helper/diff: add ID to diff

helper/diff/resource_builder.go

@@ -108,6 +108,13 @@ func (b *ResourceBuilder) Diff(
 				Type:        terraform.DiffAttrOutput,
 			}
 		}
+
+		// The ID will change
+		attrs["id"] = &terraform.ResourceAttrDiff{
+			Old:         s.ID,
+			NewComputed: true,
+			Type:        terraform.DiffAttrOutput,
+		}
 	}
 
 	// Build our resulting diff if we had attributes change

helper/diff/resource_builder_test.go

@@ -202,18 +202,22 @@ const testRBComplexDiff = `UPDATE
 
 const testRBNewDiff = `UPDATE
   IN  foo:        "" => "bar"
+  OUT id:         "" => "<computed>"
   OUT private_ip: "" => "<computed>"
 `
 
 const testRBRequiresNewDiff = `CREATE
   IN  ami:        "foo" => "bar" (forces new resource)
+  OUT id:         "1" => "<computed>"
   OUT private_ip: "127.0.0.1" => "<computed>"
 `
 
 const testRBUnknownDiff = `UPDATE
   IN  foo: "" => "${var.unknown}"
+  OUT id:  "" => "<computed>"
 `
 
 const testRBVarsDiff = `UPDATE
   IN  foo: "" => "bar"
+  OUT id:  "" => "<computed>"
 `

terraform/terraform_test.go

@@ -222,7 +222,23 @@ UPDATE: aws_instance.bar
   foo:  "" => "<computed>"
   type: "" => "aws_instance"
 UPDATE: aws_instance.foo
-  id:   "" => "<computed>"
+  foo:  "" => "<computed>"
+  num:  "" => "2"
+  type: "" => "aws_instance"
+
+STATE:
+
+<no state>
+`
+
+const testTerraformPlanComputedIdStr = `
+DIFF:
+
+UPDATE: aws_instance.bar
+  foo:  "" => "<computed>"
+  type: "" => "aws_instance"
+UPDATE: aws_instance.foo
+  foo:  "" => "<computed>"
   num:  "" => "2"
   type: "" => "aws_instance"
 

terraform/test-fixtures/plan-computed/main.tf

@@ -1,8 +1,8 @@
 resource "aws_instance" "foo" {
     num = "2"
-    compute = "id"
+    compute = "foo"
 }
 
 resource "aws_instance" "bar" {
-    foo = "${aws_instance.foo.id}"
+    foo = "${aws_instance.foo.foo}"
 }