Python: Add ternary overridesMethod

This one also allows easy access to the method being overridden and the
class on which it resides. This let's us simplify DocStrings.ql
accordingly.

Author: tausbn

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll

@@ -2135,8 +2135,18 @@ module DuckTyping {
   /**
    * Holds if `f` overrides a method in a superclass with the same name.
    */
-  predicate overridesMethod(Function f) {
-    exists(Class cls | f.getScope() = cls | hasMethod(getADirectSuperclass(cls), f.getName()))
+  predicate overridesMethod(Function f) { overridesMethod(f, _, _) }
+
+  /**
+   * Holds if `f` overrides `overridden` declared in `superclass`.
+   */
+  predicate overridesMethod(Function f, Class superclass, Function overridden) {
+    exists(Class cls |
+      f.getScope() = cls and
+      superclass = getADirectSuperclass+(cls) and
+      overridden = superclass.getAMethod() and
+      overridden.getName() = f.getName()
+    )
   }
 
   /**

python/ql/src/Statements/DocStrings.ql

@@ -30,9 +30,7 @@ predicate needs_docstring(Scope s) {
 
 predicate function_needs_docstring(FunctionMetrics f) {
   not exists(Function base |
-    DuckTyping::overridesMethod(f) and
-    base.getScope() = getADirectSuperclass+(f.getScope()) and
-    base.getName() = f.getName() and
+    DuckTyping::overridesMethod(f, _, base) and
     not function_needs_docstring(base)
   ) and
   f.getName() != "lambda" and