[WIP] Move tracked to an actual decorator

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+  "typescript.tsdk": "node_modules/typescript/lib"
+}

packages/ember-metal/lib/tracked.ts

@@ -96,11 +96,14 @@ class Tracker {
 
   @param dependencies Optional dependents to be tracked.
  */
-export function tracked(
-  _target: object,
-  key: string,
-  descriptor: PropertyDescriptor
-): PropertyDescriptor {
+export function tracked(...dependencies: string[]): MethodDecorator;
+export function tracked(target: any, key: any): any;
+export function tracked(target: any, key: any, descriptor: PropertyDescriptor): PropertyDescriptor;
+export function tracked(...dependencies: any[]): any {
+  let [, key, descriptor] = dependencies;
+
+  if (!descriptor) return;
+
   if ('value' in descriptor) {
     return descriptorForDataProperty(key, descriptor);
   } else {

packages/ember-metal/tests/tracked/get_test.ts

@@ -0,0 +1,140 @@
+import { EMBER_METAL_TRACKED_PROPERTIES } from '@ember/canary-features';
+import { AbstractTestCase, moduleFor } from 'internal-test-helpers';
+import { get, getWithDefault, tracked } from '../..';
+
+if (EMBER_METAL_TRACKED_PROPERTIES) {
+  function createObj() {
+    class Obj {
+      @tracked string = 'string';
+      @tracked number = 23;
+      @tracked boolTrue = true;
+      @tracked boolFalse = false;
+      @tracked nullValue = null;
+      constructor() {
+        this.string = 'string';
+        this.number = 23;
+        this.boolTrue = true;
+        this.boolFalse = false;
+        this.nullValue = null;
+      }
+    }
+
+    return new Obj();
+  }
+
+  moduleFor(
+    '@tracked decorator: get',
+    class extends AbstractTestCase {
+      '@test should get arbitrary properties on an object'() {
+        let obj = createObj();
+
+        for (let key in obj) {
+          this.assert.equal(get(obj, key), obj[key], key);
+        }
+      }
+
+      '@test should retrieve a number key on an object'() {
+        class Obj {
+          @tracked 1 = 'first';
+          constructor() {
+            this[1] = 'first';
+          }
+        }
+
+        let obj = new Obj();
+
+        this.assert.equal(get(obj, 1), 'first');
+      }
+
+      '@test should retrieve an empty key on an object'() {
+        class Obj {
+          @tracked '' = 'empty';
+          constructor() {
+            this[''] = 'empty';
+          }
+        }
+
+        let obj = new Obj();
+
+        this.assert.equal(get(obj, ''), 'empty');
+      }
+
+      '@test should get a @tracked path'() {
+        class Key {
+          @tracked value = 'value';
+          constructor() {
+            this.value = 'value';
+          }
+        }
+
+        class Path {
+          @tracked key = new Key();
+          constructor() {
+            this.key = new Key();
+          }
+        }
+
+        class Obj {
+          @tracked path = new Path();
+          constructor() {
+            this.path = new Path();
+          }
+        }
+
+        let obj = new Obj();
+
+        this.assert.equal(get(obj, 'path.key.value'), 'value');
+      }
+
+      '@test should not access a property more than once'() {
+        let count = 20;
+
+        class Count {
+          @tracked
+          get id() {
+            return ++count;
+          }
+        }
+
+        let obj = new Count();
+
+        get(obj, 'id');
+
+        this.assert.equal(count, 21);
+      }
+    }
+  );
+
+  moduleFor(
+    '@tracked decorator: getWithDefault',
+    class extends AbstractTestCase {
+      ['@test should get arbitrary properties on an object']() {
+        let obj = createObj();
+
+        for (let key in obj) {
+          this.assert.equal(getWithDefault(obj, key, 'fail'), obj[key], key);
+        }
+
+        class Obj {
+          @tracked undef: string | undefined = undefined;
+          constructor() {
+            this.undef = undefined;
+          }
+        }
+
+        let obj2 = new Obj();
+
+        this.assert.equal(
+          getWithDefault(obj2, 'undef', 'default'),
+          'default',
+          'explicit undefined retrieves the default'
+        );
+        this.assert.equal(
+          getWithDefault(obj2, 'not-present', 'default'),
+          'default',
+          'non-present key retrieves the default'
+        );
+      }
+    }
+  );
+}

packages/internal-test-helpers/index.d.ts

@@ -0,0 +1 @@
+declare module "internal-test-helpers";