[Fixes #6030] Bevy scene optional serde (#6076)

# Objective

Fixes #6030, making ``serde`` optional.

## Solution

This was solved by making a ``serialize`` feature that can activate ``serde``, which is now optional. 

When ``serialize`` is deactivated, the ``Plugin`` implementation for ``ScenePlugin`` does nothing.


Co-authored-by: Linus Käll <linus.kall.business@gmail.com>

crates/bevy_internal/Cargo.toml

@@ -45,7 +45,7 @@ wav = ["bevy_audio/wav"]
 # Enable watching file system for asset hot reload
 filesystem_watcher = ["bevy_asset/filesystem_watcher"]
 
-serialize = ["bevy_core/serialize", "bevy_input/serialize", "bevy_time/serialize", "bevy_window/serialize", "bevy_transform/serialize", "bevy_math/serialize"]
+serialize = ["bevy_core/serialize", "bevy_input/serialize", "bevy_time/serialize", "bevy_window/serialize", "bevy_transform/serialize", "bevy_math/serialize", "bevy_scene/serialize"]
 
 # Display server protocol support (X11 is enabled by default)
 wayland = ["bevy_winit/wayland"]

crates/bevy_scene/Cargo.toml

@@ -8,6 +8,10 @@ repository = "https://github.com/bevyengine/bevy"
 license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
+[features]
+default = ["serialize"]
+serialize = ["dep:serde", "uuid/serde"]
+
 [dependencies]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.9.0" }
@@ -21,9 +25,9 @@ bevy_utils = { path = "../bevy_utils", version = "0.9.0" }
 bevy_render = { path = "../bevy_render", version = "0.9.0" }
 
 # other
-serde = { version = "1.0", features = ["derive"] }
+serde = { version = "1.0", features = ["derive"], optional = true }
 ron = "0.8.0"
-uuid = { version = "1.1", features = ["v4", "serde"] }
+uuid = { version = "1.1", features = ["v4"] }
 anyhow = "1.0.4"
 thiserror = "1.0"
 

crates/bevy_scene/src/dynamic_scene.rs

@@ -1,4 +1,4 @@
-use crate::{serde::SceneSerializer, DynamicSceneBuilder, Scene, SceneSpawnError};
+use crate::{DynamicSceneBuilder, Scene, SceneSpawnError};
 use anyhow::Result;
 use bevy_app::AppTypeRegistry;
 use bevy_ecs::{
@@ -7,6 +7,10 @@ use bevy_ecs::{
     world::World,
 };
 use bevy_reflect::{Reflect, TypeRegistryArc, TypeUuid};
+
+#[cfg(feature = "serialize")]
+use crate::serde::SceneSerializer;
+#[cfg(feature = "serialize")]
 use serde::Serialize;
 
 /// A collection of serializable dynamic entities, each with its own run-time defined set of components.
@@ -116,12 +120,14 @@ impl DynamicScene {
 
     // TODO: move to AssetSaver when it is implemented
     /// Serialize this dynamic scene into rust object notation (ron).
+    #[cfg(feature = "serialize")]
     pub fn serialize_ron(&self, registry: &TypeRegistryArc) -> Result<String, ron::Error> {
         serialize_ron(SceneSerializer::new(self, registry))
     }
 }
 
 /// Serialize a given Rust data structure into rust object notation (ron).
+#[cfg(feature = "serialize")]
 pub fn serialize_ron<S>(serialize: S) -> Result<String, ron::Error>
 where
     S: Serialize,

crates/bevy_scene/src/lib.rs

@@ -4,6 +4,8 @@ mod dynamic_scene_builder;
 mod scene;
 mod scene_loader;
 mod scene_spawner;
+
+#[cfg(feature = "serialize")]
 pub mod serde;
 
 pub use bundle::*;
@@ -27,6 +29,7 @@ use bevy_ecs::prelude::*;
 #[derive(Default)]
 pub struct ScenePlugin;
 
+#[cfg(feature = "serialize")]
 impl Plugin for ScenePlugin {
     fn build(&self, app: &mut App) {
         app.add_asset::<DynamicScene>()
@@ -38,3 +41,8 @@ impl Plugin for ScenePlugin {
             .add_system_to_stage(CoreStage::PreUpdate, scene_spawner);
     }
 }
+
+#[cfg(not(feature = "serialize"))]
+impl Plugin for ScenePlugin {
+    fn build(&self, _: &mut App) {}
+}

crates/bevy_scene/src/scene_loader.rs

@@ -5,6 +5,8 @@ use bevy_asset::{AssetLoader, LoadContext, LoadedAsset};
 use bevy_ecs::world::{FromWorld, World};
 use bevy_reflect::TypeRegistryArc;
 use bevy_utils::BoxedFuture;
+
+#[cfg(feature = "serialize")]
 use serde::de::DeserializeSeed;
 
 #[derive(Debug)]
@@ -21,6 +23,7 @@ impl FromWorld for SceneLoader {
     }
 }
 
+#[cfg(feature = "serialize")]
 impl AssetLoader for SceneLoader {
     fn load<'a>(
         &'a self,