Implement trait-based entry point declaration

Adds the `#[gdnative::init::callbacks]` attribute macro and
`GDNativeCallbacks` trait for entry point declaration, replacing the old
system of init macros. `godot_init!` is kept as a shim and deprecated.

This also adds support for the following callbacks:

- `gdnative_singleton`
- `nativescript_terminate`
- `nativescript_frame`
- `nativescript_thread_enter`
- `nativescript_thread_exit`

As a side effect, most of the init boilerplate are no longer emitted
into the user crate, instead staying in `gdnative-core`. Some further
internal refactoring might be necessary to improve code organization.

Close #985, Close #338

Author: chitoyuu

examples/builder-export/src/lib.rs

@@ -57,8 +57,11 @@ impl ExportsArrays {
     }
 }
 
-fn init(handle: InitHandle) {
-    handle.add_class::<ExportsArrays>();
-}
+struct BuilderExportLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for BuilderExportLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<ExportsArrays>();
+    }
+}

examples/dodge-the-creeps/src/lib.rs

@@ -5,11 +5,14 @@ mod main_scene;
 mod mob;
 mod player;
 
-fn init(handle: InitHandle) {
-    handle.add_class::<player::Player>();
-    handle.add_class::<mob::Mob>();
-    handle.add_class::<main_scene::Main>();
-    handle.add_class::<hud::Hud>();
-}
+struct DtcLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for DtcLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<player::Player>();
+        handle.add_class::<mob::Mob>();
+        handle.add_class::<main_scene::Main>();
+        handle.add_class::<hud::Hud>();
+    }
+}

examples/godot_tps_controller_port/src/lib.rs

@@ -2,8 +2,11 @@ use gdnative::prelude::*;
 
 mod player;
 
-fn init(handle: InitHandle) {
-    handle.add_class::<player::Player>();
-}
+struct TpsLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for TpsLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<player::Player>();
+    }
+}

examples/hello-world/src/lib.rs

@@ -16,8 +16,11 @@ impl HelloWorld {
     }
 }
 
-fn init(handle: InitHandle) {
-    handle.add_class::<HelloWorld>();
-}
+struct HelloWorldLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for HelloWorldLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<HelloWorld>();
+    }
+}

examples/native-plugin/src/lib.rs

@@ -54,9 +54,12 @@ impl MyButton {
     }
 }
 
-fn init(handle: InitHandle) {
-    handle.add_tool_class::<CustomNode>();
-    handle.add_tool_class::<MyButton>();
-}
+struct PluginLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for PluginLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_tool_class::<CustomNode>();
+        handle.add_tool_class::<MyButton>();
+    }
+}

examples/property-export/src/lib.rs

@@ -41,8 +41,11 @@ impl PropertyExport {
     }
 }
 
-fn init(handle: InitHandle) {
-    handle.add_class::<PropertyExport>();
-}
+struct PropertyExportLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for PropertyExportLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<PropertyExport>();
+    }
+}

examples/resource/src/lib.rs

@@ -46,9 +46,12 @@ impl Greeter {
     }
 }
 
-fn init(handle: InitHandle) {
-    handle.add_class::<Greeter>();
-    handle.add_class::<GreetingResource>();
-}
+struct ResourceLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for ResourceLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<Greeter>();
+        handle.add_class::<GreetingResource>();
+    }
+}

examples/rpc/src/lib.rs

@@ -3,9 +3,12 @@ use gdnative::prelude::*;
 mod client;
 mod server;
 
-fn init(handle: InitHandle) {
-    handle.add_class::<client::ServerPuppet>();
-    handle.add_class::<server::Server>();
-}
+struct RpcLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for RpcLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<client::ServerPuppet>();
+        handle.add_class::<server::Server>();
+    }
+}

examples/scene-create/src/lib.rs

@@ -100,10 +100,6 @@ impl SceneCreate {
     }
 }
 
-fn init(handle: InitHandle) {
-    handle.add_class::<SceneCreate>();
-}
-
 pub fn load_scene(path: &str) -> Option<Ref<PackedScene, ThreadLocal>> {
     let scene = load::<PackedScene>(path)?;
     let scene = unsafe { scene.assume_thread_local() };
@@ -151,4 +147,11 @@ fn update_panel(owner: &Spatial, num_children: i64) {
     }
 }
 
-godot_init!(init);
+struct SceneCreateLibrary;
+
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for SceneCreateLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<SceneCreate>();
+    }
+}

examples/signals/src/lib.rs

@@ -95,9 +95,12 @@ impl SignalSubscriber {
     }
 }
 
-fn init(handle: InitHandle) {
-    handle.add_class::<SignalEmitter>();
-    handle.add_class::<SignalSubscriber>();
-}
+struct SignalLibrary;
 
-godot_init!(init);
+#[gdnative::init::callbacks]
+impl GDNativeCallbacks for SignalLibrary {
+    fn nativescript_init(handle: InitHandle) {
+        handle.add_class::<SignalEmitter>();
+        handle.add_class::<SignalSubscriber>();
+    }
+}