Create GDExtension clases for PhysicsServer3D

* Allows creating a GDExtension based 3D Physics Server (for Bullet, PhysX, etc. support)
* Some changes on native struct binding for PhysicsServer

This allows a 3D Physics server created entirely from GDExtension. Once it works, the idea is to port the 2D one to it.

3 files changed, 44 insertions, 2 deletions

diff --git a/core/object/class_db.cpp b/core/object/class_db.cpp
index 08e12dfcaa..e09c6cb97c 100644
--- a/core/object/class_db.cpp
+++ b/core/object/class_db.cpp
@@ -1606,7 +1606,7 @@ Variant ClassDB::class_get_default_property_value(const StringName &p_class, con
 		if (Engine::get_singleton()->has_singleton(p_class)) {
 			c = Engine::get_singleton()->get_singleton_object(p_class);
 			cleanup_c = false;
-		} else if (ClassDB::can_instantiate(p_class)) {
+		} else if (ClassDB::can_instantiate(p_class) && !ClassDB::is_virtual(p_class)) {
 			c = ClassDB::instantiate(p_class);
 			cleanup_c = true;
 		}
@@ -1694,6 +1694,30 @@ void ClassDB::unregister_extension_class(const StringName &p_class) {
 	classes.erase(p_class);
 }
 
+Map<StringName, ClassDB::NativeStruct> ClassDB::native_structs;
+void ClassDB::register_native_struct(const StringName &p_name, const String &p_code, uint64_t p_current_size) {
+	NativeStruct ns;
+	ns.ccode = p_code;
+	ns.struct_size = p_current_size;
+	native_structs[p_name] = ns;
+}
+
+void ClassDB::get_native_struct_list(List<StringName> *r_names) {
+	for (const KeyValue<StringName, NativeStruct> &E : native_structs) {
+		r_names->push_back(E.key);
+	}
+}
+
+String ClassDB::get_native_struct_code(const StringName &p_name) {
+	ERR_FAIL_COND_V(!native_structs.has(p_name), String());
+	return native_structs[p_name].ccode;
+}
+
+uint64_t ClassDB::get_native_struct_size(const StringName &p_name) {
+	ERR_FAIL_COND_V(!native_structs.has(p_name), 0);
+	return native_structs[p_name].struct_size;
+}
+
 RWLock ClassDB::lock;
 
 void ClassDB::cleanup_defaults() {
@@ -1717,6 +1741,7 @@ void ClassDB::cleanup() {
 	classes.clear();
 	resource_base_extensions.clear();
 	compat_classes.clear();
+	native_structs.clear();
 }
 
 //
diff --git a/core/object/class_db.h b/core/object/class_db.h
index 580ae3582f..32e4bf7644 100644
--- a/core/object/class_db.h
+++ b/core/object/class_db.h
@@ -144,6 +144,13 @@ public:
 	static HashMap<StringName, HashMap<StringName, Variant>> default_values;
 	static Set<StringName> default_values_cached;
 
+	// Native structs, used by binder
+	struct NativeStruct {
+		String ccode; // C code to create the native struct, fields separated by ; Arrays accepted (even containing other structs), also function pointers. All types must be Godot types.
+		uint64_t struct_size; // local size of struct, for comparison
+	};
+	static Map<StringName, NativeStruct> native_structs;
+
 private:
 	// Non-locking variants of get_parent_class and is_parent_class.
 	static StringName _get_parent_class(const StringName &p_class);
@@ -390,6 +397,11 @@ public:
 	static APIType get_current_api();
 	static void cleanup_defaults();
 	static void cleanup();
+
+	static void register_native_struct(const StringName &p_name, const String &p_code, uint64_t p_current_size);
+	static void get_native_struct_list(List<StringName> *r_names);
+	static String get_native_struct_code(const StringName &p_name);
+	static uint64_t get_native_struct_size(const StringName &p_name); // Used for asserting
 };
 
 #ifdef DEBUG_METHODS_ENABLED
@@ -448,6 +460,8 @@ _FORCE_INLINE_ Vector<Error> errarray(P... p_args) {
 		::ClassDB::register_abstract_class<m_class>(); \
 	}
 
+#define GDREGISTER_NATIVE_STRUCT(m_class, m_code) ClassDB::register_native_struct(#m_class, m_code, sizeof(m_class))
+
 #include "core/disabled_classes.gen.h"
 
 #endif // CLASS_DB_H
diff --git a/core/object/make_virtuals.py b/core/object/make_virtuals.py
index 2e909b8042..64ee5940b0 100644
--- a/core/object/make_virtuals.py
+++ b/core/object/make_virtuals.py
@@ -28,7 +28,8 @@ _FORCE_INLINE_ bool _gdvirtual_##m_name##_call($CALLARGS) $CONST { \\
 	}\\
 	\\
 	if (required) {\\
-	        WARN_PRINT_ONCE("Required virtual method: "+get_class()+"::" + #m_name + " must be overriden before calling.");\\
+	        ERR_PRINT_ONCE("Required virtual method: "+get_class()+"::" + #m_name + " must be overriden before calling.");\\
+	        $RVOID\\
     }\\
 \\
     return false;\\
@@ -66,10 +67,12 @@ def generate_version(argcount, const=False, returns=False):
     if returns:
         sproto += "R"
         s = s.replace("$RET", "m_ret, ")
+        s = s.replace("$RVOID", "(void)r_ret;")  # If required, may lead to uninitialized errors
         s = s.replace("$CALLPTRRETDEF", "PtrToArg<m_ret>::EncodeT ret;")
         method_info += "\tmethod_info.return_val = GetTypeInfo<m_ret>::get_class_info();\\\n"
     else:
         s = s.replace("$RET", "")
+        s = s.replace("$RVOID", "")
         s = s.replace("$CALLPTRRETDEF", "")
 
     if const: