Add polling as a fallback to native filesystem events in server watch

Fixes #8720
Fixes #6849
Fixes #7930

commands/commands.go

@@ -204,6 +204,7 @@ type hugoBuilderCommon struct {
 	environment string
 
 	buildWatch bool
+	poll       bool
 
 	gc bool
 
@@ -291,6 +292,7 @@ func (cc *hugoBuilderCommon) handleFlags(cmd *cobra.Command) {
 	cmd.Flags().StringVarP(&cc.baseURL, "baseURL", "b", "", "hostname (and path) to the root, e.g. http://spf13.com/")
 	cmd.Flags().Bool("enableGitInfo", false, "add Git revision, date and author info to the pages")
 	cmd.Flags().BoolVar(&cc.gc, "gc", false, "enable to run some cleanup tasks (remove unused cache files) after the build")
+	cmd.Flags().BoolVar(&cc.poll, "poll", false, "use a poll based approach to watch for file system changes")
 
 	cmd.Flags().Bool("templateMetrics", false, "display metrics about template executions")
 	cmd.Flags().Bool("templateMetricsHints", false, "calculate some improvement hints when combined with --templateMetrics")

commands/hugo.go

@@ -523,7 +523,7 @@ func (c *commandeer) build() error {
 
 		c.logger.Printf("Watching for changes in %s%s{%s}\n", baseWatchDir, helpers.FilePathSeparator, rootWatchDirs)
 		c.logger.Println("Press Ctrl+C to stop")
-		watcher, err := c.newWatcher(watchDirs...)
+		watcher, err := c.newWatcher(c.h.poll, watchDirs...)
 		checkErr(c.Logger, err)
 		defer watcher.Close()
 
@@ -820,7 +820,7 @@ func (c *commandeer) fullRebuild(changeType string) {
 }
 
 // newWatcher creates a new watcher to watch filesystem events.
-func (c *commandeer) newWatcher(dirList ...string) (*watcher.Batcher, error) {
+func (c *commandeer) newWatcher(poll bool, dirList ...string) (*watcher.Batcher, error) {
 	if runtime.GOOS == "darwin" {
 		tweakLimit()
 	}
@@ -830,7 +830,10 @@ func (c *commandeer) newWatcher(dirList ...string) (*watcher.Batcher, error) {
 		return nil, err
 	}
 
-	watcher, err := watcher.New(1 * time.Second)
+	// The second interval is used by the poll based watcher.
+	// Setting a shorter interval would make it snappier,
+	// but it would consume more CPU.
+	watcher, err := watcher.New(500*time.Millisecond, 700*time.Millisecond, poll)
 	if err != nil {
 		return nil, err
 	}
@@ -859,7 +862,7 @@ func (c *commandeer) newWatcher(dirList ...string) (*watcher.Batcher, error) {
 					// Need to reload browser to show the error
 					livereload.ForceRefresh()
 				}
-			case err := <-watcher.Errors:
+			case err := <-watcher.Errors():
 				if err != nil {
 					c.logger.Errorln("Error while watching:", err)
 				}

commands/server.go

@@ -262,7 +262,7 @@ func (sc *serverCmd) server(cmd *cobra.Command, args []string) error {
 		for _, group := range watchGroups {
 			jww.FEEDBACK.Printf("Watching for changes in %s\n", group)
 		}
-		watcher, err := c.newWatcher(watchDirs...)
+		watcher, err := c.newWatcher(sc.poll, watchDirs...)
 		if err != nil {
 			return err
 		}