Fix bsn! enum variant subexpression hoisting

Hoist native subexpressions in process_enum_field the same way process_field already does, so SceneFunction closures stay static.

Author: akshitj11

crates/bevy_scene/macros/src/bsn/codegen.rs

@@ -633,6 +633,17 @@ impl BsnType {
             return Ok(quote! {#(#type_assigns)*});
         }
 
+        if let Some(
+            value @ (BsnValue::Ident(_)
+            | BsnValue::Expr(_)
+            | BsnValue::Closure(_)
+            | BsnValue::Tuple(_)),
+        ) = value
+        {
+            let ident = ctx.hoisted_expressions.hoist(value);
+            return Ok(quote! { *#bind_name = #ident; });
+        }
+
         // NOTE: It is very important to still produce outputs for None field values. This is what
         // enables field autocomplete in Rust Analyzer
         value
@@ -995,6 +1006,49 @@ mod tests {
             .contains("Duplicate field `x` found in BSN enum variant"));
     }
 
+    #[test]
+    fn enum_variant_expr_is_hoisted() {
+        let mut refs = EntityRefs::default();
+        let paths = TestPaths::new();
+        let mut exprs = HoistedExpressions::default();
+        let mut ctx = paths.ctx(&mut refs, &mut exprs);
+        let mut assignments = vec![];
+        let handle = BsnType {
+            path: parse_quote!(FontSourceTemplate),
+            enum_variant: Some(parse_quote!(Handle)),
+            fields: BsnFields::Tuple(vec![BsnUnnamedField {
+                value: BsnValue::Expr(quote!(some_borrow.clone())),
+            }]),
+        };
+
+        let res = handle.push_enum_patch(
+            &mut ctx,
+            &parse_quote!(Handle),
+            &mut assignments,
+            PatchTarget {
+                path: &[],
+                is_ref: false,
+            },
+        );
+
+        assert!(res.is_ok());
+        assert_eq!(ctx.errors.len(), 0);
+        assert_eq!(exprs.expressions.len(), 1);
+        assert_eq!(
+            exprs.expressions[0].to_string(),
+            "let _expr0 = { some_borrow . clone () } . into () ;"
+        );
+        let assignment_output: String = assignments.iter().map(|t| t.to_string()).collect();
+        assert!(
+            assignment_output.contains("_expr0"),
+            "expected hoisted ident in assignment output: {assignment_output}"
+        );
+        assert!(
+            !assignment_output.contains("some_borrow"),
+            "borrow should not appear inline in assignment output: {assignment_output}"
+        );
+    }
+
     #[test]
     fn bsn_root_preserves_inference_on_error() {
         // Arrange

crates/bevy_scene/src/lib.rs

@@ -2881,6 +2881,48 @@ mod tests {
         assert_eq!(entity.get::<TextFont>().unwrap().font_size, FontSize(24));
     }
 
+    #[test]
+    fn enum_variant_subexpressions_are_hoisted() {
+        #[derive(Component, FromTemplate, PartialEq, Eq, Debug, Clone)]
+        enum FontSource {
+            #[default]
+            Handle { value: String },
+        }
+
+        struct Config {
+            value: String,
+        }
+
+        fn make_scene(config: &Config) -> impl Scene {
+            bsn! {
+                Children [
+                    (FontSource::Handle { value: { config.value.clone() } }),
+                    (FontSource::Handle { value: { config.value.clone() } }),
+                ]
+            }
+        }
+
+        let mut app = test_app();
+        let world = app.world_mut();
+        let config = Config {
+            value: "test".to_string(),
+        };
+        let entity = world.spawn_scene(make_scene(&config)).unwrap().id();
+        let children = world.entity(entity).get::<Children>().unwrap();
+        assert_eq!(
+            world.entity(children[0]).get::<FontSource>().unwrap(),
+            &FontSource::Handle {
+                value: "test".to_string(),
+            }
+        );
+        assert_eq!(
+            world.entity(children[1]).get::<FontSource>().unwrap(),
+            &FontSource::Handle {
+                value: "test".to_string(),
+            }
+        );
+    }
+
     #[test]
     fn field_name_shorthand() {
         let mut app = test_app();