terraform: tests that computed placeholders get inserted proprely

terraform/diff_test.go

@@ -19,11 +19,16 @@ func testDiffStr(d *Diff) string {
 		r := d.Resources[n]
 		buf.WriteString(fmt.Sprintf("%s\n", n))
 		for attr, attrDiff := range r {
+			v := attrDiff.New
+			if attrDiff.NewComputed {
+				v = "<computed>"
+			}
+
 			buf.WriteString(fmt.Sprintf(
 				"  %s: %#v => %#v\n",
 				attr,
 				attrDiff.Old,
-				attrDiff.New,
+				v,
 			))
 		}
 	}

terraform/terraform.go

@@ -106,9 +106,6 @@ func (t *Terraform) diffWalkFn(
 	// Initialize the result diff so we can write to it
 	result.init()
 
-	// This is the value that will be used for computed properties
-	computedId := "computed"
-
 	// Initialize the variables for application
 	vars := make(map[string]string)
 	for k, v := range t.variables {
@@ -167,7 +164,7 @@ func (t *Terraform) diffWalkFn(
 		result.Resources[r.Id()] = diff.Attributes
 
 		// Determine the new state and update variables
-		rs = rs.MergeDiff(diff.Attributes, computedId)
+		rs = rs.MergeDiff(diff.Attributes, ComputedPlaceholder)
 		for ak, av := range rs.Attributes {
 			vars[fmt.Sprintf("%s.%s", r.Id(), ak)] = av
 		}

terraform/terraform_test.go

@@ -202,6 +202,25 @@ func TestTerraformDiff(t *testing.T) {
 	}
 }
 
+func TestTerraformDiff_computed(t *testing.T) {
+	tf := testTerraform(t, "diff-computed")
+
+	diff, err := tf.Diff(nil)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if len(diff.Resources) < 2 {
+		t.Fatalf("bad: %#v", diff.Resources)
+	}
+
+	actual := strings.TrimSpace(testDiffStr(diff))
+	expected := strings.TrimSpace(testTerraformDiffComputedStr)
+	if actual != expected {
+		t.Fatalf("bad:\n%s", actual)
+	}
+}
+
 func testConfig(t *testing.T, name string) *config.Config {
 	c, err := config.Load(filepath.Join(fixtureDir, name, "main.tf"))
 	if err != nil {
@@ -230,10 +249,25 @@ func testProviderFunc(n string, rs []string) ResourceProviderFactory {
 					continue
 				}
 
-				diff.Attributes[k] = &ResourceAttrDiff{
+				if k == "compute" {
+					diff.Attributes[v.(string)] = &ResourceAttrDiff{
+						Old:         "",
+						New:         "",
+						NewComputed: true,
+					}
+					continue
+				}
+
+				attrDiff := &ResourceAttrDiff{
 					Old: "",
 					New: v.(string),
 				}
+
+				if strings.Contains(attrDiff.New, ComputedPlaceholder) {
+					attrDiff.NewComputed = true
+				}
+
+				diff.Attributes[k] = attrDiff
 			}
 
 			return diff, nil
@@ -326,3 +360,11 @@ aws_instance.bar
 aws_instance.foo
   num: "" => "2"
 `
+
+const testTerraformDiffComputedStr = `
+aws_instance.bar
+  foo: "" => "<computed>"
+aws_instance.foo
+  num: "" => "2"
+  id: "" => "<computed>"
+`

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

@@ -0,0 +1,8 @@
+resource "aws_instance" "foo" {
+    num = "2"
+    compute = "id"
+}
+
+resource "aws_instance" "bar" {
+    foo = "${aws_instance.foo.id}"
+}