From 0dc2ec0159e3042dd25d2989c47d383bb0ac54fc Mon Sep 17 00:00:00 2001
From: Ellen <supbscripter@gmail.com>
Date: Thu, 15 Apr 2021 04:26:07 +0100
Subject: [PATCH] Fix unsoundness in query component access

---
 crates/bevy_ecs/src/lib.rs          | 7 +++++++
 crates/bevy_ecs/src/query/fetch.rs  | 8 ++++++++
 crates/bevy_ecs/src/query/filter.rs | 4 ++++
 3 files changed, 19 insertions(+)

diff --git a/crates/bevy_ecs/src/lib.rs b/crates/bevy_ecs/src/lib.rs
index a85e95a2a7f9a..4db81495b3866 100644
--- a/crates/bevy_ecs/src/lib.rs
+++ b/crates/bevy_ecs/src/lib.rs
@@ -1071,6 +1071,13 @@ mod tests {
         world.query::<(&A, &mut A)>();
     }
 
+    #[test]
+    #[should_panic]
+    fn mut_and_ref_query_panic() {
+        let mut world = World::new();
+        world.query::<(&mut A, &A)>();
+    }
+
     #[test]
     #[should_panic]
     fn mut_and_mut_query_panic() {
diff --git a/crates/bevy_ecs/src/query/fetch.rs b/crates/bevy_ecs/src/query/fetch.rs
index 91f423be28725..0350651f6808f 100644
--- a/crates/bevy_ecs/src/query/fetch.rs
+++ b/crates/bevy_ecs/src/query/fetch.rs
@@ -206,6 +206,10 @@ unsafe impl<T: Component> FetchState for ReadState<T> {
     }
 
     fn update_component_access(&self, access: &mut FilteredAccess<ComponentId>) {
+        if access.access().has_write(self.component_id) {
+            panic!("&{} conflicts with a previous access in this query. Shared access cannot coincide with exclusive access.",
+                std::any::type_name::<T>());
+        }
         access.add_read(self.component_id)
     }
 
@@ -656,6 +660,10 @@ unsafe impl<T: Component> FetchState for ChangeTrackersState<T> {
     }
 
     fn update_component_access(&self, access: &mut FilteredAccess<ComponentId>) {
+        if access.access().has_write(self.component_id) {
+            panic!("ChangeTrackers<{}> conflicts with a previous access in this query. Shared access cannot coincide with exclusive access.",
+                std::any::type_name::<T>());
+        }
         access.add_read(self.component_id)
     }
 
diff --git a/crates/bevy_ecs/src/query/filter.rs b/crates/bevy_ecs/src/query/filter.rs
index ed611b5b7b323..d745f456d59ce 100644
--- a/crates/bevy_ecs/src/query/filter.rs
+++ b/crates/bevy_ecs/src/query/filter.rs
@@ -501,6 +501,10 @@ macro_rules! impl_tick_filter {
 
             #[inline]
             fn update_component_access(&self, access: &mut FilteredAccess<ComponentId>) {
+                if access.access().has_write(self.component_id) {
+                    panic!("$state_name<{}> conflicts with a previous access in this query. Shared access cannot coincide with exclusive access.",
+                        std::any::type_name::<T>());
+                }
                 access.add_read(self.component_id);
             }