Merge pull request #989 from godot-rust/feature/static-callable

Support static functions in `Callable`

Author: Bromeon

godot-core/src/builtin/callable.rs

@@ -8,8 +8,8 @@
 use godot_ffi as sys;
 
 use crate::builtin::{inner, GString, StringName, Variant, VariantArray};
-use crate::classes::Object;
-use crate::meta::{AsArg, CallContext, GodotType, ToGodot};
+use crate::classes;
+use crate::meta::{GodotType, ToGodot};
 use crate::obj::bounds::DynMemory;
 use crate::obj::Bounds;
 use crate::obj::{Gd, GodotClass, InstanceId};
@@ -43,7 +43,7 @@ impl Callable {
         Self { opaque }
     }
 
-    /// Create a callable for the method `object::method_name`.
+    /// Create a callable for the non-static method `object.method_name`.
     ///
     /// See also [`Gd::callable()`].
     ///
@@ -65,6 +65,55 @@ impl Callable {
         }
     }
 
+    /// Create a callable for the static method `class_name::function` (single-threaded).
+    ///
+    /// Allows you to call static functions through `Callable`.
+    ///
+    /// Note that due to varying support across different engine versions, the resulting `Callable` has unspecified behavior for
+    /// methods such as [`method_name()`][Self::method_name], [`object()`][Self::object], [`object_id()`][Self::object_id] or
+    /// [`get_argument_count()`][Self::arg_len] among others. It is recommended to only use this for calling the function.
+    pub fn from_local_static(
+        class_name: impl meta::AsArg<StringName>,
+        function_name: impl meta::AsArg<StringName>,
+    ) -> Self {
+        meta::arg_into_owned!(class_name);
+        meta::arg_into_owned!(function_name);
+
+        // Modern implementation: use ClassDb::class_call_static().
+        #[cfg(since_api = "4.4")]
+        {
+            let callable_name = format!("{class_name}.{function_name}");
+
+            Self::from_local_fn(&callable_name, move |args| {
+                let args = args.iter().cloned().cloned().collect::<Vec<_>>();
+
+                let result: Variant = classes::ClassDb::singleton().class_call_static(
+                    &class_name,
+                    &function_name,
+                    args.as_slice(),
+                );
+                Ok(result)
+            })
+        }
+
+        // Polyfill for <= Godot 4.3: use GDScript expressions.
+        #[cfg(before_api = "4.4")]
+        {
+            use crate::obj::NewGd;
+
+            let code = format!(
+                "static func __callable():\n\treturn Callable({class_name}, \"{function_name}\")"
+            );
+
+            let mut script = classes::GDScript::new_gd();
+            script.set_source_code(&code);
+            script.reload();
+
+            let callable = script.call("__callable", &[]);
+            callable.to()
+        }
+    }
+
     #[cfg(since_api = "4.2")]
     fn default_callable_custom_info() -> CallableCustomInfo {
         CallableCustomInfo {
@@ -94,7 +143,7 @@ impl Callable {
     pub fn from_local_fn<F, S>(name: S, rust_function: F) -> Self
     where
         F: 'static + FnMut(&[&Variant]) -> Result<Variant, ()>,
-        S: AsArg<GString>,
+        S: meta::AsArg<GString>,
     {
         meta::arg_into_owned!(name);
 
@@ -129,7 +178,7 @@ impl Callable {
     pub fn from_sync_fn<F, S>(name: S, rust_function: F) -> Self
     where
         F: 'static + Send + Sync + FnMut(&[&Variant]) -> Result<Variant, ()>,
-        S: AsArg<GString>,
+        S: meta::AsArg<GString>,
     {
         meta::arg_into_owned!(name);
 
