SetId should set the attribute as well

The update protocol shims will also check for this this, but eventually
"id" will only be a normal attribute, and we shouldn't have to special
case this.

helper/schema/resource_data.go

@@ -219,10 +219,16 @@ func (d *ResourceData) Id() string {
 
 	if d.state != nil {
 		result = d.state.ID
+		if result == "" {
+			result = d.state.Attributes["id"]
+		}
 	}
 
 	if d.newState != nil {
 		result = d.newState.ID
+		if result == "" {
+			result = d.newState.Attributes["id"]
+		}
 	}
 
 	return result
@@ -246,6 +252,10 @@ func (d *ResourceData) ConnInfo() map[string]string {
 func (d *ResourceData) SetId(v string) {
 	d.once.Do(d.init)
 	d.newState.ID = v
+
+	// once we transition away from the legacy state types, "id" will no longer
+	// be a special field, and will become a normal attribute.
+	d.setWriter.unsafeWriteField("id", v)
 }
 
 // SetConnInfo sets the connection info for a resource.

helper/schema/resource_data_test.go

@@ -3440,7 +3440,10 @@ func TestResourceDataSetId(t *testing.T) {
 	d.SetId("foo")
 
 	actual := d.State()
-	if actual.ID != "foo" {
+
+	// SetId should set both the ID field as well as the attribute, to aid in
+	// transitioning to the new type system.
+	if actual.ID != "foo" && actual.Attributes["id"] != "foo" {
 		t.Fatalf("bad: %#v", actual)
 	}
 }