Exclude 'methods' used in initialisation, and allow self for metaclass methods

Author: joefarebrother

python/ql/src/Functions/MethodArgNames.qll

@@ -2,6 +2,7 @@
 
 import python
 import semmle.python.ApiGraphs
+import DataFlow
 
 /** Holds if `f` is a method of the class `c`. */
 private predicate methodOfClass(Function f, Class c) { f.getScope() = c }
@@ -34,13 +35,29 @@ private predicate isZopeInterface(Class c) {
         .asExpr()
 }
 
+/**
+ * Holds if `f` is used in the initialisation of `c`.
+ * This means `f` isn't being used as a normal method.
+ * Ideally it should be a `@staticmethod`; however this wasn't possible prior to Python 3.10.
+ * We exclude this case from the `not-named-self` query.
+ * However there is potential for a new query that specifically covers and alerts for this case.
+ */
+private predicate usedInInit(Function f, Class c) {
+  methodOfClass(f, c) and
+  exists(Call call |
+    call.getScope() = c and
+    DataFlow::localFlow(DataFlow::exprNode(f.getDefinition()), DataFlow::exprNode(call.getFunc()))
+  )
+}
+
 /** Holds if the first parameter of `f` should be named `self`. */
 predicate shouldBeSelf(Function f, Class c) {
   methodOfClass(f, c) and
   not isStaticMethod(f) and
   not isClassMethod(f) and
   not isMetaclass(c) and
-  not isZopeInterface(c)
+  not isZopeInterface(c) and
+  not usedInInit(f, c)
 }
 
 /** Holds if the first parameter of `f` should be named `cls`. */
@@ -73,8 +90,17 @@ predicate firstArgShouldBeNamedSelfAndIsnt(Function f) {
   not firstArgNamedSelf(f)
 }
 
+/** Holds if `f` is a regular method of a metaclass, and its first argument is named `self`. */
+private predicate metaclassNamedSelf(Function f, Class c) {
+  methodOfClass(f, c) and
+  firstArgNamedSelf(f) and
+  isMetaclass(c) and
+  not isClassMethod(f)
+}
+
 /** Holds if the first parameter of `f` should be named `cls`, but isn't. */
 predicate firstArgShouldBeNamedClsAndIsnt(Function f) {
   shouldBeCls(f, _) and
-  not firstArgNamedCls(f)
+  not firstArgNamedCls(f) and
+  not metaclassNamedSelf(f, _)
 }