remove gcc_unused

[[maybe_unused]] (introduced in C++17) is standard C++. https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused says that this is equivalent to the GNU unused attribute. Signed-off-by: Rosen Penev <rosenp@gmail.com>

remove gcc_unused
97425d56 · Rosen Penev · 0afb156a · 97425d56 · 97425d56 · 97425d56
Unverified Commit 97425d56 authored Mar 12, 2020 by Rosen Penev
101 changed files
--- a/src/Instance.cxx
+++ b/src/Instance.cxx
@@ -150,13 +150,13 @@ Instance::OnDatabaseSongRemoved(const char *uri) noexcept
 #ifdef ENABLE_NEIGHBOR_PLUGINS

 void
-Instance::FoundNeighbor(gcc_unused const NeighborInfo &info) noexcept
+Instance::FoundNeighbor([[maybe_unused]] const NeighborInfo &info) noexcept
 {
 	EmitIdle(IDLE_NEIGHBOR);
 }

 void
-Instance::LostNeighbor(gcc_unused const NeighborInfo &info) noexcept
+Instance::LostNeighbor([[maybe_unused]] const NeighborInfo &info) noexcept
 {
 	EmitIdle(IDLE_NEIGHBOR);
 }

--- a/src/LogInit.cxx
+++ b/src/LogInit.cxx
@@ -46,7 +46,7 @@
 #define LOG_DATE_BUF_SIZE 16
 #define LOG_DATE_LEN (LOG_DATE_BUF_SIZE - 1)

-gcc_unused
+[[maybe_unused]]
 static constexpr Domain log_domain("log");

 #ifndef ANDROID

--- a/src/command/AllCommands.cxx
+++ b/src/command/AllCommands.cxx
@@ -216,8 +216,8 @@ static constexpr unsigned num_commands = std::size(commands);

 gcc_pure
 static bool
-command_available(gcc_unused const Partition &partition,
-		  gcc_unused const struct command *cmd) noexcept
+command_available([[maybe_unused]] const Partition &partition,
+		  [[maybe_unused]] const struct command *cmd) noexcept
 {
 #ifdef ENABLE_SQLITE
 	if (StringIsEqual(cmd->cmd, "sticker"))
@@ -272,14 +272,14 @@ PrintUnavailableCommands(Response &r, unsigned permission) noexcept

 /* don't be fooled, this is the command handler for "commands" command */
 static CommandResult
-handle_commands(Client &client, gcc_unused Request request, Response &r)
+handle_commands(Client &client, [[maybe_unused]] Request request, Response &r)
 {
 	return PrintAvailableCommands(r, client.GetPartition(),
 				      client.GetPermission());
 }

 static CommandResult
-handle_not_commands(Client &client, gcc_unused Request request, Response &r)
+handle_not_commands(Client &client, [[maybe_unused]] Request request, Response &r)
 {
 	return PrintUnavailableCommands(r, client.GetPermission());
 }

--- a/src/command/ClientCommands.cxx
+++ b/src/command/ClientCommands.cxx
@@ -27,15 +27,15 @@
 #include "util/StringAPI.hxx"

 CommandResult
-handle_close(gcc_unused Client &client, gcc_unused Request args,
-	     gcc_unused Response &r)
+handle_close([[maybe_unused]] Client &client, [[maybe_unused]] Request args,
+	     [[maybe_unused]] Response &r)
 {
 	return CommandResult::FINISH;
 }

 CommandResult
-handle_ping(gcc_unused Client &client, gcc_unused Request args,
-	    gcc_unused Response &r)
+handle_ping([[maybe_unused]] Client &client, [[maybe_unused]] Request args,
+	    [[maybe_unused]] Response &r)
 {
 	return CommandResult::OK;
 }

--- a/src/command/MessageCommands.cxx
+++ b/src/command/MessageCommands.cxx
@@ -72,7 +72,7 @@ handle_unsubscribe(Client &client, Request args, Response &r)
 }

 CommandResult
-handle_channels(Client &client, gcc_unused Request args, Response &r)
+handle_channels(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	assert(args.empty());

@@ -92,7 +92,7 @@ handle_channels(Client &client, gcc_unused Request args, Response &r)

 CommandResult
 handle_read_messages(Client &client,
-		     gcc_unused Request args, Response &r)
+		     [[maybe_unused]] Request args, Response &r)
 {
 	assert(args.empty());


--- a/src/command/NeighborCommands.cxx
+++ b/src/command/NeighborCommands.cxx
@@ -34,7 +34,7 @@ neighbor_commands_available(const Instance &instance) noexcept
 }

 CommandResult
-handle_listneighbors(Client &client, gcc_unused Request args, Response &r)
+handle_listneighbors(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	const NeighborGlue *const neighbors =
 		client.GetInstance().neighbors.get();

--- a/src/command/OtherCommands.cxx
+++ b/src/command/OtherCommands.cxx
@@ -69,7 +69,7 @@ print_spl_list(Response &r, const PlaylistVector &list)
 }

 CommandResult
-handle_urlhandlers(Client &client, gcc_unused Request args, Response &r)
+handle_urlhandlers(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	if (client.IsLocal())
 		r.Format("handler: file://\n");
@@ -78,7 +78,7 @@ handle_urlhandlers(Client &client, gcc_unused Request args, Response &r)
 }

 CommandResult
-handle_decoders(gcc_unused Client &client, gcc_unused Request args,
+handle_decoders([[maybe_unused]] Client &client, [[maybe_unused]] Request args,
 		Response &r)
 {
 	decoder_list_print(r);
@@ -86,8 +86,8 @@ handle_decoders(gcc_unused Client &client, gcc_unused Request args,
 }

 CommandResult
-handle_kill(gcc_unused Client &client, gcc_unused Request request,
-	    gcc_unused Response &r)
+handle_kill([[maybe_unused]] Client &client, [[maybe_unused]] Request request,
+	    [[maybe_unused]] Response &r)
 {
 	return CommandResult::KILL;
 }
@@ -307,7 +307,7 @@ handle_update(Client &client, Request args, Response &r, bool discard)
 }

 CommandResult
-handle_update(Client &client, Request args, gcc_unused Response &r)
+handle_update(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	return handle_update(client, args, r, false);
 }
@@ -360,14 +360,14 @@ handle_volume(Client &client, Request args, Response &r)
 }

 CommandResult
-handle_stats(Client &client, gcc_unused Request args, Response &r)
+handle_stats(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	stats_print(r, client.GetPartition());
 	return CommandResult::OK;
 }

 CommandResult
-handle_config(Client &client, gcc_unused Request args, Response &r)
+handle_config(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	if (!client.IsLocal()) {
 		r.Error(ACK_ERROR_PERMISSION,

--- a/src/command/OutputCommands.cxx
+++ b/src/command/OutputCommands.cxx
@@ -118,7 +118,7 @@ handle_outputset(Client &client, Request request, Response &response)
 }

 CommandResult
-handle_devices(Client &client, gcc_unused Request args, Response &r)
+handle_devices(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	assert(args.empty());


--- a/src/command/PlayerCommands.cxx
+++ b/src/command/PlayerCommands.cxx
@@ -60,7 +60,7 @@
 #define COMMAND_STATUS_UPDATING_DB	"updating_db"

 CommandResult
-handle_play(Client &client, Request args, gcc_unused Response &r)
+handle_play(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	int song = args.ParseOptional(0, -1);

@@ -69,7 +69,7 @@ handle_play(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_playid(Client &client, Request args, gcc_unused Response &r)
+handle_playid(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	int id = args.ParseOptional(0, -1);

@@ -78,21 +78,21 @@ handle_playid(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_stop(Client &client, gcc_unused Request args, gcc_unused Response &r)
+handle_stop(Client &client, [[maybe_unused]] Request args, [[maybe_unused]] Response &r)
 {
 	client.GetPartition().Stop();
 	return CommandResult::OK;
 }

 CommandResult
-handle_currentsong(Client &client, gcc_unused Request args, Response &r)
+handle_currentsong(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	playlist_print_current(r, client.GetPlaylist());
 	return CommandResult::OK;
 }

 CommandResult
-handle_pause(Client &client, Request args, gcc_unused Response &r)
+handle_pause(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	auto &pc = client.GetPlayerControl();

@@ -106,7 +106,7 @@ handle_pause(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_status(Client &client, gcc_unused Request args, Response &r)
+handle_status(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	auto &partition = client.GetPartition();
 	auto &pc = partition.pc;
@@ -216,7 +216,7 @@ handle_status(Client &client, gcc_unused Request args, Response &r)
 }

 CommandResult
-handle_next(Client &client, gcc_unused Request args, gcc_unused Response &r)
+handle_next(Client &client, [[maybe_unused]] Request args, [[maybe_unused]] Response &r)
 {
 	playlist &playlist = client.GetPlaylist();

@@ -234,15 +234,15 @@ handle_next(Client &client, gcc_unused Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_previous(Client &client, gcc_unused Request args,
-		gcc_unused Response &r)
+handle_previous(Client &client, [[maybe_unused]] Request args,
+		[[maybe_unused]] Response &r)
 {
 	client.GetPartition().PlayPrevious();
 	return CommandResult::OK;
 }

