Split time functionality into bevy_time (bevyengine#4187)

# Objective

Reduce the catch-all grab-bag of functionality in bevy_core by minimally splitting off time functionality into bevy_time. Functionality like that provided by bevyengine#3002 would increase the complexity of bevy_time, so this is a good candidate for pulling into its own unit.

A step in addressing bevyengine#2931 and splitting bevy_core into more specific locations.

## Solution

Pull the time module of bevy_core into a new crate, bevy_time.

# Migration guide

- Time related types (e.g. `Time`, `Timer`, `Stopwatch`, `FixedTimestep`, etc.) should be imported from `bevy::time::*` rather than `bevy::core::*`.
- If you were adding `CorePlugin` manually, you'll also want to add `TimePlugin` from `bevy::time`.
- The `bevy::core::CorePlugin::Time` system label is replaced with `bevy::time::TimeSystem`.

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

crates/bevy_animation/Cargo.toml

@@ -15,6 +15,7 @@ bevy_asset = { path = "../bevy_asset", version = "0.8.0-dev" }
 bevy_core = { path = "../bevy_core", version = "0.8.0-dev" }
 bevy_math = { path = "../bevy_math", version = "0.8.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.8.0-dev", features = ["bevy"] }
+bevy_time = { path = "../bevy_time", version = "0.8.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.8.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.8.0-dev" }
 bevy_transform = { path = "../bevy_transform", version = "0.8.0-dev" }

crates/bevy_animation/src/lib.rs

@@ -6,7 +6,7 @@ use std::ops::Deref;
 
 use bevy_app::{App, CoreStage, Plugin};
 use bevy_asset::{AddAsset, Assets, Handle};
-use bevy_core::{Name, Time};
+use bevy_core::Name;
 use bevy_ecs::{
     change_detection::DetectChanges,
     entity::Entity,
@@ -18,6 +18,7 @@ use bevy_ecs::{
 use bevy_hierarchy::{Children, HierarchySystem};
 use bevy_math::{Quat, Vec3};
 use bevy_reflect::{Reflect, TypeUuid};
+use bevy_time::Time;
 use bevy_transform::{prelude::Transform, TransformSystem};
 use bevy_utils::{tracing::warn, HashMap};
 

crates/bevy_core/src/lib.rs

@@ -3,40 +3,26 @@
 
 mod name;
 mod task_pool_options;
-mod time;
 
 pub use bytemuck::{bytes_of, cast_slice, Pod, Zeroable};
 pub use name::*;
 pub use task_pool_options::*;
-pub use time::*;
 
 pub mod prelude {
     //! The Bevy Core Prelude.
     #[doc(hidden)]
-    pub use crate::{DefaultTaskPoolOptions, Name, Time, Timer};
+    pub use crate::{DefaultTaskPoolOptions, Name};
 }
 
 use bevy_app::prelude::*;
-use bevy_ecs::{
-    entity::Entity,
-    schedule::{ExclusiveSystemDescriptorCoercion, SystemLabel},
-    system::IntoExclusiveSystem,
-};
+use bevy_ecs::entity::Entity;
 use bevy_utils::HashSet;
 use std::ops::Range;
 
 /// Adds core functionality to Apps.
 #[derive(Default)]
 pub struct CorePlugin;
 
-/// A `SystemLabel` enum for ordering systems relative to core Bevy systems.
-#[derive(Debug, PartialEq, Eq, Clone, Hash, SystemLabel)]
-pub enum CoreSystem {
-    /// Updates the elapsed time. Any system that interacts with [Time] component should run after
-    /// this.
-    Time,
-}
-
 impl Plugin for CorePlugin {
     fn build(&self, app: &mut App) {
         // Setup the default bevy task pools
@@ -46,20 +32,11 @@ impl Plugin for CorePlugin {
             .unwrap_or_default()
             .create_default_pools(&mut app.world);
 
