JS: Add UnderlyingTypes.qll

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

@@ -0,0 +1,128 @@
+/**
+ * Provides name resolution and propagates type information.
+ */
+
+private import javascript
+private import semmle.javascript.internal.NameResolution::NameResolution
+
+/**
+ * Provides name resolution and propagates type information.
+ */
+module UnderlyingTypes {
+  private predicate subtypeStep(Node node1, Node node2) {
+    exists(ClassOrInterface cls |
+      (
+        node1 = cls.getSuperClass() or
+        node1 = cls.getASuperInterface()
+      ) and
+      node2 = cls
+    )
+  }
+
+  predicate underlyingTypeStep(Node node1, Node node2) {
+    exists(UnionOrIntersectionTypeExpr type |
+      node1 = type.getAnElementType() and
+      node2 = type
+    )
+    or
+    exists(ReadonlyTypeExpr type |
+      node1 = type.getElementType() and
+      node2 = type
+    )
+    or
+    exists(OptionalTypeExpr type |
+      node1 = type.getElementType() and
+      node2 = type
+    )
+    or
+    exists(GenericTypeExpr type |
+      node1 = type.getTypeAccess() and
+      node2 = type
+    )
+    or
+    exists(ExpressionWithTypeArguments e |
+      node1 = e.getExpression() and
+      node2 = e
+    )
+    or
+    exists(JSDocUnionTypeExpr type |
+      node1 = type.getAnAlternative() and
+      node2 = type
+    )
+    or
+    exists(JSDocNonNullableTypeExpr type |
+      node1 = type.getTypeExpr() and
+      node2 = type
+    )
+    or
+    exists(JSDocNullableTypeExpr type |
+      node1 = type.getTypeExpr() and
+      node2 = type
+    )
+    or
+    exists(JSDocAppliedTypeExpr type |
+      node1 = type.getHead() and
+      node2 = type
+    )
+    or
+    exists(JSDocOptionalParameterTypeExpr type |
+      node1 = type.getUnderlyingType() and
+      node2 = type
+    )
+  }
+
+  predicate nodeHasUnderlyingType(Node node, string mod, string name) {
+    nodeRefersToModule(node, mod, name)
+    or
+    exists(JSDocLocalTypeAccess type |
+      node = type and
+      not exists(type.getALexicalName()) and
+      not type = any(JSDocQualifiedTypeAccess t).getBase() and
+      name = type.getName() and
+      mod = "global"
+    )
+    or
+    exists(LocalTypeAccess type |
+      node = type and
+      not exists(type.getLocalTypeName()) and
+      name = type.getName() and
+      mod = "global"
+    )
+    or
+    exists(Node mid | nodeHasUnderlyingType(mid, mod, name) |
+      TypeFlow::step(mid, node)
+      or
+      underlyingTypeStep(mid, node)
+      or
+      subtypeStep(mid, node)
+    )
+  }
+
+  pragma[nomagic]
+  predicate nodeHasUnderlyingType(Node node, string name) {
+    nodeHasUnderlyingType(node, "global", name)
+  }
+
+  predicate nodeHasUnderlyingClassType(Node node, DataFlow::ClassNode cls) {
+    node = cls.getAstNode()
+    or
+    exists(string name |
+      classHasGlobalName(cls, name) and
+      nodeHasUnderlyingType(node, name)
+    )
+    or
+    exists(Node mid | nodeHasUnderlyingClassType(mid, cls) |
+      TypeFlow::step(mid, node)
+      or
+      underlyingTypeStep(mid, node)
+      // Note: unlike for external types, we do not use subtype steps here.
+      // The caller is responsible for handling the class hierarchy.
+    )
+  }
+
+  pragma[nomagic]
+  private predicate classHasGlobalName(DataFlow::ClassNode cls, string name) {
+    cls.flowsTo(AccessPath::getAnAssignmentTo(name)) and
+    not cls.getTopLevel().isExterns() // don't propagate externs classes
+  }
+}