 CommandResult
-handle_repeat(Client &client, Request args, gcc_unused Response &r)
+handle_repeat(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	bool status = args.ParseBool(0);
 	client.GetPartition().SetRepeat(status);
@@ -250,7 +250,7 @@ handle_repeat(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_single(Client &client, Request args, gcc_unused Response &r)
+handle_single(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	auto new_mode = SingleFromString(args.front());
 	client.GetPartition().SetSingle(new_mode);
@@ -258,7 +258,7 @@ handle_single(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_consume(Client &client, Request args, gcc_unused Response &r)
+handle_consume(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	bool status = args.ParseBool(0);
 	client.GetPartition().SetConsume(status);
@@ -266,7 +266,7 @@ handle_consume(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_random(Client &client, Request args, gcc_unused Response &r)
+handle_random(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	bool status = args.ParseBool(0);
 	auto &partition = client.GetPartition();
@@ -276,15 +276,15 @@ handle_random(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_clearerror(Client &client, gcc_unused Request args,
-		  gcc_unused Response &r)
+handle_clearerror(Client &client, [[maybe_unused]] Request args,
+		  [[maybe_unused]] Response &r)
 {
 	client.GetPlayerControl().LockClearError();
 	return CommandResult::OK;
 }

 CommandResult
-handle_seek(Client &client, Request args, gcc_unused Response &r)
+handle_seek(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned song = args.ParseUnsigned(0);
 	SongTime seek_time = args.ParseSongTime(1);
@@ -294,7 +294,7 @@ handle_seek(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_seekid(Client &client, Request args, gcc_unused Response &r)
+handle_seekid(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned id = args.ParseUnsigned(0);
 	SongTime seek_time = args.ParseSongTime(1);
@@ -304,7 +304,7 @@ handle_seekid(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_seekcur(Client &client, Request args, gcc_unused Response &r)
+handle_seekcur(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	const char *p = args.front();
 	bool relative = *p == '+' || *p == '-';
@@ -315,7 +315,7 @@ handle_seekcur(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_crossfade(Client &client, Request args, gcc_unused Response &r)
+handle_crossfade(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	FloatDuration duration{args.ParseUnsigned(0)};
 	client.GetPlayerControl().SetCrossFade(duration);
@@ -323,7 +323,7 @@ handle_crossfade(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_mixrampdb(Client &client, Request args, gcc_unused Response &r)
+handle_mixrampdb(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	float db = args.ParseFloat(0);
 	client.GetPlayerControl().SetMixRampDb(db);
@@ -331,7 +331,7 @@ handle_mixrampdb(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_mixrampdelay(Client &client, Request args, gcc_unused Response &r)
+handle_mixrampdelay(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	FloatDuration delay_secs{args.ParseFloat(0)};
 	client.GetPlayerControl().SetMixRampDelay(delay_secs);
@@ -349,7 +349,7 @@ handle_replay_gain_mode(Client &client, Request args, Response &)
 }

 CommandResult
-handle_replay_gain_status(Client &client, gcc_unused Request args,
+handle_replay_gain_status(Client &client, [[maybe_unused]] Request args,
 			  Response &r)
 {
 	r.Format("replay_gain_mode: %s\n",

--- a/src/command/PlaylistCommands.cxx
+++ b/src/command/PlaylistCommands.cxx
@@ -60,14 +60,14 @@ print_spl_list(Response &r, const PlaylistVector &list)
 }

 CommandResult
-handle_save(Client &client, Request args, gcc_unused Response &r)
+handle_save(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	spl_save_playlist(args.front(), client.GetPlaylist());
 	return CommandResult::OK;
 }

 CommandResult
-handle_load(Client &client, Request args, gcc_unused Response &r)
+handle_load(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	const auto uri = LocateUri(UriPluginKind::PLAYLIST, args.front(),
 				   &client
@@ -132,7 +132,7 @@ handle_listplaylistinfo(Client &client, Request args, Response &r)
 }

 CommandResult
-handle_rm(gcc_unused Client &client, Request args, gcc_unused Response &r)
+handle_rm([[maybe_unused]] Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	const char *const name = args.front();

@@ -141,7 +141,7 @@ handle_rm(gcc_unused Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_rename(gcc_unused Client &client, Request args, gcc_unused Response &r)
+handle_rename([[maybe_unused]] Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	const char *const old_name = args[0];
 	const char *const new_name = args[1];
@@ -151,8 +151,8 @@ handle_rename(gcc_unused Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_playlistdelete(gcc_unused Client &client,
-		      Request args, gcc_unused Response &r)
+handle_playlistdelete([[maybe_unused]] Client &client,
+		      Request args, [[maybe_unused]] Response &r)
 {
 	const char *const name = args[0];
 	unsigned from = args.ParseUnsigned(1);
@@ -162,8 +162,8 @@ handle_playlistdelete(gcc_unused Client &client,
 }

 CommandResult
-handle_playlistmove(gcc_unused Client &client,
-		    Request args, gcc_unused Response &r)
+handle_playlistmove([[maybe_unused]] Client &client,
+		    Request args, [[maybe_unused]] Response &r)
 {
 	const char *const name = args.front();
 	unsigned from = args.ParseUnsigned(1);
@@ -174,8 +174,8 @@ handle_playlistmove(gcc_unused Client &client,
 }

 CommandResult
-handle_playlistclear(gcc_unused Client &client,
-		     Request args, gcc_unused Response &r)
+handle_playlistclear([[maybe_unused]] Client &client,
+		     Request args, [[maybe_unused]] Response &r)
 {
 	const char *const name = args.front();

@@ -184,7 +184,7 @@ handle_playlistclear(gcc_unused Client &client,
 }

 CommandResult
-handle_playlistadd(Client &client, Request args, gcc_unused Response &r)
+handle_playlistadd(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	const char *const playlist = args[0];
 	const char *const uri = args[1];
@@ -209,7 +209,7 @@ handle_playlistadd(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_listplaylists(gcc_unused Client &client, gcc_unused Request args,
+handle_listplaylists([[maybe_unused]] Client &client, [[maybe_unused]] Request args,
 		     Response &r)
 {
 	print_spl_list(r, ListPlaylistFiles());

--- a/src/command/QueueCommands.cxx
+++ b/src/command/QueueCommands.cxx
@@ -51,7 +51,7 @@ AddUri(Client &client, const LocatedUri &uri)

 static CommandResult
 AddDatabaseSelection(Client &client, const char *uri,
-		     gcc_unused Response &r)
+		     [[maybe_unused]] Response &r)
 {
 #ifdef ENABLE_DATABASE
 	auto &partition = client.GetPartition();
@@ -179,7 +179,7 @@ handle_rangeid(Client &client, Request args, Response &r)
 }

 CommandResult
-handle_delete(Client &client, Request args, gcc_unused Response &r)
+handle_delete(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	RangeArg range = args.ParseRange(0);
 	client.GetPartition().DeleteRange(range.start, range.end);
@@ -187,7 +187,7 @@ handle_delete(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_deleteid(Client &client, Request args, gcc_unused Response &r)
+handle_deleteid(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned id = args.ParseUnsigned(0);
 	client.GetPartition().DeleteId(id);
@@ -195,14 +195,14 @@ handle_deleteid(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_playlist(Client &client, gcc_unused Request args, Response &r)
+handle_playlist(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	playlist_print_uris(r, client.GetPlaylist());
 	return CommandResult::OK;
 }

 CommandResult
-handle_shuffle(gcc_unused Client &client, Request args, gcc_unused Response &r)
+handle_shuffle([[maybe_unused]] Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	RangeArg range = args.ParseOptional(0, RangeArg::All());
 	client.GetPartition().Shuffle(range.start, range.end);
@@ -210,7 +210,7 @@ handle_shuffle(gcc_unused Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_clear(Client &client, gcc_unused Request args, gcc_unused Response &r)
+handle_clear(Client &client, [[maybe_unused]] Request args, [[maybe_unused]] Response &r)
 {
 	client.GetPartition().ClearQueue();
 	return CommandResult::OK;
@@ -291,7 +291,7 @@ handle_playlistsearch(Client &client, Request args, Response &r)
 }

 CommandResult
-handle_prio(Client &client, Request args, gcc_unused Response &r)
+handle_prio(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned priority = args.ParseUnsigned(0, 0xff);
 	args.shift();
@@ -307,7 +307,7 @@ handle_prio(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_prioid(Client &client, Request args, gcc_unused Response &r)
+handle_prioid(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned priority = args.ParseUnsigned(0, 0xff);
 	args.shift();
@@ -323,7 +323,7 @@ handle_prioid(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_move(Client &client, Request args, gcc_unused Response &r)
+handle_move(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	RangeArg range = args.ParseRange(0);
 	int to = args.ParseInt(1);
@@ -332,7 +332,7 @@ handle_move(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_moveid(Client &client, Request args, gcc_unused Response &r)
+handle_moveid(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned id = args.ParseUnsigned(0);
 	int to = args.ParseInt(1);
@@ -341,7 +341,7 @@ handle_moveid(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_swap(Client &client, Request args, gcc_unused Response &r)
+handle_swap(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned song1 = args.ParseUnsigned(0);
 	unsigned song2 = args.ParseUnsigned(1);
@@ -350,7 +350,7 @@ handle_swap(Client &client, Request args, gcc_unused Response &r)
 }

