Add --print-changes support

Author: bduffany

Makefile

@@ -0,0 +1,7 @@
+.PHONY: godemon test
+
+godemon:
+	go build -o godemon ./cmd/godemon
+
+test:
+	go test ./...

config.go

@@ -53,6 +53,10 @@ type Config struct {
 	// godemon [ flags ... ] sh -c 'clear && exec {command}'
 	Clear bool `json:"clear,omitempty"`
 
+	// PrintChanges specifies whether to print change events to stdout without
+	// running any command. When enabled, no command should be specified.
+	PrintChanges bool `json:"printChanges,omitempty"`
+
 	// TODO: FollowSymlinks
 
 	// Private fields below

godemon.go

@@ -35,6 +35,7 @@ Advanced options:
   --no-gitignore       disable adding patterns from .gitignore to ignore list
   -s, --signal         restart signal name or number (default SIGINT)
   -v, --verbose        log more info; set twice to log lower level debug info
+  --print-changes      print change events to stdout without running a command
 `)
 }
 
@@ -97,6 +98,10 @@ func parseConfig(args []string) (*Config, error) {
 			clearTerminal = true
 			continue
 		}
+		if arg == "--print-changes" {
+			cfg.PrintChanges = true
+			continue
+		}
 
 		// Parse string flags
 		for _, spec := range []struct {
@@ -230,8 +235,14 @@ func parseConfig(args []string) (*Config, error) {
 		}
 		cfg.notifySignal = s
 	}
-	if len(cfg.Command) == 0 {
-		return nil, fmt.Errorf("must specify a command to run")
+	if cfg.PrintChanges {
+		if len(cfg.Command) > 0 {
+			return nil, fmt.Errorf("--print-changes cannot be used with a command")
+		}
+	} else {
+		if len(cfg.Command) == 0 {
+			return nil, fmt.Errorf("must specify a command to run")
+		}
 	}
 	cfg.dryRun = dryRun
 
@@ -619,20 +630,23 @@ func (g *godemon) Start() error {
 
 	shutdownCh := make(chan struct{}, 1)
 
-	// Command worker
-	restart := throttleRestarts(events)
-
 	if g.cfg.dryRun {
 		// Allow 1s for file watchers to be set up.
 		// TODO: Wait till addCh settles instead.
 		time.Sleep(1 * time.Second)
 		notifyf("Exiting due to --dry-run flag.")
 	}
 
-	go g.loopCommand(restart, shutdownCh)
-
-	// Wait for events and dispatch to the appropriate handler.
-	g.handleEvents(addCh, events, shutdownCh)
+	if g.cfg.PrintChanges {
+		// In print-changes mode, just print events to stdout without running a command.
+		g.handlePrintChanges(addCh, shutdownCh)
+	} else {
+		// Command worker
+		restart := throttleRestarts(events)
+		go g.loopCommand(restart, shutdownCh)
+		// Wait for events and dispatch to the appropriate handler.
+		g.handleEvents(addCh, events, shutdownCh)
+	}
 
 	return nil
 }
@@ -802,6 +816,37 @@ func (g *godemon) handleEvents(addCh chan<- string, restartCh chan<- struct{}, s
 	}
 }
 
+func (g *godemon) handlePrintChanges(addCh chan<- string, shutdownCh <-chan struct{}) {
+	sig := make(chan os.Signal, 4)
+	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
+
+	go func() {
+		<-sig
+		os.Exit(0)
+	}()
+
+	for {
+		select {
+		case err := <-g.w.Errors:
+			warnf("%s", err)
+		case event := <-g.w.Events:
+			if g.shouldIgnore(event.Name) {
+				infof("Ignoring event: %s %q", event.Op, event.Name)
+				continue
+			}
+			// Print the change event to stdout
+			fmt.Printf("%s %s\n", event.Op, event.Name)
+			// When creating new dirs, add them to the watch list.
+			if event.Op == fsnotify.Create && isDir(event.Name) {
+				addCh <- event.Name
+			}
+		case <-shutdownCh:
+			debugf("handlePrintChanges: got shutdown signal")
+			return
+		}
+	}
+}
+
 func waitForLockfileRemoval(path string) error {
 	debugf("Waiting for removal of lockfile %s", path)
 

godemon_test.go

@@ -9,7 +9,6 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
-	"runtime"
 	"strconv"
 	"strings"
 	"syscall"