Make get_resource (and friends) infallible (#4047)

# Objective

- In the large majority of cases, users were calling `.unwrap()` immediately after `.get_resource`.
- Attempting to add more helpful error messages here resulted in endless manual boilerplate (see #3899 and the linked PRs).

## Solution

- Add an infallible variant named `.resource` and so on.
- Use these infallible variants over `.get_resource().unwrap()` across the code base.

## Notes

I did not provide equivalent methods on `WorldCell`, in favor of removing it entirely in #3939.

## Migration Guide

Infallible variants of `.get_resource` have been added that implicitly panic, rather than needing to be unwrapped.

Replace `world.get_resource::<Foo>().unwrap()` with `world.resource::<Foo>()`.

## Impact

- `.unwrap` search results before: 1084
- `.unwrap` search results after: 942
- internal `unwrap_or_else` calls added: 4
- trivial unwrap calls removed from tests and code: 146
- uses of the new `try_get_resource` API: 11
- percentage of the time the unwrapping API was used internally: 93%

crates/bevy_app/src/app.rs

@@ -839,10 +839,7 @@ impl App {
     #[cfg(feature = "bevy_reflect")]
     pub fn register_type<T: bevy_reflect::GetTypeRegistration>(&mut self) -> &mut Self {
         {
-            let registry = self
-                .world
-                .get_resource_mut::<bevy_reflect::TypeRegistryArc>()
-                .unwrap();
+            let registry = self.world.resource_mut::<bevy_reflect::TypeRegistryArc>();
             registry.write().register::<T>();
         }
         self

crates/bevy_asset/src/asset_server.rs

@@ -794,24 +794,18 @@ mod test {
         app.add_system(update_asset_storage_system::<PngAsset>.after(FreeUnusedAssets));
 
         fn load_asset(path: AssetPath, world: &World) -> HandleUntyped {
-            let asset_server = world.get_resource::<AssetServer>().unwrap();
+            let asset_server = world.resource::<AssetServer>();
             let id = futures_lite::future::block_on(asset_server.load_async(path.clone(), true))
                 .unwrap();
             asset_server.get_handle_untyped(id)
         }
 
         fn get_asset(id: impl Into<HandleId>, world: &World) -> Option<&PngAsset> {
-            world
-                .get_resource::<Assets<PngAsset>>()
-                .unwrap()
-                .get(id.into())
+            world.resource::<Assets<PngAsset>>().get(id.into())
         }
 
         fn get_load_state(id: impl Into<HandleId>, world: &World) -> LoadState {
-            world
-                .get_resource::<AssetServer>()
-                .unwrap()
-                .get_load_state(id.into())
+            world.resource::<AssetServer>().get_load_state(id.into())
         }
 
         // ---

crates/bevy_asset/src/assets.rs

@@ -287,7 +287,7 @@ impl AddAsset for App {
             return self;
         }
         let assets = {
-            let asset_server = self.world.get_resource::<AssetServer>().unwrap();
+            let asset_server = self.world.resource::<AssetServer>();
             asset_server.register_asset_type::<T>()
         };
 