 CommandResult
-handle_swapid(Client &client, Request args, gcc_unused Response &r)
+handle_swapid(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	unsigned id1 = args.ParseUnsigned(0);
 	unsigned id2 = args.ParseUnsigned(1);

--- a/src/command/StorageCommands.cxx
+++ b/src/command/StorageCommands.cxx
@@ -143,7 +143,7 @@ print_storage_uri(Client &client, Response &r, const Storage &storage)
 }

 CommandResult
-handle_listmounts(Client &client, gcc_unused Request args, Response &r)
+handle_listmounts(Client &client, [[maybe_unused]] Request args, Response &r)
 {
 	Storage *_composite = client.GetInstance().storage;
 	if (_composite == nullptr) {

--- a/src/db/Interface.hxx
+++ b/src/db/Interface.hxx
@@ -126,8 +126,8 @@ public:
 	 *
 	 * @return the job id or 0 if not implemented
 	 */
-	virtual unsigned Update(gcc_unused const char *uri_utf8,
-				gcc_unused bool discard) {
+	virtual unsigned Update([[maybe_unused]] const char *uri_utf8,
+				[[maybe_unused]] bool discard) {
 		/* not implemented: return 0 */
 		return 0;
 	}

--- a/src/db/plugins/ProxyDatabasePlugin.cxx
+++ b/src/db/plugins/ProxyDatabasePlugin.cxx
@@ -575,7 +575,7 @@ ProxyDatabase::Disconnect() noexcept
 }

 bool
-ProxyDatabase::OnSocketReady(gcc_unused unsigned flags) noexcept
+ProxyDatabase::OnSocketReady([[maybe_unused]] unsigned flags) noexcept
 {
 	assert(connection != nullptr);


--- a/src/db/plugins/simple/SimpleDatabasePlugin.cxx
+++ b/src/db/plugins/simple/SimpleDatabasePlugin.cxx
@@ -70,7 +70,7 @@ inline SimpleDatabase::SimpleDatabase(const ConfigBlock &block)

 inline SimpleDatabase::SimpleDatabase(AllocatedPath &&_path,
 #ifndef ENABLE_ZLIB
-				      gcc_unused
+				      [[maybe_unused]]
 #endif
 				      bool _compress) noexcept
 	:Database(simple_db_plugin),
@@ -85,7 +85,7 @@ inline SimpleDatabase::SimpleDatabase(AllocatedPath &&_path,

 DatabasePtr
 SimpleDatabase::Create(EventLoop &, EventLoop &,
-		       gcc_unused DatabaseListener &listener,
+		       [[maybe_unused]] DatabaseListener &listener,
 		       const ConfigBlock &block)
 {
 	return std::make_unique<SimpleDatabase>(block);
@@ -248,7 +248,7 @@ SimpleDatabase::GetSong(const char *uri) const
 }

 void
-SimpleDatabase::ReturnSong(gcc_unused const LightSong *song) const noexcept
+SimpleDatabase::ReturnSong([[maybe_unused]] const LightSong *song) const noexcept
 {
 	assert(song != nullptr);
 	assert(song == prefixed_light_song || song == &light_song.Get());

--- a/src/db/plugins/upnp/UpnpDatabasePlugin.cxx
+++ b/src/db/plugins/upnp/UpnpDatabasePlugin.cxx
@@ -145,7 +145,7 @@ private:

 DatabasePtr
 UpnpDatabase::Create(EventLoop &, EventLoop &io_event_loop,
-		     gcc_unused DatabaseListener &listener,
+		     [[maybe_unused]] DatabaseListener &listener,
 		     const ConfigBlock &) noexcept
 {
 	return std::make_unique<UpnpDatabase>(io_event_loop);

--- a/src/db/update/InotifySource.cxx
+++ b/src/db/update/InotifySource.cxx
@@ -31,7 +31,7 @@
 #include <sys/inotify.h>

 bool
-InotifySource::OnSocketReady(gcc_unused unsigned flags) noexcept
+InotifySource::OnSocketReady([[maybe_unused]] unsigned flags) noexcept
 {
 	uint8_t buffer[4096];
 	static_assert(sizeof(buffer) >= sizeof(struct inotify_event) + NAME_MAX + 1,

--- a/src/db/update/InotifyUpdate.cxx
+++ b/src/db/update/InotifyUpdate.cxx
@@ -236,7 +236,7 @@ WatchDirectory::GetDepth() const noexcept

 static void
 mpd_inotify_callback(int wd, unsigned mask,
-		     gcc_unused const char *name, gcc_unused void *ctx)
+		     [[maybe_unused]] const char *name, [[maybe_unused]] void *ctx)
 {
 	WatchDirectory *directory;


--- a/src/db/update/Walk.hxx
+++ b/src/db/update/Walk.hxx
@@ -111,10 +111,10 @@ private:


 #else
-	bool UpdateArchiveFile(gcc_unused Directory &directory,
-			       gcc_unused const char *name,
-			       gcc_unused const char *suffix,
-			       gcc_unused const StorageFileInfo &info) noexcept {
+	bool UpdateArchiveFile([[maybe_unused]] Directory &directory,
+			       [[maybe_unused]] const char *name,
+			       [[maybe_unused]] const char *suffix,
+			       [[maybe_unused]] const StorageFileInfo &info) noexcept {
 		return false;
 	}
 #endif

--- a/src/decoder/plugins/FlacDecoderPlugin.cxx
+++ b/src/decoder/plugins/FlacDecoderPlugin.cxx
@@ -53,7 +53,7 @@ static void flacPrintErroredState(FLAC__StreamDecoderState state)
 	LogError(flac_domain, FLAC__StreamDecoderStateString[state]);
 }

-static void flacMetadata(gcc_unused const FLAC__StreamDecoder * dec,
+static void flacMetadata([[maybe_unused]] const FLAC__StreamDecoder * dec,
 			 const FLAC__StreamMetadata * block, void *vdata)
 {
 	auto &fd = *(FlacDecoder *)vdata;
@@ -307,7 +307,7 @@ flac_decode(DecoderClient &client, InputStream &input_stream)
 }

 static bool
-oggflac_init(gcc_unused const ConfigBlock &block)
+oggflac_init([[maybe_unused]] const ConfigBlock &block)
 {
 	return !!FLAC_API_SUPPORTS_OGG_FLAC;
 }

--- a/src/decoder/plugins/FlacInput.cxx
+++ b/src/decoder/plugins/FlacInput.cxx
@@ -98,7 +98,7 @@ FlacInput::Error(FLAC__StreamDecoderErrorStatus status)
 }

 FLAC__StreamDecoderReadStatus
-FlacInput::Read(gcc_unused const FLAC__StreamDecoder *flac_decoder,
+FlacInput::Read([[maybe_unused]] const FLAC__StreamDecoder *flac_decoder,
 		FLAC__byte buffer[], size_t *bytes,
 		void *client_data)
 {
@@ -108,7 +108,7 @@ FlacInput::Read(gcc_unused const FLAC__StreamDecoder *flac_decoder,
 }

 FLAC__StreamDecoderSeekStatus
-FlacInput::Seek(gcc_unused const FLAC__StreamDecoder *flac_decoder,
+FlacInput::Seek([[maybe_unused]] const FLAC__StreamDecoder *flac_decoder,
 		FLAC__uint64 absolute_byte_offset, void *client_data)
 {
 	auto *i = (FlacInput *)client_data;
@@ -117,7 +117,7 @@ FlacInput::Seek(gcc_unused const FLAC__StreamDecoder *flac_decoder,
 }

 FLAC__StreamDecoderTellStatus
-FlacInput::Tell(gcc_unused const FLAC__StreamDecoder *flac_decoder,
+FlacInput::Tell([[maybe_unused]] const FLAC__StreamDecoder *flac_decoder,
 		FLAC__uint64 *absolute_byte_offset, void *client_data)
 {
 	auto *i = (FlacInput *)client_data;
@@ -126,7 +126,7 @@ FlacInput::Tell(gcc_unused const FLAC__StreamDecoder *flac_decoder,
 }

 FLAC__StreamDecoderLengthStatus
-FlacInput::Length(gcc_unused const FLAC__StreamDecoder *flac_decoder,
+FlacInput::Length([[maybe_unused]] const FLAC__StreamDecoder *flac_decoder,
 		  FLAC__uint64 *stream_length, void *client_data)
 {
 	auto *i = (FlacInput *)client_data;
@@ -135,7 +135,7 @@ FlacInput::Length(gcc_unused const FLAC__StreamDecoder *flac_decoder,
 }

