terraform: fix potential case where cycle is made

depgraph/dependency.go

@@ -1,6 +1,8 @@
 package depgraph
 
 import (
+	"fmt"
+
 	"github.com/hashicorp/terraform/digraph"
 )
 
@@ -31,6 +33,14 @@ func (d *Dependency) Tail() digraph.Node {
 	return d.Target
 }
 
+func (d *Dependency) GoString() string {
+	return fmt.Sprintf(
+		"*Dependency{Name: %s, Source: %s, Target: %s}",
+		d.Name,
+		d.Source.Name,
+		d.Target.Name)
+}
+
 func (d *Dependency) String() string {
 	return d.Name
 }

depgraph/noun.go

@@ -1,6 +1,8 @@
 package depgraph
 
 import (
+	"fmt"
+
 	"github.com/hashicorp/terraform/digraph"
 )
 
@@ -22,6 +24,10 @@ func (n *Noun) Edges() []digraph.Edge {
 	return edges
 }
 
+func (n *Noun) GoString() string {
+	return fmt.Sprintf("*%#v", *n)
+}
+
 func (n *Noun) String() string {
 	return n.Name
 }

terraform/graph.go

@@ -376,6 +376,11 @@ func graphAddDiff(g *depgraph.Graph, d *Diff) error {
 		// dependencies. Look to see if they're managed.
 		for _, dep := range deps {
 			for _, n2 := range nlist {
+				// Don't ever depend on ourselves
+				if n2.Name == n.Name {
+					continue
+				}
+
 				rn2 := n2.Meta.(*GraphNodeResource)
 				if rn2.Resource.State.ID == dep.ID {
 					n2.Deps = append(n2.Deps, &depgraph.Dependency{