Build the CLAP plugin descriptor

This requires a _lot_ of CStrings.

src/wrapper/clap/factory.rs

@@ -1,8 +1,12 @@
 use clap_sys::host::clap_host;
 use clap_sys::plugin::{clap_plugin, clap_plugin_descriptor};
 use clap_sys::plugin_factory::clap_plugin_factory;
+use clap_sys::version::CLAP_VERSION;
+use std::ffi::CString;
 use std::marker::PhantomData;
+use std::mem::MaybeUninit;
 use std::os::raw::c_char;
+use std::ptr;
 
 use crate::ClapPlugin;
 
@@ -14,23 +18,92 @@ 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,
 
+    // We need [CString]s for all of `ClapPlugin`'s `&str` fields
+    clap_id: CString,
+    name: CString,
+    vendor: CString,
+    url: CString,
+    clap_manual_url: CString,
+    clap_support_url: CString,
+    version: CString,
+    clap_description: CString,
+    clap_features: Vec<CString>,
+    clap_features_ptrs: MaybeUninit<CStrPtrs>,
+
+    /// We only support a single plugin per factory right now, so we'll fill in the plugin
+    /// descriptor upfront. We also need to initialize the `CString` fields above first before we
+    /// can initialize this plugin descriptor.
+    plugin_descriptor: MaybeUninit<clap_plugin_descriptor>,
+
     /// The type will be used for constructing plugin instances later.
     _phantom: PhantomData<P>,
 }
 
+/// Needed for the Send+Sync implementation for lazy_static.
+struct CStrPtrs(Vec<*const c_char>);
+
 impl<P: ClapPlugin> Default for Factory<P> {
     fn default() -> Self {
-        Self {
+        let mut factory = Self {
             clap_plugin_factory: clap_plugin_factory {
                 get_plugin_count: Self::get_plugin_count,
                 get_plugin_descriptor: Self::get_plugin_descriptor,
                 create_plugin: Self::create_plugin,
             },
+            clap_id: CString::new(P::CLAP_ID).expect("`CLAP_ID` contained null bytes"),
+            name: CString::new(P::NAME).expect("`NAME` contained null bytes"),
+            vendor: CString::new(P::VENDOR).expect("`VENDOR` contained null bytes"),
+            url: CString::new(P::URL).expect("`URL` contained null bytes"),
+            clap_manual_url: CString::new(P::CLAP_MANUAL_URL)
+                .expect("`CLAP_MANUAL_URL` contained null bytes"),
+            clap_support_url: CString::new(P::CLAP_SUPPORT_URL)
+                .expect("`CLAP_SUPPORT_URL` contained null bytes"),
+            version: CString::new(P::VERSION).expect("`VERSION` contained null bytes"),
+            clap_description: CString::new(P::CLAP_DESCRIPTION)
+                .expect("`CLAP_DESCRIPTION` contained null bytes"),
+            clap_features: P::CLAP_FEATURES
+                .iter()
+                .map(|s| CString::new(*s).expect("`CLAP_FEATURES` contained null bytes"))
+                .collect(),
+            clap_features_ptrs: MaybeUninit::uninit(),
+            plugin_descriptor: MaybeUninit::uninit(),
             _phantom: PhantomData,
-        }
+        };
+
+        // The keyword list is an environ-like list of char pointers terminated by a null pointer
+        let mut clap_features_ptrs: Vec<*const c_char> = factory
+            .clap_features
+            .iter()
+            .map(|feature| feature.as_ptr())
+            .collect();
+        clap_features_ptrs.push(ptr::null());
+        factory
+            .clap_features_ptrs
+            .write(CStrPtrs(clap_features_ptrs));
+
+        // We couldn't initialize this directly because of all the CStrings
+        factory.plugin_descriptor.write(clap_plugin_descriptor {
+            clap_version: CLAP_VERSION,
+            id: factory.clap_id.as_ptr(),
+            name: factory.name.as_ptr(),
+            vendor: factory.vendor.as_ptr(),
+            url: factory.url.as_ptr(),
+            manual_url: factory.clap_manual_url.as_ptr(),
+            support_url: factory.clap_support_url.as_ptr(),
+            version: factory.version.as_ptr(),
+            description: factory.clap_description.as_ptr(),
+            features: unsafe { factory.clap_features_ptrs.assume_init_ref() }
+                .0
+                .as_ptr(),
+        });
+
+        factory
     }
 }
 
+unsafe impl Send for CStrPtrs {}
+unsafe impl Sync for CStrPtrs {}
+
 impl<P: ClapPlugin> Factory<P> {
     unsafe extern "C" fn get_plugin_count(_factory: *const clap_plugin_factory) -> u32 {
         1
@@ -40,7 +113,13 @@ impl<P: ClapPlugin> Factory<P> {
         factory: *const clap_plugin_factory,
         index: u32,
     ) -> *const clap_plugin_descriptor {
-        todo!()
+        let factory = &*(factory as *const Self);
+
+        if index == 0 {
+            factory.plugin_descriptor.assume_init_ref()
+        } else {
+            ptr::null()
+        }
     }
 
     unsafe extern "C" fn create_plugin(