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.

Author: tausbn

python/ql/src/Classes/InconsistentMRO.ql

@@ -17,7 +17,10 @@ private import semmle.python.dataflow.new.internal.DataFlowDispatch
 /**
  * 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() }
+Class getBaseType(Class cls, int i) {
+  cls.getBase(i) = classTracker(result).asExpr() and
+  result != cls
+}
 
 Class left_base(Class type, Class base) {
   exists(int i | i > 0 and getBaseType(type, i) = base and result = getBaseType(type, i - 1))