helper/schema: show computed lists in diffs

helper/schema/schema.go

@@ -248,15 +248,25 @@ func (m schemaMap) diffList(
 	newLen = len(vs)
 
 	// If the counts are not the same, then record that diff
-	if oldLen != newLen {
+	changed := oldLen != newLen
+	computed := oldLen == 0 && newLen == 0 && schema.Computed
+	if changed || computed {
 		countSchema := &Schema{
 			Type:     TypeInt,
+			Computed: schema.Computed,
 			ForceNew: schema.ForceNew,
 		}
 
+		oldStr := ""
+		newStr := ""
+		if !computed {
+			oldStr = strconv.FormatInt(int64(oldLen), 10)
+			newStr = strconv.FormatInt(int64(newLen), 10)
+		}
+
 		diff.Attributes[k+".#"] = countSchema.finalizeDiff(&terraform.ResourceAttrDiff{
-			Old: strconv.FormatInt(int64(oldLen), 10),
-			New: strconv.FormatInt(int64(newLen), 10),
+			Old: oldStr,
+			New: newStr,
 		})
 	}
 

helper/schema/schema_test.go

@@ -181,7 +181,7 @@ func TestSchemaMap_Diff(t *testing.T) {
 			Diff: &terraform.ResourceDiff{
 				Attributes: map[string]*terraform.ResourceAttrDiff{
 					"ports.#": &terraform.ResourceAttrDiff{
-						Old: "",
+						Old: "0",
 						New: "3",
 					},
 					"ports.0": &terraform.ResourceAttrDiff{
@@ -285,7 +285,7 @@ func TestSchemaMap_Diff(t *testing.T) {
 			Diff: &terraform.ResourceDiff{
 				Attributes: map[string]*terraform.ResourceAttrDiff{
 					"ports.#": &terraform.ResourceAttrDiff{
-						Old:         "",
+						Old:         "0",
 						New:         "3",
 						RequiresNew: true,
 					},
@@ -310,6 +310,32 @@ func TestSchemaMap_Diff(t *testing.T) {
 			Err: false,
 		},
 
+		{
+			Schema: map[string]*Schema{
+				"ports": &Schema{
+					Type:     TypeList,
+					Optional: true,
+					Computed: true,
+					Elem:     &Schema{Type: TypeInt},
+				},
+			},
+
+			State: nil,
+
+			Config: map[string]interface{}{},
+
+			Diff: &terraform.ResourceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"ports.#": &terraform.ResourceAttrDiff{
+						Old: "",
+						NewComputed: true,
+					},
+				},
+			},
+
+			Err: false,
+		},
+
 		/*
 		 * List of structure decode
 		 */
@@ -343,7 +369,7 @@ func TestSchemaMap_Diff(t *testing.T) {
 			Diff: &terraform.ResourceDiff{
 				Attributes: map[string]*terraform.ResourceAttrDiff{
 					"ingress.#": &terraform.ResourceAttrDiff{
-						Old: "",
+						Old: "0",
 						New: "1",
 					},
 					"ingress.0.from": &terraform.ResourceAttrDiff{
@@ -632,7 +658,6 @@ func TestSchemaMap_Diff(t *testing.T) {
 	}
 
 	for i, tc := range cases {
-		if i != 1 { continue }
 		c, err := config.NewRawConfig(tc.Config)
 		if err != nil {
 			t.Fatalf("err: %s", err)