Ensure consistent IRO for all objects.issue49

This requires switching some tests to the plain unittest runner right now because of cyclic dependencies.

Fixes #49

7 files changed, 76 insertions, 18 deletions

diff --git a/.travis.yml b/.travis.yml
index 05ad82f..3c93078 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,19 +1,36 @@
 language: python
 sudo: false
+
+env:
+  global:
+    ZOPE_INTERFACE_STRICT_IRO: 1
+
 python:
   - 2.7
-  - 3.4
   - 3.5
   - 3.6
+  - 3.7
+  - 3.8
   - pypy
   - pypy3
-matrix:
+jobs:
   include:
-    - python: "3.7"
-      dist: xenial
-      sudo: true
+    - name: Documentation
+      python: 3.8
+      install:
+        - pip install -U -e .[docs]
+      env: ZOPE_INTERFACE_STRICT_IRO=0
+      script:
+        - sphinx-build -b html -d docs/_build/doctrees docs docs/_build/html
+        - sphinx-build -b doctest -d docs/_build/doctrees docs docs/_build/doctest
+      after_success:
+
+
 script:
-  - coverage run -m zope.testrunner --test-path=src  --auto-color --auto-progress
+# Temporary work around. Avoid zope.testrunner
+# pending https://github.com/zopefoundation/zope.security/issues/71
+# due to cyclic dependency.
+  - coverage run -m unittest discover -s src
 
 after_success:
   - coveralls
diff --git a/CHANGES.rst b/CHANGES.rst
index ad1b358..b083fb9 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -4,7 +4,12 @@ Changes
 4.4.0 (unreleased)
 ------------------
 
-- Nothing changed yet.
+- Ensure a consistent interface resolution order for all objects. See
+  `issue 49 <https://github.com/zopefoundation/zope.configuration/issues/49>`_.
+
+- Drop support for Python 3.4.
+
+- Add support for Python 3.8.
 
 
 4.3.1 (2019-02-12)
diff --git a/setup.py b/setup.py
index 90a1c03..003eeaf 100644
--- a/setup.py
+++ b/setup.py
@@ -54,10 +54,10 @@ setup(name='zope.configuration',
           "Programming Language :: Python :: 2",
           'Programming Language :: Python :: 2.7',
           "Programming Language :: Python :: 3",
-          'Programming Language :: Python :: 3.4',
           'Programming Language :: Python :: 3.5',
           'Programming Language :: Python :: 3.6',
           'Programming Language :: Python :: 3.7',
+          'Programming Language :: Python :: 3.8',
           'Programming Language :: Python :: Implementation :: CPython',
           'Programming Language :: Python :: Implementation :: PyPy',
           'Natural Language :: English',
diff --git a/src/zope/configuration/_compat.py b/src/zope/configuration/_compat.py
index a7d8286..e8b1b51 100644
--- a/src/zope/configuration/_compat.py
+++ b/src/zope/configuration/_compat.py
@@ -42,3 +42,27 @@ else: # pragma: no cover
 def reraise(tp, value, tb=None):
     raise tp, value, tb
 """)
+
+
+class implementer_if_needed(object):
+    # Helper to make sure we don't redundantly implement
+    # interfaces already inherited. Doing so tends to produce
+    # problems with the C3 order. In this package, we could easily
+    # statically determine to elide the relevant interfaces, but
+    # this is a defense against changes in parent classes and lessens
+    # the testing burden.
+    def __init__(self, *ifaces):
+        self._ifaces = ifaces
+
+    def __call__(self, cls):
+        from zope.interface import implementedBy
+        from zope.interface import implementer
+
+        ifaces_needed = []
+        implemented = implementedBy(cls)
+        ifaces_needed = [
+            iface
+            for iface in self._ifaces
+            if not implemented.isOrExtends(iface)
+        ]
+        return implementer(*ifaces_needed)(cls)
diff --git a/src/zope/configuration/config.py b/src/zope/configuration/config.py
index 0123021..30a7566 100644
--- a/src/zope/configuration/config.py
+++ b/src/zope/configuration/config.py
@@ -37,6 +37,7 @@ from zope.configuration._compat import builtins
 from zope.configuration._compat import reraise
 from zope.configuration._compat import string_types
 from zope.configuration._compat import text_type
+from zope.configuration._compat import implementer_if_needed
 