@@ -307,8 +307,7 @@ impl AddAsset for App {
             self.add_system(crate::debug_asset_server::sync_debug_assets::<T>);
             let mut app = self
                 .world
-                .get_non_send_resource_mut::<crate::debug_asset_server::DebugAssetApp>()
-                .unwrap();
+                .non_send_resource_mut::<crate::debug_asset_server::DebugAssetApp>();
             app.add_asset::<T>()
                 .init_resource::<crate::debug_asset_server::HandleMap<T>>();
         }
@@ -331,8 +330,7 @@ impl AddAsset for App {
         {
             let mut app = self
                 .world
-                .get_non_send_resource_mut::<crate::debug_asset_server::DebugAssetApp>()
-                .unwrap();
+                .non_send_resource_mut::<crate::debug_asset_server::DebugAssetApp>();
             app.init_asset_loader::<T>();
         }
         self
@@ -342,10 +340,7 @@ impl AddAsset for App {
     where
         T: AssetLoader,
     {
-        self.world
-            .get_resource_mut::<AssetServer>()
-            .expect("AssetServer does not exist. Consider adding it as a resource.")
-            .add_loader(loader);
+        self.world.resource_mut::<AssetServer>().add_loader(loader);
         self
     }
 }
@@ -357,8 +352,7 @@ macro_rules! load_internal_asset {
         {
             let mut debug_app = $app
                 .world
-                .get_non_send_resource_mut::<bevy_asset::debug_asset_server::DebugAssetApp>()
-                .unwrap();
+                .non_send_resource_mut::<bevy_asset::debug_asset_server::DebugAssetApp>();
             bevy_asset::debug_asset_server::register_handle_with_loader(
                 $loader,
                 &mut debug_app,
@@ -367,10 +361,7 @@ macro_rules! load_internal_asset {
                 $path_str,
             );
         }
-        let mut assets = $app
-            .world
-            .get_resource_mut::<bevy_asset::Assets<_>>()
-            .unwrap();
+        let mut assets = $app.world.resource_mut::<bevy_asset::Assets<_>>();
         assets.set_untracked($handle, ($loader)(include_str!($path_str)));
     }};
 }
@@ -379,10 +370,7 @@ macro_rules! load_internal_asset {
 #[macro_export]
 macro_rules! load_internal_asset {
     ($app: ident, $handle: ident, $path_str: expr, $loader: expr) => {{
-        let mut assets = $app
-            .world
-            .get_resource_mut::<bevy_asset::Assets<_>>()
-            .unwrap();
+        let mut assets = $app.world.resource_mut::<bevy_asset::Assets<_>>();
         assets.set_untracked($handle, ($loader)(include_str!($path_str)));
     }};
 }
@@ -402,10 +390,10 @@ mod tests {
         app.add_plugin(bevy_core::CorePlugin)
             .add_plugin(crate::AssetPlugin);
         app.add_asset::<MyAsset>();
-        let mut assets_before = app.world.get_resource_mut::<Assets<MyAsset>>().unwrap();
+        let mut assets_before = app.world.resource_mut::<Assets<MyAsset>>();
         let handle = assets_before.add(MyAsset);
         app.add_asset::<MyAsset>(); // Ensure this doesn't overwrite the Asset
-        let assets_after = app.world.get_resource_mut::<Assets<MyAsset>>().unwrap();
+        let assets_after = app.world.resource_mut::<Assets<MyAsset>>();
         assert!(assets_after.get(handle).is_some());
     }
 }

crates/bevy_asset/src/lib.rs

@@ -81,13 +81,8 @@ pub fn create_platform_default_asset_io(app: &mut App) -> Box<dyn AssetIo> {
 
 impl Plugin for AssetPlugin {
     fn build(&self, app: &mut App) {
-        if app.world.get_resource::<AssetServer>().is_none() {
-            let task_pool = app
-                .world
-                .get_resource::<IoTaskPool>()
-                .expect("`IoTaskPool` resource not found.")
-                .0
-                .clone();
+        if !app.world.contains_resource::<AssetServer>() {
+            let task_pool = app.world.resource::<IoTaskPool>().0.clone();
 
             let source = create_platform_default_asset_io(app);
 

crates/bevy_core/src/time/fixed_timestep.rs

@@ -209,7 +209,7 @@ impl System for FixedTimestep {
         )));
         self.internal_system.initialize(world);
         if let Some(ref label) = self.state.label {
-            let mut fixed_timesteps = world.get_resource_mut::<FixedTimesteps>().unwrap();
+            let mut fixed_timesteps = world.resource_mut::<FixedTimesteps>();
             fixed_timesteps.fixed_timesteps.insert(
                 label.clone(),
                 FixedTimestepState {
@@ -257,25 +257,25 @@ mod test {
         // if time does not progress, the step does not run
         schedule.run(&mut world);
         schedule.run(&mut world);
-        assert_eq!(0, *world.get_resource::<Count>().unwrap());
+        assert_eq!(0, *world.resource::<Count>());
         assert_eq!(0., get_accumulator_deciseconds(&world));
 
         // let's progress less than one step
         advance_time(&mut world, instance, 0.4);
         schedule.run(&mut world);
-        assert_eq!(0, *world.get_resource::<Count>().unwrap());
+        assert_eq!(0, *world.resource::<Count>());
         assert_eq!(4., get_accumulator_deciseconds(&world));
 
         // finish the first step with 0.1s above the step length
         advance_time(&mut world, instance, 0.6);
         schedule.run(&mut world);
-        assert_eq!(1, *world.get_resource::<Count>().unwrap());
+        assert_eq!(1, *world.resource::<Count>());
         assert_eq!(1., get_accumulator_deciseconds(&world));
 
