DEV: Ensure `DModal` model argument is still available during destroy (#22411)

Previously, the `@model` argument would be unset before the component's `willDestroy` hook was called. Wrapping up the component and the opts in a single tracked `activeModal` field, and then using the `#each` helper with an array of 1 element means that Glimmer will keep the `@model` argument available until the end of the component's lifecycle.

app/assets/javascripts/discourse/app/components/modal-container.hbs

@@ -1,11 +1,14 @@
 <div class="modal-container" {{did-insert this.modal.setContainerElement}}>
 </div>
 
-{{#if this.modal.modalBodyComponent}}
-  <this.modal.modalBodyComponent
-    @model={{this.modal.opts.model}}
+{{#if this.modal.activeModal}}
+  {{#each (array this.modal.activeModal) as |activeModal|}}
+    {{! #each ensures that the activeModal component/model are updated atomically }}
+    <activeModal.component
+      @model={{activeModal.opts.model}}
       @closeModal={{this.closeModal}}
     />
+  {{/each}}
 {{/if}}
 
 {{! Legacy modals depend on this wrapper being in the DOM at all times. Eventually this will be dropped.

app/assets/javascripts/discourse/app/services/modal.js

@@ -20,10 +20,10 @@ const LEGACY_OPTS = new Set([
 
 @disableImplicitInjections
 class ModalService extends Service {
-  @tracked modalBodyComponent;
+  @tracked activeModal;
   @tracked opts = {};
+
   @tracked containerElement;
-  #resolveShowPromise;
 
   @action
   setContainerElement(element) {
@@ -42,12 +42,13 @@ class ModalService extends Service {
   show(modal, opts) {
     this.close({ initiatedBy: CLOSE_INITIATED_BY_MODAL_SHOW });
 
+    let resolveShowPromise;
     const promise = new Promise((resolve) => {
-      this.#resolveShowPromise = resolve;
+      resolveShowPromise = resolve;
     });
 
     this.opts = opts || {};
-    this.modalBodyComponent = modal;
+    this.activeModal = { component: modal, opts, resolveShowPromise };
 
     const unsupportedOpts = Object.keys(opts).filter((key) =>
       LEGACY_OPTS.has(key)
@@ -64,8 +65,8 @@ class ModalService extends Service {
   }
 
   close(data) {
-    this.#resolveShowPromise?.(data);
-    this.#resolveShowPromise = this.modalBodyComponent = null;
+    this.activeModal?.resolveShowPromise?.(data);
+    this.activeModal = null;
     this.opts = {};
   }
 }
@@ -240,6 +241,6 @@ export default class ModalServiceWithLegacySupport extends ModalService {
   }
 
   get isLegacy() {
-    return this.name && !this.modalBodyComponent;
+    return this.name && !this.activeModal;
   }
 }

app/assets/javascripts/discourse/tests/acceptance/modal-service-test.js

@@ -109,5 +109,44 @@ acceptance("Modal service: component-based API", function () {
     );
   });
 
+  test("lifecycle hooks and arguments", async function (assert) {
+    await visit("/");
+
+    const events = [];
+
+    class ModalWithLifecycleHooks extends MyModalClass {
+      constructor() {
+        super(...arguments);
+        events.push(`constructor: ${this.args.model?.data}`);
+      }
+
+      willDestroy() {
+        events.push(`willDestroy: ${this.args.model?.data}`);
+      }
+    }
+
+    const modalService = getOwner(this).lookup("service:modal");
+
+    modalService.show(ModalWithLifecycleHooks, {
+      model: { data: "argumentValue" },
+    });
+    await settled();
+
+    assert.deepEqual(
+      events,
+      ["constructor: argumentValue"],
+      "constructor called with args available"
+    );
+
+    modalService.close();
+    await settled();
+
+    assert.deepEqual(
+      events,
+      ["constructor: argumentValue", "willDestroy: argumentValue"],
+      "constructor called with args available"
+    );
+  });
+
   // (See also, `tests/integration/component/d-modal-test.js`)
 });