fix(v2): fix theme array deduplication bug (#5000)

packages/docusaurus-utils-common/src/__tests__/uniq.test.ts

@@ -0,0 +1,33 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import uniq from '../uniq';
+
+describe('uniq', () => {
+  test('remove duplicate primitives', () => {
+    expect(uniq(['A', 'B', 'C', 'B', 'A', 'D'])).toEqual(['A', 'B', 'C', 'D']);
+    expect(uniq([3, 3, 5, 1, 6, 3, 5])).toEqual([3, 5, 1, 6]);
+    expect(uniq([null, undefined, 3, null, 4, 3])).toEqual([
+      null,
+      undefined,
+      3,
+      4,
+    ]);
+  });
+
+  test('remove duplicate objects/arrays by identity', () => {
+    const obj1 = {};
+    const obj2 = {};
+    const obj3 = {};
+    const array1: unknown[] = [];
+    const array2: unknown[] = [];
+    const array3: unknown[] = [];
+    expect(
+      uniq([obj1, obj1, obj2, array1, obj2, array3, array2, array1, obj3]),
+    ).toEqual([obj1, obj2, array1, array3, array2, obj3]);
+  });
+});

packages/docusaurus-utils-common/src/index.ts

@@ -6,3 +6,4 @@
  */
 
 export {default as applyTrailingSlash} from './applyTrailingSlash';
+export {default as uniq} from './uniq';

packages/docusaurus-utils-common/src/uniq.ts

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// Remove duplicate array items (similar to _.uniq)
+export default function uniq<T>(array: T[]): T[] {
+  // Note: had problems with [...new Set()]: https://github.com/facebook/docusaurus/issues/4972#issuecomment-863895061
+  return Array.from(new Set(array));
+}