@@ -273,11 +322,11 @@ impl Callable {
     /// target or not). Also returns `None` if the object is dead. You can differentiate these two cases using [`object_id()`][Self::object_id].
     ///
     /// _Godot equivalent: `get_object`_
-    pub fn object(&self) -> Option<Gd<Object>> {
+    pub fn object(&self) -> Option<Gd<classes::Object>> {
         // Increment refcount because we're getting a reference, and `InnerCallable::get_object` doesn't
         // increment the refcount.
         self.as_inner().get_object().map(|mut object| {
-            <Object as Bounds>::DynMemory::maybe_inc_ref(&mut object.raw);
+            <classes::Object as Bounds>::DynMemory::maybe_inc_ref(&mut object.raw);
             object
         })
     }
@@ -482,7 +531,7 @@ mod custom_callable {
             let c: &C = CallableUserdata::inner_from_raw(callable_userdata);
             c.to_string()
         };
-        let ctx = CallContext::custom_callable(name.as_str());
+        let ctx = meta::CallContext::custom_callable(name.as_str());
 
         crate::private::handle_varcall_panic(&ctx, &mut *r_error, move || {
             // Get the RustCallable again inside closure so it doesn't have to be UnwindSafe.
@@ -508,7 +557,7 @@ mod custom_callable {
             let w: &FnWrapper<F> = CallableUserdata::inner_from_raw(callable_userdata);
             w.name.to_string()
         };
-        let ctx = CallContext::custom_callable(name.as_str());
+        let ctx = meta::CallContext::custom_callable(name.as_str());
 
         crate::private::handle_varcall_panic(&ctx, &mut *r_error, move || {
             // Get the FnWrapper again inside closure so the FnMut doesn't have to be UnwindSafe.

itest/rust/src/builtin_tests/containers/callable_test.rs

@@ -41,6 +41,11 @@ impl CallableTestObj {
     fn baz(&self, a: i32, b: GString, c: Array<NodePath>, d: Gd<RefCounted>) -> VariantArray {
         varray![a, b, c, d]
     }
+
+    #[func]
+    fn static_function(c: i32) -> GString {
+        c.to_variant().stringify()
+    }
 }
 
 #[itest]
@@ -63,7 +68,9 @@ fn callable_validity() {
     assert!(!Callable::invalid().is_valid());
     assert!(Callable::invalid().is_null());
     assert!(!Callable::invalid().is_custom());
-    assert!(Callable::invalid().object().is_none());
+    assert_eq!(Callable::invalid().object(), None);
+    assert_eq!(Callable::invalid().object_id(), None);
+    assert_eq!(Callable::invalid().method_name(), None);
 }
 
 #[itest]
@@ -87,10 +94,30 @@ fn callable_object_method() {
     drop(object);
     assert_eq!(callable.object_id(), Some(object_id));
     assert_eq!(callable.object(), None);
+}
 
-    assert_eq!(Callable::invalid().object(), None);
-    assert_eq!(Callable::invalid().object_id(), None);
-    assert_eq!(Callable::invalid().method_name(), None);
+#[itest]
+fn callable_static() {
+    let callable = Callable::from_local_static("CallableTestObj", "static_function");
+
+    // Test current behavior in <4.4 and >=4.4. Although our API explicitly leaves it unspecified, we then notice change in implementation.
+    if cfg!(since_api = "4.4") {
+        assert_eq!(callable.object(), None);
+        assert_eq!(callable.object_id(), None);
+        assert_eq!(callable.method_name(), None);
+    } else {
+        assert!(callable.object().is_some());
+        assert!(callable.object_id().is_some());
+        assert_eq!(callable.method_name(), Some("static_function".into()));
+        assert_eq!(callable.to_string(), "GDScriptNativeClass::static_function");
+    }
+
+    // Calling works consistently everywhere.
+    let result = callable.callv(&varray![12345]);
+    assert_eq!(result, "12345".to_variant());
+
+    #[cfg(since_api = "4.3")]
+    assert_eq!(callable.arg_len(), 0); // Consistently doesn't work :)
 }
 
 #[itest]