Fully implement the CLAP tail extension

Trivial extension, but this required us to be able to send audio thread
callbacks first.

src/plugin/bridges/clap-impls/plugin-proxy.cpp

@@ -24,7 +24,9 @@ ClapHostExtensions::ClapHostExtensions(const clap_host& host) noexcept
       note_ports(static_cast<const clap_host_note_ports_t*>(
           host.get_extension(&host, CLAP_EXT_NOTE_PORTS))),
       params(static_cast<const clap_host_params_t*>(
-          host.get_extension(&host, CLAP_EXT_PARAMS))) {}
+          host.get_extension(&host, CLAP_EXT_PARAMS))),
+      tail(static_cast<const clap_host_tail_t*>(
+          host.get_extension(&host, CLAP_EXT_TAIL))) {}
 
 ClapHostExtensions::ClapHostExtensions() noexcept {}
 
@@ -33,7 +35,8 @@ clap::host::SupportedHostExtensions ClapHostExtensions::supported()
     return clap::host::SupportedHostExtensions{
         .supports_audio_ports = audio_ports != nullptr,
         .supports_note_ports = note_ports != nullptr,
-        .supports_params = params != nullptr};
+        .supports_params = params != nullptr,
+        .supports_tail = tail != nullptr};
 }
 
 clap_plugin_proxy::clap_plugin_proxy(ClapPluginBridge& bridge,
@@ -74,6 +77,9 @@ clap_plugin_proxy::clap_plugin_proxy(ClapPluginBridge& bridge,
           .text_to_value = ext_params_text_to_value,
           .flush = ext_params_flush,
       }),
+      ext_tail_vtable(clap_plugin_tail_t{
+          .get = ext_tail_get,
+      }),
       // These function objects are relatively large, and we probably won't be
       // getting that many of them
       pending_callbacks_(128) {}
@@ -210,6 +216,9 @@ clap_plugin_proxy::plugin_get_extension(const struct clap_plugin* plugin,
     } else if (self->supported_extensions_.supports_params &&
                strcmp(id, CLAP_EXT_PARAMS) == 0) {
         extension_ptr = &self->ext_params_vtable;
+    } else if (self->supported_extensions_.supports_tail &&
+               strcmp(id, CLAP_EXT_TAIL) == 0) {
+        extension_ptr = &self->ext_tail_vtable;
     }
 
     self->bridge_.logger_.log_extension_query("clap_plugin::get_extension",
@@ -408,3 +417,11 @@ clap_plugin_proxy::ext_params_flush(const clap_plugin_t* plugin,
     self->bridge_.send_audio_thread_message(
         clap::ext::params::plugin::Flush{.instance_id = self->instance_id()});
 }
+
+uint32_t CLAP_ABI clap_plugin_proxy::ext_tail_get(const clap_plugin_t* plugin) {
+    assert(plugin && plugin->plugin_data);
+    auto self = static_cast<const clap_plugin_proxy*>(plugin->plugin_data);
+
+    return self->bridge_.send_audio_thread_message(
+        clap::ext::tail::plugin::Get{.instance_id = self->instance_id()});
+}

src/plugin/bridges/clap-impls/plugin-proxy.h

@@ -23,6 +23,7 @@
 #include <clap/ext/audio-ports.h>
 #include <clap/ext/note-ports.h>
 #include <clap/ext/params.h>
+#include <clap/ext/tail.h>
 #include <clap/plugin.h>
 #include <rigtorp/MPMCQueue.h>
 #include <function2/function2.hpp>
@@ -61,6 +62,7 @@ struct ClapHostExtensions {
     const clap_host_audio_ports_t* audio_ports = nullptr;
     const clap_host_note_ports_t* note_ports = nullptr;
     const clap_host_params_t* params = nullptr;
+    const clap_host_tail_t* tail = nullptr;
 };
 
 /**
@@ -162,6 +164,8 @@ class clap_plugin_proxy {
                                           const clap_input_events_t* in,
                                           const clap_output_events_t* out);
 
+    static uint32_t CLAP_ABI ext_tail_get(const clap_plugin_t* plugin);
+
     /**
      * Asynchronously run a function on the host's main thread, returning the
      * result as a future.
@@ -235,9 +239,10 @@ class clap_plugin_proxy {
     // Extensions also have vtables. Whether or not we expose these to the host
     // depends on whether the plugin supported this extension when we called
     // `clap_plugin::init()`.
-    const clap_plugin_audio_ports ext_audio_ports_vtable;
-    const clap_plugin_note_ports ext_note_ports_vtable;
-    const clap_plugin_params ext_params_vtable;
+    const clap_plugin_audio_ports_t ext_audio_ports_vtable;
+    const clap_plugin_note_ports_t ext_note_ports_vtable;
+    const clap_plugin_params_t ext_params_vtable;
+    const clap_plugin_tail_t ext_tail_vtable;
 
     /**
      * The extensions supported by the bridged plugin. Set after a successful

src/plugin/bridges/clap.cpp

@@ -278,12 +278,13 @@ void ClapPluginBridge::register_plugin_proxy(
                 },
                 [&](const clap::ext::tail::host::Changed& request)
                     -> clap::ext::tail::host::Changed::Response {
-                    // FIXME:
-                    // const auto& [instance, _] =
-                    //     get_instance(request.instance_id);
+                    const auto& [plugin_proxy, _] =
+                        get_proxy(request.owner_instance_id);
 
-                    // return instance.plugin->start_processing(
-                    //     instance.plugin.get());
+                    plugin_proxy.host_extensions_.tail->changed(
+                        plugin_proxy.host_);
+
+                    return Ack{};
                 },
             });
     });