refactor: Use preprocessor for polyfill

addon/index.js

@@ -0,0 +1,36 @@
+import { createCache, getValue } from '@glimmer/tracking/primitives/cache';
+import { assert } from '@ember/debug';
+
+export function cached(...args) {
+  const [target, key, descriptor] = args;
+
+  // Error on `@cached()`, `@cached(...args)`, and `@cached propName = value;`
+  assert(
+    'You attempted to use @cached(), which is not necessary nor supported. Remove the parentheses and you will be good to go!',
+    target !== undefined
+  );
+  assert(
+    `You attempted to use @cached on with ${
+      args.length > 1 ? 'arguments' : 'an argument'
+    } ( @cached(${args
+      .map(d => `'${d}'`)
+      .join(
+        ', '
+      )}), which is not supported. Dependencies are automatically tracked, so you can just use ${'`@cached`'}`,
+    typeof target === 'object' &&
+      typeof key === 'string' &&
+      typeof descriptor === 'object' &&
+      args.length === 3
+  );
+  assert(
+    `The @cached decorator must be applied to getters. '${key}' is not a getter.`,
+    typeof descriptor.get == 'function'
+  );
+
+  const caches = new WeakMap();
+  const getter = descriptor.get;
+  descriptor.get = function () {
+    if (!caches.has(this)) caches.set(this, createCache(getter.bind(this)));
+    return getValue(caches.get(this));
+  };
+}

index.js

@@ -1,62 +1,15 @@
 'use strict';
 
-const { resolve } = require('path');
+const ReplaceImportsPreprocessor = require('./lib/replace-imports-preprocessor');
 
 module.exports = {
   name: require('./package').name,
 
-  included() {
-    this._super.included.apply(this, arguments);
-    this._ensureThisImport();
-
-    this.import('vendor/ember-cached-decorator-polyfill/index.js');
-    this.patchEmberModulesAPIPolyfill();
-  },
-
-  treeForVendor(tree) {
-    const babel = this.addons.find(a => a.name === 'ember-cli-babel');
-
-    return babel.transpileTree(tree, {
-      babel: this.options.babel,
-
-      'ember-cli-babel': {
-        compileModules: false
-      }
-    });
-  },
-
-  _ensureThisImport() {
-    if (!this.import) {
-      this._findHost = function findHostShim() {
-        let current = this;
-        let app;
-        do {
-          app = current.app || app;
-          // eslint-disable-next-line no-cond-assign
-        } while (current.parent.parent && (current = current.parent));
-        return app;
-      };
-      this.import = function importShim(asset, options) {
-        const app = this._findHost();
-        app.import(asset, options);
-      };
+  setupPreprocessorRegistry(type, registry) {
+    if (type !== 'parent') {
+      return;
     }
-  },
-
-  patchEmberModulesAPIPolyfill() {
-    const babel = this.parent.findOwnAddonByName
-      ? this.parent.findOwnAddonByName('ember-cli-babel') // parent is an addon
-      : this.parent.findAddonByName('ember-cli-babel'); // parent is an app
-
-    if (babel.__CachedDecoratorPolyfillApplied) return;
-    babel.__CachedDecoratorPolyfillApplied = true;
-
-    const { _getEmberModulesAPIPolyfill } = babel;
-    babel._getEmberModulesAPIPolyfill = function (...args) {
-      const plugins = _getEmberModulesAPIPolyfill.apply(this, args);
-      if (!plugins) return;
 
-      return [[resolve(__dirname, './lib/transpile-modules.js')], ...plugins];
-    };
+    registry.add('js', new ReplaceImportsPreprocessor());
   }
 };

lib/replace-imports-preprocessor.js

@@ -0,0 +1,22 @@
+const BroccoliReplace = require('broccoli-replace');
+
+module.exports = class ReplaceImportsPreprocessor {
+  name = 'ember-cached-decorator-polyfill-preprocessor';
+
+  toTree(tree) {
+    return new BroccoliReplace(tree, {
+      files: ['**/*.js', '**/*.ts'],
+      patterns: [
+        {
+          match: /import\s+{[\s(tracked,)]*cached[\s(,tracked)]*}\s*from\s*['"]@glimmer\/tracking['"]/m,
+          replacement: str => {
+            return str.includes('tracked')
+              ? `import { tracked } from '@glimmer/tracking';
+import { cached } from 'ember-cached-decorator-polyfill';`
+              : `import { cached } from 'ember-cached-decorator-polyfill';`;
+          }
+        }
+      ]
+    });
+  }
+};

package.json

@@ -39,13 +39,14 @@
     "test:ember-compatibility": "ember try:each"
   },
   "dependencies": {
+    "@glimmer/tracking": "^1.0.4",
+    "broccoli-replace": "^2.0.2",
     "ember-cache-primitive-polyfill": "^1.0.1",
     "ember-cli-babel": "^7.21.0"
   },
   "devDependencies": {
     "@ember/optional-features": "^2.0.0",
     "@glimmer/component": "^1.0.1",
-    "@glimmer/tracking": "^1.0.0",
     "@types/ember": "^3.16.0",
     "@types/ember-qunit": "^3.4.9",
     "@types/ember-resolver": "^5.0.9",

tests/unit/followed-import-test.ts

@@ -0,0 +1,33 @@
+import { module, test } from 'qunit';
+import { cached, tracked } from '@glimmer/tracking';
+
+module('Unit | Import | followed import', function () {
+  test('it works', function (assert) {
+    class Person {
+      @tracked firstName = 'Jen';
+      lastName = 'Weber';
+
+      @cached
+      get fullName() {
+        const fullName = `${this.firstName} ${this.lastName}`;
+        assert.step(fullName);
+        return fullName;
+      }
+    }
+
+    const person = new Person();
+    assert.verifySteps([], 'getter is not called after class initialization');
+
+    assert.strictEqual(person.fullName, 'Jen Weber');
+    assert.verifySteps(
+      ['Jen Weber'],
+      'getter was called after property access'
+    );
+
+    assert.strictEqual(person.fullName, 'Jen Weber');
+    assert.verifySteps(
+      [],
+      'getter was not called again after repeated property access'
+    );
+  });
+});

tests/unit/multi-line-import-test.ts

@@ -0,0 +1,37 @@
+import { module, test } from 'qunit';
+// prettier-ignore
+import {
+  cached,
+  tracked
+ } from "@glimmer/tracking";
+
+module('Unit | Import | multi-line import', function () {
+  test('it works', function (assert) {
+    class Person {
+      @tracked firstName = 'Jen';
+      lastName = 'Weber';
+
+      @cached
+      get fullName() {
+        const fullName = `${this.firstName} ${this.lastName}`;
+        assert.step(fullName);
+        return fullName;
+      }
+    }
+
+    const person = new Person();
+    assert.verifySteps([], 'getter is not called after class initialization');
+
+    assert.strictEqual(person.fullName, 'Jen Weber');
+    assert.verifySteps(
+      ['Jen Weber'],
+      'getter was called after property access'
+    );
+
+    assert.strictEqual(person.fullName, 'Jen Weber');
+    assert.verifySteps(
+      [],
+      'getter was not called again after repeated property access'
+    );
+  });
+});