Allow godot-visible functions to receive a Gd instead of self.

This is done by tagging the function with #[func(gd_self)].

godot-macros/src/class/data_models/field_var.rs

@@ -195,6 +195,7 @@ impl GetterSetterImpl {
             FuncDefinition {
                 func: signature,
                 rename: None,
+                has_gd_self: false,
             },
         );
 

godot-macros/src/class/data_models/func.rs

@@ -14,6 +14,7 @@ pub struct FuncDefinition {
     pub func: venial::Function,
     /// The name the function will be exposed as in Godot. If `None`, the Rust function name is used.
     pub rename: Option<String>,
+    pub has_gd_self: bool,
 }
 
 /// Returns a C function which acts as the callback when a virtual method of this instance is invoked.
@@ -24,7 +25,7 @@ pub fn make_virtual_method_callback(
     class_name: &Ident,
     method_signature: &venial::Function,
 ) -> TokenStream {
-    let signature_info = get_signature_info(method_signature);
+    let signature_info = get_signature_info(method_signature, false);
     let method_name = &method_signature.name;
 
     let wrapped_method = make_forwarding_closure(class_name, &signature_info);
@@ -54,7 +55,7 @@ pub fn make_method_registration(
     class_name: &Ident,
     func_definition: FuncDefinition,
 ) -> TokenStream {
-    let signature_info = get_signature_info(&func_definition.func);
+    let signature_info = get_signature_info(&func_definition.func, func_definition.has_gd_self);
     let sig_tuple =
         util::make_signature_tuple_type(&signature_info.ret_type, &signature_info.param_types);
 
@@ -127,6 +128,7 @@ pub fn make_method_registration(
 enum ReceiverType {
     Ref,
     Mut,
+    GdSelf,
     Static,
 }
 
@@ -167,6 +169,18 @@ fn make_forwarding_closure(class_name: &Ident, signature_info: &SignatureInfo) -
                 }
             }
         }
+        ReceiverType::GdSelf => {
+            quote! {
+                |instance_ptr, params| {
+                    let ( #(#params,)* ) = params;
+
+                    let storage =
+                        unsafe { ::godot::private::as_storage::<#class_name>(instance_ptr) };
+
+                    <#class_name>::#method_name(storage.get_gd(), #(#params),*)
+                }
+            }
+        }
         ReceiverType::Static => {
             quote! {
                 |_, params| {
@@ -178,7 +192,7 @@ fn make_forwarding_closure(class_name: &Ident, signature_info: &SignatureInfo) -
     }
 }
 
-fn get_signature_info(signature: &venial::Function) -> SignatureInfo {
+fn get_signature_info(signature: &venial::Function, gd_self: bool) -> SignatureInfo {
     let method_name = signature.name.clone();
     let mut receiver_type = ReceiverType::Static;
     let mut param_idents: Vec<Ident> = Vec::new();
@@ -192,7 +206,9 @@ fn get_signature_info(signature: &venial::Function) -> SignatureInfo {
     for (arg, _) in &signature.params.inner {
         match arg {
             venial::FnParam::Receiver(recv) => {
-                receiver_type = if recv.tk_mut.is_some() {
+                receiver_type = if gd_self {
+                    ReceiverType::GdSelf
+                } else if recv.tk_mut.is_some() {
                     ReceiverType::Mut
                 } else if recv.tk_ref.is_some() {
                     ReceiverType::Ref
@@ -228,7 +244,7 @@ fn get_signature_info(signature: &venial::Function) -> SignatureInfo {
 
 fn make_method_flags(method_type: ReceiverType) -> TokenStream {
     match method_type {
-        ReceiverType::Ref | ReceiverType::Mut => {
+        ReceiverType::Ref | ReceiverType::Mut | ReceiverType::GdSelf => {
             quote! { ::godot::engine::global::MethodFlags::METHOD_FLAGS_DEFAULT }
         }
         ReceiverType::Static => {

godot-macros/src/class/godot_api.rs

@@ -8,8 +8,8 @@ use proc_macro2::{Ident, TokenStream};
 use quote::quote;
 use quote::spanned::Spanned;
 use venial::{
-    Attribute, AttributeValue, Constant, Declaration, Error, FnParam, Function, Impl, ImplMember,
-    TyExpr,
+    Attribute, AttributeValue, Constant, Declaration, Error, FnParam, FnReceiverParam, Function,
+    Impl, ImplMember, TyExpr,
 };
 
 use crate::class::{make_method_registration, make_virtual_method_callback, FuncDefinition};
@@ -47,7 +47,10 @@ pub fn attribute_godot_api(input_decl: Declaration) -> Result<TokenStream, Error
 
 /// Attribute for user-declared function
 enum BoundAttrType {
-    Func { rename: Option<String> },
+    Func {
+        rename: Option<String>,
+        has_gd_self: bool,
+    },
     Signal(AttributeValue),
     Const(AttributeValue),
 }
@@ -229,11 +232,29 @@ fn process_godot_fns(decl: &mut Impl) -> Result<(Vec<FuncDefinition>, Vec<Functi
                 return attr.bail("generic fn parameters are not supported", method);
             }
 
