Make sure lazy engines with async routes are handled

Lazy engine routes are initially promises which resolve to
route instances once the modules are loaded. In these cases
prefetch current throws an error 'TypeError: route.prefetch is not a function'
since it tries to call prefetch directly on the promise. It
seems this used to be handled properly but was lost in a more
recent refactor. This is just adding the functionality back.
It's important to note that we do not preload the lazy engine
assets in the test environment here because preloaded engine
routes are not promises but the actual route instance.

- Adds ember-engines to dev dependencies for testing.
- Create a lazy engine in the dummy app.
- Make sure we can visit this engine without preloading its assets.

Related changes:
- Update node for CI to version 10 to satisfy the
requirements for ember-engines.
- Change CI install command to fix errors when yarn tries to
install link dependencies.

.gitignore

@@ -5,7 +5,7 @@
 /tmp/
 
 # dependencies
-/node_modules/
+**/node_modules/
 
 # misc
 /.env*

.travis.yml

@@ -3,7 +3,7 @@ language: node_js
 node_js:
   # we recommend testing addons with the same minimum supported node version as Ember CLI
   # so that your addon works for all apps
-  - "6"
+  - "10"
 
 sudo: false
 dist: trusty
@@ -57,5 +57,8 @@ before_install:
   - npm install -g npm@4
   - npm --version
 
+install:
+  - yarn install --no-lockfile --non-interactive
+
 script:
   - node_modules/.bin/ember try:one $EMBER_TRY_SCENARIO

addon/services/prefetch.js

@@ -28,11 +28,20 @@ if (gte('3.6.0')) {
                 let { route, fullParams } = changeSet.for[i];
                 if (seenRoutes.has(route)) continue;
 
-                  route._prefetched = new RSVP.Promise(r => {
-                    return r(route.prefetch(fullParams, transition))
-                  });
-                  seenRoutes.set(route, true);
-                  if (transition.isAborted) return;
+                route._prefetched = new RSVP.Promise(r => {
+                  if (route.then instanceof Function) {
+                    return r(
+                      route.then(resolvedRoute => {
+                        return resolvedRoute.prefetch(fullParams, transition);
+                      })
+                    );
+                  }
+
+                  return r(route.prefetch(fullParams, transition));
+                });
+
+                seenRoutes.set(route, true);
+                if (transition.isAborted) return;
               }
             }
           }

config/ember-try.js

@@ -9,6 +9,7 @@ module.exports = function() {
     getChannelURL('canary')
   ]).then((urls) => {
     return {
+      useYarn: true,
       scenarios: [
         {
           name: 'ember-lts-2.18',

package.json

@@ -26,6 +26,7 @@
     "ember-cli-template-lint": "^1.0.0-beta.1",
     "ember-cli-uglify": "^2.1.0",
     "ember-disable-prototype-extensions": "^1.1.3",
+    "ember-engines": "^0.8.2",
     "ember-export-application-global": "2.0.0",
     "ember-load-initializers": "^1.1.0",
     "ember-maybe-import-regenerator": "^0.1.6",
@@ -38,6 +39,7 @@
     "ember-try": "^1.0.0",
     "eslint-plugin-ember": "^5.2.0",
     "eslint-plugin-node": "^7.0.1",
+    "lazy-engine": "link:./tests/dummy/lib/lazy-engine",
     "loader.js": "^4.7.0",
     "qunit-dom": "^0.8.0"
   },

tests/acceptance/lazy-engine-test.js

@@ -0,0 +1,13 @@
+import { module, test } from 'qunit';
+import { visit, currentURL } from '@ember/test-helpers';
+import { setupApplicationTest } from 'ember-qunit';
+
+module('Acceptance | lazy engine', function(hooks) {
+  setupApplicationTest(hooks);
+
+  test('it can load an async route from a lazy loaded engine', async function(assert) {
+    await visit('/lazy-engine');
+
+    assert.equal(currentURL(), '/lazy-engine');
+  });
+});

tests/dummy/app/router.js

@@ -31,6 +31,7 @@ Router.map(function() {
   this.route('abort-transition-to-child', function() {
     this.route('child');
   });
+  this.mount('lazy-engine');
 });
 
 export default Router;

tests/dummy/lib/lazy-engine/addon/engine.js

@@ -0,0 +1,14 @@
+import Engine from 'ember-engines/engine';
+import loadInitializers from 'ember-load-initializers';
+import Resolver from './resolver';
+import config from './config/environment';
+
+const { modulePrefix } = config;
+const Eng = Engine.extend({
+  modulePrefix,
+  Resolver
+});
+
+loadInitializers(Eng, modulePrefix);
+
+export default Eng;

tests/dummy/lib/lazy-engine/addon/resolver.js

@@ -0,0 +1,3 @@
+import Resolver from 'ember-resolver';
+
+export default Resolver;

tests/dummy/lib/lazy-engine/addon/routes.js

@@ -0,0 +1,5 @@
+import buildRoutes from 'ember-engines/routes';
+
+export default buildRoutes(function() {
+  // Define your engine's route map here
+});

tests/dummy/lib/lazy-engine/addon/templates/application.hbs

@@ -0,0 +1 @@
+{{outlet}}

tests/dummy/lib/lazy-engine/ember-config/environment.js

@@ -0,0 +1,11 @@
+/* eslint-env node */
+'use strict';
+
+module.exports = function(environment) {
+  let ENV = {
+    modulePrefix: 'lazy-engine',
+    environment
+  };
+
+  return ENV;
+};

tests/dummy/lib/lazy-engine/index.js

@@ -0,0 +1,17 @@
+/* eslint-env node */
+'use strict';
+
+// eslint-disable-next-line node/no-extraneous-require
+const EngineAddon = require('ember-engines/lib/engine-addon');
+
+module.exports = EngineAddon.extend({
+  name: 'lazy-engine',
+
+  lazyLoading: Object.freeze({
+    enabled: true
+  }),
+
+  isDevelopingAddon() {
+    return true;
+  }
+});

tests/dummy/lib/lazy-engine/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "lazy-engine",
+  "version": "0.0.0",
+  "keywords": [
+    "ember-addon",
+    "ember-engine"
+  ],
+  "ember-addon": {
+    "engineConfigPath": "ember-config"
+  },
+  "dependencies": {
+    "ember-cli-babel": "*",
+    "ember-cli-htmlbars": "*"
+  }
+}