Prevent widget constructors from being marked as functional components

A widget factory generated via asFactory() may be passed a "parent"
factory as the second parameter to make it work as a selector. If the
given function was not actually a factory but a widget constructor
this would override the existing functionality of that constructor
as a selector, resulting in very confusing behavior.

Check that the parent factory is not a constructor for an object
that can be used as a JSX Element (and therefore as a selector).

Fix #2137

Change-Id: Ib0de0131436583f138adf8564914e30221771b18

Author: tbuschto

src/tabris/JsxProcessor.ts

@@ -214,8 +214,16 @@ function createFactoryProxy(processor: JsxProcessor, constructor: ElementFn): El
   const handler: ProxyHandler<ElementFn> = {
     apply(target, _thisArg, args) {
       const [attributes, functionalComponent] = args;
+      if (args.length > 1) {
+        if (!(functionalComponent instanceof Function)) {
+          throw new TypeError('Second parameter must be a function');
+        }
+        if (functionalComponent.prototype && functionalComponent.prototype[JSX.jsxFactory]) {
+          throw new TypeError('Second parameter must be a factory');
+        }
+      }
       const result = processor.createElement(proxy, attributes);
-      if (functionalComponent instanceof Function && result instanceof Object) {
+      if (args.length > 1 && result instanceof Object) {
         functionalComponent[JSX.jsxType] = true;
         result[JSX.jsxType] = functionalComponent;
       }

test/tabris/JsxProcessor.test.js

@@ -806,6 +806,10 @@ describe('JsxProcessor', function() {
         expect(parent.children('asdf').length).to.equal(0);
       });
 
+      it('throws for widget class as selector', function() {
+        expect(() => CompositeFactory({}, Composite)).to.throw(TypeError);
+      });
+
       it('still has static members', function() {
         expect(CompositeFactory.defineChangeEvent).to.equal(Composite.defineChangeEvent);
       });