From 36614dccf815c187c8547c995475a8e289112cfc Mon Sep 17 00:00:00 2001
From: Andrey Nering <andrey.nering@gmail.com>
Date: Sat, 25 Mar 2017 16:06:49 -0300
Subject: [PATCH] More sophisticated cyclic dependency detection

---
 cyclic.go      | 28 ++++++++++++++++++++++++++++
 cyclic_test.go | 36 ++++++++++++++++++++++++++++++++++++
 task.go        | 20 +++++---------------
 3 files changed, 69 insertions(+), 15 deletions(-)
 create mode 100644 cyclic.go
 create mode 100644 cyclic_test.go

diff --git a/cyclic.go b/cyclic.go
new file mode 100644
index 00000000..afa52895
--- /dev/null
+++ b/cyclic.go
@@ -0,0 +1,28 @@
+package task
+
+func HasCyclicDep(m map[string]*Task) bool {
+	visits := make(map[string]struct{}, len(m))
+
+	var checkCyclicDep func(string, *Task) bool
+	checkCyclicDep = func(name string, t *Task) bool {
+		if _, ok := visits[name]; ok {
+			return false
+		}
+		visits[name] = struct{}{}
+		defer delete(visits, name)
+
+		for _, d := range t.Deps {
+			if !checkCyclicDep(d, m[d]) {
+				return false
+			}
+		}
+		return true
+	}
+
+	for k, v := range m {
+		if !checkCyclicDep(k, v) {
+			return true
+		}
+	}
+	return false
+}
diff --git a/cyclic_test.go b/cyclic_test.go
new file mode 100644
index 00000000..08f8e087
--- /dev/null
+++ b/cyclic_test.go
@@ -0,0 +1,36 @@
+package task_test
+
+import (
+	"testing"
+
+	"github.com/go-task/task"
+)
+
+func TestCyclicDepCheck(t *testing.T) {
+	isCyclic := map[string]*task.Task{
+		"task-a": &task.Task{
+			Deps: []string{"task-b"},
+		},
+		"task-b": &task.Task{
+			Deps: []string{"task-a"},
+		},
+	}
+
+	if !task.HasCyclicDep(isCyclic) {
+		t.Error("Task should be cyclic")
+	}
+
+	isNotCyclic := map[string]*task.Task{
+		"task-a": &task.Task{
+			Deps: []string{"task-c"},
+		},
+		"task-b": &task.Task{
+			Deps: []string{"task-c"},
+		},
+		"task-c": &task.Task{},
+	}
+
+	if task.HasCyclicDep(isNotCyclic) {
+		t.Error("Task should not be cyclic")
+	}
+}
diff --git a/task.go b/task.go
index d21c47de..22d61ef7 100644
--- a/task.go
+++ b/task.go
@@ -21,9 +21,6 @@ var (
 
 	// Tasks constains the tasks parsed from Taskfile
 	Tasks = make(map[string]*Task)
-
-	runnedTasks = make(map[string]struct{})
-	mu          sync.Mutex
 )
 
 // Task represents a task
@@ -55,6 +52,10 @@ func Run() {
 		log.Fatal(err)
 	}
 
+	if HasCyclicDep(Tasks) {
+		log.Fatal("Cyclic dependency detected")
+	}
+
 	// check if given tasks exist
 	for _, a := range args {
 		if _, ok := Tasks[a]; !ok {
@@ -74,18 +75,6 @@ func Run() {
 
 // RunTask runs a task by its name
 func RunTask(name string) error {
-	if strings.HasPrefix(name, "^") {
-		name = strings.TrimPrefix(name, "^")
-	} else {
-		mu.Lock()
-		if _, found := runnedTasks[name]; found {
-			mu.Unlock()
-			return &cyclicDepError{name}
-		}
-		runnedTasks[name] = struct{}{}
-		mu.Unlock()
-	}
-
 	t, ok := Tasks[name]
 	if !ok {
 		return &taskNotFoundError{name}
@@ -180,6 +169,7 @@ func (t *Task) runCommand(i int) error {
 	}
 
 	if strings.HasPrefix(c, "^") {
+		c = strings.TrimPrefix(c, "^")
 		if err = RunTask(c); err != nil {
 			return err
 		}