From 44a572e4e66d946c696d17f532171489404ffa8e Mon Sep 17 00:00:00 2001
From: JoJoJet <21144246+JoJoJet@users.noreply.github.com>
Date: Fri, 3 Feb 2023 09:17:48 +0000
Subject: [PATCH] Fix ignored lifetimes in `#[derive(SystemParam)]` (#7458)

# Objective

Fix #7447.

The `SystemParam` derive uses the wrong lifetimes for ignored fields.

## Solution

Use type inference instead of explicitly naming the types of ignored fields. This allows the compiler to automatically use the correct lifetime.
---
 crates/bevy_ecs/macros/src/lib.rs          | 2 +-
 crates/bevy_ecs/src/system/system_param.rs | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/crates/bevy_ecs/macros/src/lib.rs b/crates/bevy_ecs/macros/src/lib.rs
index 07d01a8c870ab..d914f3488c430 100644
--- a/crates/bevy_ecs/macros/src/lib.rs
+++ b/crates/bevy_ecs/macros/src/lib.rs
@@ -506,7 +506,7 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
                     >::get_param(&mut state.state, system_meta, world, change_tick);
                     #struct_name {
                         #(#fields: #field_locals,)*
-                        #(#ignored_fields: <#ignored_field_types>::default(),)*
+                        #(#ignored_fields: std::default::Default::default(),)*
                     }
                 }
             }
diff --git a/crates/bevy_ecs/src/system/system_param.rs b/crates/bevy_ecs/src/system/system_param.rs
index 4dc3a85bdbf1b..c97dcf397e396 100644
--- a/crates/bevy_ecs/src/system/system_param.rs
+++ b/crates/bevy_ecs/src/system/system_param.rs
@@ -1541,11 +1541,12 @@ mod tests {
     }
 
     // Compile test for https://github.com/bevyengine/bevy/pull/6919.
+    // Regression test for https://github.com/bevyengine/bevy/issues/7447.
     #[derive(SystemParam)]
-    struct MyParam<'w, T: Resource, Marker: 'static> {
+    struct IgnoredParam<'w, T: Resource, Marker: 'static> {
         _foo: Res<'w, T>,
         #[system_param(ignore)]
-        marker: PhantomData<Marker>,
+        marker: PhantomData<&'w Marker>,
     }
 
     // Compile tests for https://github.com/bevyengine/bevy/pull/6957.