From acbf03d723f904f7fb3ad6758298eb99a0309227 Mon Sep 17 00:00:00 2001
From: NullVoxPopuli <199018+NullVoxPopuli@users.noreply.github.com>
Date: Mon, 20 Mar 2023 12:11:13 -0400
Subject: [PATCH] fix: #835 incorrect value returned when last task was dropped

Co-Authored-By: rpemberton <19560029+rpemberton@users.noreply.github.com>
---
 .changeset/mean-moons-grab.md                 |  6 ++++
 ember-resources/src/util/ember-concurrency.ts |  2 +-
 .../tests/utils/ember-concurrency/js-test.ts  | 34 ++++++++++++++++++-
 3 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/mean-moons-grab.md

diff --git a/.changeset/mean-moons-grab.md b/.changeset/mean-moons-grab.md
new file mode 100644
index 000000000..9e271f7be
--- /dev/null
+++ b/.changeset/mean-moons-grab.md
@@ -0,0 +1,6 @@
+---
+"ember-resources": patch
+---
+
+Fixes [#835](https://github.com/NullVoxPopuli/ember-resources/issues/835) - resolves regression introduced by [PR: #808 ](https://github.com/NullVoxPopuli/ember-resources/pull/808) which aimed to correctly return the _previous_ task instance's value if the _current task_ hasn't finished yet. The regression described by #835 was that if a task in cancelled (e.g.: dropped), it is considered finished, and that canceled task's value would be used instead of the last compuleted task. In normal ember-concurrency APIs, this is abstracted over via the `.lastSuccessful` property on the `TaskProperty`. The goal of the `.value` on `trackedTask` is to mimic the property chain: `taskProperty.lastSuccessful?.value`.
+
diff --git a/ember-resources/src/util/ember-concurrency.ts b/ember-resources/src/util/ember-concurrency.ts
index f031e819b..da4fbd7ea 100644
--- a/ember-resources/src/util/ember-concurrency.ts
+++ b/ember-resources/src/util/ember-concurrency.ts
@@ -214,7 +214,7 @@ export class TaskResource<
   declare lastTask: TaskInstance<Return> | undefined;
 
   get value() {
-    if (this.currentTask?.isFinished) {
+    if (this.currentTask?.isFinished && !this.currentTask.isCanceled) {
       return this.currentTask.value;
     }
 
diff --git a/test-app/tests/utils/ember-concurrency/js-test.ts b/test-app/tests/utils/ember-concurrency/js-test.ts
index ec764cbd7..96d67a3d4 100644
--- a/test-app/tests/utils/ember-concurrency/js-test.ts
+++ b/test-app/tests/utils/ember-concurrency/js-test.ts
@@ -1,10 +1,11 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 import { tracked } from '@glimmer/tracking';
 import { settled } from '@ember/test-helpers';
+import { waitFor } from '@ember/test-waiters';
 import { module, test } from 'qunit';
 import { setupTest } from 'ember-qunit';
 
-import { restartableTask, timeout } from 'ember-concurrency';
+import { dropTask, restartableTask, timeout } from 'ember-concurrency';
 import { taskFor } from 'ember-concurrency-ts';
 import { trackedTask } from 'ember-resources/util/ember-concurrency';
 
@@ -168,6 +169,37 @@ module('useTask', function () {
         assert.false(foo.search.isRunning);
         assert.strictEqual(foo.search.value, null);
       });
+
+      test('it returns correct task value when tasks have been dropped', async function (assert) {
+        class Test {
+          @tracked input = 'initial value';
+
+          search = trackedTask(this, taskFor(this._search), () => [this.input]);
+
+          @dropTask
+          @waitFor
+          *_search(input: string) {
+            yield new Promise((resolve) => setTimeout(() => resolve('')));
+
+            return input;
+          }
+        }
+
+        let foo = new Test();
+
+        // task is initiated upon first access
+        foo.search.value;
+
+        // immediately start another task (this will be dropped/cancelled)
+        foo.input = 'updated value';
+        foo.search.value;
+
+        await settled();
+
+        assert.strictEqual(foo.search.value, 'initial value', 'returns value from first task');
+        assert.true(foo.search.isFinished);
+        assert.false(foo.search.isRunning);
+      });
     });
   });
 });