         // runs multiple times if the delta is multiple step lengths
         advance_time(&mut world, instance, 1.7);
         schedule.run(&mut world);
-        assert_eq!(3, *world.get_resource::<Count>().unwrap());
+        assert_eq!(3, *world.resource::<Count>());
         assert_eq!(2., get_accumulator_deciseconds(&world));
     }
 
@@ -285,15 +285,13 @@ mod test {
 
     fn advance_time(world: &mut World, instance: Instant, seconds: f32) {
         world
-            .get_resource_mut::<Time>()
-            .unwrap()
+            .resource_mut::<Time>()
             .update_with_instant(instance.add(Duration::from_secs_f32(seconds)));
     }
 
     fn get_accumulator_deciseconds(world: &World) -> f64 {
         world
-            .get_resource::<FixedTimesteps>()
-            .unwrap()
+            .resource::<FixedTimesteps>()
             .get(LABEL)
             .unwrap()
             .accumulator

crates/bevy_core_pipeline/src/clear_pass.rs

@@ -50,8 +50,8 @@ impl Node for ClearPassNode {
         world: &World,
     ) -> Result<(), NodeRunError> {
         let mut cleared_targets = HashSet::new();
-        let clear_color = world.get_resource::<ClearColor>().unwrap();
-        let render_target_clear_colors = world.get_resource::<RenderTargetClearColors>().unwrap();
+        let clear_color = world.resource::<ClearColor>();
+        let render_target_clear_colors = world.resource::<RenderTargetClearColors>();
 
         // This gets all ViewTargets and ViewDepthTextures and clears its attachments
         // TODO: This has the potential to clear the same target multiple times, if there
@@ -89,8 +89,8 @@ impl Node for ClearPassNode {
         // TODO: This is a hack to ensure we don't call present() on frames without any work,
         // which will cause panics. The real fix here is to clear "render targets" directly
         // instead of "views". This should be removed once full RenderTargets are implemented.
-        let windows = world.get_resource::<ExtractedWindows>().unwrap();
-        let images = world.get_resource::<RenderAssets<Image>>().unwrap();
+        let windows = world.resource::<ExtractedWindows>();
+        let images = world.resource::<RenderAssets<Image>>();
         for target in render_target_clear_colors.colors.keys().cloned().chain(
             windows
                 .values()

crates/bevy_core_pipeline/src/lib.rs

@@ -145,7 +145,7 @@ impl Plugin for CorePipelinePlugin {
         let clear_pass_node = ClearPassNode::new(&mut render_app.world);
         let pass_node_2d = MainPass2dNode::new(&mut render_app.world);
         let pass_node_3d = MainPass3dNode::new(&mut render_app.world);
-        let mut graph = render_app.world.get_resource_mut::<RenderGraph>().unwrap();
+        let mut graph = render_app.world.resource_mut::<RenderGraph>();
 
         let mut draw_2d_graph = RenderGraph::default();
         draw_2d_graph.add_node(draw_2d_graph::node::MAIN_PASS, pass_node_2d);

crates/bevy_core_pipeline/src/main_pass_2d.rs

@@ -53,9 +53,7 @@ impl Node for MainPass2dNode {
             depth_stencil_attachment: None,
         };
 
-        let draw_functions = world
-            .get_resource::<DrawFunctions<Transparent2d>>()
-            .unwrap();
+        let draw_functions = world.resource::<DrawFunctions<Transparent2d>>();
 
         let render_pass = render_context
             .command_encoder

crates/bevy_core_pipeline/src/main_pass_3d.rs

@@ -75,7 +75,7 @@ impl Node for MainPass3dNode {
                 }),
             };
 
-            let draw_functions = world.get_resource::<DrawFunctions<Opaque3d>>().unwrap();
+            let draw_functions = world.resource::<DrawFunctions<Opaque3d>>();
 
             let render_pass = render_context
                 .command_encoder
@@ -109,7 +109,7 @@ impl Node for MainPass3dNode {
                 }),
             };
 
