terraform: build resource graph, validate

config/config.go

@@ -9,6 +9,10 @@ import (
 	"github.com/hashicorp/terraform/depgraph"
 )
 
+// ResourceGraphRoot is the name of the resource graph root that should be
+// ignored since it doesn't map to an exact resource.
+const ResourceGraphRoot = "root"
+
 // Config is the configuration that comes from loading a collection
 // of Terraform templates.
 type Config struct {
@@ -116,7 +120,7 @@ func (c *Config) ResourceGraph() *depgraph.Graph {
 	}
 
 	// Create a root that just depends on everything else finishing.
-	root := &depgraph.Noun{Name: "root"}
+	root := &depgraph.Noun{Name: ResourceGraphRoot}
 	for _, n := range nounsList {
 		root.Deps = append(root.Deps, &depgraph.Dependency{
 			Name:   n.Name,

terraform/state.go

@@ -4,17 +4,5 @@ package terraform
 // can use to keep track of what real world resources it is actually
 // managing.
 type State struct {
-	resources map[string]resourceState
-}
-
-// resourceState is the state of a single resource.
-//
-// The ID is required and is some opaque string used to recognize
-// the realized resource.
-//
-// Extra is arbitrary extra metadata that the resource provider returns
-// that is sent back into the resource provider when it is needed.
-type resourceState struct {
-	ID    string
-	Extra map[string]interface{}
+	resources map[string]ResourceState
 }

terraform/terraform.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"github.com/hashicorp/terraform/config"
+	"github.com/hashicorp/terraform/depgraph"
 )
 
 // Terraform is the primary structure that is used to interact with
@@ -12,6 +13,7 @@ import (
 // all resources, a resource tree, a specific resource, etc.
 type Terraform struct {
 	config    *config.Config
+	graph     *depgraph.Graph
 	mapping   map[*config.Resource]ResourceProvider
 	variables map[string]string
 }
@@ -98,6 +100,13 @@ func New(c *Config) (*Terraform, error) {
 		mapping[r] = provider
 	}
 
+	// Build the resource graph
+	graph := c.Config.ResourceGraph()
+	if err := graph.Validate(); err != nil {
+		errs = append(errs, fmt.Errorf(
+			"Resource graph has an error: %s", err))
+	}
+
 	// If we accumulated any errors, then return them all
 	if len(errs) > 0 {
 		return nil, &MultiError{Errors: errs}
@@ -105,6 +114,7 @@ func New(c *Config) (*Terraform, error) {
 
 	return &Terraform{
 		config:    c.Config,
+		graph:     graph,
 		mapping:   mapping,
 		variables: c.Variables,
 	}, nil

terraform/terraform_test.go

@@ -80,6 +80,24 @@ func TestNew(t *testing.T) {
 	}
 }
 
+func TestNew_graphCycle(t *testing.T) {
+	config := testConfig(t, "new-graph-cycle")
+	tfConfig := &Config{
+		Config: config,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFunc("aws", []string{"aws_instance"}),
+		},
+	}
+
+	tf, err := New(tfConfig)
+	if err == nil {
+		t.Fatal("should error")
+	}
+	if tf != nil {
+		t.Fatalf("should not return tf")
+	}
+}
+
 func TestNew_variables(t *testing.T) {
 	config := testConfig(t, "new-variables")
 	tfConfig := &Config{

terraform/test-fixtures/new-graph-cycle/main.tf

@@ -0,0 +1,7 @@
+resource "aws_instance" "foo" {
+  ami = "${aws_instance.bar.id}"
+}
+
+resource "aws_instance" "bar" {
+  ami = "${aws_instance.foo.id}"
+}