Allow a closure to be used as a required component default

Author: fluffiac

crates/bevy_ecs/macros/src/component.rs

@@ -9,7 +9,7 @@ use syn::{
     punctuated::Punctuated,
     spanned::Spanned,
     token::{Comma, Paren},
-    DeriveInput, ExprPath, Ident, LitStr, Path, Result,
+    DeriveInput, ExprPath, ExprClosure, Ident, LitStr, Path, Result
 };
 
 pub fn derive_event(input: TokenStream) -> TokenStream {
@@ -84,14 +84,22 @@ pub fn derive_component(input: TokenStream) -> TokenStream {
             register_recursive_requires.push(quote! {
                 <#ident as Component>::register_required_components(components, storages, required_components);
             });
-            if let Some(func) = &require.func {
-                register_required.push(quote! {
-                    required_components.register(components, storages, || { let x: #ident = #func().into(); x });
-                });
-            } else {
-                register_required.push(quote! {
-                    required_components.register(components, storages, <#ident as Default>::default);
-                });
+            match &require.func {
+                Some(RequireFunc::Path(func)) => {
+                    register_required.push(quote! {
+                        required_components.register(components, storages, || { let x: #ident = #func().into(); x });
+                    });
+                },
+                Some(RequireFunc::Closure(func)) => {
+                    register_required.push(quote! {
+                        required_components.register(components, storages, || { let x: #ident = (#func)().into(); x });
+                    });
+                },
+                None => {
+                    register_required.push(quote! {
+                        required_components.register(components, storages, <#ident as Default>::default);
+                    });
+                }
             }
         }
     }
@@ -162,7 +170,12 @@ enum StorageTy {
 
 struct Require {
     path: Path,
-    func: Option<Path>,
+    func: Option<RequireFunc>,
+}
+
+enum RequireFunc {
+    Path(Path),
+    Closure(ExprClosure)   
 }
 
 // values for `storage` attribute
@@ -238,8 +251,12 @@ impl Parse for Require {
         let func = if input.peek(Paren) {
             let content;
             parenthesized!(content in input);
-            let func = content.parse::<Path>()?;
-            Some(func)
+            if let Ok(func) = content.parse::<ExprClosure>() {
+                Some(RequireFunc::Closure(func))
+            } else {
+                let func = content.parse::<Path>()?;
+                Some(RequireFunc::Path(func))
+            }
         } else {
             None
         };