[backbone.marionette] Added parameter for model to childview function of CollectionView (#27441)

* Added model param to childview function of CollectionView

* Added private property to MyOtherView to ensure type difference

types/backbone.marionette/backbone.marionette-tests.ts

@@ -135,6 +135,15 @@ class MyView extends Marionette.View<MyModel> {
     }
 }
 
+class MyOtherView extends MyView {
+    private readonly foo: string;
+
+    constructor(model: MyModel) {
+        super(model);
+        this.foo = 'bar';
+    }
+}
+
 class MainRegion extends Marionette.Region {
     constructor() {
         super();
@@ -185,10 +194,20 @@ class MyHtmlElRegion extends Marionette.Region {
     }
 }
 
-class MyCollectionView extends Marionette.CollectionView<MyModel, MyView> {
+class MyCollectionView extends Marionette.CollectionView<MyModel, MyView | MyOtherView> {
     constructor() {
         super();
+
+        this.childView = (model: MyModel) => {
+            if (model.get('isFoo')) {
+                return MyView;
+            }
+
+            return MyOtherView;
+        };
+
         this.childView = MyView;
+
         this.childViewEvents = {
             render() {
                 console.log('a childView has been rendered');
@@ -282,7 +301,7 @@ function CollectionViewTests() {
     cv.collection.add(new MyModel());
     app.mainRegion.show(cv);
     cv.emptyView = MyView;
-    const view: Marionette.CollectionView<MyModel, MyView> = cv.destroy();
+    const view: Marionette.CollectionView<MyModel, MyView | MyOtherView> = cv.destroy();
 }
 
 class MyController {

types/backbone.marionette/index.d.ts

@@ -3,7 +3,8 @@
 // Definitions by: Zeeshan Hamid <https://github.com/zhamid>,
 //                 Natan Vivo <https://github.com/nvivo>,
 //                 Sven Tschui <https://github.com/sventschui>,
-//                 Volker Nauruhn <https://github.com/razorness>
+//                 Volker Nauruhn <https://github.com/razorness>,
+//                 Ard Timmerman <https://github.com/confususs>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
@@ -1157,7 +1158,7 @@ export interface CollectionViewOptions<
     /**
      * Specify a child view to use.
      */
-    childView?: (() => typeof Backbone.View) | typeof Backbone.View;
+    childView?: ((model: TModel) => typeof Backbone.View) | typeof Backbone.View;
 
     /**
      * Define options to pass to the childView constructor.
@@ -1219,7 +1220,7 @@ export class CollectionView<TModel extends Backbone.Model, TView extends View<TM
     /**
      * Specify a child view to use.
      */
-    childView: (() => { new(...args: any[]): TView }) | { new(...args: any[]): TView };
+    childView: ((model: TModel) => { new(...args: any[]): TView }) | { new(...args: any[]): TView };
 
     /**
      * Define options to pass to the childView constructor.