 FLAC__bool
-FlacInput::Eof(gcc_unused const FLAC__StreamDecoder *flac_decoder,
+FlacInput::Eof([[maybe_unused]] const FLAC__StreamDecoder *flac_decoder,
 	       void *client_data)
 {
 	auto *i = (FlacInput *)client_data;
@@ -144,7 +144,7 @@ FlacInput::Eof(gcc_unused const FLAC__StreamDecoder *flac_decoder,
 }

 void
-FlacInput::Error(gcc_unused const FLAC__StreamDecoder *decoder,
+FlacInput::Error([[maybe_unused]] const FLAC__StreamDecoder *decoder,
 		 FLAC__StreamDecoderErrorStatus status, void *client_data)
 {
 	auto *i = (FlacInput *)client_data;

--- a/src/decoder/plugins/FluidsynthDecoderPlugin.cxx
+++ b/src/decoder/plugins/FluidsynthDecoderPlugin.cxx
@@ -196,7 +196,7 @@ fluidsynth_file_decode(DecoderClient &client, Path path_fs)

 static bool
 fluidsynth_scan_file(Path path_fs,
-		     gcc_unused TagHandler &handler) noexcept
+		     [[maybe_unused]] TagHandler &handler) noexcept
 {
 	return fluid_is_midifile(path_fs.c_str());
 }

--- a/src/decoder/plugins/GmeDecoderPlugin.cxx
+++ b/src/decoder/plugins/GmeDecoderPlugin.cxx
@@ -62,7 +62,7 @@ static int gme_accuracy;
 #endif

 static bool
-gme_plugin_init(gcc_unused const ConfigBlock &block)
+gme_plugin_init([[maybe_unused]] const ConfigBlock &block)
 {
 #if GME_VERSION >= 0x000600
 	auto accuracy = block.GetBlockParam("accuracy");

--- a/src/decoder/plugins/Mpg123DecoderPlugin.cxx
+++ b/src/decoder/plugins/Mpg123DecoderPlugin.cxx
@@ -37,7 +37,7 @@
 static constexpr Domain mpg123_domain("mpg123");

 static bool
-mpd_mpg123_init(gcc_unused const ConfigBlock &block)
+mpd_mpg123_init([[maybe_unused]] const ConfigBlock &block)
 {
 	mpg123_init();


--- a/src/decoder/plugins/OpusDecoderPlugin.cxx
+++ b/src/decoder/plugins/OpusDecoderPlugin.cxx
@@ -64,7 +64,7 @@ IsOpusTags(const ogg_packet &packet) noexcept
 }

 bool
-mpd_opus_init(gcc_unused const ConfigBlock &block)
+mpd_opus_init([[maybe_unused]] const ConfigBlock &block)
 {
 	LogDebug(opus_domain, opus_get_version_string());


--- a/src/decoder/plugins/SndfileDecoderPlugin.cxx
+++ b/src/decoder/plugins/SndfileDecoderPlugin.cxx
@@ -34,7 +34,7 @@
 static constexpr Domain sndfile_domain("sndfile");

 static bool
-sndfile_init(gcc_unused const ConfigBlock &block)
+sndfile_init([[maybe_unused]] const ConfigBlock &block)
 {
       LogDebug(sndfile_domain, sf_version_string());
       return true;
@@ -109,9 +109,9 @@ sndfile_vio_read(void *ptr, sf_count_t count, void *user_data)
 }

 static sf_count_t
-sndfile_vio_write(gcc_unused const void *ptr,
-		  gcc_unused sf_count_t count,
-		  gcc_unused void *user_data)
+sndfile_vio_write([[maybe_unused]] const void *ptr,
+		  [[maybe_unused]] sf_count_t count,
+		  [[maybe_unused]] void *user_data)
 {
 	/* no writing! */
 	return -1;

--- a/src/decoder/plugins/VorbisDecoderPlugin.cxx
+++ b/src/decoder/plugins/VorbisDecoderPlugin.cxx
@@ -311,7 +311,7 @@ VorbisDecoder::OnOggEnd()
 /* public */

 static bool
-vorbis_init(gcc_unused const ConfigBlock &block)
+vorbis_init([[maybe_unused]] const ConfigBlock &block)
 {
 #ifndef HAVE_TREMOR
 	LogDebug(vorbis_domain, vorbis_version_string());

--- a/src/decoder/plugins/WavpackDecoderPlugin.cxx
+++ b/src/decoder/plugins/WavpackDecoderPlugin.cxx
@@ -143,7 +143,7 @@ format_samples_int(void *buffer, uint32_t count)
 * No conversion necessary.
 */
 static void
-format_samples_nop(gcc_unused void *buffer, gcc_unused uint32_t count)
+format_samples_nop([[maybe_unused]] void *buffer, [[maybe_unused]] uint32_t count)
 {
 	/* do nothing */
 }

--- a/src/encoder/EncoderInterface.hxx
+++ b/src/encoder/EncoderInterface.hxx
@@ -84,7 +84,7 @@ public:
 	 *
 	 * @param tag the tag object
 	 */
-	virtual void SendTag(gcc_unused const Tag &tag) {
+	virtual void SendTag([[maybe_unused]] const Tag &tag) {
 	}

 	/**

--- a/src/encoder/plugins/FlacEncoderPlugin.cxx
+++ b/src/encoder/plugins/FlacEncoderPlugin.cxx
@@ -69,8 +69,8 @@ private:
 	static FLAC__StreamEncoderWriteStatus WriteCallback(const FLAC__StreamEncoder *,
 							    const FLAC__byte data[],
 							    size_t bytes,
-							    gcc_unused unsigned samples,
-							    gcc_unused unsigned current_frame,
+							    [[maybe_unused]] unsigned samples,
+							    [[maybe_unused]] unsigned current_frame,
 							    void *client_data) noexcept {
 		auto &encoder = *(FlacEncoder *)client_data;
 		encoder.output_buffer.Append((const uint8_t *)data, bytes);

--- a/src/encoder/plugins/NullEncoderPlugin.cxx
+++ b/src/encoder/plugins/NullEncoderPlugin.cxx
@@ -49,7 +49,7 @@ public:
 };

 static PreparedEncoder *
-null_encoder_init(gcc_unused const ConfigBlock &block)
+null_encoder_init([[maybe_unused]] const ConfigBlock &block)
 {
 	return new PreparedNullEncoder();
 }

--- a/src/encoder/plugins/WaveEncoderPlugin.cxx
+++ b/src/encoder/plugins/WaveEncoderPlugin.cxx
@@ -98,7 +98,7 @@ fill_wave_header(WaveHeader *header, int channels, int bits,
 }

 static PreparedEncoder *
-wave_encoder_init(gcc_unused const ConfigBlock &block)
+wave_encoder_init([[maybe_unused]] const ConfigBlock &block)
 {
 	return new PreparedWaveEncoder();
 }

--- a/src/event/Loop.cxx
+++ b/src/event/Loop.cxx
@@ -271,7 +271,7 @@ EventLoop::HandleDeferred() noexcept
 }

 bool
-EventLoop::OnSocketReady(gcc_unused unsigned flags) noexcept
+EventLoop::OnSocketReady([[maybe_unused]] unsigned flags) noexcept
 {
 	assert(IsInside());


--- a/src/event/PollGroupEpoll.hxx
+++ b/src/event/PollGroupEpoll.hxx
@@ -89,7 +89,7 @@ public:
 		return epoll.Remove(fd);
 	}

-	bool Abandon(gcc_unused int fd) noexcept {
+	bool Abandon([[maybe_unused]] int fd) noexcept {
 		// Nothing to do in this implementation.
 		// Closed descriptors are automatically unregistered.
 		return true;

--- a/src/event/ServerSocket.cxx
+++ b/src/event/ServerSocket.cxx
@@ -161,7 +161,7 @@ ServerSocket::OneServerSocket::Accept() noexcept
 }

 bool
-ServerSocket::OneServerSocket::OnSocketReady(gcc_unused unsigned flags) noexcept
+ServerSocket::OneServerSocket::OnSocketReady([[maybe_unused]] unsigned flags) noexcept
 {
 	Accept();
 	return true;

--- a/src/filter/Observer.cxx
+++ b/src/filter/Observer.cxx
@@ -43,7 +43,7 @@ public:
 		observer.proxy = nullptr;
 	}

-	void Clear(gcc_unused Proxy *_child) noexcept {
+	void Clear([[maybe_unused]] Proxy *_child) noexcept {
 		assert(child == _child);
 		child = nullptr;
 	}

--- a/src/filter/plugins/NormalizeFilterPlugin.cxx
+++ b/src/filter/plugins/NormalizeFilterPlugin.cxx
@@ -53,7 +53,7 @@ public:
 };

 static std::unique_ptr<PreparedFilter>
-normalize_filter_init(gcc_unused const ConfigBlock &block)
+normalize_filter_init([[maybe_unused]] const ConfigBlock &block)
 {
 	return std::make_unique<PreparedNormalizeFilter>();
 }

