feat!: change #[from_entity_instance] to use references (#149)

EntityInstance is a rather large struct, and cloning it requires allocating
for several fields. Despite this fact, each use of the #[from_entity_instance]
attribute was cloning the struct once, wasting CPU time for no good
reason - especially for Bundles that contain several #[from_entity_instance]
fields.

Change the attribute to work on From<&EntityInstance> instead of
From<EntityInstance>, avoiding the implicit clone in most cases. The clone
is still necessary when a plain EntityInstance field exists in a struct
deriving LdtkEntity, which is handled by having EntityInstance implement
From<&EntityInstance>.

While being a breaking change, fixing up users should be trivial - in
most cases no owned EntityInstance is needed at all, and where it is an
explicit clone can be inserted.

examples/platformer/components.rs

@@ -24,8 +24,8 @@ pub struct SensorBundle {
     pub rotation_constraints: LockedAxes,
 }
 
-impl From<EntityInstance> for ColliderBundle {
-    fn from(entity_instance: EntityInstance) -> ColliderBundle {
+impl From<&EntityInstance> for ColliderBundle {
+    fn from(entity_instance: &EntityInstance) -> ColliderBundle {
         let rotation_constraints = LockedAxes::ROTATION_LOCKED;
 
         match entity_instance.identifier.as_ref() {
@@ -81,8 +81,8 @@ impl From<IntGridCell> for SensorBundle {
 #[derive(Clone, Component, Debug, Eq, Default, PartialEq)]
 pub struct Items(Vec<String>);
 
-impl From<EntityInstance> for Items {
-    fn from(entity_instance: EntityInstance) -> Self {
+impl From<&EntityInstance> for Items {
+    fn from(entity_instance: &EntityInstance) -> Self {
         let mut items: Vec<String> = vec![];
 
         if let Some(field_instance) = entity_instance
@@ -128,7 +128,7 @@ pub struct PlayerBundle {
     pub climber: Climber,
     pub ground_detection: GroundDetection,
 
-    // Build Items Component manually by using `impl From<EntityInstance>
+    // Build Items Component manually by using `impl From<&EntityInstance>`
     #[from_entity_instance]
     items: Items,
 

macros/src/ldtk_entity.rs

@@ -318,7 +318,7 @@ fn expand_from_entity_instance_attribute(
     {
         syn::Meta::Path(_) => {
             quote! {
-                #field_name: <#field_type as From<bevy_ecs_ldtk::prelude::EntityInstance>>::from(entity_instance.clone()),
+                #field_name: <#field_type as From<&bevy_ecs_ldtk::prelude::EntityInstance>>::from(entity_instance),
             }
         }
         _ => {

src/app/ldtk_entity.rs

@@ -207,19 +207,20 @@ use crate::app::register_ldtk_objects::RegisterLdtkObjects;
 /// ```
 ///
 /// ### `#[from_entity_instance]`
-/// Indicates that a component or bundle that implements [From<EntityInstance>] should be created
+/// Indicates that a component or bundle that implements [From<&EntityInstance>] should be created
 /// using that conversion.
 /// This allows for more modular and custom component construction, and for different structs that
 /// contain the same component to have different constructions of that component, without having to
 /// `impl LdtkEntity` for both of them.
-/// It also allows you to have an [EntityInstance] field, since all types `T` implement `From<T>`.
+/// It also allows you to have an [EntityInstance] field, since `EntityInstance` implements
+/// `From<&EntityInstance>`.
 /// ```
 /// # use bevy::prelude::*;
 /// # use bevy_ecs_ldtk::prelude::*;
 /// # #[derive(Component, Default)]
 /// # struct Sellable { value: i32 }
-/// impl From<EntityInstance> for Sellable {
-///     fn from(entity_instance: EntityInstance) -> Sellable {
+/// impl From<&EntityInstance> for Sellable {
+///     fn from(entity_instance: &EntityInstance) -> Sellable {
 ///         let sell_value = match entity_instance.identifier.as_str() {
 ///             "gem" => 1000,
 ///             "nickel" => 5,

src/ldtk/mod.rs

@@ -1023,6 +1023,13 @@ pub struct EntityInstance {
     pub width: i32,
 }
 
+// Allow using #[from_entity_instance] to add EntityInstance fields when deriving LdtkEntity
+impl From<&EntityInstance> for EntityInstance {
+    fn from(value: &EntityInstance) -> Self {
+        value.clone()
+    }
+}
+
 /// This object is used in Field Instances to describe an EntityRef value.
 #[derive(Eq, PartialEq, Debug, Default, Clone, Serialize, Deserialize)]
 pub struct FieldInstanceEntityReference {