-            let draw_functions = world.get_resource::<DrawFunctions<AlphaMask3d>>().unwrap();
+            let draw_functions = world.resource::<DrawFunctions<AlphaMask3d>>();
 
             let render_pass = render_context
                 .command_encoder
@@ -145,9 +145,7 @@ impl Node for MainPass3dNode {
                 }),
             };
 
-            let draw_functions = world
-                .get_resource::<DrawFunctions<Transparent3d>>()
-                .unwrap();
+            let draw_functions = world.resource::<DrawFunctions<Transparent3d>>();
 
             let render_pass = render_context
                 .command_encoder

crates/bevy_core_pipeline/src/main_pass_driver.rs

@@ -14,7 +14,7 @@ impl Node for MainPassDriverNode {
         _render_context: &mut RenderContext,
         world: &World,
     ) -> Result<(), NodeRunError> {
-        let extracted_cameras = world.get_resource::<ExtractedCameraNames>().unwrap();
+        let extracted_cameras = world.resource::<ExtractedCameraNames>();
         if let Some(camera_2d) = extracted_cameras.entities.get(CameraPlugin::CAMERA_2D) {
             graph.run_sub_graph(
                 crate::draw_2d_graph::NAME,

crates/bevy_ecs/src/lib.rs

@@ -1010,29 +1010,26 @@ mod tests {
             .get_archetype_component_id(resource_id)
             .unwrap();
 
-        assert_eq!(*world.get_resource::<i32>().expect("resource exists"), 123);
+        assert_eq!(*world.resource::<i32>(), 123);
         assert!(world.contains_resource::<i32>());
         assert!(world.is_resource_added::<i32>());
         assert!(world.is_resource_changed::<i32>());
 
         world.insert_resource(456u64);
-        assert_eq!(
-            *world.get_resource::<u64>().expect("resource exists"),
-            456u64
-        );
+        assert_eq!(*world.resource::<u64>(), 456u64);
 
         world.insert_resource(789u64);
-        assert_eq!(*world.get_resource::<u64>().expect("resource exists"), 789);
+        assert_eq!(*world.resource::<u64>(), 789);
 
         {
-            let mut value = world.get_resource_mut::<u64>().expect("resource exists");
+            let mut value = world.resource_mut::<u64>();
             assert_eq!(*value, 789);
             *value = 10;
         }
 
         assert_eq!(
-            world.get_resource::<u64>(),
-            Some(&10),
+            world.resource::<u64>(),
+            &10,
             "resource changes are preserved"
         );
 
@@ -1183,8 +1180,8 @@ mod tests {
         let mut world = World::default();
         world.insert_non_send_resource(123i32);
         world.insert_non_send_resource(456i64);
-        assert_eq!(*world.get_non_send_resource::<i32>().unwrap(), 123);
-        assert_eq!(*world.get_non_send_resource_mut::<i64>().unwrap(), 456);
+        assert_eq!(*world.non_send_resource::<i32>(), 123);
+        assert_eq!(*world.non_send_resource_mut::<i64>(), 456);
     }
 
     #[test]
@@ -1193,7 +1190,7 @@ mod tests {
         let mut world = World::default();
         world.insert_non_send_resource(0i32);
         std::thread::spawn(move || {
-            let _ = world.get_non_send_resource_mut::<i32>();
+            let _ = world.non_send_resource_mut::<i32>();
         })
         .join()
         .unwrap();
@@ -1323,7 +1320,7 @@ mod tests {
             *value += 1;
             assert!(!world.contains_resource::<i32>());
         });
-        assert_eq!(*world.get_resource::<i32>().unwrap(), 1);
+        assert_eq!(*world.resource::<i32>(), 1);
     }
 
     #[test]
@@ -1389,7 +1386,7 @@ mod tests {
             "world should not have any entities"
         );
         assert_eq!(
-            *world.get_resource::<i32>().unwrap(),
+            *world.resource::<i32>(),
             0,
             "world should still contain resources"
         );

crates/bevy_ecs/src/schedule/executor_parallel.rs

@@ -350,11 +350,7 @@ mod tests {
 
     fn receive_events(world: &World) -> Vec<SchedulingEvent> {
         let mut events = Vec::new();
-        while let Ok(event) = world
-            .get_resource::<Receiver<SchedulingEvent>>()
-            .unwrap()
-            .try_recv()
-        {
+        while let Ok(event) = world.resource::<Receiver<SchedulingEvent>>().try_recv() {
             events.push(event);
         }
         events