Adds fix for __init_subclass__ bug. (#2390)

* Adds fix for __init_subclass__ bug.

* Adds test case.

* Move test on name.

I think it makes more sense here, alongside the other "special" method names.

Author: BekaValentine

python/ql/src/Functions/NonSelf.ql

@@ -31,6 +31,7 @@ where
         cls.isNewStyle() and
         not name = "__new__" and
         not name = "__metaclass__" and
+        not name = "__init_subclass__" and
         /* declared in scope */
         f.getScope() = cls.getScope()
     ) and

python/ql/test/query-tests/Functions/general/parameter_names.py

@@ -117,3 +117,18 @@ def meth(arg):
         pass
 
 Z().meth(0)
+
+
+
+# The `__init_subclass__` method is a new method introduced into Python 3.6
+# which does not follow the normal conventions, and is in fact a class method
+# despite not being marked as such with other means. The name alone is what
+# makes it such. As a consequence, the query `py/not-named-self` and other
+# relevant queries need to account for this.
+#
+# This has come up in the wild via LGTM as a false positive. For example,
+# https://docs.python.org/3/reference/datamodel.html#customizing-class-creation
+
+class InitSubclass(object):
+    def __init_subclass__(cls):
+        pass