Actually register the new OnTransition schedule

crates/bevy_app/src/app.rs

@@ -359,7 +359,16 @@ impl App {
         // These are different for loops to avoid conflicting access to self
         for variant in S::variants() {
             self.add_schedule(OnEnter(variant.clone()), Schedule::new());
-            self.add_schedule(OnExit(variant), Schedule::new());
+            self.add_schedule(OnExit(variant.clone()), Schedule::new());
+
+            for second in S::variants() {
+                if second == variant {
+                    // skip adding OnTransition for A -> A
+                    continue;
+                }
+
+                self.add_schedule(OnTransition(variant.clone(), second), Schedule::new());
+            }
         }
 
         self

crates/bevy_ecs/src/lib.rs

@@ -43,8 +43,8 @@ pub mod prelude {
         schedule::{
             apply_state_transition, apply_system_buffers, common_conditions::*, Condition,
             IntoSystemConfig, IntoSystemConfigs, IntoSystemSet, IntoSystemSetConfig,
-            IntoSystemSetConfigs, NextState, OnEnter, OnExit, OnUpdate, Schedule, Schedules, State,
-            States, SystemSet,
+            IntoSystemSetConfigs, NextState, OnEnter, OnExit, OnTransition, OnUpdate, Schedule,
+            Schedules, State, States, SystemSet,
         },
         system::{
             adapter as system_adapter,