Add a dummy struct to see if it works on the godot side

src/dummy.rs

+use godot::{
+    classes::{ISprite2D, Sprite2D},
+    prelude::*,
+};
+
+#[derive(GodotClass)]
+#[class(base=Sprite2D)]
+struct Player {
+    speed: f64,
+    angular_speed: f64,
+
+    base: Base<Sprite2D>,
+}
+
+#[godot_api]
+impl ISprite2D for Player {
+    fn init(base: Base<Sprite2D>) -> Self {
+        godot_print!("Hello, world!"); // Prints to the Godot console
+
+        Self {
+            speed: 400.0,
+            angular_speed: std::f64::consts::PI,
+            base,
+        }
+    }
+
+    fn physics_process(&mut self, delta: f64) {
+        // GDScript code:
+        //
+        // rotation += angular_speed * delta
+        // var velocity = Vector2.UP.rotated(rotation) * speed
+        // position += velocity * delta
+
+        let radians = (self.angular_speed * delta) as f32;
+        self.base_mut().rotate(radians);
+
+        let rotation = self.base().get_rotation();
+        let velocity = Vector2::UP.rotated(rotation) * self.speed as f32;
+        self.base_mut().translate(velocity * delta as f32);
+
+        // or verbose:
+        // let this = self.base_mut();
+        // this.set_position(
+        //     this.position() + velocity * delta as f32
+        // );
+    }
+}
+
+#[godot_api]
+impl Player {
+    #[func]
+    fn increase_speed(&mut self, amount: f64) {
+        self.speed += amount;
+        self.base_mut().emit_signal("speed_increased", &[]);
+    }
+
+    #[signal]
+    fn speed_increased();
+}

src/lib.rs

@@ -2,3 +2,12 @@ pub mod spell;
 pub mod expr;
 pub mod state;
 pub mod error;
+
+pub mod dummy;
+
+use godot::prelude::*;
+
+struct GrimoireExtension;
+
+#[gdextension]
+unsafe impl ExtensionLibrary for GrimoireExtension {}