Begin clap objects with vtables for pointer casts

src/wrapper/clap.rs

@@ -44,7 +44,7 @@ macro_rules! nih_export_clap {
                             ::nih_plug::wrapper::clap::CLAP_PLUGIN_FACTORY_ID,
                         ) }
                 {
-                    &(*factory).clap_plugin_factory() as *const _ as *const ::std::ffi::c_void
+                    &(*factory).clap_plugin_factory as *const _ as *const ::std::ffi::c_void
                 } else {
                     std::ptr::null()
                 }

src/wrapper/clap/factory.rs

@@ -1,13 +1,16 @@
 use clap_sys::plugin_factory::clap_plugin_factory;
 use std::marker::PhantomData;
-use std::mem;
 
 use crate::ClapPlugin;
 
 /// The plugin's factory. Initialized using a lazy_static from the entry poiunt's `get_factory()`
 /// function. From this point onwards we don't need to generate code with macros anymore.
 #[doc(hidden)]
+#[repr(C)]
 pub struct Factory<P: ClapPlugin> {
+    // Keep the vtable as the first field so we can do a simple pointer cast
+    pub clap_plugin_factory: clap_plugin_factory,
+
     /// The type will be used for constructing plugin instances later.
     _phantom: PhantomData<P>,
 }
@@ -15,17 +18,18 @@ pub struct Factory<P: ClapPlugin> {
 impl<P: ClapPlugin> Default for Factory<P> {
     fn default() -> Self {
         Self {
+            clap_plugin_factory: clap_plugin_factory {
+                get_plugin_count: Self::get_plugin_count,
+                get_plugin_descriptor: todo!(),
+                create_plugin: todo!(),
+            },
             _phantom: PhantomData,
         }
     }
 }
 
 impl<P: ClapPlugin> Factory<P> {
-    pub fn clap_plugin_factory(&self) -> clap_plugin_factory {
+    unsafe extern "C" fn get_plugin_count(_factory: *const clap_plugin_factory) -> u32 {
-        clap_plugin_factory {
+        1
-            get_plugin_count: todo!(),
-            get_plugin_descriptor: todo!(),
-            create_plugin: todo!(),
-        }
     }
 }