Prevent creation of superfluous empty table

Author: omaskery

crates/bevy_ecs/src/storage/table/mod.rs

@@ -743,6 +743,10 @@ impl Tables {
         component_ids: &[ComponentId],
         components: &Components,
     ) -> TableId {
+        if component_ids.is_empty() {
+            return TableId::empty();
+        }
+
         let tables = &mut self.tables;
         let (_key, value) = self
             .table_ids
@@ -816,14 +820,26 @@ mod tests {
         component::{Component, Components, Tick},
         entity::Entity,
         ptr::OwningPtr,
-        storage::{Storages, TableBuilder, TableRow},
+        storage::{Storages, TableBuilder, TableId, TableRow, Tables},
     };
     #[cfg(feature = "track_change_detection")]
     use core::panic::Location;
 
     #[derive(Component)]
     struct W<T>(T);
 
+    #[test]
+    fn only_one_empty_table() {
+        let components = Components::default();
+        let mut tables = Tables::default();
+
+        let component_ids = &[];
+        // SAFETY: component_ids is empty, so we know it cannot reference invalid component IDs
+        let table_id = unsafe { tables.get_id_or_insert(component_ids, &components) };
+
+        assert_eq!(table_id, TableId::empty());
+    }
+
     #[test]
     fn table() {
         let mut components = Components::default();