Add non-overwriting variants of component/resource insertion functions

crates/bevy_ecs/src/bundle.rs

@@ -2,7 +2,10 @@ pub use bevy_ecs_macros::Bundle;
 
 use crate::{
     archetype::ComponentStatus,
-    component::{Component, ComponentId, ComponentTicks, Components, StorageType, TypeInfo},
+    component::{
+        CollisionBehaviour, Component, ComponentId, ComponentTicks, Components, StorageType,
+        TypeInfo,
+    },
     entity::Entity,
     storage::{SparseSetIndex, SparseSets, Table},
 };
@@ -135,6 +138,7 @@ impl BundleInfo {
         bundle_status: &[ComponentStatus],
         bundle: T,
         change_tick: u32,
+        overwrite_existing: CollisionBehaviour,
     ) {
         // NOTE: get_components calls this closure on each component in "bundle order".
         // bundle_info.component_ids are also in "bundle order"
@@ -145,21 +149,30 @@ impl BundleInfo {
             let component_status = bundle_status.get_unchecked(bundle_component);
             match self.storage_types[bundle_component] {
                 StorageType::Table => {
-                    let column = table.get_column(component_id).unwrap();
-                    column.set_unchecked(table_row, component_ptr);
-                    let column_status = column.get_ticks_unchecked_mut(table_row);
-                    match component_status {
-                        ComponentStatus::Added => {
-                            *column_status = ComponentTicks::new(change_tick);
-                        }
-                        ComponentStatus::Mutated => {
-                            column_status.set_changed(change_tick);
+                    if !matches!(
+                        (component_status, overwrite_existing),
+                        (ComponentStatus::Mutated, CollisionBehaviour::Skip),
+                    ) {
+                        let column = table.get_column(component_id).unwrap();
+                        column.set_unchecked(table_row, component_ptr);
+                        let column_status = column.get_ticks_unchecked_mut(table_row);
+                        match component_status {
+                            ComponentStatus::Added => {
+                                *column_status = ComponentTicks::new(change_tick);
+                            }
+                            ComponentStatus::Mutated => {
+                                column_status.set_changed(change_tick);
+                            }
                         }
                     }
                 }
                 StorageType::SparseSet => {
-                    let sparse_set = sparse_sets.get_mut(component_id).unwrap();
-                    sparse_set.insert(entity, component_ptr, change_tick);
+                    if matches!(component_status, ComponentStatus::Added)
+                        || matches!(overwrite_existing, CollisionBehaviour::Overwrite)
+                    {
+                        let sparse_set = sparse_sets.get_mut(component_id).unwrap();
+                        sparse_set.insert(entity, component_ptr, change_tick);
+                    }
                 }
             }
             bundle_component += 1;

crates/bevy_ecs/src/component/mod.rs

@@ -370,3 +370,14 @@ fn check_tick(last_change_tick: &mut u32, change_tick: u32) {
         *last_change_tick = change_tick.wrapping_sub(MAX_DELTA);
     }
 }
+
+/// Used by [BundleInfo::write_components](crate::bundle::BundleInfo::write_components())
+/// and [World::write_components](crate::world::World::insert_resource_with_id()) to control
+/// how collisions between newly inserted and existing component types should be handled.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum CollisionBehaviour {
+    /// Overwrite existing component/resource of the same type.
+    Overwrite,
+    /// Skip and do not write the new component if it already exists.
+    Skip,
+}

crates/bevy_ecs/src/lib.rs

@@ -941,6 +941,27 @@ mod tests {
         );
     }
 
+    #[test]
+    fn try_insert_resource_no_collision() {
+        let mut world = World::default();
+        world.try_insert_resource(64u64);
+        assert_eq!(
+            *world.get_resource::<u64>().expect("Resource exists"),
+            64u64
+        );
+    }
+
+    #[test]
+    fn try_insert_resource_collision() {
+        let mut world = World::default();
+        world.insert_resource(32u64);
+        world.try_insert_resource(64u64);
+        assert_eq!(
+            *world.get_resource::<u64>().expect("Resource exists"),
+            32u64
+        );
+    }
+
     #[test]
     fn remove_intersection() {
         let mut world = World::default();

crates/bevy_ecs/src/system/commands.rs

@@ -198,6 +198,10 @@ impl<'a, 'b> EntityCommands<'a, 'b> {
     }
 
     /// Adds a [`Bundle`] of components to the current entity.
+    ///
+    /// If any of the components in the [`Bundle`] are already present on the entity,
+    /// those components will be overwritten. To add only the components in the Bundle which
+    /// are not already present on the entity, see [try_insert_bundle](Self::try_insert_bundle()).
     pub fn insert_bundle(&mut self, bundle: impl Bundle) -> &mut Self {
         self.commands.add(InsertBundle {
             entity: self.entity,
@@ -206,8 +210,23 @@ impl<'a, 'b> EntityCommands<'a, 'b> {
         self
     }
 
+    /// Adds a [`Bundle`] of components to the current entity.
+    ///
+    /// If any of the components in the [`Bundle`] are already present on the entity,
+    /// those components will be silenty skipped. To overwrite components already present
+    /// on the entity with the value in the Bundle, see [insert_bundle](Self::insert_bundle()).
+    pub fn try_insert_bundle(&mut self, bundle: impl Bundle) -> &mut Self {
+        self.commands.add(TryInsertBundle {
+            entity: self.entity,
+            bundle,
+        });
+        self
+    }
+
     /// Adds a single [`Component`] to the current entity.
     ///
+    /// If an instance of the Component is already present on the entity, that component will be overwritten.
+    /// For adding a [`Component`] to an entity only when an instance is not already present, see [try_insert](Self::try_insert()).
     ///
     /// # Warning
     ///
@@ -246,6 +265,25 @@ impl<'a, 'b> EntityCommands<'a, 'b> {
         self
     }
 
