config: can generate depgraph

config/config.go

@@ -3,14 +3,17 @@
 package config
 
 import (
+	"fmt"
 	"strings"
+
+	"github.com/hashicorp/terraform/depgraph"
 )
 
 // Config is the configuration that comes from loading a collection
 // of Terraform templates.
 type Config struct {
 	Variables map[string]Variable
-	Resources []Resource
+	Resources []*Resource
 }
 
 // A resource represents a single Terraform resource in the configuration.
@@ -57,6 +60,70 @@ type UserVariable struct {
 	key string
 }
 
+// A unique identifier for this resource.
+func (r *Resource) Id() string {
+	return fmt.Sprintf("%s.%s", r.Type, r.Name)
+}
+
+// ResourceGraph returns a dependency graph of the resources from this
+// Terraform configuration.
+func (c *Config) ResourceGraph() *depgraph.Graph {
+	resource2Noun := func(r *Resource) *depgraph.Noun {
+		return &depgraph.Noun{
+			Name: r.Id(),
+			Meta: r,
+		}
+	}
+
+	nouns := make(map[string]*depgraph.Noun)
+	for _, r := range c.Resources {
+		noun := resource2Noun(r)
+		nouns[noun.Name] = noun
+	}
+
+	for _, noun := range nouns {
+		r := noun.Meta.(*Resource)
+		for _, v := range r.Variables {
+			// Only resource variables impose dependencies
+			rv, ok := v.(*ResourceVariable)
+			if !ok {
+				continue
+			}
+
+			// Build the dependency
+			dep := &depgraph.Dependency{
+				Name:   rv.ResourceId(),
+				Source: noun,
+				Target: nouns[rv.ResourceId()],
+			}
+
+			noun.Deps = append(noun.Deps, dep)
+		}
+	}
+
+	// Create the list of nouns that the depgraph.Graph struct expects
+	nounsList := make([]*depgraph.Noun, 0, len(nouns))
+	for _, n := range nouns {
+		nounsList = append(nounsList, n)
+	}
+
+	// Create a root that just depends on everything else finishing.
+	root := &depgraph.Noun{Name: "root"}
+	for _, n := range nounsList {
+		root.Deps = append(root.Deps, &depgraph.Dependency{
+			Name:   n.Name,
+			Source: root,
+			Target: n,
+		})
+	}
+	nounsList = append(nounsList, root)
+
+	return &depgraph.Graph{
+		Name:  "resources",
+		Nouns: nounsList,
+	}
+}
+
 func NewResourceVariable(key string) (*ResourceVariable, error) {
 	parts := strings.SplitN(key, ".", 3)
 	return &ResourceVariable{
@@ -67,6 +134,10 @@ func NewResourceVariable(key string) (*ResourceVariable, error) {
 	}, nil
 }
 
+func (v *ResourceVariable) ResourceId() string {
+	return fmt.Sprintf("%s.%s", v.Type, v.Name)
+}
+
 func (v *ResourceVariable) FullKey() string {
 	return v.key
 }

config/config_test.go

@@ -1,12 +1,33 @@
 package config
 
 import (
+	"path/filepath"
+	"strings"
 	"testing"
 )
 
 // This is the directory where our test fixtures are.
 const fixtureDir = "./test-fixtures"
 
+func TestConfigResourceGraph(t *testing.T) {
+	c, err := Load(filepath.Join(fixtureDir, "resource_graph.tf"))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	graph := c.ResourceGraph()
+	if err := graph.Validate(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(graph.String())
+	expected := resourceGraphValue
+
+	if actual != strings.TrimSpace(expected) {
+		t.Fatalf("bad:\n%s", actual)
+	}
+}
+
 func TestNewResourceVariable(t *testing.T) {
 	v, err := NewResourceVariable("foo.bar.baz")
 	if err != nil {
@@ -41,3 +62,15 @@ func TestNewUserVariable(t *testing.T) {
 		t.Fatalf("bad: %#v", v)
 	}
 }
+
+const resourceGraphValue = `
+root: root
+  root -> aws_security_group.firewall
+  root -> aws_instance.web
+aws_security_group.firewall
+aws_instance.web
+  aws_instance.web -> aws_security_group.firewall
+root
+  root -> aws_security_group.firewall
+  root -> aws_instance.web
+`

config/config_tree.go

@@ -68,7 +68,7 @@ func mergeConfig(c1, c2 *Config) (*Config, error) {
 
 	// Merge resources: If they collide, we just take the latest one
 	// for now. In the future, we might provide smarter merge functionality.
-	resources := make(map[string]Resource)
+	resources := make(map[string]*Resource)
 	for _, r := range c1.Resources {
 		id := fmt.Sprintf("%s[%s]", r.Type, r.Name)
 		resources[id] = r
@@ -78,7 +78,7 @@ func mergeConfig(c1, c2 *Config) (*Config, error) {
 		resources[id] = r
 	}
 
