add methods for checking the type of label IDs

Author: joseph-gio

crates/bevy_app/src/app.rs

@@ -373,9 +373,9 @@ impl App {
         stage_label: impl StageLabel,
         system: impl IntoSystemDescriptor<Params>,
     ) -> &mut Self {
-        use std::any::TypeId;
+        let stage_label = stage_label.as_label();
         assert!(
-            stage_label.type_id() != TypeId::of::<StartupStage>(),
+            !stage_label.is::<StartupStage>(),
             "add systems to a startup stage using App::add_startup_system_to_stage"
         );
         self.schedule.add_system_to_stage(stage_label, system);
@@ -408,9 +408,9 @@ impl App {
         stage_label: impl StageLabel,
         system_set: SystemSet,
     ) -> &mut Self {
-        use std::any::TypeId;
+        let stage_label = stage_label.as_label();
         assert!(
-            stage_label.type_id() != TypeId::of::<StartupStage>(),
+            !stage_label.is::<StartupStage>(),
             "add system sets to a startup stage using App::add_startup_system_set_to_stage"
         );
         self.schedule

crates/bevy_utils/src/label.rs

@@ -131,5 +131,15 @@ macro_rules! define_label {
                 self.data().hash(state);
             }
         }
+
+        impl $id_name {
+            /// Returns true if this label was constructed from an instance of type `L`.
+            pub fn is<L: $label_name>(self) -> bool {
+                // FIXME: This is potentially incorrect, due to the
+                // compiler unifying identical functions. We'll likely
+                // have to store some kind of hash of the TypeId.
+                (self.f as usize) == (<L as $label_name>::fmt as usize)
+            }
+        }
     };
 }