Add copy method to VarSet

pkg/target/kusttarget_test.go

@@ -453,7 +453,7 @@ bases:
 		t.Fatalf("expected var collision")
 	}
 	if !strings.Contains(err.Error(),
-		"var AWARD already encountered") {
+		"var 'AWARD' already encountered") {
 		t.Fatalf("unexpected error: %v", err)
 	}
 }

pkg/types/var.go

@@ -92,20 +92,29 @@ func (vs *VarSet) MergeSet(incoming VarSet) error {
 	return vs.MergeSlice(incoming.set)
 }
 
-// MergeSlice absorbs other vars with error on name collision.
+// MergeSlice absorbs a Var slice with error on name collision.
 // Empty fields in incoming vars are defaulted.
 func (vs *VarSet) MergeSlice(incoming []Var) error {
 	for _, v := range incoming {
-		if vs.Contains(v) {
-			return fmt.Errorf(
-				"var %s already encountered", v.Name)
+		if err := vs.Merge(v); err != nil {
+			return err
 		}
-		v.defaulting()
-		vs.insert(v)
 	}
 	return nil
 }
 
+// Merge absorbs another Var with error on name collision.
+// Empty fields in incoming Var is defaulted.
+func (vs *VarSet) Merge(v Var) error {
+	if vs.Contains(v) {
+		return fmt.Errorf(
+			"var '%s' already encountered", v.Name)
+	}
+	v.defaulting()
+	vs.insert(v)
+	return nil
+}
+
 func (vs *VarSet) insert(v Var) {
 	index := sort.Search(
 		len(vs.set),

pkg/types/var_test.go

@@ -132,7 +132,7 @@ func TestVarSet(t *testing.T) {
 	if err == nil {
 		t.Fatalf("expected err")
 	}
-	if !strings.Contains(err.Error(), "var SHELLVARS already encountered") {
+	if !strings.Contains(err.Error(), "var 'SHELLVARS' already encountered") {
 		t.Fatalf("unexpected err: %v", err)
 	}
 	v := set2.Get("BACKEND")