-	c.Resources = make([]Resource, 0, len(resources))
+	c.Resources = make([]*Resource, 0, len(resources))
 	for _, r := range resources {
 		c.Resources = append(c.Resources, r)
 	}

config/loader_libucl.go

@@ -120,7 +120,7 @@ func loadFileLibucl(root string) (configurable, []string, error) {
 // The resulting resources may not be unique, but each resource
 // represents exactly one resource definition in the libucl configuration.
 // We leave it up to another pass to merge them together.
-func loadResourcesLibucl(o *libucl.Object) ([]Resource, error) {
+func loadResourcesLibucl(o *libucl.Object) ([]*Resource, error) {
 	var allTypes []*libucl.Object
 
 	// Libucl object iteration is really nasty. Below is likely to make
@@ -154,7 +154,7 @@ func loadResourcesLibucl(o *libucl.Object) ([]Resource, error) {
 	iter.Close()
 
 	// Where all the results will go
-	var result []Resource
+	var result []*Resource
 
 	// Now go over all the types and their children in order to get
 	// all of the actual resources.
@@ -186,7 +186,7 @@ func loadResourcesLibucl(o *libucl.Object) ([]Resource, error) {
 					err)
 			}
 
-			result = append(result, Resource{
+			result = append(result, &Resource{
 				Name:      r.Key(),
 				Type:      t.Key(),
 				Config:    config,

config/loader_test.go

@@ -58,7 +58,7 @@ func TestLoadBasic_import(t *testing.T) {
 
 // This helper turns a resources field into a deterministic
 // string value for comparison in tests.
-func resourcesStr(rs []Resource) string {
+func resourcesStr(rs []*Resource) string {
 	result := ""
 	for _, r := range rs {
 		result += fmt.Sprintf(

config/test-fixtures/resource_graph.tf

@@ -0,0 +1,15 @@
+variable "foo" {
+    default = "bar";
+    description = "bar";
+}
+
+resource "aws_security_group" "firewall" {
+}
+
+resource aws_instance "web" {
+    ami = "${var.foo}"
+    security_groups = [
+        "foo",
+        "${aws_security_group.firewall.foo}"
+    ]
+}

depgraph/graph.go

@@ -8,7 +8,6 @@ package depgraph
 import (
 	"bytes"
 	"fmt"
-	"strings"
 
 	"github.com/hashicorp/terraform/digraph"
 )
@@ -111,33 +110,21 @@ func (g *Graph) CheckConstraints() error {
 func (g *Graph) String() string {
 	var buf bytes.Buffer
 
-	cb := func(n *Noun, depth int) {
+	buf.WriteString(fmt.Sprintf("root: %s\n", g.Root.Name))
+	for _, dep := range g.Root.Deps {
 		buf.WriteString(fmt.Sprintf(
-			"%s%s\n",
-			strings.Repeat("  ", depth),
-			n.Name))
+			"  %s -> %s\n",
+			dep.Source,
+			dep.Target))
 		}
 
-	type listItem struct {
-		n *Noun
-		d int
-	}
-	nodes := []listItem{{g.Root, 0}}
-	for len(nodes) > 0 {
-		// Pop current node
-		n := len(nodes)
-		current := nodes[n-1]
-		nodes = nodes[:n-1]
-
-		// Visit
-		cb(current.n, current.d)
-
-		// Traverse
-		for _, dep := range current.n.Deps {
-			nodes = append(nodes, listItem{
-				n: dep.Target,
-				d: current.d + 1,
-			})
+	for _, n := range g.Nouns {
+		buf.WriteString(fmt.Sprintf("%s\n", n.Name))
+		for _, dep := range n.Deps {
+			buf.WriteString(fmt.Sprintf(
+				"  %s -> %s\n",
+				dep.Source,
+				dep.Target))
 		}
 	}
 

depgraph/graph_test.go

@@ -69,13 +69,20 @@ c -> e`)
 	actual := g.String()
 
 	expected := `
+root: a
+  a -> b
+  a -> c
 a
-  c
-    e
-    d
+  a -> b
+  a -> c
 b
-    e
+  b -> d
+  b -> e
+c
+  c -> d
+  c -> e
 d
+e
 `
 
 	actual = strings.TrimSpace(actual)