Format generic labels

Author: joseph-gio

crates/bevy_ecs/examples/derive_label.rs

@@ -18,6 +18,18 @@ fn main() {
         GenericLabel::<f64>::One.as_label(),
         GenericLabel::<char>::One.as_label(),
     );
+
+    assert_eq!(format!("{:?}", UnitLabel.as_label()), "UnitLabel");
+    assert_eq!(format!("{:?}", WeirdLabel(1).as_label()), "WeirdLabel");
+    assert_eq!(format!("{:?}", WeirdLabel(2).as_label()), "WeirdLabel");
+    assert_eq!(
+        format!("{:?}", GenericLabel::<f64>::One.as_label()),
+        "GenericLabel::One::<f64>"
+    );
+    assert_eq!(
+        format!("{:?}", ConstGenericLabel::<21>.as_label()),
+        "ConstGenericLabel::<21>"
+    );
 }
 
 #[derive(SystemLabel)]
@@ -40,6 +52,9 @@ pub enum GenericLabel<T> {
     Two(PhantomData<T>),
 }
 
+#[derive(SystemLabel)]
+pub struct ConstGenericLabel<const N: usize>;
+
 // FIXME: this should be a compile_fail test
 /*#[derive(SystemLabel)]
 pub union Foo {

crates/bevy_macro_utils/src/lib.rs

@@ -271,14 +271,33 @@ fn derive_named_label(
         }
     };
 
+    // Formatting for generics
+    let generics = input.generics.params.iter();
+    let fmt_generics = generics
+        .filter_map(|p| match p {
+            syn::GenericParam::Type(ty) => Some({
+                let ident = &ty.ident;
+                quote! { write!(f, "{}", ::std::any::type_name::<#ident>()) }
+            }),
+            syn::GenericParam::Const(c) => Some({
+                let ident = &c.ident;
+                quote! { write!(f, "{:?}", { #ident }) }
+            }),
+            _ => None,
+        })
+        .reduce(|a, b| quote! { #a?; write!(f, ", ")?; #b })
+        .map(|x| quote! { write!(f, "::<")?; #x?; write!(f, ">")?; });
+
     Ok(quote! {
         impl #impl_generics #trait_path for #ident #ty_generics #where_clause {
             #[inline]
             fn data(&self) -> u64 {
                 #data
             }
             fn fmt(data: u64, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
-                #fmt
+                #fmt?;
+                #fmt_generics
+                Ok(())
             }
         }
     })