fix: opt-in server.fs.cachedChecks (#17807)

Co-authored-by: Bjorn Lu <[email protected]>

Author: patak-dev

docs/config/server-options.md

@@ -328,6 +328,14 @@ export default defineConfig({
 
 Blocklist for sensitive files being restricted to be served by Vite dev server. This will have higher priority than [`server.fs.allow`](#server-fs-allow). [picomatch patterns](https://github.com/micromatch/picomatch#globbing-features) are supported.
 
+## server.fs.cachedChecks
+
+- **Type:** `boolean`
+- **Default:** `false`
+- **Experimental**
+
+Caches filenames of accessed directories to avoid repeated filesystem operations. Particularly in Windows, this could result in a performance boost. It is disabled by default due to edge cases when writing a file in a cached folder and immediately importing it.
+
 ## server.origin
 
 - **Type:** `string`

packages/vite/src/node/fsUtils.ts

@@ -46,12 +46,14 @@ export function getFsUtils(config: ResolvedConfig): FsUtils {
   if (!fsUtils) {
     if (
       config.command !== 'serve' ||
-      config.server.fs.cachedChecks === false ||
+      config.server.fs.cachedChecks !== true ||
       config.server.watch?.ignored ||
       process.versions.pnp
     ) {
       // cached fsUtils is only used in the dev server for now
-      // it is enabled by default only when there aren't custom watcher ignored patterns configured
+      // it is disabled by default due to potential edge cases when writing a file
+      // and reading it immediately
+      // It is also disabled when there aren't custom watcher ignored patterns configured
       // and if yarn pnp isn't used
       fsUtils = commonFsUtils
     } else if (