Don't panic if godot_nativescript_init is called again

If this happens, the .gdnlib should probably be marked as not-reloadable for other reasons, but we should at least avoid panicking here.

Author: Waridley

gdnative-core/src/nativescript/init.rs

@@ -55,22 +55,32 @@ pub use self::method::{
     Method, MethodBuilder, RpcMode, ScriptMethod, ScriptMethodAttributes, ScriptMethodFn, Varargs,
 };
 pub use self::property::{Export, ExportInfo, PropertyBuilder, Usage as PropertyUsage};
+use std::any::TypeId;
+use std::collections::HashSet;
+use std::sync::Mutex;
 
 /// A handle that can register new classes to the engine during initialization.
 ///
 /// See [`godot_nativescript_init`](macro.godot_nativescript_init.html) and
 /// [`godot_init`](macro.godot_init.html).
 #[derive(Copy, Clone)]
-pub struct InitHandle {
+pub struct InitHandle<'a> {
     #[doc(hidden)]
     handle: *mut libc::c_void,
+    registered_classes: &'a Mutex<HashSet<TypeId>>,
 }
 
-impl InitHandle {
+impl<'a> InitHandle<'a> {
     #[doc(hidden)]
     #[inline]
-    pub unsafe fn new(handle: *mut libc::c_void) -> Self {
-        InitHandle { handle }
+    pub unsafe fn new(
+        handle: *mut libc::c_void,
+        registered_classes: &'a Mutex<HashSet<TypeId>>,
+    ) -> Self {
+        InitHandle {
+            handle,
+            registered_classes,
+        }
     }
 
     /// Registers a new class to the engine.
@@ -96,12 +106,20 @@ impl InitHandle {
     where
         C: NativeClassMethods,
     {
-        if !class_registry::register_class::<C>() {
+        if !self
+            .registered_classes
+            .lock()
+            .unwrap()
+            .insert(TypeId::of::<C>())
+        {
             panic!(
-                "`{type_name}` has already been registered",
+                "`{type_name}` has already been registered with this handle",
                 type_name = std::any::type_name::<C>()
             );
         }
+        if !class_registry::register_class::<C>() {
+            // perhaps the library was kept alive while no NativeScripts referenced it
+        }
         unsafe {
             let class_name = CString::new(C::class_name()).unwrap();
             let base_name = CString::new(C::Base::class_name()).unwrap();

gdnative-core/src/nativescript/macros.rs

@@ -36,7 +36,13 @@ macro_rules! godot_nativescript_init {
             }
 
             let __result = ::std::panic::catch_unwind(|| {
-                $callback($crate::nativescript::init::InitHandle::new(handle));
+                let mut registered_classes = ::std::sync::Mutex::new(
+                    ::std::collections::HashSet::<::std::any::TypeId>::new(),
+                );
+                $callback($crate::nativescript::init::InitHandle::new(
+                    handle,
+                    &registered_classes,
+                ));
             });
 
             if __result.is_err() {