--- a/src/filter/plugins/NullFilterPlugin.cxx
+++ b/src/filter/plugins/NullFilterPlugin.cxx
@@ -38,7 +38,7 @@ public:
 };

 static std::unique_ptr<PreparedFilter>
-null_filter_init(gcc_unused const ConfigBlock &block)
+null_filter_init([[maybe_unused]] const ConfigBlock &block)
 {
 	return std::make_unique<PreparedNullFilter>();
 }

--- a/src/fs/io/FileOutputStream.cxx
+++ b/src/fs/io/FileOutputStream.cxx
@@ -81,7 +81,7 @@ FileOutputStream::Open()
 #ifdef _WIN32

 inline void
-FileOutputStream::OpenCreate(gcc_unused bool visible)
+FileOutputStream::OpenCreate([[maybe_unused]] bool visible)
 {
 	handle = CreateFile(path.c_str(), GENERIC_WRITE, 0, nullptr,
 			    CREATE_ALWAYS,

--- a/src/input/InputStream.cxx
+++ b/src/input/InputStream.cxx
@@ -69,7 +69,7 @@ InputStream::CheapSeeking() const noexcept
 }

 void
-InputStream::Seek(std::unique_lock<Mutex> &, gcc_unused offset_type new_offset)
+InputStream::Seek(std::unique_lock<Mutex> &, [[maybe_unused]] offset_type new_offset)
 {
 	throw std::runtime_error("Seeking is not implemented");
 }

--- a/src/input/plugins/AlsaInputPlugin.cxx
+++ b/src/input/plugins/AlsaInputPlugin.cxx
@@ -110,7 +110,7 @@ protected:
 		InvalidateSockets();
 	}

-	void DoSeek(gcc_unused offset_type new_offset) override {
+	void DoSeek([[maybe_unused]] offset_type new_offset) override {
 		/* unreachable because seekable==false */
 		SeekDone();
 	}

--- a/src/lib/curl/Global.cxx
+++ b/src/lib/curl/Global.cxx
@@ -108,7 +108,7 @@ CurlGlobal::CurlGlobal(EventLoop &_loop)
 }

 int
-CurlSocket::SocketFunction(gcc_unused CURL *easy,
+CurlSocket::SocketFunction([[maybe_unused]] CURL *easy,
 			   curl_socket_t s, int action,
 			   void *userp, void *socketp) noexcept
 {
@@ -230,7 +230,7 @@ CurlGlobal::UpdateTimeout(long timeout_ms) noexcept
 }

 int
-CurlGlobal::TimerFunction(gcc_unused CURLM *_multi, long timeout_ms,
+CurlGlobal::TimerFunction([[maybe_unused]] CURLM *_multi, long timeout_ms,
 			  void *userp) noexcept
 {
 	auto &global = *(CurlGlobal *)userp;

--- a/src/lib/ffmpeg/LogCallback.cxx
+++ b/src/lib/ffmpeg/LogCallback.cxx
@@ -47,7 +47,7 @@ FfmpegImportLogLevel(int level) noexcept
 }

 void
-FfmpegLogCallback(gcc_unused void *ptr, int level, const char *fmt, std::va_list vl)
+FfmpegLogCallback(void *ptr, int level, const char *fmt, std::va_list vl)
 {
 	const AVClass * cls = nullptr;


--- a/src/lib/nfs/Connection.cxx
+++ b/src/lib/nfs/Connection.cxx
@@ -172,7 +172,7 @@ NfsConnection::CancellableCallback::Callback(int err, void *data) noexcept

 void
 NfsConnection::CancellableCallback::Callback(int err,
-					     gcc_unused struct nfs_context *nfs,
+					     [[maybe_unused]] struct nfs_context *nfs,
 					     void *data,
 					     void *private_data) noexcept
 {
@@ -551,8 +551,8 @@ NfsConnection::OnSocketReady(unsigned flags) noexcept
 }

 inline void
-NfsConnection::MountCallback(int status, gcc_unused nfs_context *nfs,
-			     gcc_unused void *data) noexcept
+NfsConnection::MountCallback(int status, [[maybe_unused]] nfs_context *nfs,
+			     [[maybe_unused]] void *data) noexcept
 {
 	assert(GetEventLoop().IsInside());
 	assert(context == nfs);

--- a/src/lib/smbclient/Init.cxx
+++ b/src/lib/smbclient/Init.cxx
@@ -27,11 +27,11 @@
 #include <string.h>

 static void
-mpd_smbc_get_auth_data(gcc_unused const char *srv,
-		       gcc_unused const char *shr,
-		       char *wg, gcc_unused int wglen,
-		       char *un, gcc_unused int unlen,
-		       char *pw, gcc_unused int pwlen)
+mpd_smbc_get_auth_data([[maybe_unused]] const char *srv,
+		       [[maybe_unused]] const char *shr,
+		       char *wg, [[maybe_unused]] int wglen,
+		       char *un, [[maybe_unused]] int unlen,
+		       char *pw, [[maybe_unused]] int pwlen)
 {
 	// TODO: implement
 	strcpy(wg, "WORKGROUP");

--- a/src/lib/sqlite/Util.hxx
+++ b/src/lib/sqlite/Util.hxx
@@ -54,7 +54,7 @@ Bind(sqlite3_stmt *stmt, unsigned i, const char *value)

 template<typename... Args>
 static void
-BindAll2(gcc_unused sqlite3_stmt *stmt, gcc_unused unsigned i)
+BindAll2([[maybe_unused]] sqlite3_stmt *stmt, [[maybe_unused]] unsigned i)
 {
 	assert(int(i - 1) == sqlite3_bind_parameter_count(stmt));
 }

--- a/src/lib/upnp/Action.hxx
+++ b/src/lib/upnp/Action.hxx
@@ -32,7 +32,7 @@ CountNameValuePairs() noexcept

 template<typename... Args>
 static constexpr unsigned
-CountNameValuePairs(gcc_unused const char *name, gcc_unused const char *value,
+CountNameValuePairs([[maybe_unused]] const char *name, [[maybe_unused]] const char *value,
 		    Args... args) noexcept
 {
 	return 1 + CountNameValuePairs(args...);

--- a/src/lib/xiph/FlacIOHandle.cxx
+++ b/src/lib/xiph/FlacIOHandle.cxx
@@ -119,7 +119,7 @@ FlacIOEof(FLAC__IOHandle handle)
 }

 static int
-FlacIOClose(gcc_unused FLAC__IOHandle handle)
+FlacIOClose([[maybe_unused]] FLAC__IOHandle handle)
 {
 	/* no-op because the libFLAC caller is responsible for closing
 	   the #InputStream */

--- a/src/mixer/plugins/AlsaMixerPlugin.cxx
+++ b/src/mixer/plugins/AlsaMixerPlugin.cxx
@@ -173,7 +173,7 @@ AlsaMixer::Configure(const ConfigBlock &block)
 }

 static Mixer *
-alsa_mixer_init(EventLoop &event_loop, gcc_unused AudioOutput &ao,
+alsa_mixer_init(EventLoop &event_loop, [[maybe_unused]] AudioOutput &ao,
 		MixerListener &listener,
 		const ConfigBlock &block)
 {

--- a/src/mixer/plugins/HaikuMixerPlugin.cxx
+++ b/src/mixer/plugins/HaikuMixerPlugin.cxx
@@ -47,9 +47,9 @@ public:
 };

 static Mixer *
-haiku_mixer_init(gcc_unused EventLoop &event_loop, AudioOutput &ao,
+haiku_mixer_init([[maybe_unused]] EventLoop &event_loop, AudioOutput &ao,
 		MixerListener &listener,
-		gcc_unused const ConfigBlock &block)
+		[[maybe_unused]] const ConfigBlock &block)
 {
 	return new HaikuMixer((HaikuOutput &)ao, listener);
 }

--- a/src/mixer/plugins/NullMixerPlugin.cxx
+++ b/src/mixer/plugins/NullMixerPlugin.cxx
@@ -49,10 +49,10 @@ public:
 };

 static Mixer *
-null_mixer_init(gcc_unused EventLoop &event_loop,
-		gcc_unused AudioOutput &ao,
+null_mixer_init([[maybe_unused]] EventLoop &event_loop,
+		[[maybe_unused]] AudioOutput &ao,
 		MixerListener &listener,
-		gcc_unused const ConfigBlock &block)
+		[[maybe_unused]] const ConfigBlock &block)
 {
 	return new NullMixer(listener);
 }

--- a/src/mixer/plugins/OSXMixerPlugin.cxx
+++ b/src/mixer/plugins/OSXMixerPlugin.cxx
@@ -54,9 +54,9 @@ OSXMixer::SetVolume(unsigned new_volume)
 }

 static Mixer *
-osx_mixer_init(gcc_unused EventLoop &event_loop, AudioOutput &ao,
+osx_mixer_init([[maybe_unused]] EventLoop &event_loop, AudioOutput &ao,
 		MixerListener &listener,
-		gcc_unused const ConfigBlock &block)
+		[[maybe_unused]] const ConfigBlock &block)
 {
 	OSXOutput &osxo = (OSXOutput &)ao;
 	return new OSXMixer(osxo, listener);

--- a/src/mixer/plugins/OssMixerPlugin.cxx
+++ b/src/mixer/plugins/OssMixerPlugin.cxx
@@ -97,8 +97,8 @@ OssMixer::Configure(const ConfigBlock &block)
 }

 static Mixer *
-oss_mixer_init(gcc_unused EventLoop &event_loop,
-	       gcc_unused AudioOutput &ao,
+oss_mixer_init([[maybe_unused]] EventLoop &event_loop,
+	       [[maybe_unused]] AudioOutput &ao,
 	       MixerListener &listener,
 	       const ConfigBlock &block)
 {

--- a/src/mixer/plugins/PulseMixerPlugin.cxx
+++ b/src/mixer/plugins/PulseMixerPlugin.cxx
@@ -104,7 +104,7 @@ PulseMixer::VolumeCallback(const pa_sink_input_info *i, int eol)
 * value.
 */
 static void
-pulse_mixer_volume_cb(gcc_unused pa_context *context, const pa_sink_input_info *i,
+pulse_mixer_volume_cb([[maybe_unused]] pa_context *context, const pa_sink_input_info *i,
 		      int eol, void *userdata)
 {
 	auto *pm = (PulseMixer *)userdata;
@@ -133,7 +133,7 @@ PulseMixer::Update(pa_context *context, pa_stream *stream)
 }

 void
-pulse_mixer_on_connect(gcc_unused PulseMixer &pm,
+pulse_mixer_on_connect([[maybe_unused]] PulseMixer &pm,
 		       struct pa_context *context)
 {
 	pa_operation *o;
@@ -182,7 +182,7 @@ parse_volume_scale_factor(const char *value) {
 }

 static Mixer *
-pulse_mixer_init(gcc_unused EventLoop &event_loop, AudioOutput &ao,
+pulse_mixer_init([[maybe_unused]] EventLoop &event_loop, AudioOutput &ao,
 		 MixerListener &listener,
 		 const ConfigBlock &block)
 {

--- a/src/mixer/plugins/SndioMixerPlugin.cxx
+++ b/src/mixer/plugins/SndioMixerPlugin.cxx
@@ -45,10 +45,10 @@ public:
 };

 static Mixer *
-sndio_mixer_init(gcc_unused EventLoop &event_loop,
+sndio_mixer_init([[maybe_unused]] EventLoop &event_loop,
 		AudioOutput &ao,
 		MixerListener &listener,
-		gcc_unused const ConfigBlock &block)
+		[[maybe_unused]] const ConfigBlock &block)
 {
 	return new SndioMixer((SndioOutput &)ao, listener);
 }

--- a/src/mixer/plugins/SoftwareMixerPlugin.cxx
+++ b/src/mixer/plugins/SoftwareMixerPlugin.cxx
@@ -57,10 +57,10 @@ public:
 };

 static Mixer *
-software_mixer_init(gcc_unused EventLoop &event_loop,
-		    gcc_unused AudioOutput &ao,
+software_mixer_init([[maybe_unused]] EventLoop &event_loop,
+		    [[maybe_unused]] AudioOutput &ao,
 		    MixerListener &listener,
-		    gcc_unused const ConfigBlock &block)
+		    [[maybe_unused]] const ConfigBlock &block)
 {
 	return new SoftwareMixer(listener);
 }

--- a/src/mixer/plugins/WinmmMixerPlugin.cxx
+++ b/src/mixer/plugins/WinmmMixerPlugin.cxx
@@ -63,9 +63,9 @@ winmm_volume_encode(int volume)
 }

 static Mixer *
-winmm_mixer_init(gcc_unused EventLoop &event_loop, AudioOutput &ao,
+winmm_mixer_init([[maybe_unused]] EventLoop &event_loop, AudioOutput &ao,
 		 MixerListener &listener,
-		 gcc_unused const ConfigBlock &block)
+		 [[maybe_unused]] const ConfigBlock &block)
 {
 	return new WinmmMixer((WinmmOutput &)ao, listener);
 }

--- a/src/neighbor/plugins/SmbclientNeighborPlugin.cxx
+++ b/src/neighbor/plugins/SmbclientNeighborPlugin.cxx
@@ -252,9 +252,9 @@ SmbclientNeighborExplorer::ThreadFunc() noexcept
 }

 static std::unique_ptr<NeighborExplorer>
-smbclient_neighbor_create(gcc_unused EventLoop &loop,
+smbclient_neighbor_create([[maybe_unused]] EventLoop &loop,
 			  NeighborListener &listener,
-			  gcc_unused const ConfigBlock &block)
+			  [[maybe_unused]] const ConfigBlock &block)
 {
 	SmbclientInit();


--- a/src/neighbor/plugins/UdisksNeighborPlugin.cxx
+++ b/src/neighbor/plugins/UdisksNeighborPlugin.cxx
@@ -259,7 +259,7 @@ UdisksNeighborExplorer::HandleMessage(DBusConnection *connection,
 static std::unique_ptr<NeighborExplorer>
 udisks_neighbor_create(EventLoop &event_loop,
 		     NeighborListener &listener,
-		     gcc_unused const ConfigBlock &block)
+		     [[maybe_unused]] const ConfigBlock &block)
 {
 	return std::make_unique<UdisksNeighborExplorer>(event_loop, listener);
 }

--- a/src/neighbor/plugins/UpnpNeighborPlugin.cxx
+++ b/src/neighbor/plugins/UpnpNeighborPlugin.cxx
@@ -127,7 +127,7 @@ UpnpNeighborExplorer::LostUPnP(const ContentDirectoryService &service)
 static std::unique_ptr<NeighborExplorer>
 upnp_neighbor_create(EventLoop &event_loop,
 		     NeighborListener &listener,
-		     gcc_unused const ConfigBlock &block)
+		     [[maybe_unused]] const ConfigBlock &block)
 {
 	return std::make_unique<UpnpNeighborExplorer>(event_loop, listener);
 }

--- a/src/output/Interface.cxx
+++ b/src/output/Interface.cxx
@@ -23,8 +23,8 @@
 #include <stdexcept>

 void
-AudioOutput::SetAttribute(gcc_unused std::string &&name,
-			  gcc_unused std::string &&value)
+AudioOutput::SetAttribute([[maybe_unused]] std::string &&name,
+			  [[maybe_unused]] std::string &&value)
 {
 	throw std::invalid_argument("Unsupported attribute");
 }
--- a/src/output/SharedPipeConsumer.hxx
+++ b/src/output/SharedPipeConsumer.hxx
@@ -76,7 +76,7 @@ public:

 	const MusicChunk *Get() noexcept;

-	void Consume(gcc_unused const MusicChunk &_chunk) {
+	void Consume([[maybe_unused]] const MusicChunk &_chunk) {
 		assert(chunk != nullptr);
 		assert(chunk == &_chunk);

@@ -86,7 +86,7 @@ public:
 	gcc_pure
 	bool IsConsumed(const MusicChunk &_chunk) const noexcept;

-	void ClearTail(gcc_unused const MusicChunk &_chunk) noexcept {
+	void ClearTail([[maybe_unused]] const MusicChunk &_chunk) noexcept {
 		assert(chunk == &_chunk);
 		assert(consumed);
 		chunk = nullptr;

--- a/src/output/plugins/HaikuOutputPlugin.cxx
+++ b/src/output/plugins/HaikuOutputPlugin.cxx
@@ -81,9 +81,9 @@ private:
 	std::chrono::steady_clock::duration Delay() const noexcept override;

 	static void _FillBuffer(void* cookie, void* _buffer, size_t size,
-		gcc_unused const media_raw_audio_format& _format);
+		[[maybe_unused]] const media_raw_audio_format& _format);
 	void FillBuffer(void* _buffer, size_t size,
-		gcc_unused const media_raw_audio_format& _format);
+		[[maybe_unused]] const media_raw_audio_format& _format);

 	void SendTag(const Tag &tag) override;
 };
@@ -154,7 +154,7 @@ HaikuOutput::_FillBuffer(void* cookie, void* buffer, size_t size,

 void
 HaikuOutput::FillBuffer(void* _buffer, size_t size,
-	gcc_unused const media_raw_audio_format& _format)
+	[[maybe_unused]] const media_raw_audio_format& _format)
 {

 	buffer = (uint8*)_buffer;

--- a/src/output/plugins/NullOutputPlugin.cxx
+++ b/src/output/plugins/NullOutputPlugin.cxx
@@ -53,7 +53,7 @@ private:
 			: std::chrono::steady_clock::duration::zero();
 	}

-	size_t Play(gcc_unused const void *chunk, size_t size) override {
+	size_t Play([[maybe_unused]] const void *chunk, size_t size) override {
 		if (sync) {
 			if (!timer->IsStarted())
 				timer->Start();