-        app.init_resource::<Time>()
-            .init_resource::<FixedTimesteps>()
-            .register_type::<HashSet<String>>()
+        app.register_type::<HashSet<String>>()
             .register_type::<Option<String>>()
             .register_type::<Entity>()
             .register_type::<Name>()
-            .register_type::<Range<f32>>()
-            .register_type::<Timer>()
-            // time system is added as an "exclusive system" to ensure it runs before other systems
-            // in CoreStage::First
-            .add_system_to_stage(
-                CoreStage::First,
-                time_system.exclusive_system().label(CoreSystem::Time),
-            );
+            .register_type::<Range<f32>>();
 
         register_rust_types(app);
         register_math_types(app);

crates/bevy_diagnostic/Cargo.toml

@@ -12,7 +12,7 @@ keywords = ["bevy"]
 [dependencies]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.8.0-dev" }
-bevy_core = { path = "../bevy_core", version = "0.8.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.8.0-dev" }
 bevy_log = { path = "../bevy_log", version = "0.8.0-dev" }
+bevy_time = { path = "../bevy_time", version = "0.8.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.8.0-dev" }

crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs

@@ -1,7 +1,7 @@
 use crate::{Diagnostic, DiagnosticId, Diagnostics};
 use bevy_app::prelude::*;
-use bevy_core::Time;
 use bevy_ecs::system::{Res, ResMut};
+use bevy_time::Time;
 
 /// Adds "frame time" diagnostic to an App, specifically "frame time", "fps" and "frame count"
 #[derive(Default)]

crates/bevy_diagnostic/src/log_diagnostics_plugin.rs

@@ -1,8 +1,8 @@
 use super::{Diagnostic, DiagnosticId, Diagnostics};
 use bevy_app::prelude::*;
-use bevy_core::{Time, Timer};
 use bevy_ecs::system::{Res, ResMut};
 use bevy_log::{debug, info};
+use bevy_time::{Time, Timer};
 use bevy_utils::Duration;
 
 /// An App Plugin that logs diagnostics to the console

crates/bevy_internal/Cargo.toml

@@ -78,6 +78,7 @@ bevy_math = { path = "../bevy_math", version = "0.8.0-dev" }
 bevy_ptr = { path = "../bevy_ptr", version = "0.8.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.8.0-dev", features = ["bevy"] }
 bevy_scene = { path = "../bevy_scene", version = "0.8.0-dev" }
+bevy_time = { path = "../bevy_time", version = "0.8.0-dev" }
 bevy_transform = { path = "../bevy_transform", version = "0.8.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.8.0-dev" }
 bevy_window = { path = "../bevy_window", version = "0.8.0-dev" }

crates/bevy_internal/src/default_plugins.rs

@@ -3,6 +3,7 @@ use bevy_app::{PluginGroup, PluginGroupBuilder};
 /// This plugin group will add all the default plugins:
 /// * [`LogPlugin`](bevy_log::LogPlugin)
 /// * [`CorePlugin`](bevy_core::CorePlugin)
+/// * [`TimePlugin`](bevy_time::TimePlugin)
 /// * [`TransformPlugin`](bevy_transform::TransformPlugin)
 /// * [`HierarchyPlugin`](bevy_hierarchy::HierarchyPlugin)
 /// * [`DiagnosticsPlugin`](bevy_diagnostic::DiagnosticsPlugin)
@@ -27,6 +28,7 @@ impl PluginGroup for DefaultPlugins {
     fn build(&mut self, group: &mut PluginGroupBuilder) {
         group.add(bevy_log::LogPlugin::default());
         group.add(bevy_core::CorePlugin::default());
+        group.add(bevy_time::TimePlugin::default());
         group.add(bevy_transform::TransformPlugin::default());
         group.add(bevy_hierarchy::HierarchyPlugin::default());
         group.add(bevy_diagnostic::DiagnosticsPlugin::default());
@@ -76,6 +78,7 @@ impl PluginGroup for DefaultPlugins {
 
