refactor(fs): reduce overhead of watch (#2613)

plugins/fs/guest-js/index.ts

@@ -1245,15 +1245,44 @@ type WatchEventKindRemove =
   | { kind: 'folder' }
   | { kind: 'other' }
 
+// TODO: Remove this in v3, return `Watcher` instead
 /**
  * @since 2.0.0
  */
 type UnwatchFn = () => void
 
-async function unwatch(rid: number): Promise<void> {
-  await invoke('plugin:fs|unwatch', { rid })
+class Watcher extends Resource {}
+
+async function watchInternal(
+  paths: string | string[] | URL | URL[],
+  cb: (event: WatchEvent) => void,
+  options: DebouncedWatchOptions
+): Promise<UnwatchFn> {
+  const watchPaths = Array.isArray(paths) ? paths : [paths]
+
+  for (const path of watchPaths) {
+    if (path instanceof URL && path.protocol !== 'file:') {
+      throw new TypeError('Must be a file URL.')
+    }
+  }
+
+  const onEvent = new Channel<WatchEvent>()
+  onEvent.onmessage = cb
+
+  const rid: number = await invoke('plugin:fs|watch', {
+    paths: watchPaths.map((p) => (p instanceof URL ? p.toString() : p)),
+    options,
+    onEvent
+  })
+
+  const watcher = new Watcher(rid)
+
+  return () => {
+    void watcher.close()
+  }
 }
 
+// TODO: Return `Watcher` instead in v3
 /**
  * Watch changes (after a delay) on files or directories.
  *
@@ -1264,34 +1293,13 @@ async function watch(
   cb: (event: WatchEvent) => void,
   options?: DebouncedWatchOptions
 ): Promise<UnwatchFn> {
-  const opts = {
-    recursive: false,
+  return await watchInternal(paths, cb, {
     delayMs: 2000,
     ...options
-  }
-
-  const watchPaths = Array.isArray(paths) ? paths : [paths]
-
-  for (const path of watchPaths) {
-    if (path instanceof URL && path.protocol !== 'file:') {
-      throw new TypeError('Must be a file URL.')
-    }
-  }
-
-  const onEvent = new Channel<WatchEvent>()
-  onEvent.onmessage = cb
-
-  const rid: number = await invoke('plugin:fs|watch', {
-    paths: watchPaths.map((p) => (p instanceof URL ? p.toString() : p)),
-    options: opts,
-    onEvent
   })
-
-  return () => {
-    void unwatch(rid)
-  }
 }
 
+// TODO: Return `Watcher` instead in v3
 /**
  * Watch changes on files or directories.
  *
@@ -1302,32 +1310,10 @@ async function watchImmediate(
   cb: (event: WatchEvent) => void,
   options?: WatchOptions
 ): Promise<UnwatchFn> {
-  const opts = {
-    recursive: false,
+  return await watchInternal(paths, cb, {
     ...options,
-    delayMs: null
-  }
-
-  const watchPaths = Array.isArray(paths) ? paths : [paths]
-
-  for (const path of watchPaths) {
-    if (path instanceof URL && path.protocol !== 'file:') {
-      throw new TypeError('Must be a file URL.')
-    }
-  }
-
-  const onEvent = new Channel<WatchEvent>()
-  onEvent.onmessage = cb
-
-  const rid: number = await invoke('plugin:fs|watch', {
-    paths: watchPaths.map((p) => (p instanceof URL ? p.toString() : p)),
-    options: opts,
-    onEvent
+    delayMs: undefined
   })
-
-  return () => {
-    void unwatch(rid)
-  }
 }
 
 /**