--- a/src/output/plugins/OSXOutputPlugin.cxx
+++ b/src/output/plugins/OSXOutputPlugin.cxx
@@ -710,9 +710,9 @@ osx_output_set_device(OSXOutput *oo)
 */
 static OSStatus
 osx_render(void *vdata,
-	   gcc_unused AudioUnitRenderActionFlags *io_action_flags,
-	   gcc_unused const AudioTimeStamp *in_timestamp,
-	   gcc_unused UInt32 in_bus_number,
+	   [[maybe_unused]] AudioUnitRenderActionFlags *io_action_flags,
+	   [[maybe_unused]] const AudioTimeStamp *in_timestamp,
+	   [[maybe_unused]] UInt32 in_bus_number,
 	   UInt32 in_number_frames,
 	   AudioBufferList *buffer_list)
 {

--- a/src/output/plugins/PipeOutputPlugin.cxx
+++ b/src/output/plugins/PipeOutputPlugin.cxx
@@ -57,7 +57,7 @@ PipeOutput::PipeOutput(const ConfigBlock &block)
 }

 inline void
-PipeOutput::Open(gcc_unused AudioFormat &audio_format)
+PipeOutput::Open([[maybe_unused]] AudioFormat &audio_format)
 {
 	fh = popen(cmd.c_str(), "w");
 	if (fh == nullptr)

--- a/src/output/plugins/PulseOutputPlugin.cxx
+++ b/src/output/plugins/PulseOutputPlugin.cxx
@@ -62,7 +62,7 @@ class PulseOutput final : AudioOutput {
 public:
 	void SetMixer(PulseMixer &_mixer);

-	void ClearMixer(gcc_unused PulseMixer &old_mixer) {
+	void ClearMixer([[maybe_unused]] PulseMixer &old_mixer) {
 		assert(mixer == &old_mixer);

 		mixer = nullptr;
@@ -277,8 +277,8 @@ pulse_wait_for_operation(struct pa_threaded_mainloop *mainloop,
 * the caller thread, to wake pulse_wait_for_operation() up.
 */
 static void
-pulse_output_stream_success_cb(gcc_unused pa_stream *s,
-			       gcc_unused int success, void *userdata)
+pulse_output_stream_success_cb([[maybe_unused]] pa_stream *s,
+			       [[maybe_unused]] int success, void *userdata)
 {
 	PulseOutput &po = *(PulseOutput *)userdata;

@@ -342,7 +342,7 @@ PulseOutput::OnServerLayoutChanged(pa_subscription_event_type_t t,
 }

 static void
-pulse_output_subscribe_cb(gcc_unused pa_context *context,
+pulse_output_subscribe_cb([[maybe_unused]] pa_context *context,
 			  pa_subscription_event_type_t t,
 			  uint32_t idx, void *userdata)
 {
@@ -508,7 +508,7 @@ PulseOutput::WaitConnection()
 }

 inline void
-PulseOutput::OnStreamSuspended(gcc_unused pa_stream *_stream)
+PulseOutput::OnStreamSuspended([[maybe_unused]] pa_stream *_stream)
 {
 	assert(_stream == stream || stream == nullptr);
 	assert(mainloop != nullptr);
@@ -574,7 +574,7 @@ PulseOutput::OnStreamWrite(size_t nbytes)
 }

 static void
-pulse_output_stream_write_cb(gcc_unused pa_stream *stream, size_t nbytes,
+pulse_output_stream_write_cb([[maybe_unused]] pa_stream *stream, size_t nbytes,
 			     void *userdata)
 {
 	PulseOutput &po = *(PulseOutput *)userdata;

--- a/src/output/plugins/httpd/HttpdOutputPlugin.cxx
+++ b/src/output/plugins/httpd/HttpdOutputPlugin.cxx
@@ -121,7 +121,7 @@ HttpdOutput::OnDeferredBroadcast() noexcept

 void
 HttpdOutput::OnAccept(UniqueSocketDescriptor fd,
-		      SocketAddress, gcc_unused int uid) noexcept
+		      SocketAddress, [[maybe_unused]] int uid) noexcept
 {
 	/* the listener socket has become readable - a client has
 	   connected */

--- a/src/output/plugins/sles/SlesOutputPlugin.cxx
+++ b/src/output/plugins/sles/SlesOutputPlugin.cxx
@@ -111,7 +111,7 @@ private:
 	 * been consumed.  It synthesises and enqueues the next
 	 * buffer.
 	 */
-	static void PlayedCallback(gcc_unused SLAndroidSimpleBufferQueueItf caller,
+	static void PlayedCallback([[maybe_unused]] SLAndroidSimpleBufferQueueItf caller,
 				   void *pContext)
 	{
 		SlesOutput &sles = *(SlesOutput *)pContext;

--- a/src/playlist/plugins/EmbeddedCuePlaylistPlugin.cxx
+++ b/src/playlist/plugins/EmbeddedCuePlaylistPlugin.cxx
@@ -82,7 +82,7 @@ ExtractCuesheetTagHandler::OnPair(StringView name, StringView value) noexcept

 static std::unique_ptr<SongEnumerator>
 embcue_playlist_open_uri(const char *uri,
-			 gcc_unused Mutex &mutex)
+			 [[maybe_unused]] Mutex &mutex)
 {
 	if (!PathTraitsUTF8::IsAbsolute(uri))
 		/* only local files supported */

--- a/src/playlist/plugins/XspfPlaylistPlugin.cxx
+++ b/src/playlist/plugins/XspfPlaylistPlugin.cxx
@@ -79,7 +79,7 @@ static constexpr struct tag_table xspf_tag_elements[] = {

 static void XMLCALL
 xspf_start_element(void *user_data, const XML_Char *element_name,
-		   gcc_unused const XML_Char **atts)
+		   [[maybe_unused]] const XML_Char **atts)
 {
 	auto *parser = (XspfParser *)user_data;
 	parser->value.clear();

--- a/src/storage/MemoryDirectoryReader.cxx
+++ b/src/storage/MemoryDirectoryReader.cxx
@@ -36,7 +36,7 @@ MemoryStorageDirectoryReader::Read() noexcept
 }

 StorageFileInfo
-MemoryStorageDirectoryReader::GetInfo(gcc_unused bool follow)
+MemoryStorageDirectoryReader::GetInfo([[maybe_unused]] bool follow)
 {
 	assert(!first);
 	assert(!entries.empty());

--- a/src/storage/StorageInterface.cxx
+++ b/src/storage/StorageInterface.cxx
@@ -22,7 +22,7 @@
 #include "fs/Traits.hxx"

 AllocatedPath
-Storage::MapFS(gcc_unused const char *uri_utf8) const noexcept
+Storage::MapFS([[maybe_unused]] const char *uri_utf8) const noexcept
 {
 	return nullptr;
 }

--- a/src/storage/plugins/CurlStorage.cxx
+++ b/src/storage/plugins/CurlStorage.cxx
@@ -315,7 +315,7 @@ private:

 	/* virtual methods from CommonExpatParser */
 	void StartElement(const XML_Char *name,
-			  gcc_unused const XML_Char **attrs) final {
+			  [[maybe_unused]] const XML_Char **attrs) final {
 		switch (state) {
 		case State::ROOT:
 			if (strcmp(name, "DAV:|response") == 0)
@@ -447,7 +447,7 @@ protected:
 };

 StorageFileInfo
-CurlStorage::GetInfo(const char *uri_utf8, gcc_unused bool follow)
+CurlStorage::GetInfo(const char *uri_utf8, [[maybe_unused]] bool follow)
 {
 	// TODO: escape the given URI


--- a/src/storage/plugins/NfsStorage.cxx
+++ b/src/storage/plugins/NfsStorage.cxx
@@ -288,7 +288,7 @@ protected:
 			connection.Lstat(path, *this);
 	}

-	void HandleResult(gcc_unused unsigned status, void *data) noexcept override {
+	void HandleResult([[maybe_unused]] unsigned status, void *data) noexcept override {
 		Copy(info, *(const struct nfs_stat_64 *)data);
 	}
 };
@@ -356,7 +356,7 @@ protected:
 		connection.OpenDirectory(path, *this);
 	}

-	void HandleResult(gcc_unused unsigned status,
+	void HandleResult([[maybe_unused]] unsigned status,
 			  void *data) noexcept override {
 		auto *const dir = (struct nfsdir *)data;


--- a/src/storage/plugins/SmbclientStorage.cxx
+++ b/src/storage/plugins/SmbclientStorage.cxx
@@ -117,7 +117,7 @@ GetInfo(const char *path)
 }

 StorageFileInfo
-SmbclientStorage::GetInfo(const char *uri_utf8, gcc_unused bool follow)
+SmbclientStorage::GetInfo(const char *uri_utf8, [[maybe_unused]] bool follow)
 {
 	const std::string mapped = MapUTF8(uri_utf8);
 	return ::GetInfo(mapped.c_str());
@@ -172,14 +172,14 @@ SmbclientDirectoryReader::Read() noexcept
 }

