zope.interface.exceptions import InvalidInterface
 from zope.interface.exceptions import BrokenImplementation
+
+# This ensures that ``Interface`` winds up in the flattened()
+# list of the immutable declaration. It correctly overrides changed()
+# as a no-op, so we bypass that.
+from zope.interface.declarations import _empty
+Specification.changed(_empty, _empty)
diff --git a/src/zope/interface/tests/test_declarations.py b/src/zope/interface/tests/test_declarations.py
index b0875c4..9344968 100644
--- a/src/zope/interface/tests/test_declarations.py
+++ b/src/zope/interface/tests/test_declarations.py
@@ -74,7 +74,51 @@ class NamedTests(unittest.TestCase):
         self.assertEqual(foo.__component_name__, u'foo')
 
 
-class DeclarationTests(unittest.TestCase):
+class EmptyDeclarationTests(unittest.TestCase):
+    # Tests that should pass for all objects that are empty
+    # declarations. This includes a Declaration explicitly created
+    # that way, and the empty ImmutableDeclaration.
+    def _getEmpty(self):
+        from zope.interface.declarations import Declaration
+        return Declaration()
+
+    def test___iter___empty(self):
+        decl = self._getEmpty()
+        self.assertEqual(list(decl), [])
+
+    def test_flattened_empty(self):
+        from zope.interface.interface import Interface
+        decl = self._getEmpty()
+        self.assertEqual(list(decl.flattened()), [Interface])
+
+    def test___contains___empty(self):
+        from zope.interface.interface import Interface
+        decl = self._getEmpty()
+        self.assertNotIn(Interface, decl)
+
+    def test_extends_empty(self):
+        from zope.interface.interface import Interface
+        decl = self._getEmpty()
+        self.assertTrue(decl.extends(Interface))
+        self.assertTrue(decl.extends(Interface, strict=True))
+
+    def test_interfaces_empty(self):
+        decl = self._getEmpty()
+        l = list(decl.interfaces())
+        self.assertEqual(l, [])
+
+    def test___sro___(self):
+        from zope.interface.interface import Interface
+        decl = self._getEmpty()
+        self.assertEqual(decl.__sro__, (decl, Interface,))
+
+    def test___iro___(self):
+        from zope.interface.interface import Interface
+        decl = self._getEmpty()
+        self.assertEqual(decl.__iro__, (Interface,))
+
+
+class DeclarationTests(EmptyDeclarationTests):
 
     def _getTargetClass(self):
         from zope.interface.declarations import Declaration
@@ -128,10 +172,6 @@ class DeclarationTests(unittest.TestCase):
         decl = self._makeOne(IFoo)
         self.assertIn(IFoo, decl)
 
-    def test___iter___empty(self):
-        decl = self._makeOne()
-        self.assertEqual(list(decl), [])
-
     def test___iter___single_base(self):
         from zope.interface.interface import InterfaceClass
         IFoo = InterfaceClass('IFoo')
@@ -159,11 +199,6 @@ class DeclarationTests(unittest.TestCase):
         decl = self._makeOne(IBar, (IFoo, IBar))
         self.assertEqual(list(decl), [IBar, IFoo])
 
-    def test_flattened_empty(self):
-        from zope.interface.interface import Interface
-        decl = self._makeOne()
-        self.assertEqual(list(decl.flattened()), [Interface])
-
     def test_flattened_single_base(self):
         from zope.interface.interface import Interface
         from zope.interface.interface import InterfaceClass
@@ -244,7 +279,7 @@ class DeclarationTests(unittest.TestCase):
         self.assertEqual(list(after), [IFoo, IBar, IBaz])
 
 
-class TestImmutableDeclaration(unittest.TestCase):
+class TestImmutableDeclaration(EmptyDeclarationTests):
 
     def _getTargetClass(self):
         from zope.interface.declarations import _ImmutableDeclaration
@@ -297,6 +332,7 @@ class TestImmutableDeclaration(unittest.TestCase):
         self.assertIsNone(self._getEmpty().get('name'))
         self.assertEqual(self._getEmpty().get('name', 42), 42)
 
+
 class TestImplements(NameAndModuleComparisonTestsMixin,
                      unittest.TestCase):