-            match attr.ty {
-                BoundAttrType::Func { rename } => {
+            match &attr.ty {
+                BoundAttrType::Func {
+                    rename,
+                    has_gd_self,
+                } => {
                     // Signatures are the same thing without body
-                    let sig = util::reduce_to_signature(method);
-                    func_definitions.push(FuncDefinition { func: sig, rename });
+                    let mut sig = util::reduce_to_signature(method);
+                    if *has_gd_self {
+                        if sig.params.is_empty() {
+                            return attr.bail("with attribute key `gd_self`, the method must have a first parameter of type Gd<Self>", method);
+                        }
+                        sig.params[0].0 = FnParam::Receiver(FnReceiverParam {
+                            attributes: vec![],
+                            tk_ref: Some(proc_macro2::Punct::new('&', proc_macro2::Spacing::Alone)),
+                            tk_mut: None,
+                            tk_self: Ident::new("self", proc_macro2::Span::call_site()),
+                        });
+                    }
+                    func_definitions.push(FuncDefinition {
+                        func: sig,
+                        rename: rename.clone(),
+                        has_gd_self: *has_gd_self,
+                    });
                 }
                 BoundAttrType::Signal(ref _attr_val) => {
                     if method.return_ty.is_some() {
@@ -316,11 +337,15 @@ where
                 let mut parser = KvParser::parse(attributes, "func")?.unwrap();
 
                 let rename = parser.handle_expr("rename")?.map(|ts| ts.to_string());
+                let has_gd_self = parser.handle_alone("gd_self")?;
 
                 Some(BoundAttr {
                     attr_name: attr_name.clone(),
                     index,
-                    ty: BoundAttrType::Func { rename },
+                    ty: BoundAttrType::Func {
+                        rename,
+                        has_gd_self,
+                    },
                 })
             }
             name if name == "signal" => {

itest/godot/ManualFfiTests.gd

@@ -304,3 +304,22 @@ func test_func_rename():
 	assert_eq(func_rename.has_method("renamed_static"), false)
 	assert_eq(func_rename.has_method("spell_static"), true)
 	assert_eq(func_rename.spell_static(), "static")
+
+var gd_self_reference: GdSelfReference
+func update_self_reference(value):
+	gd_self_reference.update_internal(value)
+
+func test_gd_self_reference_fails():
+	# Create the gd_self_reference and connect its signal to a gdscript method that calls back into it.
+	gd_self_reference = GdSelfReference.new()
+	gd_self_reference.update_internal_signal.connect(update_self_reference)
+
+	# The returned value will still be 0 because update_internal can't be called in update_self_reference due to a borrowing issue.
+	assert_eq(gd_self_reference.fail_to_update_internal_value_due_to_conflicting_borrow(10), 0)
+
+func test_gd_self_reference_succeeds():
+	# Create the gd_self_reference and connect its signal to a gdscript method that calls back into it.
+	gd_self_reference = GdSelfReference.new()
+	gd_self_reference.update_internal_signal.connect(update_self_reference)
+
+	assert_eq(gd_self_reference.succeed_at_updating_internal_value(10), 10)

itest/rust/src/register_tests/func_test.rs

@@ -7,7 +7,7 @@
 use godot::prelude::*;
 
 #[derive(GodotClass)]
-#[class(base=RefCounted)]
+#[class(init, base=RefCounted)]
 struct FuncRename;
 
 #[godot_api]
@@ -40,9 +40,70 @@ impl FuncRename {
     }
 }
 
+#[derive(GodotClass)]
+#[class(base=RefCounted)]
+struct GdSelfReference {
+    internal_value: i32,
+
+    #[base]
+    base: Base<RefCounted>,
+}
+
+#[godot_api]
+impl GdSelfReference {
+    // A signal that will be looped back to update_internal through gdscript.
+    #[signal]
+    fn update_internal_signal(new_internal: i32);
+
+    #[func]
+    fn update_internal(&mut self, new_value: i32) {
+        self.internal_value = new_value;
+    }
+
+    #[func]
+    fn fail_to_update_internal_value_due_to_conflicting_borrow(
+        &mut self,
+        new_internal: i32,
+    ) -> i32 {
+        // Since a self reference is held while the signal is emitted, when
+        // GDScript tries to call update_internal(), there will be a failure due
+        // to the double borrow and self.internal_value won't be changed.
+        self.base.emit_signal(
+            "update_internal_signal".into(),
+            &[new_internal.to_variant()],
+        );
+        return self.internal_value;
+    }
+
+    #[func(gd_self)]
+    fn succeed_at_updating_internal_value(mut this: Gd<Self>, new_internal: i32) -> i32 {
+        // Since this isn't bound while the signal is emitted, GDScript will succeed at calling
+        // update_internal() and self.internal_value will be changed.
+        this.emit_signal(
+            "update_internal_signal".into(),
+            &[new_internal.to_variant()],
+        );
+        return this.bind().internal_value;
+    }
+
+    #[func(gd_self)]
+    fn takes_gd_as_equivalent(mut this: Gd<GdSelfReference>) -> bool {
+        this.bind_mut();
+        true
+    }
+
+    #[func(gd_self)]
+    fn takes_gd_as_self_no_return_type(this: Gd<GdSelfReference>) {
+        this.bind();
+    }
+}
+
 #[godot_api]
-impl RefCountedVirtual for FuncRename {
-    fn init(_base: Base<Self::Base>) -> Self {
-        Self
+impl RefCountedVirtual for GdSelfReference {
+    fn init(base: Base<Self::Base>) -> Self {
+        Self {
+            internal_value: 0,
+            base,
+        }
     }
 }