From 164d1c7c88a75d39909adb3885aae4b62363b336 Mon Sep 17 00:00:00 2001
From: Hennadii Chernyshchyk <genaloner@gmail.com>
Date: Fri, 7 Nov 2025 00:27:28 +0200
Subject: [PATCH] Avoid panicking when `Signature` inserted during replication

---
 CHANGELOG.md                        |  1 +
 src/shared/replication/signature.rs | 22 ++++++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9b981b17..00a403ac 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Avoid sending despawn for entities that weren't sent.
+- Avoid panicking when `Signature` inserted during replication.
 
 ### Removed
 
diff --git a/src/shared/replication/signature.rs b/src/shared/replication/signature.rs
index d3afa5bc..3442ed3b 100644
--- a/src/shared/replication/signature.rs
+++ b/src/shared/replication/signature.rs
@@ -307,14 +307,22 @@ fn register_hash(mut world: DeferredWorld, ctx: HookContext) {
     let mut signature = entity.get_mut::<Signature>().unwrap();
     signature.hash = hash;
 
-    world
-        .resource_mut::<SignatureMap>()
-        .insert(ctx.entity, hash);
+    if let Some(mut map) = world.get_resource_mut::<SignatureMap>() {
+        map.insert(ctx.entity, hash);
+    } else {
+        // Can't be handled manually like with unregistering below.
+        // However, when it's inserted during replication, entities
+        // don't need to be mapped. For example, the signature could
+        // be a required component to map local player entities,
+        // but ignored for remote ones.
+        debug!("ignoring hash 0x{hash:016x} for `{}`", ctx.entity);
+    }
 }
 
 fn unregister_hash(mut world: DeferredWorld, ctx: HookContext) {
     // The map will be unavailable during replication because the
-    // resource will be temporarily removed from the world.
+    // resource will be temporarily removed from the world,
+    // so it's handled manually there.
     if let Some(mut map) = world.get_resource_mut::<SignatureMap>() {
         map.remove(ctx.entity);
     }
@@ -395,6 +403,12 @@ variadics_please::all_tuples!(impl_signature_components, 0, 6, C);
 mod tests {
     use super::*;
 
+    #[test]
+    fn no_panic_without_map() {
+        let mut world = World::new();
+        world.spawn(Signature::from(0)).despawn();
+    }
+
     #[test]
     fn single_component() {
         let mut world = World::new();