Allow to omit #[inherit] attribute in NativeClass derive (defaults to Reference)

Author: Bromeon

gdnative-derive/src/lib.rs

@@ -83,9 +83,10 @@ pub fn profiled(meta: TokenStream, input: TokenStream) -> TokenStream {
 
 /// Makes it possible to use a type as a NativeScript.
 ///
-/// ## Required attributes
+/// ## Type attributes
 ///
-/// The following attributes are required on the type deriving `NativeClass`:
+/// The behavior of the derive macro can be customized using attributes on the type
+/// deriving `NativeClass`. All type attributes are optional.
 ///
 /// ### `#[inherit(gdnative::api::BaseClass)]`
 ///
@@ -97,9 +98,10 @@ pub fn profiled(meta: TokenStream, input: TokenStream) -> TokenStream {
 /// Inheritance from other scripts, either in Rust or other languages, is
 /// not supported.
 ///
-/// ## Optional type attributes
+/// If no `#[inherit(...)]` is provided, [`gdnative::api::Reference`](../gdnative/api/struct.Reference.html)
+/// is used as a base class. This behavior is consistent with GDScript: omitting the
+/// `extends` keyword will inherit `Reference`.
 ///
-/// Behavior of the derive macro can be customized using attribute on the type:
 ///
 /// ### `#[user_data(gdnative::user_data::SomeWrapper<Self>)]`
 ///
@@ -134,7 +136,10 @@ pub fn profiled(meta: TokenStream, input: TokenStream) -> TokenStream {
 ///
 /// See documentation on `Instance::emplace` for an example on how this can be used.
 ///
-/// ## Optional field attributes
+///
+/// ## Field attributes
+///
+/// All field attributes are optional.
 ///
 /// ### `#[property]`
 ///

gdnative-derive/src/native_script.rs

@@ -144,14 +144,14 @@ fn parse_derive_input(input: &DeriveInput) -> Result<DeriveData, syn::Error> {
 
     let ident = input.ident.clone();
 
-    let inherit_attr = input
-        .attrs
-        .iter()
-        .find(|a| a.path.is_ident("inherit"))
-        .ok_or_else(|| syn::Error::new(span, "No \"inherit\" attribute found"))?;
+    let inherit_attr = input.attrs.iter().find(|a| a.path.is_ident("inherit"));
 
     // read base class
-    let base = inherit_attr.parse_args::<Type>()?;
+    let base = if let Some(attr) = inherit_attr {
+        attr.parse_args::<Type>()?
+    } else {
+        syn::parse2::<Type>(quote! { ::gdnative::api::Reference }).unwrap()
+    };
 
     let register_callback = input
         .attrs