Python: Exclude "self-inheritance" results

It's not possible for a class to actually inherit from itself, so if
this happens, something has gone wrong with our analysis. We therefore
explicitly exclude these results so they don't result in false
positives.

python/ql/src/Classes/InconsistentMRO.ql

@@ -12,19 +12,27 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-ClassObject left_base(ClassObject type, ClassObject base) {
-  exists(int i | i > 0 and type.getBaseType(i) = base and result = type.getBaseType(i - 1))
+/**
+ * Gets the `i`th base class of `cls`, if it can be resolved to a user-defined class.
+ */
+Class getBaseType(Class cls, int i) {
+  cls.getBase(i) = classTracker(result).asExpr() and
+  result != cls
 }
 
-predicate invalid_mro(ClassObject t, ClassObject left, ClassObject right) {
-  t.isNewStyle() and
+Class left_base(Class type, Class base) {
+  exists(int i | i > 0 and getBaseType(type, i) = base and result = getBaseType(type, i - 1))
+}
+
+predicate invalid_mro(Class t, Class left, Class right) {
+  DuckTyping::isNewStyle(t) and
   left = left_base(t, right) and
-  left = right.getAnImproperSuperType()
+  left = getADirectSuperclass*(right)
 }
 
-from ClassObject t, ClassObject left, ClassObject right
+from Class t, Class left, Class right
 where invalid_mro(t, left, right)
 select t,
   "Construction of class " + t.getName() +

python/ql/test/2/query-tests/Classes/inconsistent-mro/InconsistentMRO.expected

@@ -1 +1 @@
-| inconsistent_mro.py:9:1:9:14 | class Z | Construction of class Z can fail due to invalid method resolution order(MRO) for bases $@ and $@. | inconsistent_mro.py:3:1:3:16 | class X | X | inconsistent_mro.py:6:1:6:11 | class Y | Y |
+| inconsistent_mro.py:9:1:9:14 | Class Z | Construction of class Z can fail due to invalid method resolution order(MRO) for bases $@ and $@. | inconsistent_mro.py:3:1:3:16 | Class X | X | inconsistent_mro.py:6:1:6:11 | Class Y | Y |

python/ql/test/3/query-tests/Classes/inconsistent-mro/InconsistentMRO.expected

@@ -1,2 +1 @@
-| inconsistent_mro.py:9:1:9:14 | class Z | Construction of class Z can fail due to invalid method resolution order(MRO) for bases $@ and $@. | inconsistent_mro.py:3:1:3:16 | class X | X | inconsistent_mro.py:6:1:6:11 | class Y | Y |
-| inconsistent_mro.py:16:1:16:19 | class N | Construction of class N can fail due to invalid method resolution order(MRO) for bases $@ and $@. | file://:Compiled Code:0:0:0:0 | builtin-class object | object | inconsistent_mro.py:12:1:12:8 | class O | O |
+| inconsistent_mro.py:9:1:9:14 | Class Z | Construction of class Z can fail due to invalid method resolution order(MRO) for bases $@ and $@. | inconsistent_mro.py:3:1:3:16 | Class X | X | inconsistent_mro.py:6:1:6:11 | Class Y | Y |