The update_frame_count system should be placed in CorePlugin (bevye…

…ngine#6676)

# Objective

Latest Release, "bevy 0.9" move the FrameCount updater into RenderPlugin, it leads to user who only run app with Core/Minimal Plugin cannot get the right number of FrameCount, it always return 0.

As for use cases like a server app, we don't want to add render dependencies to the app.

More detail in bevyengine#6656

## Solution

- Move the `update_frame_count` into CorePlugin

crates/bevy_core/src/lib.rs

@@ -6,7 +6,7 @@ mod name;
 mod serde;
 mod task_pool_options;
 
-use bevy_ecs::system::Resource;
+use bevy_ecs::system::{ResMut, Resource};
 pub use bytemuck::{bytes_of, cast_slice, Pod, Zeroable};
 pub use name::*;
 pub use task_pool_options::*;
@@ -55,6 +55,7 @@ impl Plugin for CorePlugin {
         register_math_types(app);
 
         app.init_resource::<FrameCount>();
+        app.add_system(update_frame_count);
     }
 }
 
@@ -112,6 +113,10 @@ fn register_math_types(app: &mut App) {
 #[derive(Default, Resource, Clone, Copy)]
 pub struct FrameCount(pub u32);
 
+fn update_frame_count(mut frame_count: ResMut<FrameCount>) {
+    frame_count.0 = frame_count.0.wrapping_add(1);
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -149,4 +154,14 @@ mod tests {
         compute_rx.try_recv().unwrap();
         io_rx.try_recv().unwrap();
     }
+
+    #[test]
+    fn frame_counter_update() {
+        let mut app = App::new();
+        app.add_plugin(CorePlugin::default());
+        app.update();
+
+        let frame_count = app.world.resource::<FrameCount>();
+        assert_eq!(1, frame_count.0);
+    }
 }

crates/bevy_render/src/globals.rs

@@ -19,12 +19,17 @@ impl Plugin for GlobalsPlugin {
             render_app
                 .init_resource::<GlobalsBuffer>()
                 .init_resource::<Time>()
+                .add_system_to_stage(RenderStage::Extract, extract_frame_count)
                 .add_system_to_stage(RenderStage::Extract, extract_time)
                 .add_system_to_stage(RenderStage::Prepare, prepare_globals_buffer);
         }
     }
 }
 
+fn extract_frame_count(mut commands: Commands, frame_count: Extract<Res<FrameCount>>) {
+    commands.insert_resource(**frame_count);
+}
+
 fn extract_time(mut commands: Commands, time: Extract<Res<Time>>) {
     commands.insert_resource(time.clone());
 }