From fbb9b3644189aa2164cbdade33aebdf8ea0fc428 Mon Sep 17 00:00:00 2001
From: Isaac Corbrey <icorbrey@gmail.com>
Date: Wed, 18 Sep 2024 09:43:06 -0400
Subject: [PATCH] Throw real error messages on all failed attempts to get
 `StateTransition` schedule (#15284)

# Objective

Make it clear to the user why their program is failing rather than
having an unhelpful `called Option::unwrap() on a None value` message.

## Solution

Change the `unwrap()` calls to `expect()` calls, mirroring previously
implemented error messages.

## Testing

I have not tested these changes, but they are fairly trivial so I do not
necessarily feel they need it.
---
 crates/bevy_state/src/app.rs | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/crates/bevy_state/src/app.rs b/crates/bevy_state/src/app.rs
index f550e8daa0..4541a1cd5d 100644
--- a/crates/bevy_state/src/app.rs
+++ b/crates/bevy_state/src/app.rs
@@ -117,7 +117,7 @@ impl AppExtStates for SubApp {
                 .init_resource::<NextState<S>>()
                 .add_event::<StateTransitionEvent<S>>();
             let schedule = self.get_schedule_mut(StateTransition).expect(
-                "The `StateTransition` schedule is missing. Did you forget to add StatesPlugin or DefaultPlugins before calling init_state?"
+                "The `StateTransition` schedule is missing. Did you forget to add StatesPlugin or DefaultPlugins before calling insert_state?"
             );
             S::register_state(schedule);
             self.world_mut().send_event(StateTransitionEvent {
@@ -146,7 +146,9 @@ impl AppExtStates for SubApp {
             .contains_resource::<Events<StateTransitionEvent<S>>>()
         {
             self.add_event::<StateTransitionEvent<S>>();
-            let schedule = self.get_schedule_mut(StateTransition).unwrap();
+            let schedule = self.get_schedule_mut(StateTransition).expect(
+                "The `StateTransition` schedule is missing. Did you forget to add StatesPlugin or DefaultPlugins before calling add_computed_state?"
+            );
             S::register_computed_state_systems(schedule);
             let state = self
                 .world()
@@ -172,7 +174,9 @@ impl AppExtStates for SubApp {
         {
             self.init_resource::<NextState<S>>();
             self.add_event::<StateTransitionEvent<S>>();
-            let schedule = self.get_schedule_mut(StateTransition).unwrap();
+            let schedule = self.get_schedule_mut(StateTransition).expect(
+                "The `StateTransition` schedule is missing. Did you forget to add StatesPlugin or DefaultPlugins before calling add_sub_state?"
+            );
             S::register_sub_state_systems(schedule);
             let state = self
                 .world()