Extend API

crates/bevy_app/src/app_builder.rs

@@ -6,7 +6,7 @@ use crate::{
 };
 use bevy_ecs::{
     clear_trackers_system, FromResources, IntoExclusiveSystem, IntoSystem, Resources, RunOnce,
-    Schedule, Stage, SystemDescriptor, SystemStage, World,
+    Schedule, Stage, SystemDescriptor, SystemSet, SystemStage, World,
 };
 use bevy_utils::tracing::debug;
 
@@ -129,6 +129,10 @@ impl AppBuilder {
         self.add_system_to_stage(stage::UPDATE, system)
     }
 
+    pub fn add_system_set(&mut self, system_set: SystemSet) -> &mut Self {
+        self.add_system_set_to_stage(stage::UPDATE, system_set)
+    }
+
     pub fn add_system_to_stage(
         &mut self,
         stage_name: &'static str,
@@ -138,6 +142,17 @@ impl AppBuilder {
         self
     }
 
+    pub fn add_system_set_to_stage(
+        &mut self,
+        stage_name: &'static str,
+        system_set: SystemSet,
+    ) -> &mut Self {
+        self.app
+            .schedule
+            .add_system_set_to_stage(stage_name, system_set);
+        self
+    }
+
     pub fn add_startup_system(&mut self, system: impl Into<SystemDescriptor>) -> &mut Self {
         self.add_startup_system_to_stage(startup_stage::STARTUP, system)
     }

crates/bevy_ecs/src/schedule/mod.rs

@@ -125,6 +125,23 @@ impl Schedule {
         self
     }
 
+    pub fn add_system_set_to_stage(
+        &mut self,
+        stage_name: &'static str,
+        system_set: SystemSet,
+    ) -> &mut Self {
+        let stage = self
+            .get_stage_mut::<SystemStage>(stage_name)
+            .unwrap_or_else(|| {
+                panic!(
+                    "Stage '{}' does not exist or is not a SystemStage",
+                    stage_name
+                )
+            });
+        stage.add_system_set(system_set);
+        self
+    }
+
     pub fn stage<T: Stage, F: FnOnce(&mut T) -> &mut T>(
         &mut self,
         name: &str,