Python: Fix Builtin.isClass() and use in ClassObject. Also fix a couple of typos.

Author: markshannon

python/ql/src/semmle/python/types/Builtins.qll

@@ -40,6 +40,7 @@ class Builtin extends @py_cobject {
     }
 
     Builtin getBaseClass() {
+        /* The extractor uses the special name ".super." to indicate the super class of a builtin class */
         py_cmembers_versioned(this, ".super.", result, major_version().toString())
     }
 
@@ -54,7 +55,9 @@ class Builtin extends @py_cobject {
     }
 
     predicate isClass() {
-        py_cobjecttypes(_, this) or this = Builtin::unknownType()
+        py_cobjecttypes(_, this) or
+        this = Builtin::unknownType() or
+        exists(Builtin meta | meta.inheritsFromType() and py_cobjecttypes(this, meta))
     }
 
     predicate isFunction() {

python/ql/src/semmle/python/types/ClassObject.qll

@@ -22,9 +22,7 @@ class ClassObject extends Object {
 
     ClassObject() {
         this.getOrigin() instanceof ClassExpr or
-        exists(Builtin o | o.getClass() = this.asBuiltin()) or
-        this.asBuiltin().getClass().inheritsFromType() or
-        this.asBuiltin() = Builtin::special("_semmle_unknown_type")
+        this.asBuiltin().isClass()
     }
 
     private predicate isStr() {

python/ql/src/semmle/python/types/Object.qll

@@ -37,7 +37,7 @@ class Object extends @py_object {
     ClassObject getAnInferredType() {
         exists(ControlFlowNode somewhere | somewhere.refersTo(this, result, _))
         or
-        this.asBuiltin().getClass() = result.asBuiltin()and not this = unknownValue()
+        this.asBuiltin().getClass() = result.asBuiltin() and not this = unknownValue()
         or
         this = unknownValue() and result = theUnknownType()
     }