fix(watch): build watch fails when outDir is empty string (#15979)

Author: btea

packages/vite/src/node/watch.ts

@@ -9,17 +9,22 @@ export function resolveChokidarOptions(
   config: ResolvedConfig,
   options: WatchOptions | undefined,
 ): WatchOptions {
-  const { ignored = [], ...otherOptions } = options ?? {}
+  const { ignored: ignoredList, ...otherOptions } = options ?? {}
+  const ignored: WatchOptions['ignored'] = [
+    '**/.git/**',
+    '**/node_modules/**',
+    '**/test-results/**', // Playwright
+    glob.escapePath(config.cacheDir) + '/**',
+    ...arraify(ignoredList || []),
+  ]
+  if (config.build.outDir) {
+    ignored.push(
+      glob.escapePath(path.resolve(config.root, config.build.outDir)) + '/**',
+    )
+  }
 
   const resolvedWatchOptions: WatchOptions = {
-    ignored: [
-      '**/.git/**',
-      '**/node_modules/**',
-      '**/test-results/**', // Playwright
-      glob.escapePath(config.cacheDir) + '/**',
-      glob.escapePath(path.resolve(config.root, config.build.outDir)) + '/**',
-      ...arraify(ignored),
-    ],
+    ignored,
     ignoreInitial: true,
     ignorePermissionErrors: true,
     ...otherOptions,