From f5039a476d48ec19bd74c94e83e10772565c68f1 Mon Sep 17 00:00:00 2001
From: Alice Cecile <alice.i.cecile@gmail.com>
Date: Sun, 23 Jan 2022 14:24:37 +0000
Subject: [PATCH] Mark .id() methods which return an `Entity` as must_use
 (#3750)

# Objective

- Calling .id() has no purpose unless you use the Entity returned
- This is an easy source of confusion for beginners.
- This is easily missed during refactors.

## Solution

- Mark the appropriate methods as #[must_use]
---
 crates/bevy_ecs/src/lib.rs                 | 10 ++--------
 crates/bevy_ecs/src/system/commands/mod.rs |  1 +
 crates/bevy_ecs/src/system/mod.rs          |  4 ++--
 crates/bevy_ecs/src/world/entity_ref.rs    |  2 ++
 4 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/crates/bevy_ecs/src/lib.rs b/crates/bevy_ecs/src/lib.rs
index 30d70ca17e..04731b45cf 100644
--- a/crates/bevy_ecs/src/lib.rs
+++ b/crates/bevy_ecs/src/lib.rs
@@ -1130,18 +1130,12 @@ mod tests {
     #[test]
     fn remove_bundle() {
         let mut world = World::default();
-        world
-            .spawn()
-            .insert_bundle((A(1), B(1), TableStored("1")))
-            .id();
+        world.spawn().insert_bundle((A(1), B(1), TableStored("1")));
         let e2 = world
             .spawn()
             .insert_bundle((A(2), B(2), TableStored("2")))
             .id();
-        world
-            .spawn()
-            .insert_bundle((A(3), B(3), TableStored("3")))
-            .id();
+        world.spawn().insert_bundle((A(3), B(3), TableStored("3")));
 
         let mut query = world.query::<(&B, &TableStored)>();
         let results = query
diff --git a/crates/bevy_ecs/src/system/commands/mod.rs b/crates/bevy_ecs/src/system/commands/mod.rs
index 6de329856c..e2a2a5a222 100644
--- a/crates/bevy_ecs/src/system/commands/mod.rs
+++ b/crates/bevy_ecs/src/system/commands/mod.rs
@@ -372,6 +372,7 @@ impl<'w, 's, 'a> EntityCommands<'w, 's, 'a> {
     /// # my_system.system();
     /// ```
     #[inline]
+    #[must_use = "Omit the .id() call if you do not need to store the `Entity` identifier."]
     pub fn id(&self) -> Entity {
         self.entity
     }
diff --git a/crates/bevy_ecs/src/system/mod.rs b/crates/bevy_ecs/src/system/mod.rs
index a5b4c68bce..9eec231db3 100644
--- a/crates/bevy_ecs/src/system/mod.rs
+++ b/crates/bevy_ecs/src/system/mod.rs
@@ -493,8 +493,8 @@ mod tests {
         world.clear_trackers();
 
         // Then, try removing a component
-        world.spawn().insert(W(3)).id();
-        world.spawn().insert(W(4)).id();
+        world.spawn().insert(W(3));
+        world.spawn().insert(W(4));
         world.entity_mut(entity_to_remove_w_from).remove::<W<i32>>();
 
         fn validate_remove(
diff --git a/crates/bevy_ecs/src/world/entity_ref.rs b/crates/bevy_ecs/src/world/entity_ref.rs
index b85fa2b74f..eda55333fb 100644
--- a/crates/bevy_ecs/src/world/entity_ref.rs
+++ b/crates/bevy_ecs/src/world/entity_ref.rs
@@ -26,6 +26,7 @@ impl<'w> EntityRef<'w> {
     }
 
     #[inline]
+    #[must_use = "Omit the .id() call if you do not need to store the `Entity` identifier."]
     pub fn id(&self) -> Entity {
         self.entity
     }
@@ -113,6 +114,7 @@ impl<'w> EntityMut<'w> {
     }
 
     #[inline]
+    #[must_use = "Omit the .id() call if you do not need to store the `Entity` identifier."]
     pub fn id(&self) -> Entity {
         self.entity
     }