Fix CLI watcher cleanup race

Fixes a race condition where two parallel invocations of file system change events could cause some cleanup functions to get swallowed by changing cleanupWatchers to an array to retain multiple cleanup functions.

Co-authored-by: Gary Rennie <gazler@gmail.com>

Author: philipp-spiess

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Handle `'` syntax in ClojureScript when extracting classes ([#18888](https://github.com/tailwindlabs/tailwindcss/pull/18888))
 - Handle `@variant` inside `@custom-variant` ([#18885](https://github.com/tailwindlabs/tailwindcss/pull/18885))
 - Merge suggestions when using `@utility` ([#18900](https://github.com/tailwindlabs/tailwindcss/pull/18900))
+- Ensure that file system watchers created when using the CLI are always cleaned up ([#18905](https://github.com/tailwindlabs/tailwindcss/pull/18905))
 
 ## [4.1.13] - 2025-09-03
 

packages/@tailwindcss-cli/src/commands/build/index.ts

@@ -239,9 +239,9 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
 
   // Watch for changes
   if (args['--watch']) {
-    let cleanupWatchers = await createWatchers(
-      watchDirectories(scanner),
-      async function handle(files) {
+    let cleanupWatchers: (() => Promise<void>)[] = []
+    cleanupWatchers.push(
+      await createWatchers(watchDirectories(scanner), async function handle(files) {
         try {
           // If the only change happened to the output file, then we don't want to
           // trigger a rebuild because that will result in an infinite loop.
@@ -304,15 +304,15 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
 
             // Setup new watchers
             DEBUG && I.start('Setup new watchers')
-            let newCleanupWatchers = await createWatchers(watchDirectories(scanner), handle)
+            let newCleanupFunction = await createWatchers(watchDirectories(scanner), handle)
             DEBUG && I.end('Setup new watchers')
 
             // Clear old watchers
             DEBUG && I.start('Cleanup old watchers')
-            await cleanupWatchers()
+            await Promise.all(cleanupWatchers.splice(0).map((cleanup) => cleanup()))
             DEBUG && I.end('Cleanup old watchers')
 
-            cleanupWatchers = newCleanupWatchers
+            cleanupWatchers.push(newCleanupFunction)
 
             // Re-compile the CSS
             DEBUG && I.start('Build CSS')
@@ -362,14 +362,14 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
             eprintln(err.toString())
           }
         }
-      },
+      }),
     )
 
     // Abort the watcher if `stdin` is closed to avoid zombie processes. You can
     // disable this behavior with `--watch=always`.
     if (args['--watch'] !== 'always') {
       process.stdin.on('end', () => {
-        cleanupWatchers().then(
+        Promise.all(cleanupWatchers.map((fn) => fn())).then(
           () => process.exit(0),
           () => process.exit(1),
         )