conflicting system order ambiguity test

.github/workflows/main.yml

@@ -58,6 +58,8 @@ jobs:
         run: cargo test --verbose -p bevy_rapier2d
       - name: Test for bevy_rapier3d
         run: cargo test --verbose -p bevy_rapier3d
+      - name: Test for no conflicting system order ambiguity
+        run: cargo run --bin ambiguity_detection
   test-wasm:
     runs-on: ubuntu-latest
     env:

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["bevy_rapier2d", "bevy_rapier3d", "bevy_rapier_benches3d"]
+members = ["bevy_rapier2d", "bevy_rapier3d", "bevy_rapier_benches3d", "ci"]
 resolver = "2"
 
 [profile.dev]

ci/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "ci"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+bevy = "0.15.0"
+bevy_audio = "0.15.0"
+bevy_rapier3d = { path = "../bevy_rapier3d" }
+bevy_rapier2d = { path = "../bevy_rapier2d" }
+
+[[bin]]
+name = "ambiguity_detection"
+test = false
+bench = false

ci/src/bin/ambiguity_detection.rs

@@ -0,0 +1,77 @@
+//! A test to confirm that `bevy` doesn't regress its system ambiguities count when using [`DefaultPlugins`].
+//! This is run in CI.
+//!
+//! Note that because this test requires rendering, it isn't actually an integration test!
+//! Instead, it's secretly an example: you can run this test manually using `cargo run --example ambiguity_detection`.
+
+use bevy::{
+    ecs::schedule::{InternedScheduleLabel, LogLevel, ScheduleBuildSettings},
+    log::LogPlugin,
+    prelude::*,
+    utils::HashMap,
+};
+use bevy_rapier2d::plugin::NoUserData;
+use bevy_rapier3d::plugin::RapierPhysicsPlugin;
+
+fn main() {
+    check_ambiguities(RapierPhysicsPlugin::<NoUserData>::default(), true);
+    check_ambiguities(
+        RapierPhysicsPlugin::<NoUserData>::default().in_fixed_schedule(),
+        false,
+    );
+}
+
+fn check_ambiguities(plugin: RapierPhysicsPlugin, set_logger: bool) {
+    let mut app = App::new();
+    app.add_plugins((MinimalPlugins, TransformPlugin, AssetPlugin::default()));
+    if set_logger {
+        app.add_plugins(LogPlugin::default());
+    }
+    app.add_plugins(plugin);
+
+    let main_app = app.main_mut();
+    configure_ambiguity_detection(main_app);
+
+    app.finish();
+    app.cleanup();
+    app.update();
+
+    let main_app_ambiguities = count_ambiguities(app.main());
+    assert_eq!(
+        main_app_ambiguities.total(),
+        0,
+        "Main app has unexpected ambiguities among the following schedules: \n{main_app_ambiguities:#?}.",
+    );
+}
+
+/// Contains the number of conflicting systems per schedule.
+#[derive(Debug, Deref, DerefMut)]
+struct AmbiguitiesCount(pub HashMap<InternedScheduleLabel, usize>);
+
+impl AmbiguitiesCount {
+    fn total(&self) -> usize {
+        self.values().sum()
+    }
+}
+
+fn configure_ambiguity_detection(sub_app: &mut SubApp) {
+    let mut schedules = sub_app.world_mut().resource_mut::<Schedules>();
+    for (_, schedule) in schedules.iter_mut() {
+        schedule.set_build_settings(ScheduleBuildSettings {
+            ambiguity_detection: LogLevel::Ignore,
+            use_shortnames: false,
+            ..default()
+        });
+    }
+}
+
+/// Returns the number of conflicting systems per schedule.
+fn count_ambiguities(sub_app: &SubApp) -> AmbiguitiesCount {
+    let schedules = sub_app.world().resource::<Schedules>();
+    let mut ambiguities = HashMap::new();
+    for (_, schedule) in schedules.iter() {
+        let ambiguities_in_schedule = schedule.graph().conflicting_systems().len();
+        ambiguities.insert(schedule.label(), ambiguities_in_schedule);
+    }
+    AmbiguitiesCount(ambiguities)
+}