 __all__ = [
     'ConfigurationContext',
@@ -897,7 +898,7 @@ class RootStackItem(object):
     def finish(self):
         pass
 
-@implementer(IStackItem)
+@implementer_if_needed(IStackItem)
 class GroupingStackItem(RootStackItem):
     """
     Stack item for a grouping directive
diff --git a/src/zope/configuration/fields.py b/src/zope/configuration/fields.py
index c4af0ad..4a83103 100644
--- a/src/zope/configuration/fields.py
+++ b/src/zope/configuration/fields.py
@@ -31,6 +31,7 @@ from zope.schema.interfaces import InvalidValue
 
 from zope.configuration.exceptions import ConfigurationError
 from zope.configuration.interfaces import InvalidToken
+from zope.configuration._compat import implementer_if_needed
 
 __all__ = [
     'Bool',
@@ -91,7 +92,7 @@ class PythonIdentifier(schema_PythonIdentifier):
             raise ValidationError(value).with_field_and_value(self, value)
 
 
-@implementer(IFromUnicode)
+@implementer_if_needed(IFromUnicode)
 class GlobalObject(Field):
     """
     An object that can be accessed as a module global.
@@ -176,7 +177,7 @@ class GlobalObject(Field):
         return value
 
 
-@implementer(IFromUnicode)
+@implementer_if_needed(IFromUnicode)
 class GlobalInterface(GlobalObject):
     """
     An interface that can be accessed from a module.
@@ -297,7 +298,7 @@ class PathProcessor(object):
         return filename, True
 
 
-@implementer(IFromUnicode)
+@implementer_if_needed(IFromUnicode)
 class Path(Text):
     """
     A file path name, which may be input as a relative path
@@ -376,7 +377,7 @@ class Path(Text):
         return filename
 
 
-@implementer(IFromUnicode)
+@implementer_if_needed(IFromUnicode)
 class Bool(schema_Bool):
     """
     A boolean value.
@@ -428,7 +429,7 @@ class Bool(schema_Bool):
 
 
 
-@implementer(IFromUnicode)
+@implementer_if_needed(IFromUnicode)
 class MessageID(Text):
     """
     Text string that should be translated.
@@ -439,7 +440,7 @@ class MessageID(Text):
 
     __factories = {}
 
-    def fromUnicode(self, u):
+    def fromUnicode(self, value):
         """
         Translate a string to a MessageID.
 
@@ -539,7 +540,7 @@ class MessageID(Text):
             enc = sys.getfilesystemencoding() or sys.getdefaultencoding()
             domain = domain.decode(enc)
 
-        v = super(MessageID, self).fromUnicode(u)
+        v = super(MessageID, self).fromUnicode(value)
 
         # Check whether there is an explicit message is specified
         default = None
diff --git a/tox.ini b/tox.ini
index 7d1984e..6f373e6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,12 +1,15 @@
 [tox]
 envlist =
-    py27,py34,py35,py36,py37,pypy,pypy3,coverage,docs
+    py27,py35,py36,py37,pypy,pypy3,coverage,docs
 
 [testenv]
+usedevelop = true
 deps =
     .[test]
 commands =
-    zope-testrunner --test-path=src --all []
+    python -m unittest discover -s src
+setenv =
+    ZOPE_INTERFACE_STRICT_IRO = 1
 
 [testenv:coverage]
 usedevelop = true
@@ -18,6 +21,10 @@ commands =
 deps =
     {[testenv]deps}
     coverage
+# Disabling STRICT IRO is temporary.
+setenv =
+    ZOPE_INTERFACE_STRICT_IRO = 0
+
 
 [testenv:docs]
 basepython =
@@ -29,3 +36,6 @@ deps =
     {[testenv]deps}
     Sphinx
     repoze.sphinx.autointerface
+# Disabling STRICT IRO is temporary.
+setenv =
+    ZOPE_INTERFACE_STRICT_IRO = 0