fix panic

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

Author: ndeloof

pkg/watch/watcher_darwin.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sync/atomic"
 	"time"
 
 	"github.com/fsnotify/fsevents"
@@ -38,6 +39,7 @@ type fseventNotify struct {
 	stop   chan struct{}
 
 	pathsWereWatching map[string]any
+	running           atomic.Bool
 }
 
 func (d *fseventNotify) loop() {
@@ -81,17 +83,26 @@ func (d *fseventNotify) Start() error {
 		return nil
 	}
 
+	if !d.running.CompareAndSwap(false, true) {
+		return nil
+	}
+
 	numberOfWatches.Add(int64(len(d.stream.Paths)))
 
 	err := d.stream.Start()
 	if err != nil {
+		d.running.Store(false)
 		return err
 	}
 	go d.loop()
 	return nil
 }
 
 func (d *fseventNotify) Close() error {
+	if !d.running.CompareAndSwap(true, false) {
+		return nil
+	}
+
 	numberOfWatches.Add(int64(-len(d.stream.Paths)))
 
 	d.stream.Stop()

pkg/watch/watcher_darwin_test.go

@@ -0,0 +1,48 @@
+//go:build fsnotify
+
+/*
+   Copyright 2020 Docker Compose CLI authors
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package watch
+
+import (
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func TestFseventNotifyCloseIdempotent(t *testing.T) {
+	// Create a watcher with a temporary directory
+	tmpDir := t.TempDir()
+	watcher, err := newWatcher([]string{tmpDir})
+	assert.NilError(t, err)
+
+	// Start the watcher
+	err = watcher.Start()
+	assert.NilError(t, err)
+
+	// Close should work the first time
+	err = watcher.Close()
+	assert.NilError(t, err)
+
+	// Close should be idempotent - calling it again should not panic
+	err = watcher.Close()
+	assert.NilError(t, err)
+
+	// Even a third time should be safe
+	err = watcher.Close()
+	assert.NilError(t, err)
+}