From e90524dde64a0479180232a3436cefacf2b50370 Mon Sep 17 00:00:00 2001
From: Kasper Peulen <kasperpeulen@gmail.com>
Date: Mon, 18 Mar 2024 10:37:10 +0100
Subject: [PATCH] Merge pull request #26514 from
 storybookjs/kasper/fix-single-loaders-decorators

Bug: Make sure loaders/decorators can be used as array
(cherry picked from commit b016a4f37243540e9fc244b39f58069763b06df3)
---
 .../modules/store/csf/composeConfigs.test.ts  | 28 +++++++++++++++++++
 .../src/modules/store/csf/composeConfigs.ts   |  9 +++---
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/code/lib/preview-api/src/modules/store/csf/composeConfigs.test.ts b/code/lib/preview-api/src/modules/store/csf/composeConfigs.test.ts
index 238885f44ba3..147038a5a8d2 100644
--- a/code/lib/preview-api/src/modules/store/csf/composeConfigs.test.ts
+++ b/code/lib/preview-api/src/modules/store/csf/composeConfigs.test.ts
@@ -176,6 +176,34 @@ describe('composeConfigs', () => {
     });
   });
 
+  it('allows single array to be written without array', () => {
+    expect(
+      composeConfigs([
+        {
+          argsEnhancers: ['1', '2'],
+          argTypesEnhancers: ['1', '2'],
+          loaders: '1',
+        },
+        {
+          argsEnhancers: '3',
+          argTypesEnhancers: '3',
+          loaders: ['2', '3'],
+        },
+      ])
+    ).toEqual({
+      parameters: {},
+      decorators: [],
+      args: {},
+      argsEnhancers: ['1', '2', '3'],
+      argTypes: {},
+      argTypesEnhancers: ['1', '2', '3'],
+      globals: {},
+      globalTypes: {},
+      loaders: ['1', '2', '3'],
+      runStep: expect.any(Function),
+    });
+  });
+
   it('combines decorators in reverse file order', () => {
     expect(
       composeConfigs([
diff --git a/code/lib/preview-api/src/modules/store/csf/composeConfigs.ts b/code/lib/preview-api/src/modules/store/csf/composeConfigs.ts
index 862f8cbcd501..e5785a6a3f01 100644
--- a/code/lib/preview-api/src/modules/store/csf/composeConfigs.ts
+++ b/code/lib/preview-api/src/modules/store/csf/composeConfigs.ts
@@ -3,6 +3,7 @@ import { global } from '@storybook/global';
 
 import { combineParameters } from '../parameters';
 import { composeStepRunners } from './stepRunners';
+import { normalizeArrays } from './normalizeArrays';
 
 export function getField<TFieldType = any>(
   moduleExportList: ModuleExports[],
@@ -16,10 +17,10 @@ export function getArrayField<TFieldType = any>(
   field: string,
   options: { reverseFileOrder?: boolean } = {}
 ): TFieldType[] {
-  return getField(moduleExportList, field).reduce(
-    (a: any, b: any) => (options.reverseFileOrder ? [...b, ...a] : [...a, ...b]),
-    []
-  );
+  return getField(moduleExportList, field).reduce((prev: any, cur: any) => {
+    const normalized = normalizeArrays(cur);
+    return options.reverseFileOrder ? [...normalized, ...prev] : [...prev, ...normalized];
+  }, []);
 }
 
 export function getObjectField<TFieldType = Record<string, any>>(