fix: revert vitePlugins return type to T | undefined

Author: fengmk2

packages/cli/src/__tests__/index.spec.ts

@@ -36,16 +36,16 @@ test('should keep vitest exports stable', () => {
   expect(defaultBrowserPort).toBeDefined();
 });
 
-test('vitePlugins returns empty array when VP_COMMAND is unset', () => {
+test('vitePlugins returns undefined when VP_COMMAND is unset', () => {
   delete process.env.VP_COMMAND;
   const result = vitePlugins(() => [{ name: 'test' }]);
-  expect(result).toEqual([]);
+  expect(result).toBeUndefined();
 });
 
-test('vitePlugins returns empty array when VP_COMMAND is empty string', () => {
+test('vitePlugins returns undefined when VP_COMMAND is empty string', () => {
   process.env.VP_COMMAND = '';
   const result = vitePlugins(() => [{ name: 'test' }]);
-  expect(result).toEqual([]);
+  expect(result).toBeUndefined();
 });
 
 test.each(['dev', 'build', 'test', 'preview'])(
@@ -58,11 +58,11 @@ test.each(['dev', 'build', 'test', 'preview'])(
 );
 
 test.each(['lint', 'fmt', 'check', 'pack', 'install', 'run'])(
-  'vitePlugins returns empty array when VP_COMMAND is %s',
+  'vitePlugins returns undefined when VP_COMMAND is %s',
   (cmd) => {
     process.env.VP_COMMAND = cmd;
     const result = vitePlugins(() => [{ name: 'my-plugin' }]);
-    expect(result).toEqual([]);
+    expect(result).toBeUndefined();
   },
 );
 
@@ -76,10 +76,10 @@ test('vitePlugins supports async callback', async () => {
   expect(await result).toEqual([{ name: 'async-plugin' }]);
 });
 
-test('vitePlugins returns empty array for async callback when skipped', () => {
+test('vitePlugins returns undefined for async callback when skipped', () => {
   process.env.VP_COMMAND = 'lint';
   const result = vitePlugins(async () => {
     return [{ name: 'async-plugin' }];
   });
-  expect(result).toEqual([]);
+  expect(result).toBeUndefined();
 });

packages/cli/src/define-config.ts

@@ -47,10 +47,10 @@ export function defineConfig(config: ViteUserConfigExport): ViteUserConfigExport
   return viteDefineConfig(config);
 }
 
-export function vitePlugins<T>(cb: () => T): T | [] {
+export function vitePlugins<T>(cb: () => T): T | undefined {
   const cmd = process.env.VP_COMMAND;
   if (cmd === 'dev' || cmd === 'build' || cmd === 'test' || cmd === 'preview') {
     return cb();
   }
-  return [];
+  return undefined;
 }