DO nor re-run up-to-date tasks, based on ModTime and given patterns

file.go

@@ -0,0 +1,53 @@
+package task
+
+import (
+	"os"
+	"time"
+
+	"github.com/mattn/go-zglob"
+)
+
+var dirsToSkip = []string{
+	".git",
+	"node_modules",
+}
+
+func minTime(pattern string) (minTime time.Time, err error) {
+	files, err := zglob.Glob(pattern)
+	if err != nil {
+		return time.Time{}, err
+	}
+
+	for _, f := range files {
+		info, err := os.Stat(f)
+		if err != nil {
+			return time.Time{}, err
+		}
+
+		modTime := info.ModTime()
+		if minTime.IsZero() || modTime.Before(minTime) {
+			minTime = modTime
+		}
+	}
+	return
+}
+
+func maxTime(pattern string) (maxTime time.Time, err error) {
+	files, err := zglob.Glob(pattern)
+	if err != nil {
+		return time.Time{}, err
+	}
+
+	for _, f := range files {
+		info, err := os.Stat(f)
+		if err != nil {
+			return time.Time{}, err
+		}
+
+		modTime := info.ModTime()
+		if modTime.After(maxTime) {
+			maxTime = modTime
+		}
+	}
+	return
+}

task.go

@@ -30,7 +30,7 @@ func init() {
 type Task struct {
 	Cmds      []string
 	Deps      []string
-	Source    string
+	Sources   string
 	Generates string
 }
 
@@ -84,6 +84,11 @@ func RunTask(name string) error {
 		return &TaskNotFoundError{name}
 	}
 
+	if isTaskUpToDate(t) {
+		log.Printf(`Task "%s" is up to date`, name)
+		return nil
+	}
+
 	for _, d := range t.Deps {
 		if err := RunTask(d); err != nil {
 			return err
@@ -98,6 +103,24 @@ func RunTask(name string) error {
 	return nil
 }
 
+func isTaskUpToDate(t *Task) bool {
+	if t.Sources == "" || t.Generates == "" {
+		return false
+	}
+
+	sourcesMaxTime, err := maxTime(t.Sources)
+	if err != nil || sourcesMaxTime.IsZero() {
+		return false
+	}
+
+	generatesMinTime, err := minTime(t.Generates)
+	if err != nil || generatesMinTime.IsZero() {
+		return false
+	}
+
+	return generatesMinTime.After(sourcesMaxTime)
+}
+
 func runCommand(c string) error {
 	var cmd *exec.Cmd
 	if ShExists {