 /// Minimal plugin group that will add the following plugins:
 /// * [`CorePlugin`](bevy_core::CorePlugin)
+/// * [`TimePlugin`](bevy_time::TimePlugin)
 /// * [`ScheduleRunnerPlugin`](bevy_app::ScheduleRunnerPlugin)
 ///
 /// See also [`DefaultPlugins`] for a more complete set of plugins
@@ -84,6 +87,7 @@ pub struct MinimalPlugins;
 impl PluginGroup for MinimalPlugins {
     fn build(&mut self, group: &mut PluginGroupBuilder) {
         group.add(bevy_core::CorePlugin::default());
+        group.add(bevy_time::TimePlugin::default());
         group.add(bevy_app::ScheduleRunnerPlugin::default());
     }
 }

crates/bevy_internal/src/lib.rs

@@ -18,7 +18,7 @@ pub mod asset {
 }
 
 pub mod core {
-    //! Contains core plugins and utilities for time.
+    //! Contains core plugins.
     pub use bevy_core::*;
 }
 
@@ -70,6 +70,11 @@ pub mod tasks {
     pub use bevy_tasks::*;
 }
 
+pub mod time {
+    //! Contains time utilities.
+    pub use bevy_time::*;
+}
+
 pub mod hierarchy {
     //! Entity hierarchies and property inheritance
     pub use bevy_hierarchy::*;

crates/bevy_internal/src/prelude.rs

@@ -2,7 +2,8 @@
 pub use crate::{
     app::prelude::*, asset::prelude::*, core::prelude::*, ecs::prelude::*, hierarchy::prelude::*,
     input::prelude::*, log::prelude::*, math::prelude::*, reflect::prelude::*, scene::prelude::*,
-    transform::prelude::*, utils::prelude::*, window::prelude::*, DefaultPlugins, MinimalPlugins,
+    time::prelude::*, transform::prelude::*, utils::prelude::*, window::prelude::*, DefaultPlugins,
+    MinimalPlugins,
 };
 
 pub use bevy_derive::{bevy_main, Deref, DerefMut};

crates/bevy_time/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "bevy_time"
+version = "0.8.0-dev"
+edition = "2021"
+description = "Provides time functionality for Bevy Engine"
+homepage = "https://bevyengine.org"
+repository = "https://github.com/bevyengine/bevy"
+license = "MIT OR Apache-2.0"
+keywords = ["bevy"]
+
+
+[dependencies]
+# bevy
+bevy_app = { path = "../bevy_app", version = "0.8.0-dev" }
+bevy_ecs = { path = "../bevy_ecs", version = "0.8.0-dev", features = ["bevy_reflect"] }
+bevy_reflect = { path = "../bevy_reflect", version = "0.8.0-dev", features = ["bevy"] }
+bevy_utils = { path = "../bevy_utils", version = "0.8.0-dev" }

crates/bevy_time/src/lib.rs

@@ -0,0 +1,46 @@
+mod fixed_timestep;
+mod stopwatch;
+#[allow(clippy::module_inception)]
+mod time;
+mod timer;
+
+pub use fixed_timestep::*;
+pub use stopwatch::*;
+pub use time::*;
+pub use timer::*;
+
+pub mod prelude {
+    //! The Bevy Time Prelude.
+    #[doc(hidden)]
+    pub use crate::{Time, Timer};
+}
+
+use bevy_app::prelude::*;
+use bevy_ecs::prelude::*;
+
+/// Adds time functionality to Apps.
+#[derive(Default)]
+pub struct TimePlugin;
+
+#[derive(Debug, PartialEq, Eq, Clone, Hash, SystemLabel)]
+/// Updates the elapsed time. Any system that interacts with [Time] component should run after
+/// this.
+pub struct TimeSystem;
+
+impl Plugin for TimePlugin {
+    fn build(&self, app: &mut App) {
+        app.init_resource::<Time>()
+            .init_resource::<FixedTimesteps>()
+            .register_type::<Timer>()
+            // time system is added as an "exclusive system" to ensure it runs before other systems
+            // in CoreStage::First
+            .add_system_to_stage(
+                CoreStage::First,
+                time_system.exclusive_system().at_start().label(TimeSystem),
+            );
+    }
+}
+
+fn time_system(mut time: ResMut<Time>) {
+    time.update();
+}

