command/diff: use state

command/diff.go

@@ -3,6 +3,7 @@ package command
 import (
 	"flag"
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/hashicorp/terraform/config"
@@ -18,7 +19,10 @@ type DiffCommand struct {
 }
 
 func (c *DiffCommand) Run(args []string) int {
+	var statePath string
+
 	cmdFlags := flag.NewFlagSet("diff", flag.ContinueOnError)
+	cmdFlags.StringVar(&statePath, "state", "", "path")
 	cmdFlags.Usage = func() { c.Ui.Error(c.Help()) }
 	if err := cmdFlags.Parse(args); err != nil {
 		return 1
@@ -33,6 +37,23 @@ func (c *DiffCommand) Run(args []string) int {
 		return 1
 	}
 
+	// Load up the state
+	var state *terraform.State
+	if statePath != "" {
+		f, err := os.Open(statePath)
+		if err != nil {
+			c.Ui.Error(fmt.Sprintf("Error loading state: %s", err))
+			return 1
+		}
+
+		state, err = terraform.ReadState(f)
+		f.Close()
+		if err != nil {
+			c.Ui.Error(fmt.Sprintf("Error loading state: %s", err))
+			return 1
+		}
+	}
+
 	b, err := config.Load(args[0])
 	if err != nil {
 		c.Ui.Error(fmt.Sprintf("Error loading blueprint: %s", err))
@@ -48,7 +69,7 @@ func (c *DiffCommand) Run(args []string) int {
 		return 1
 	}
 
-	diff, err := tf.Diff(nil)
+	diff, err := tf.Diff(state)
 	if err != nil {
 		c.Ui.Error(fmt.Sprintf("Error running diff: %s", err))
 		return 1

command/diff_test.go

@@ -0,0 +1,80 @@
+package command
+
+import (
+	"io/ioutil"
+	"os"
+	"reflect"
+	"testing"
+
+	"github.com/hashicorp/terraform/terraform"
+	"github.com/mitchellh/cli"
+)
+
+func TestDiff_noState(t *testing.T) {
+	p := testProvider()
+	ui := new(cli.MockUi)
+	c := &DiffCommand{
+		TFConfig: testTFConfig(p),
+		Ui:       ui,
+	}
+
+	args := []string{
+		testFixturePath("diff"),
+	}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+
+	// Verify that the provider was called with the existing state
+	expectedState := &terraform.ResourceState{
+		Type: "test_instance",
+	}
+	if !reflect.DeepEqual(p.DiffState, expectedState) {
+		t.Fatalf("bad: %#v", p.DiffState)
+	}
+}
+func TestDiff_state(t *testing.T) {
+	// Write out some prior state
+	tf, err := ioutil.TempFile("", "tf")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	statePath := tf.Name()
+	defer os.Remove(tf.Name())
+
+	originalState := &terraform.State{
+		Resources: map[string]*terraform.ResourceState{
+			"test_instance.foo": &terraform.ResourceState{
+				ID:   "bar",
+				Type: "test_instance",
+			},
+		},
+	}
+
+	err = terraform.WriteState(originalState, tf)
+	tf.Close()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	p := testProvider()
+	ui := new(cli.MockUi)
+	c := &DiffCommand{
+		TFConfig: testTFConfig(p),
+		Ui:       ui,
+	}
+
+	args := []string{
+		"-state", statePath,
+		testFixturePath("diff"),
+	}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+
+	// Verify that the provider was called with the existing state
+	expectedState := originalState.Resources["test_instance.foo"]
+	if !reflect.DeepEqual(p.DiffState, expectedState) {
+		t.Fatalf("bad: %#v", p.DiffState)
+	}
+}

command/test-fixtures/diff/main.tf

@@ -0,0 +1,3 @@
+resource "test_instance" "foo" {
+    ami = "bar"
+}