terraform: fix crash if depends_on used when state has orphans

terraform/graph.go

@@ -744,6 +744,11 @@ func graphAddExplicitDeps(g *depgraph.Graph) {
 		if !ok {
 			continue
 		}
+		if rn.Config == nil {
+			// Orphan. It can't be depended on or have depends (explicit)
+			// anyways.
+			continue
+		}
 
 		rs[rn.Resource.Id] = n
 		if rn.Config != nil && len(rn.Config.DependsOn) > 0 {

terraform/graph_test.go

@@ -97,6 +97,37 @@ func TestGraph_dependsOnCount(t *testing.T) {
 	}
 }
 
+func TestGraph_dependsOnWithOrphan(t *testing.T) {
+	m := testModule(t, "graph-depends-on")
+
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: []string{"root"},
+				Resources: map[string]*ResourceState{
+					"aws_instance.old": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "foo",
+						},
+					},
+				},
+			},
+		},
+	}
+
+	g, err := Graph(&GraphOpts{Module: m, State: state})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTerraformGraphDependsOrphanStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
 func TestGraph_modules(t *testing.T) {
 	m := testModule(t, "graph-modules")
 
@@ -1012,6 +1043,18 @@ root
   root -> aws_instance.web
 `
 
+const testTerraformGraphDependsOrphanStr = `
+root: root
+aws_instance.db
+  aws_instance.db -> aws_instance.web
+aws_instance.old
+aws_instance.web
+root
+  root -> aws_instance.db
+  root -> aws_instance.old
+  root -> aws_instance.web
+`
+
 const testTerraformGraphDiffStr = `
 root: root
 aws_instance.foo