feat: making ember-on-modifier a true polyfill (#57)

* Making ember-on-modifier a true polyfill.

Uses ember-cli-version-checker to determine if the modifier should included in the addon tree. If the modifier is not included and ember-event-helpers is installed, a message is displayed that ember-on-modifier can be removed from a project's depenendencies.

* Improving deprecation messaging.

* Fixing typo in tree funnel logic.

index.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const VersionChecker = require('ember-cli-version-checker');
 const Funnel = require('broccoli-funnel');
 
 module.exports = {
@@ -8,9 +9,26 @@ module.exports = {
   included(...args) {
     this._super.included.apply(this, args);
 
+    const checker = new VersionChecker(this.project);
+    const ember = checker.forEmber();
+
+    this.hasNativeOnModifier = ember.gte('3.11.0-beta.1');
+
     this.hasEventHelpers = Boolean(
       this.project.findAddonByName('ember-event-helpers')
     );
+
+    if (this.hasNativeOnModifier && this.parent === this.project) {
+      let message =
+        'The `{{on}}` modifier is available natively since Ember 3.11.0-beta.1. You can remove `ember-on-modifier` from your `package.json`.';
+
+      if (!this.hasEventHelpers) {
+        message +=
+          ' If you use the `(prevent-default)` helper, please install `ember-event-helpers`.';
+      }
+
+      this.ui.writeDeprecateLine(message);
+    }
   },
 
   treeForApp(...args) {
@@ -22,10 +40,15 @@ module.exports = {
   },
 
   filterTree(tree) {
+    const exclude = [];
+
+    if (this.hasNativeOnModifier) {
+      exclude.push(/modifiers/);
+    }
     if (this.hasEventHelpers) {
-      return new Funnel(tree, { exclude: [/helpers/] });
+      exclude.push(/helpers/);
     }
 
-    return tree;
+    return new Funnel(tree, { exclude });
   }
 };

package.json

@@ -29,6 +29,7 @@
   "dependencies": {
     "broccoli-funnel": "^2.0.2",
     "ember-cli-babel": "^7.7.3",
+    "ember-cli-version-checker": "^3.1.3",
     "ember-modifier-manager-polyfill": "^1.0.3"
   },
   "devDependencies": {

tests/helpers/ember-on-modifier-polyfill.js

@@ -0,0 +1,6 @@
+import { test, skip } from 'qunit';
+import { gte } from 'ember-compatibility-helpers';
+
+export const onModifierPolyfilled = !gte('3.11.0-beta.1');
+
+export const testIfOnModifierPolyfilled = onModifierPolyfilled ? test : skip;