Add checker for membership rules and testsmembership-test-checker

Idea of checking is very simple: value used to the right of the 'in' operator
should support membership test protocol (i.e. define either __contains__ or
__iter__ or __getitem__).

Fixes issue #589.

1 files changed, 36 insertions, 0 deletions

diff --git a/pylint/test/functional/membership_protocol_py3.py b/pylint/test/functional/membership_protocol_py3.py
new file mode 100644
index 0000000..6a77f20
--- /dev/null
+++ b/pylint/test/functional/membership_protocol_py3.py
@@ -0,0 +1,36 @@
+# pylint: disable=missing-docstring,too-few-public-methods,no-init,no-self-use,unused-argument,pointless-statement,expression-not-assigned
+
+# metaclasses that support membership test protocol
+class MetaIterable(type):
+    def __iter__(cls):
+        return iter((1, 2, 3))
+
+class MetaOldIterable(type):
+    def __getitem__(cls, key):
+        if key < 10:
+            return key ** 2
+        else:
+            raise IndexError("bad index")
+
+class MetaContainer(type):
+    def __contains__(cls, key):
+        return False
+
+
+class IterableClass(metaclass=MetaOldIterable):
+    pass
+
+class OldIterableClass(metaclass=MetaOldIterable):
+    pass
+
+class ContainerClass(metaclass=MetaContainer):
+    pass
+
+
+def test():
+    1 in IterableClass
+    1 in OldIterableClass
+    1 in ContainerClass
+    1 in IterableClass()  # [unsupported-membership-test]
+    1 in OldIterableClass()  # [unsupported-membership-test]
+    1 in ContainerClass()  # [unsupported-membership-test]