Backtracking re-render during lazy initialization

packages/@glimmer-workspace/integration-tests/test/lazy-initialization-test.ts

@@ -0,0 +1,95 @@
+import { modifierCapabilities, setModifierManager } from '@glimmer/manager';
+import { assign } from '@glimmer/util';
+
+import {
+  BaseEnv,
+  GlimmerishComponent,
+  JitRenderDelegate,
+  RenderTest,
+  suite,
+  test,
+  tracked,
+} from '..';
+
+class LazyInitializationTest extends RenderTest {
+  static suiteName = 'Application test: lazy initialization';
+
+  @test 'Should be able to lazily initialize a tracked property'() {
+    class X extends GlimmerishComponent {
+      @tracked _counts: number | undefined = undefined;
+
+      get counts() {
+        if (this._counts === undefined) {
+          this._counts = 0;
+        }
+
+        return this._counts;
+      }
+
+      increment = () => this._counts!++;
+    }
+    this.registerComponent(
+      'Glimmer',
+      'HelloWorld',
+      `
+      {{this._counts}}
+      {{this.counts}}
+    `,
+      X
+    );
+
+    this.render(`<HelloWorld />`);
+
+    this.assertHTML(`0 0`);
+  }
+
+  @test 'Should be able to lazily initialize with a modifier'() {
+    const modifier = (callback: () => unknown) => {
+      setModifierManager(
+        () => ({
+          capabilities: modifierCapabilities('3.22'),
+          createModifier() {},
+          installModifier() {
+            callback();
+          },
+          updateModifier() {},
+          destroyModifier() {},
+        }),
+        callback
+      );
+
+      return callback;
+    };
+
+    class Thing extends GlimmerishComponent {
+      @tracked something: string | null = null;
+
+      thing = modifier(() => {
+        if (!this.something) {
+          this.something = 'something';
+        }
+      });
+    }
+
+    this.registerComponent(
+      'Glimmer',
+      'HelloWorld',
+      `
+<div {{this.thing}}>
+  {{this.something}}
+</div>
+`,
+      Thing
+    );
+
+    this.render(`<HelloWorld />`);
+
+    this.assertHTML(`<div>something</div>`);
+  }
+}
+
+suite(LazyInitializationTest, JitRenderDelegate, {
+  env: assign({}, BaseEnv, {
+    enableDebugTooling: false,
+  }),
+});