For classes with #[base] field, add to_gd() utility method

Author: Bromeon

godot-core/src/obj/traits.rs

@@ -206,6 +206,18 @@ pub trait IndexEnum: EngineEnum {
     }
 }
 
+/// Trait that's implemented for user-defined classes that provide a `#[base]` field.
+///
+/// Gives direct access to the containing `Gd<Self>` from `Self`.
+// Possible alternative for builder APIs, although even less ergonomic: Base<T> could be Base<T, Self> and return Gd<Self>.
+pub trait WithBaseField: GodotClass {
+    /// Returns the `Gd` pointer containing this object.
+    ///
+    /// This is intended to be stored or passed to engine methods. You cannot call `bind()` or `bind_mut()` on it, while the method
+    /// calling `to_gd()` is still running; that would lead to a double borrow panic.
+    fn to_gd(&self) -> Gd<Self>;
+}
+
 // ----------------------------------------------------------------------------------------------------------------------------------------------
 
 /// Capability traits, providing dedicated functionalities for Godot classes
@@ -257,17 +269,6 @@ pub mod cap {
         }
     }
 
-    /// Trait that's implemented for user-defined classes that provide a `#[base]` field.
-    ///
-    /// Gives direct access to the base pointer without going through upcast FFI.
-    pub trait WithBaseField: GodotClass {
-        #[doc(hidden)]
-        fn __godot_base(&self) -> &Gd<Self::Base>;
-
-        #[doc(hidden)]
-        fn __godot_base_mut(&mut self) -> &mut Gd<Self::Base>;
-    }
-
     // TODO Evaluate whether we want this public or not
     #[doc(hidden)]
     pub trait GodotToString: GodotClass {

godot-macros/src/class/derive_godot_class.rs

@@ -50,6 +50,18 @@ pub fn derive_godot_class(decl: Declaration) -> ParseResult<TokenStream> {
         quote! {}
     };
 
+    let godot_withbase_impl = if let Some(Field { name, .. }) = &fields.base_field {
+        quote! {
+            impl ::godot::obj::WithBaseField for #class_name {
+                fn to_gd(&self) -> Gd<Self> {
+                    ::godot::obj::Gd::clone(&*self.#name).cast()
+                }
+            }
+        }
+    } else {
+        quote! {}
+    };
+
     let (godot_init_impl, create_fn, recreate_fn);
     if struct_cfg.has_generated_init {
         godot_init_impl = make_godot_init_impl(class_name, fields);
@@ -78,11 +90,10 @@ pub fn derive_godot_class(decl: Declaration) -> ParseResult<TokenStream> {
                 ::godot::builtin::meta::ClassName::from_ascii_cstr(#class_name_cstr)
             }
         }
-        impl ::godot::obj::UserClass for #class_name {
-
-        }
+        impl ::godot::obj::UserClass for #class_name {}
 
         #godot_init_impl
+        #godot_withbase_impl
         #godot_exports_impl
         #config_impl
 

godot-macros/src/lib.rs

@@ -100,7 +100,7 @@ use crate::util::ident;
 /// #[class(base = Node2D)]
 /// struct MyStruct {
 ///     #[base]
-///     base: Gd<Node2D>,
+///     base: Base<Node2D>,
 /// }
 /// ```
 ///

godot/src/lib.rs

@@ -235,5 +235,6 @@ pub mod prelude {
     // Make trait methods available
     pub use super::engine::NodeExt as _;
     pub use super::obj::EngineEnum as _;
-    pub use super::obj::UserClass as _; // new_gd(), self_gd()
+    pub use super::obj::UserClass as _; // new_gd(), alloc_gd()
+    pub use super::obj::WithBaseField as _; // to_gd()
 }

itest/rust/src/object_tests/base_test.rs

@@ -93,6 +93,19 @@ fn base_with_init() {
     obj.free();
 }
 
+#[itest]
+fn base_gd_self() {
+    let obj = Based::alloc_gd();
+    let obj2 = obj.bind().access_gd_self();
+
+    assert_eq!(obj, obj2);
+    assert_eq!(obj.instance_id(), obj2.instance_id());
+
+    obj.free();
+}
+
+// ----------------------------------------------------------------------------------------------------------------------------------------------
+
 #[derive(GodotClass)]
 #[class(init, base=Node2D)]
 struct Based {
@@ -102,6 +115,13 @@ struct Based {
     i: i32,
 }
 
+impl Based {
+    fn access_gd_self(&self) -> Gd<Self> {
+        use godot::obj::WithBaseField as _;
+        self.to_gd()
+    }
+}
+
 #[derive(GodotClass)]
 #[class(init, base=Node2D)]
 struct Baseless {