make sure id really gets set in SetId

SetId needs to overwrite the newState as well, since the internal calls
to DataSource.Id() will override the set attribute.

helper/schema/resource_data.go

@@ -255,7 +255,15 @@ func (d *ResourceData) SetId(v string) {
 
 	// once we transition away from the legacy state types, "id" will no longer
 	// be a special field, and will become a normal attribute.
+	// set the attribute normally
 	d.setWriter.unsafeWriteField("id", v)
+
+	// Make sure the newState is also set, otherwise the old value
+	// may get precedence.
+	if d.newState.Attributes == nil {
+		d.newState.Attributes = map[string]string{}
+	}
+	d.newState.Attributes["id"] = v
 }
 
 // SetConnInfo sets the connection info for a resource.

helper/schema/resource_data_test.go

@@ -3499,14 +3499,27 @@ func TestResourceDataSetMeta_Timeouts(t *testing.T) {
 }
 
 func TestResourceDataSetId(t *testing.T) {
-	d := &ResourceData{}
+	d := &ResourceData{
+		state: &terraform.InstanceState{
+			ID: "test",
+			Attributes: map[string]string{
+				"id": "test",
+			},
+		},
+	}
 	d.SetId("foo")
 
 	actual := d.State()
 
 	// 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" {
+	if actual.ID != "foo" || actual.Attributes["id"] != "foo" {
+		t.Fatalf("bad: %#v", actual)
+	}
+
+	d.SetId("")
+	actual = d.State()
+	if actual != nil {
 		t.Fatalf("bad: %#v", actual)
 	}
 }