revert stringstack.go changes

common/stringstack/stringstack.go

@@ -6,7 +6,8 @@ import (
 
 // StringStack is a basic LIFO "stack" for storing strings.
 type StringStack struct {
-	stack []string
+	Locked bool
+	stack  []string
 }
 
 // New creates a new instance of StringStack
@@ -19,6 +20,20 @@ func (s *StringStack) Set(v string) {
 	s.stack = []string{v}
 }
 
+// Lock freezes the StringStack
+func (s *StringStack) Lock() {
+	if !s.Locked {
+		s.Locked = true
+	}
+}
+
+// Unlock unfreezes the StringStack
+func (s *StringStack) Unlock() {
+	if s.Locked {
+		s.Locked = false
+	}
+}
+
 // Push pushes a string onto the stack.
 func (s *StringStack) Push(v string) {
 	s.stack = append(s.stack, v)
@@ -26,11 +41,12 @@ func (s *StringStack) Push(v string) {
 
 // Pop pops a string from the stack.
 func (s *StringStack) Pop() (string, error) {
+	var x string
 	if len(s.stack) == 0 {
-		return "", errors.New("no items on stack")
+		return x, errors.New("no items on stack")
 	}
 
-	x := s.stack[len(s.stack)-1]
+	x = s.stack[len(s.stack)-1]
 	s.stack = s.stack[:len(s.stack)-1]
 
 	return x, nil