Modernise equals-hash-mismatch

Author: joefarebrother

python/ql/src/Classes/Comparisons/EqualsOrHash.ql

@@ -14,50 +14,13 @@
 
 import python
 
-CallableValue defines_equality(ClassValue c, string name) {
-  (
-    name = "__eq__"
-    or
-    major_version() = 2 and name = "__cmp__"
-  ) and
-  result = c.declaredAttribute(name)
+predicate missingEquality(Class cls, Function defined) {
+  defined = cls.getMethod("__hash__") and
+  not exists(cls.getMethod("__eq__"))
+  // In python 3, the case of defined eq without hash automatically makes the class unhashable (even if a superclass defined hash)
+  // So this is not an issue.
 }
 
-CallableValue implemented_method(ClassValue c, string name) {
-  result = defines_equality(c, name)
-  or
-  result = c.declaredAttribute("__hash__") and name = "__hash__"
-}
-
-string unimplemented_method(ClassValue c) {
-  not exists(defines_equality(c, _)) and
-  (
-    result = "__eq__" and major_version() = 3
-    or
-    major_version() = 2 and result = "__eq__ or __cmp__"
-  )
-  or
-  /* Python 3 automatically makes classes unhashable if __eq__ is defined, but __hash__ is not */
-  not c.declaresAttribute(result) and result = "__hash__" and major_version() = 2
-}
-
-/** Holds if this class is unhashable */
-predicate unhashable(ClassValue cls) {
-  cls.lookup("__hash__") = Value::named("None")
-  or
-  cls.lookup("__hash__").(CallableValue).neverReturns()
-}
-
-predicate violates_hash_contract(ClassValue c, string present, string missing, Value method) {
-  not unhashable(c) and
-  missing = unimplemented_method(c) and
-  method = implemented_method(c, present) and
-  not c.failedInference(_)
-}
-
-from ClassValue c, string present, string missing, CallableValue method
-where
-  violates_hash_contract(c, present, missing, method) and
-  exists(c.getScope()) // Suppress results that aren't from source
-select method, "Class $@ implements " + present + " but does not define " + missing + ".", c,
-  c.getName()
+from Class cls, Function defined
+where missingEquality(cls, defined)
+select cls, "This class implements $@, but does not implement __eq__.", defined, defined.getName()