crates/bevy_core/src/time/stopwatch.rs → crates/bevy_time/src/stopwatch.rs

@@ -7,7 +7,7 @@ use bevy_utils::Duration;
 /// # Examples
 ///
 /// ```
-/// # use bevy_core::*;
+/// # use bevy_time::*;
 /// use std::time::Duration;
 /// let mut stopwatch = Stopwatch::new();
 /// assert_eq!(stopwatch.elapsed_secs(), 0.0);
@@ -35,7 +35,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// let stopwatch = Stopwatch::new();
     /// assert_eq!(stopwatch.elapsed_secs(), 0.0);
     /// assert_eq!(stopwatch.paused(), false);
@@ -49,7 +49,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// use std::time::Duration;
     /// let mut stopwatch = Stopwatch::new();
     /// stopwatch.tick(Duration::from_secs(1));
@@ -69,7 +69,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// use std::time::Duration;
     /// let mut stopwatch = Stopwatch::new();
     /// stopwatch.tick(Duration::from_secs(1));
@@ -88,7 +88,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// use std::time::Duration;
     /// let mut stopwatch = Stopwatch::new();
     /// stopwatch.set_elapsed(Duration::from_secs_f32(1.0));
@@ -105,7 +105,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// use std::time::Duration;
     /// let mut stopwatch = Stopwatch::new();
     /// stopwatch.tick(Duration::from_secs_f32(1.5));
@@ -123,7 +123,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// use std::time::Duration;
     /// let mut stopwatch = Stopwatch::new();
     /// stopwatch.pause();
@@ -140,7 +140,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// use std::time::Duration;
     /// let mut stopwatch = Stopwatch::new();
     /// stopwatch.pause();
@@ -159,7 +159,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// let mut stopwatch = Stopwatch::new();
     /// assert!(!stopwatch.paused());
     /// stopwatch.pause();
@@ -176,7 +176,7 @@ impl Stopwatch {
     ///
     /// # Examples
     /// ```
-    /// # use bevy_core::*;
+    /// # use bevy_time::*;
     /// use std::time::Duration;
     /// let mut stopwatch = Stopwatch::new();
     /// stopwatch.tick(Duration::from_secs_f32(1.5));

crates/bevy_core/src/time/time.rs → crates/bevy_time/src/time.rs

@@ -1,4 +1,3 @@
-use bevy_ecs::system::ResMut;
 use bevy_utils::{Duration, Instant};
 
 /// Tracks elapsed time since the last update and since the App has started
@@ -32,7 +31,7 @@ impl Time {
     ///
     /// Calling this method on the [`Time`] resource as part of your app will most likely result in
     /// inaccurate timekeeping, as the resource is ordinarily managed by the
-    /// [`CorePlugin`](crate::CorePlugin).
+    /// [`TimePlugin`](crate::TimePlugin).
     pub fn update(&mut self) {
         self.update_with_instant(Instant::now());
     }
@@ -41,12 +40,12 @@ impl Time {
     ///
     /// This method is provided for use in tests. Calling this method on the [`Time`] resource as
     /// part of your app will most likely result in inaccurate timekeeping, as the resource is
-    /// ordinarily managed by the [`CorePlugin`](crate::CorePlugin).
+    /// ordinarily managed by the [`TimePlugin`](crate::TimePlugin).
     ///
     /// # Examples
     ///
     /// ```
-    /// # use bevy_core::prelude::*;
+    /// # use bevy_time::prelude::*;
     /// # use bevy_ecs::prelude::*;
     /// # use bevy_utils::Duration;
     /// # fn main () {
@@ -143,10 +142,6 @@ impl Time {
     }
 }
 
-pub(crate) fn time_system(mut time: ResMut<Time>) {
-    time.update();
-}
-
 #[cfg(test)]
 #[allow(clippy::float_cmp)]
 mod tests {