JS: Subtyping

Author: asgerf

javascript/ql/lib/semmle/javascript/internal/TypeResolution.qll

@@ -10,7 +10,8 @@ private import javascript
 module TypeResolution {
   private class NodeBase =
     @expr or @typeexpr or @lexical_name or @toplevel or @function_decl_stmt or @class_decl_stmt or
-        @namespace_declaration or @enum_declaration or @jsdoc_type_expr;
+        @namespace_declaration or @enum_declaration or @interface_declaration or
+        @type_alias_declaration or @jsdoc_type_expr;
 
   /**
    * A node in a graph which we use to perform name and type resolution.

javascript/ql/lib/semmle/javascript/internal/UnderlyingTypes.qll

@@ -74,7 +74,7 @@ module UnderlyingTypes {
   private predicate subtypeStep(Node node1, Node node2) {
     exists(ClassOrInterface cls |
       (
-        node1 = cls.getSuperClass() or // TODO: test that type flow actually reaches the super class
+        node1 = cls.getSuperClass() or
         node1 = cls.getASuperInterface()
       ) and
       node2 = cls

javascript/ql/test/library-tests/UnderlyingTypes/subtype.ts

@@ -0,0 +1,20 @@
+import * as express from 'express';
+
+interface MyRequest extends express.Request {
+
+}
+
+function t1(req: MyRequest) { // $ hasUnderlyingType='express'.Request
+}
+
+class MyRequestClass extends express.Request {
+}
+
+function t2(req: MyRequestClass) { // $ hasUnderlyingType='express'.Request
+}
+
+class MyRequestClass2 implements express.Request {
+}
+
+function t3(req: MyRequestClass2) { // $ hasUnderlyingType='express'.Request
+}