Fix panic when placing ghost (#765)

* Add EntityCommands::try_remove and try_insert

* Swap to try_insert

* Add try_add_child

* Use try_add_child and fix the panic

* Clippy

emergence_lib/src/lib.rs

@@ -11,7 +11,6 @@
 pub mod asset_management;
 pub mod construction;
 pub mod crafting;
-pub mod curves;
 pub mod enum_iter;
 pub mod filtered_array_iter;
 pub mod graphics;
@@ -25,6 +24,7 @@ pub mod structures;
 pub mod terrain;
 pub mod ui;
 pub mod units;
+pub mod utils;
 pub mod world_gen;
 
 /// Various app configurations, used for testing.

emergence_lib/src/ui/status.rs

@@ -16,6 +16,7 @@ use crate::{
         goals::{Goal, GoalKind},
         unit_manifest::Unit,
     },
+    utils::fallible_commands::FallibleEntityCommandExt,
 };
 
 use super::ui_assets::Icons;
@@ -185,10 +186,10 @@ fn add_status_displays(
         // - it will be hidden when the parent entity is hidden
         commands
             .entity(parent_entity)
-            .insert(StatusParent {
+            .try_insert(StatusParent {
                 entity: status_entity,
             })
-            .add_child(status_entity);
+            .try_add_child(status_entity);
     }
 }
 

emergence_lib/src/utils/fallible_commands.rs

@@ -0,0 +1,58 @@
+//! Contains [`FallibleEntityCommandExt`] and related code.
+
+use bevy::{ecs::system::EntityCommands, prelude::*};
+
+/// An extension trait for [`EntityCommands`] that has fallible versions of
+/// the most commonly used commands.
+
+pub trait FallibleEntityCommandExt<'w, 's, 'a> {
+    /// Attempts to add a component or bundle to the entity.
+    ///
+    /// Fails silently (rather than panicking) if the entity does not exist.
+    ///
+    /// Fallible version of [`EntityCommands::insert`].
+    fn try_insert(&mut self, bundle: impl Bundle) -> &mut EntityCommands<'w, 's, 'a>;
+
+    /// Attempts to remove a component or bundle from the entity.
+    ///
+    /// Fails silently (rather than panicking) if the entity does not exist.
+    ///
+    /// Fallible version of [`EntityCommands::remove`].
+    fn try_remove<B: Bundle>(&mut self) -> &mut EntityCommands<'w, 's, 'a>;
+
+    /// Attempts to add a child entity to the entity.
+    ///
+    /// Fails silently (rather than panicking) if the entity does not exist.
+    ///
+    /// Fallible version of [`BuildChildren::add_child`].
+    fn try_add_child(&mut self, child: Entity) -> &mut EntityCommands<'w, 's, 'a>;
+}
+
+impl<'w, 's, 'a> FallibleEntityCommandExt<'w, 's, 'a> for EntityCommands<'w, 's, 'a> {
+    fn try_insert(&mut self, bundle: impl Bundle) -> &mut Self {
+        self.add(|entity, world: &mut World| {
+            if let Some(mut entity_mut) = world.get_entity_mut(entity) {
+                entity_mut.insert(bundle);
+            }
+        });
+        self
+    }
+
+    fn try_remove<B: Bundle>(&mut self) -> &mut Self {
+        self.add(|entity, world: &mut World| {
+            if let Some(mut entity_mut) = world.get_entity_mut(entity) {
+                entity_mut.remove::<B>();
+            }
+        });
+        self
+    }
+
+    fn try_add_child(&mut self, child: Entity) -> &mut EntityCommands<'w, 's, 'a> {
+        self.add(move |entity, world: &mut World| {
+            if let Some(mut entity_mut) = world.get_entity_mut(entity) {
+                entity_mut.add_child(child);
+            }
+        });
+        self
+    }
+}

emergence_lib/src/utils/mod.rs

@@ -0,0 +1,4 @@
+//! Simple gameplay-agnostic utilities.
+
+pub mod curves;
+pub mod fallible_commands;