PluginUnavailable: add subclass PluginUnconfigured

PluginUnconfigured exceptions are logged with level "info" instead of
"error".  This suppresses some rather boring messages in the default
log level.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/565

src/PluginUnavailable.hxx

@@ -1,5 +1,5 @@
 /*
- * Copyright 2003-2018 The Music Player Daemon Project
+ * Copyright 2003-2019 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -27,11 +27,24 @@
  * that this plugin is unavailable.  It will be disabled, and MPD can
  * continue initialization.
  */
-class PluginUnavailable final : public std::runtime_error {
+class PluginUnavailable : public std::runtime_error {
 public:
 	template<typename M>
 	explicit PluginUnavailable(M &&msg) noexcept
 		:std::runtime_error(std::forward<M>(msg)) {}
 };
 
+/**
+ * Like #PluginUnavailable, but denotes that the plugin is not
+ * available because it was not explicitly enabled in the
+ * configuration.  The message may describe the necessary steps to
+ * enable it.
+ */
+class PluginUnconfigured : public PluginUnavailable {
+public:
+	template<typename M>
+	explicit PluginUnconfigured(M &&msg) noexcept
+		:PluginUnavailable(std::forward<M>(msg)) {}
+};
+
 #endif

src/input/Init.cxx

@@ -58,6 +58,11 @@ input_stream_global_init(const ConfigData &config, EventLoop &event_loop)
 			if (plugin->init != nullptr)
 				plugin->init(event_loop, *block);
 			input_plugins_enabled[i] = true;
+		} catch (const PluginUnconfigured &e) {
+			LogFormat(LogLevel::INFO, e,
+				  "Input plugin '%s' is not configured",
+				  plugin->name);
+			continue;
 		} catch (const PluginUnavailable &e) {
 			FormatError(e,
 				    "Input plugin '%s' is unavailable",

src/input/plugins/QobuzInputPlugin.cxx

@@ -133,11 +133,11 @@ InitQobuzInput(EventLoop &event_loop, const ConfigBlock &block)
 
 	const char *app_id = block.GetBlockValue("app_id");
 	if (app_id == nullptr)
-		throw PluginUnavailable("No Qobuz app_id configured");
+		throw PluginUnconfigured("No Qobuz app_id configured");
 
 	const char *app_secret = block.GetBlockValue("app_secret");
 	if (app_secret == nullptr)
-		throw PluginUnavailable("No Qobuz app_secret configured");
+		throw PluginUnconfigured("No Qobuz app_secret configured");
 
 	const char *device_manufacturer_id = block.GetBlockValue("device_manufacturer_id",
 								 "df691fdc-fa36-11e7-9718-635337d7df8f");
@@ -145,11 +145,11 @@ InitQobuzInput(EventLoop &event_loop, const ConfigBlock &block)
 	const char *username = block.GetBlockValue("username");
 	const char *email = block.GetBlockValue("email");
 	if (username == nullptr && email == nullptr)
-		throw PluginUnavailable("No Qobuz username configured");
+		throw PluginUnconfigured("No Qobuz username configured");
 
 	const char *password = block.GetBlockValue("password");
 	if (password == nullptr)
-		throw PluginUnavailable("No Qobuz password configured");
+		throw PluginUnconfigured("No Qobuz password configured");
 
 	const char *format_id = block.GetBlockValue("format_id", "5");
 

src/input/plugins/TidalInputPlugin.cxx

@@ -170,15 +170,15 @@ InitTidalInput(EventLoop &event_loop, const ConfigBlock &block)
 
 	const char *token = block.GetBlockValue("token");
 	if (token == nullptr)
-		throw PluginUnavailable("No Tidal application token configured");
+		throw PluginUnconfigured("No Tidal application token configured");
 
 	const char *username = block.GetBlockValue("username");
 	if (username == nullptr)
-		throw PluginUnavailable("No Tidal username configured");
+		throw PluginUnconfigured("No Tidal username configured");
 
 	const char *password = block.GetBlockValue("password");
 	if (password == nullptr)
-		throw PluginUnavailable("No Tidal password configured");
+		throw PluginUnconfigured("No Tidal password configured");
 
 	tidal_audioquality = block.GetBlockValue("audioquality", "HIGH");