Add DummyResource

src/plugin.rs

@@ -12,7 +12,7 @@ use bevy::reflect::TypePath;
 use bevy::time::run_fixed_main_schedule;
 #[cfg(feature = "ui")]
 use bevy::ui::UiSystem;
-use updating::{CentralInputStore, InputUpdateSystem};
+use updating::{CentralInputStore, DummyResource, InputUpdateSystem};
 
 use crate::action_state::{ActionState, ButtonData};
 use crate::clashing_inputs::ClashStrategy;
@@ -282,6 +282,8 @@ pub struct CentralInputStorePlugin;
 
 impl Plugin for CentralInputStorePlugin {
  fn build(&self, app: &mut App) {
+ app.init_resource::<DummyResource>();
+
  let mut central_input_store = CentralInputStore::default();
  central_input_store.register_standard_input_kinds(app);
 

src/user_input/updating.rs

@@ -39,7 +39,7 @@ impl CentralInputStore {
  /// Registers a new kind of input.
  ///
  /// This will allow the input to be updated based on the state of the world,
- /// by adding the [`UpdatableUserInput::update`] system to one of the [`InputUpdateSystem`] sets,
+ /// by adding the [`UpdatableUserInput::compute`] system to one of the [`InputUpdateSystem`] sets,
  /// and thus to [`InputManagerSystem::Update`] during [`PreUpdate`].
  ///
  /// This method has no effect if the input kind has already been registered.
@@ -50,7 +50,7 @@ impl CentralInputStore {
  }
 
  self.registered_input_kinds.insert(TypeId::of::<I>());
- app.add_systems(PreUpdate, I::update.in_set(I::SYSTEM_SET));
+ app.add_systems(PreUpdate, I::compute.in_set(I::SYSTEM_SET));
  }
 
  /// Registers the standard input types defined by [`bevy`] and [`leafwing_input_manager`](crate).
@@ -199,6 +199,13 @@ enum UpdatedValues {
 pub trait UpdatableUserInput: UserInput {
  /// The resource data that must be fetched from the world in order to update the user input.
  ///
+ /// If your system does not need any additional data, you can use [`DummyResource`] as a placeholder,
+ /// which will be initialized by [`CentralInputStorePlugin`](crate::plugin::CentralInputStorePlugin) to avoid panicking.
+ /// Ideally one could use `()`, but that requires a [change to Bevy itself](https://github.com/bevyengine/bevy/issues/14640).
+ ///
+ /// Input types that are derived from other inputs should generally not need additional data,
+ /// as they can be computed directly from the [`CentralInputStore`].
+ ///
  /// # Panics
  ///
  /// This type cannot be [`CentralInputStore`], as that would cause mutable aliasing and panic at runtime.
@@ -214,7 +221,7 @@ pub trait UpdatableUserInput: UserInput {
  /// # Warning
  ///
  /// This system should not be added manually: instead, call [`CentralInputStore::register_input_kind`].
- fn update(central_input_store: ResMut<CentralInputStore>, source_data: Res<Self::SourceData>);
+ fn compute(central_input_store: ResMut<CentralInputStore>, source_data: Res<Self::SourceData>);
 }
 
 /// More granular system sets that belong to [`InputManagerSystem::Update`].
@@ -234,3 +241,7 @@ pub enum InputUpdateSystem {
  /// Updates that combine multiple user inputs into a single value.
  Chord,
 }
+
+/// A dummy resource that can be used as a placeholder for [`UpdatableUserInput::SourceData`].
+#[derive(Resource, Default)]
+pub struct DummyResource;