LV2 specific instrument-plugin check

libs/ardour/ardour/lv2_plugin.h

@@ -280,6 +280,7 @@ public:
 
 	PluginPtr load (Session& session);
 	virtual bool in_category (const std::string &c) const;
+	virtual bool is_instrument() const;
 
 	char * _plugin_uri;
 };

libs/ardour/lv2_plugin.cc

@@ -2602,6 +2602,23 @@ LV2PluginInfo::in_category (const std::string &c) const
 	return false;
 }
 
+bool
+LV2PluginInfo::is_instrument () const
+{
+	if (category == "Instrument") {
+		return true;
+	}
+#if 1
+	/* until we make sure that category remains untranslated in the lv2.ttl spec
+	 * and until most instruments also classify themselves as such, there's a 2nd check:
+	 */
+	if (n_inputs.n_midi() > 0 && n_inputs.n_audio() == 0 && n_outputs.n_audio() > 0) {
+		return true;
+	}
+#endif
+	return false;
+}
+
 PluginInfoList*
 LV2PluginInfo::discover()
 {