Merge pull request #36 from zopefoundation/issue34redux

Ensure all objects have consistent resolution errors

.travis.yml

@@ -2,6 +2,7 @@ language: python
 
 env:
   global:
+    ZOPE_INTERFACE_STRICT_IRO: 1
     TWINE_USERNAME: zope.wheelbuilder
     TWINE_PASSWORD:
       secure: "G1ORcUIV439Iws2toGhxPvYvQKQt6L1wyXfIMspz2xtjJvQ2D1XrqK8dRYyQ0YaGLY/OAI8BrEdTp/l7jrhiG0gXMeAs0k1KFbp7ATahcVT8rWOzvcLGMAiYRVloQ3rz5x5HjMm0CWpDjo1MAeJMmesyq8RlmYzaMu4aw1mBd/Y="

CHANGES.rst

@@ -12,6 +12,9 @@
 
 - Drop support for the deprecated ``python setup.py test`` command.
 
+- Ensure all objects have consistent interface resolution orders. This
+  may slightly change the order of interfaces for ``ContainedProxy``
+  objects. See `issue 34 <https://github.com/zopefoundation/zope.container/issues/34>`_.
 
 4.3.0 (2019-11-11)
 ==================

src/zope/container/_util.py

@@ -178,8 +178,16 @@ def find_impl():
             if static:
                 v = staticmethod(v)
             setattr(py_impl, k, v)
-        # copy the interface declarations.
+        # copy the interface declarations, being careful not
+        # to redeclare interfaces already implemented (through
+        # inheritance usually)
         implements = list(implementedBy(py_impl))
-        if implements:
+        implemented_by_c = implementedBy(c_impl)
+        implements = [
+            iface
+            for iface in implements
+            if not implemented_by_c.isOrExtends(iface)
+        ]
+        if implements: # pragma: no cover
             classImplements(c_impl, *implements)
     return c_impl

src/zope/container/contained.py

@@ -18,8 +18,9 @@
 
 import zope.component
 
-import zope.interface.declarations
-from zope.interface import providedBy, Interface
+from zope.interface import providedBy
+from zope.interface import Interface
+from zope.interface import implementedBy
 from zope.interface.declarations import getObjectSpecification
 from zope.interface.declarations import Provides
 
@@ -902,12 +903,13 @@ class DecoratorSpecificationDescriptor(
 
     When we decorate objects, what order should the interfaces come in? One
     could argue that decorators are less specific, so they should come last.
+    This is subject to respecting the C3 resolution order, of course.
 
     >>> [interface.getName() for interface in list(providedBy(D1(x)))]
     ['I4', 'I3', 'I1', 'IContained', 'IPersistent']
 
     >>> [interface.getName() for interface in list(providedBy(D2(D1(x))))]
-    ['I4', 'I3', 'I1', 'IContained', 'IPersistent', 'I2']
+    ['I4', 'I3', 'I1', 'I2', 'IContained', 'IPersistent']
     """
     def __get__(self, inst, cls=None):
         if inst is None: # pragma: no cover (Not sure how we can get here)
@@ -918,6 +920,10 @@ def __get__(self, inst, cls=None):
         # Use type rather than __class__ because inst is a proxy and
         # will return the proxied object's class.
         cls = type(inst)
+        implemented_by_cls = implementedBy(cls)
+        for iface in list(provided):
+            if implemented_by_cls.isOrExtends(iface):
+                provided = provided - iface
         return Provides(cls, provided)
 
 

tox.ini

@@ -12,6 +12,7 @@ deps =
     coverage
 setenv =
     PURE_PYTHON=0
+    ZOPE_INTERFACE_STRICT_IRO=1
     pure: PURE_PYTHON=1
     pypy: PURE_PYTHON=1
     pypy3: PURE_PYTHON=1