commands/diff: starting up, got it loading a Terraform

command/diff.go

@@ -0,0 +1,72 @@
+package command
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/hashicorp/terraform/config"
+	"github.com/hashicorp/terraform/terraform"
+	"github.com/mitchellh/cli"
+)
+
+// DiffCommand is a Command implementation that compares a Terraform
+// configuration to an actual infrastructure and shows the differences.
+type DiffCommand struct {
+	TFConfig *terraform.Config
+	Ui       cli.Ui
+}
+
+func (c *DiffCommand) Run(args []string) int {
+	cmdFlags := flag.NewFlagSet("diff", flag.ContinueOnError)
+	cmdFlags.Usage = func() { c.Ui.Error(c.Help()) }
+	if err := cmdFlags.Parse(args); err != nil {
+		return 1
+	}
+
+	args = cmdFlags.Args()
+	if len(args) != 1 {
+		c.Ui.Error(
+			"The diff command expects only one argument with the path\n" +
+				"to a Terraform configuration.\n")
+		cmdFlags.Usage()
+		return 1
+	}
+
+	b, err := config.Load(args[0])
+	if err != nil {
+		c.Ui.Error(fmt.Sprintf("Error loading blueprint: %s", err))
+		return 1
+	}
+
+	tfconfig := c.TFConfig
+	tfconfig.Config = b
+
+	_, err = terraform.New(tfconfig)
+	if err != nil {
+		c.Ui.Error(fmt.Sprintf("Error initializing Terraform: %s", err))
+		return 1
+	}
+
+	return 0
+}
+
+func (c *DiffCommand) Help() string {
+	helpText := `
+Usage: terraform diff [options] [terraform.tf]
+
+  Shows the differences between the Terraform configuration and
+  the actual state of an infrastructure.
+
+Options:
+
+  -state=statefile    Path to a Terraform state file to use to look
+                      up Terraform-managed resources.
+
+`
+	return strings.TrimSpace(helpText)
+}
+
+func (c *DiffCommand) Synopsis() string {
+	return "Show changes between Terraform config and infrastructure"
+}

commands.go

@@ -20,6 +20,13 @@ func init() {
 			}, nil
 		},
 
+		"diff": func() (cli.Command, error) {
+			return &command.DiffCommand{
+				TFConfig: &TFConfig,
+				Ui:       ui,
+			}, nil
+		},
+
 		"version": func() (cli.Command, error) {
 			return &command.VersionCommand{
 				Revision:          GitCommit,

config.go

@@ -1,9 +1,16 @@
 package main
 
 import (
+	"github.com/hashicorp/terraform/terraform"
 	"github.com/mitchellh/go-libucl"
 )
 
+// TFConfig is the global base configuration that has the
+// basic providers registered. Users of this configuration
+// should copy it (call the Copy method) before using it so
+// that it isn't corrupted.
+var TFConfig terraform.Config
+
 // Config is the structure of the configuration for the Terraform CLI.
 //
 // This is not the configuration for Terraform itself. That is in the