The _empty singleton has no-op subscribe/unsubscribe methods.issue162

Turns out they can be called in some very strange error cases. See #162 and #163 for details.

This should fix #162 (at least the provided test case, five.intid, passes now).

It also does enough work on #163 that (a) the test can be written and run in pure-python mode, which was needed to debug it and (b) five.intid runs in pure-python mode (well, with a bunch of other small hacks to Acquisition, ExtensionClass, DocumentTemplate and AccessControl), but I won't claim that it fully fixes #163. For one thing, there are no specific tests. For another, I see more such differences.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/zope/interface/tests/test_adapter.py b/src/zope/interface/tests/test_adapter.py
index 25cb4bb..6703a48 100644
--- a/src/zope/interface/tests/test_adapter.py
+++ b/src/zope/interface/tests/test_adapter.py
@@ -997,6 +997,24 @@ class AdapterLookupBaseTests(unittest.TestCase):
         result = alb.queryMultiAdapter((foo,), IBar, default=_default)
         self.assertTrue(result is _default)
 
+    def test_queryMultiAdapter_errors_on_attribute_access(self):
+        # Which leads to using the _empty singleton as "requires"
+        # argument. See https://github.com/zopefoundation/zope.interface/issues/162
+        from zope.interface.interface import InterfaceClass
+        IFoo = InterfaceClass('IFoo')
+        registry = self._makeRegistry()
+        alb = self._makeOne(registry)
+        alb.lookup = alb._uncached_lookup
+        class UnexpectedErrorsLikeAcquisition(object):
+
+            def __getattribute__(self, name):
+                raise RuntimeError("Acquisition does this. Ha-ha!")
+
+        result = alb.queryMultiAdapter(
+            (UnexpectedErrorsLikeAcquisition(),),
+            IFoo,
+        )
+
     def test_queryMultiAdaptor_factory_miss(self):
         from zope.interface.declarations import implementer
         from zope.interface.interface import InterfaceClass