[BUGFIX beta] join runloop in Helper#recompute

#14774
(cherry picked from commit 9f66f13)

packages/@ember/-internals/glimmer/lib/helper.ts

@@ -6,6 +6,7 @@ import { Factory } from '@ember/-internals/owner';
 import { FrameworkObject, setFrameworkClass } from '@ember/-internals/runtime';
 import { symbol } from '@ember/-internals/utils';
 import { EMBER_FRAMEWORK_OBJECT_OWNER_ARGUMENT } from '@ember/canary-features';
+import { join } from '@ember/runloop';
 import { Dict, Opaque } from '@glimmer/interfaces';
 import { DirtyableTag } from '@glimmer/reference';
 
@@ -116,7 +117,7 @@ let Helper = FrameworkObject.extend({
     @since 1.13.0
   */
   recompute() {
-    this[RECOMPUTE_TAG].inner.dirty();
+    join(() => this[RECOMPUTE_TAG].inner.dirty());
   },
 
   /**

packages/@ember/-internals/glimmer/tests/integration/helpers/custom-helper-test.js

@@ -155,6 +155,43 @@ moduleFor(
       assert.strictEqual(destroyCount, 0, 'destroy is not called on recomputation');
     }
 
+    // https://github.com/emberjs/ember.js/issues/14774
+    ['@test class-based helper with static arguments can recompute a new value without a runloop'](
+      assert
+    ) {
+      let destroyCount = 0;
+      let computeCount = 0;
+      let helper;
+
+      this.registerHelper('hello-world', {
+        init() {
+          this._super(...arguments);
+          helper = this;
+        },
+        compute() {
+          return ++computeCount;
+        },
+        destroy() {
+          destroyCount++;
+          this._super();
+        },
+      });
+
+      this.render('{{hello-world "whut"}}');
+
+      this.assertText('1');
+
+      runTask(() => this.rerender());
+
+      this.assertText('1');
+
+      helper.recompute();
+
+      this.assertText('2');
+
+      assert.strictEqual(destroyCount, 0, 'destroy is not called on recomputation');
+    }
+
     ['@test helper params can be returned']() {
       this.registerHelper('hello-world', values => {
         return values;