+    /// Adds a single [`Component`] to the current entity.
+    ///
+    /// If an instance of the Component is already present on the entity, `try_insert` will silently return without changing it.
+    /// For adding a [`Component`] to an entity and overwriting the existing instance, see [insert](Self::insert()).
+    ///
+    /// # Warning
+    ///
+    /// It's possible to call this with a bundle, but this is likely not intended and
+    /// [`Self::try_insert_bundle`] should be used instead. If `try_insert` is called with a bundle, the
+    /// bundle itself will be added as a component instead of the bundles' inner components each
+    /// being added.
+    pub fn try_insert(&mut self, component: impl Component) -> &mut Self {
+        self.commands.add(TryInsert {
+            entity: self.entity,
+            component,
+        });
+        self
+    }
+
     /// See [`EntityMut::remove_bundle`](crate::world::EntityMut::remove_bundle).
     pub fn remove_bundle<T>(&mut self) -> &mut Self
     where
@@ -342,6 +380,20 @@ where
     }
 }
 
+pub struct TryInsertBundle<T> {
+    entity: Entity,
+    bundle: T,
+}
+
+impl<T> Command for TryInsertBundle<T>
+where
+    T: Bundle + 'static,
+{
+    fn write(self: Box<Self>, world: &mut World) {
+        world.entity_mut(self.entity).try_insert_bundle(self.bundle);
+    }
+}
+
 #[derive(Debug)]
 pub struct Insert<T> {
     pub entity: Entity,
@@ -357,6 +409,21 @@ where
     }
 }
 
+#[derive(Debug)]
+pub(crate) struct TryInsert<T> {
+    entity: Entity,
+    component: T,
+}
+
+impl<T> Command for TryInsert<T>
+where
+    T: Component,
+{
+    fn write(self: Box<Self>, world: &mut World) {
+        world.entity_mut(self.entity).try_insert(self.component);
+    }
+}
+
 #[derive(Debug)]
 pub struct Remove<T> {
     entity: Entity,
@@ -451,6 +518,103 @@ mod tests {
         assert_eq!(results2, vec![]);
     }
 
+    #[test]
+    fn try_insert_component_not_present() {
+        let mut world = World::default();
+        let mut command_queue = CommandQueue::default();
+        let _ = Commands::new(&mut command_queue, &world)
+            .spawn()
+            .try_insert(2u32)
+            .id();
+
+        command_queue.apply(&mut world);
+        assert!(world.entities().len() == 1);
+        let results = world
+            .query::<&u32>()
+            .iter(&world)
+            .copied()
+            .collect::<Vec<_>>();
+        assert_eq!(results, vec![2u32]);
+    }
+
+    #[test]
+    fn try_insert_component_present() {
+        let mut world = World::default();
+        let mut command_queue = CommandQueue::default();
+        let _ = Commands::new(&mut command_queue, &world)
+            .spawn()
+            .insert(1u32)
+            .try_insert(2u32)
+            .id();
+
+        command_queue.apply(&mut world);
+        assert!(world.entities().len() == 1);
+        let results = world
+            .query::<&u32>()
+            .iter(&world)
+            .copied()
+            .collect::<Vec<_>>();
+        assert_eq!(results, vec![1u32]);
+    }
+
+    #[test]
+    fn try_insert_bundle_components_not_present() {
+        let mut world = World::default();
+        let mut command_queue = CommandQueue::default();
+        let _ = Commands::new(&mut command_queue, &world)
+            .spawn()
+            .try_insert_bundle((2u32, 4u64))
+            .id();
+
+        command_queue.apply(&mut world);
+        assert!(world.entities().len() == 1);
+        let results = world
+            .query::<(&u32, &u64)>()
+            .iter(&world)
+            .map(|(a, b)| (*a, *b))
+            .collect::<Vec<_>>();
+        assert_eq!(results, vec![(2u32, 4u64)]);
+    }
+
+    #[test]
+    fn try_insert_bundle_components_all_present() {
+        let mut world = World::default();
+        let mut command_queue = CommandQueue::default();
+        let _ = Commands::new(&mut command_queue, &world)
+            .spawn_bundle((1u32, 2u64))
+            .try_insert_bundle((2u32, 4u64))
+            .id();
+
+        command_queue.apply(&mut world);
+        assert!(world.entities().len() == 1);
+        let results = world
+            .query::<(&u32, &u64)>()
+            .iter(&world)
+            .map(|(a, b)| (*a, *b))
+            .collect::<Vec<_>>();
+        assert_eq!(results, vec![(1u32, 2u64)]);
+    }
+
+    #[test]
+    fn try_insert_bundle_components_some_present() {
+        let mut world = World::default();
+        let mut command_queue = CommandQueue::default();
+        let _ = Commands::new(&mut command_queue, &world)
+            .spawn()
+            .insert(1u32)
+            .try_insert_bundle((2u32, 4u64))
+            .id();
+
+        command_queue.apply(&mut world);
+        assert!(world.entities().len() == 1);
+        let results = world
+            .query::<(&u32, &u64)>()
+            .iter(&world)
+            .map(|(a, b)| (*a, *b))
+            .collect::<Vec<_>>();
+        assert_eq!(results, vec![(1u32, 4u64)]);
+    }
+
     #[test]
     fn remove_components() {
         let mut world = World::default();