Python: Fix non-container FP relating to `MappingProxyType`.

Fixes #2307.

Also modernises the query to use the `Value` API.

python/ql/src/Expressions/ContainsNonContainer.ql

@@ -11,6 +11,7 @@
  */
 
 import python
+import semmle.python.pointsto.PointsTo
 
 predicate rhs_in_expr(ControlFlowNode rhs, Compare cmp) {
     exists(Cmpop op, int i | cmp.getOp(i) = op and cmp.getComparator(i) = rhs.getNode() |
@@ -18,13 +19,15 @@ predicate rhs_in_expr(ControlFlowNode rhs, Compare cmp) {
     )
 }
 
-from ControlFlowNode non_seq, Compare cmp, ClassObject cls, ControlFlowNode origin
+from ControlFlowNode non_seq, Compare cmp, Value v, ClassValue cls, ControlFlowNode origin
 where rhs_in_expr(non_seq, cmp) and
-non_seq.refersTo(_, cls, origin) and
-not cls.failedInference() and
+non_seq.pointsTo(_, v, origin) and
+v.getClass() = cls and
+not Types::failedInference(cls, _) and
 not cls.hasAttribute("__contains__") and
 not cls.hasAttribute("__iter__") and
 not cls.hasAttribute("__getitem__") and
-not cls = theNoneType()
+not cls = ClassValue::nonetype() and
+not cls = Value::named("types.MappingProxyType")
 
 select cmp, "This test may raise an Exception as the $@ may be of non-container class $@.", origin, "target", cls, cls.getName()

python/ql/src/semmle/python/objects/ObjectAPI.qll

@@ -660,4 +660,9 @@ module ClassValue {
         result = TBuiltinClassObject(Builtin::special("ModuleType"))
     }
 
+    /** Get the `ClassValue` for the `NoneType` class. */
+    ClassValue nonetype() {
+        result = TBuiltinClassObject(Builtin::special("NoneType"))
+    }
+
 }

python/ql/test/query-tests/Expressions/general/expressions_test.py

@@ -234,3 +234,11 @@ def func():
     except TypeError:
       return 1
     return 0
+
+# False positive for py/member-test-non-container
+
+# Container wrapped in MappingProxyType
+from types import MappingProxyType
+
+def mpt_arg(d=MappingProxyType({})):
+    return 1 in d