Python: Refactor special method query

Moves a bunch of `owner.declaredAttribute(name) = f` instances to the
top level, in the process greatly cleaning up the code. The behaviour
should be the unchanged.

Having done this, there's only one place where we depend on points-to,
and that's in the remaining `declaredAttribute` call. This should
greatly simplify the move away from points to.

python/ql/src/Functions/SignatureSpecialMethods.ql

@@ -40,79 +40,73 @@ predicate is_ternary_op(string name) {
 
 predicate is_quad_op(string name) { name = "__setslice__" or name = "__exit__" }
 
-int argument_count(PythonFunctionValue f, string name, ClassValue cls) {
-  cls.declaredAttribute(name) = f and
-  (
-    is_unary_op(name) and result = 1
-    or
-    is_binary_op(name) and result = 2
-    or
-    is_ternary_op(name) and result = 3
-    or
-    is_quad_op(name) and result = 4
-  )
+int argument_count(string name) {
+  is_unary_op(name) and result = 1
+  or
+  is_binary_op(name) and result = 2
+  or
+  is_ternary_op(name) and result = 3
+  or
+  is_quad_op(name) and result = 4
 }
 
 predicate incorrect_special_method_defn(
-  PythonFunctionValue func, string message, boolean show_counts, string name, ClassValue owner
+  Function func, string message, boolean show_counts, string name
 ) {
-  exists(int required | required = argument_count(func, name, owner) |
+  exists(int required | required = argument_count(name) |
     /* actual_non_default <= actual */
-    if required > func.maxParameters()
+    if required > func.getMaxPositionalArguments()
     then message = "Too few parameters" and show_counts = true
     else
-      if required < func.minParameters()
+      if required < func.getMinPositionalArguments()
       then message = "Too many parameters" and show_counts = true
       else (
-        func.minParameters() < required and
-        not func.getScope().hasVarArg() and
-        message = (required - func.minParameters()) + " default values(s) will never be used" and
+        func.getMinPositionalArguments() < required and
+        not func.hasVarArg() and
+        message =
+          (required - func.getMinPositionalArguments()) + " default values(s) will never be used" and
         show_counts = false
       )
   )
 }
 
-predicate incorrect_pow(FunctionValue func, string message, boolean show_counts, ClassValue owner) {
-  owner.declaredAttribute("__pow__") = func and
+predicate incorrect_pow(Function func, string message, boolean show_counts) {
   (
-    func.maxParameters() < 2 and message = "Too few parameters" and show_counts = true
+    func.getMaxPositionalArguments() < 2 and message = "Too few parameters" and show_counts = true
     or
-    func.minParameters() > 3 and message = "Too many parameters" and show_counts = true
+    func.getMinPositionalArguments() > 3 and message = "Too many parameters" and show_counts = true
     or
-    func.minParameters() < 2 and
-    message = (2 - func.minParameters()) + " default value(s) will never be used" and
+    func.getMinPositionalArguments() < 2 and
+    message = (2 - func.getMinPositionalArguments()) + " default value(s) will never be used" and
     show_counts = false
     or
-    func.minParameters() = 3 and
+    func.getMinPositionalArguments() = 3 and
     message = "Third parameter to __pow__ should have a default value" and
     show_counts = false
   )
 }
 
-predicate incorrect_get(FunctionValue func, string message, boolean show_counts, ClassValue owner) {
-  owner.declaredAttribute("__get__") = func and
+predicate incorrect_get(Function func, string message, boolean show_counts) {
   (
-    func.maxParameters() < 3 and message = "Too few parameters" and show_counts = true
+    func.getMaxPositionalArguments() < 3 and message = "Too few parameters" and show_counts = true
     or
-    func.minParameters() > 3 and message = "Too many parameters" and show_counts = true
+    func.getMinPositionalArguments() > 3 and message = "Too many parameters" and show_counts = true
     or
-    func.minParameters() < 2 and
-    not func.getScope().hasVarArg() and
-    message = (2 - func.minParameters()) + " default value(s) will never be used" and
+    func.getMinPositionalArguments() < 2 and
+    not func.hasVarArg() and
+    message = (2 - func.getMinPositionalArguments()) + " default value(s) will never be used" and
     show_counts = false
   )
 }
 
-string should_have_parameters(PythonFunctionValue f, string name, ClassValue owner) {
-  exists(int i | i = argument_count(f, name, owner) | result = i.toString())
-  or
-  owner.declaredAttribute(name) = f and
-  (name = "__get__" or name = "__pow__") and
-  result = "2 or 3"
+string should_have_parameters(string name) {
+  if name in ["__pow__", "__get__"]
+  then result = "2 or 3"
+  else result = argument_count(name).toString()
 }
 
-string has_parameters(PythonFunctionValue f) {
-  exists(int i | i = f.minParameters() |
+string has_parameters(Function f) {
+  exists(int i | i = f.getMinPositionalArguments() |
     i = 0 and result = "no parameters"
     or
     i = 1 and result = "1 parameter"
@@ -125,19 +119,20 @@ from
   PythonFunctionValue f, string message, string sizes, boolean show_counts, string name,
   ClassValue owner
 where
+  owner.declaredAttribute(name) = f and
   (
-    incorrect_special_method_defn(f, message, show_counts, name, owner)
+    incorrect_special_method_defn(f.getScope(), message, show_counts, name)
     or
-    incorrect_pow(f, message, show_counts, owner) and name = "__pow__"
+    incorrect_pow(f.getScope(), message, show_counts) and name = "__pow__"
     or
-    incorrect_get(f, message, show_counts, owner) and name = "__get__"
+    incorrect_get(f.getScope(), message, show_counts) and name = "__get__"
   ) and
   (
     show_counts = false and sizes = ""
     or
     show_counts = true and
     sizes =
-      ", which has " + has_parameters(f) + ", but should have " +
-        should_have_parameters(f, name, owner)
+      ", which has " + has_parameters(f.getScope()) + ", but should have " +
+        should_have_parameters(name)
   )
 select f, message + " for special method " + name + sizes + ", in class $@.", owner, owner.getName()