 StorageFileInfo
-SmbclientDirectoryReader::GetInfo(gcc_unused bool follow)
+SmbclientDirectoryReader::GetInfo([[maybe_unused]] bool follow)
 {
 	const std::string path = PathTraitsUTF8::Build(base.c_str(), name);
 	return ::GetInfo(path.c_str());
 }

 static std::unique_ptr<Storage>
-CreateSmbclientStorageURI(gcc_unused EventLoop &event_loop, const char *base)
+CreateSmbclientStorageURI([[maybe_unused]] EventLoop &event_loop, const char *base)
 {
 	if (!StringStartsWithCaseASCII(base, "smb://"))
 		return nullptr;

--- a/src/system/EventFD.cxx
+++ b/src/system/EventFD.cxx
@@ -56,6 +56,6 @@ EventFD::Write() noexcept
 	assert(fd.IsDefined());

 	static constexpr eventfd_t value = 1;
-	gcc_unused ssize_t nbytes =
+	[[maybe_unused]] ssize_t nbytes =
 		fd.Write(&value, sizeof(value));
 }
--- a/src/system/EventPipe.cxx
+++ b/src/system/EventPipe.cxx
@@ -85,7 +85,7 @@ EventPipe::Write() noexcept
 #ifdef _WIN32
 	send(fds[1], "", 1, 0);
 #else
-	gcc_unused ssize_t nbytes = write(fds[1], "", 1);
+	[[maybe_unused]] ssize_t nbytes = write(fds[1], "", 1);
 #endif
 }


--- a/src/tag/Handler.cxx
+++ b/src/tag/Handler.cxx
@@ -41,7 +41,7 @@ NullTagHandler::OnPicture(const char *, ConstBuffer<void>) noexcept
 }

 void
-NullTagHandler::OnAudioFormat(gcc_unused AudioFormat af) noexcept
+NullTagHandler::OnAudioFormat([[maybe_unused]] AudioFormat af) noexcept
 {
 }


--- a/src/tag/Handler.hxx
+++ b/src/tag/Handler.hxx
@@ -124,7 +124,7 @@ public:
 	explicit NullTagHandler(unsigned _want_mask) noexcept
 		:TagHandler(_want_mask) {}

-	void OnDuration(gcc_unused SongTime duration) noexcept override {}
+	void OnDuration([[maybe_unused]] SongTime duration) noexcept override {}
 	void OnTag(TagType type, StringView value) noexcept override;
 	void OnPair(StringView key, StringView value) noexcept override;
 	void OnAudioFormat(AudioFormat af) noexcept override;

--- a/src/thread/Name.hxx
+++ b/src/thread/Name.hxx
@@ -58,7 +58,7 @@ SetThreadName(const char *name) noexcept

 template<typename... Args>
 static inline void
-FormatThreadName(const char *fmt, gcc_unused Args&&... args) noexcept
+FormatThreadName(const char *fmt, [[maybe_unused]] Args&&... args) noexcept
 {
 #ifdef HAVE_THREAD_NAME
 	SetThreadName(StringFormat<16>(fmt, args...));

--- a/src/util/Compiler.h
+++ b/src/util/Compiler.h
@@ -74,7 +74,6 @@
 #define gcc_printf(a,b) __attribute__((format(printf, a, b)))
 #define gcc_pure __attribute__((pure))
 #define gcc_sentinel __attribute__((sentinel))
-#define gcc_unused __attribute__((unused))

 #define gcc_nonnull(...) __attribute__((nonnull(__VA_ARGS__)))
 #define gcc_nonnull_all __attribute__((nonnull))
@@ -101,7 +100,6 @@
 #define gcc_printf(a,b)
 #define gcc_pure
 #define gcc_sentinel
-#define gcc_unused

 #define gcc_nonnull(...)
 #define gcc_nonnull_all
@@ -161,12 +159,6 @@
  #define __has_feature(x) 0
 #endif

-#if __has_feature(attribute_unused_on_fields)
-#define gcc_unused_field gcc_unused
-#else
-#define gcc_unused_field
-#endif
-
 #if defined(__GNUC__) || defined(__clang__)
 #define gcc_unreachable() __builtin_unreachable()
 #else

--- a/src/util/UTF8.cxx
+++ b/src/util/UTF8.cxx
@@ -204,7 +204,7 @@ struct CheckSequenceUTF8 {

 template<>
 struct CheckSequenceUTF8<0U> {
-	constexpr bool operator()(gcc_unused const char *p) const noexcept {
+	constexpr bool operator()([[maybe_unused]] const char *p) const noexcept {
 		return true;
 	}
 };

--- a/src/win32/Win32Main.cxx
+++ b/src/win32/Win32Main.cxx
@@ -64,8 +64,8 @@ service_notify_status(DWORD status_code)
 }

 static DWORD WINAPI
-service_dispatcher(gcc_unused DWORD control, gcc_unused DWORD event_type,
-		   gcc_unused void *event_data, gcc_unused void *context)
+service_dispatcher([[maybe_unused]] DWORD control, [[maybe_unused]] DWORD event_type,
+		   [[maybe_unused]] void *event_data, [[maybe_unused]] void *context)
 {
 	switch (control) {
 	case SERVICE_CONTROL_SHUTDOWN:
@@ -78,7 +78,7 @@ service_dispatcher(gcc_unused DWORD control, gcc_unused DWORD event_type,
 }

 static void WINAPI
-service_main(gcc_unused DWORD argc, gcc_unused LPTSTR argv[])
+service_main([[maybe_unused]] DWORD argc, [[maybe_unused]] LPTSTR argv[])
 {
 	service_handle =
 		RegisterServiceCtrlHandlerEx(service_name,

--- a/src/zeroconf/ZeroconfAvahi.cxx
+++ b/src/zeroconf/ZeroconfAvahi.cxx
@@ -49,7 +49,7 @@ AvahiRegisterService(AvahiClient *c);
 static void
 AvahiGroupCallback(AvahiEntryGroup *g,
 		   AvahiEntryGroupState state,
-		   gcc_unused void *userdata)
+		   [[maybe_unused]] void *userdata)
 {
 	assert(g != nullptr);

@@ -149,7 +149,7 @@ AvahiRegisterService(AvahiClient *c)
 /* Callback when avahi changes state */
 static void
 MyAvahiClientCallback(AvahiClient *c, AvahiClientState state,
-		      gcc_unused void *userdata)
+		      [[maybe_unused]] void *userdata)
 {
 	assert(c != nullptr);


--- a/src/zeroconf/ZeroconfBonjour.cxx
+++ b/src/zeroconf/ZeroconfBonjour.cxx
@@ -48,7 +48,7 @@ public:

 protected:
 	/* virtual methods from class SocketMonitor */
-	bool OnSocketReady(gcc_unused unsigned flags) noexcept override {
+	bool OnSocketReady([[maybe_unused]] unsigned flags) noexcept override {
 		DNSServiceProcessResult(service_ref);
 		return true;
 	}
@@ -57,12 +57,12 @@ protected:
 static BonjourMonitor *bonjour_monitor;

 static void
-dnsRegisterCallback(gcc_unused DNSServiceRef sdRef,
-		    gcc_unused DNSServiceFlags flags,
+dnsRegisterCallback([[maybe_unused]] DNSServiceRef sdRef,
+		    [[maybe_unused]] DNSServiceFlags flags,
 		    DNSServiceErrorType errorCode, const char *name,
-		    gcc_unused const char *regtype,
-		    gcc_unused const char *domain,
-		    gcc_unused void *context)
+		    [[maybe_unused]] const char *regtype,
+		    [[maybe_unused]] const char *domain,
+		    [[maybe_unused]] void *context)
 {
 	if (errorCode != kDNSServiceErr_NoError) {
 		LogError(bonjour_domain,

--- a/src/zeroconf/ZeroconfGlue.cxx
+++ b/src/zeroconf/ZeroconfGlue.cxx
@@ -50,7 +50,7 @@ static constexpr Domain zeroconf_domain("zeroconf");
 static int zeroconfEnabled;

 void
-ZeroconfInit(const ConfigData &config, gcc_unused EventLoop &loop)
+ZeroconfInit(const ConfigData &config, [[maybe_unused]] EventLoop &loop)
 {
 	const char *serviceName;


--- a/test/DumpDecoderClient.cxx
+++ b/test/DumpDecoderClient.cxx
@@ -86,26 +86,26 @@ DumpDecoderClient::Read(InputStream &is, void *buffer, size_t length) noexcept
 }

 void
-DumpDecoderClient::SubmitTimestamp(gcc_unused FloatDuration t) noexcept
+DumpDecoderClient::SubmitTimestamp([[maybe_unused]] FloatDuration t) noexcept
 {
 }

 DecoderCommand
-DumpDecoderClient::SubmitData(gcc_unused InputStream *is,
+DumpDecoderClient::SubmitData([[maybe_unused]] InputStream *is,
 			      const void *data, size_t datalen,
-			      gcc_unused uint16_t kbit_rate) noexcept
+			      [[maybe_unused]] uint16_t kbit_rate) noexcept
 {
 	if (kbit_rate != prev_kbit_rate) {
 		prev_kbit_rate = kbit_rate;
 		fprintf(stderr, "%u kbit/s\n", kbit_rate);
 	}

-	gcc_unused ssize_t nbytes = write(STDOUT_FILENO, data, datalen);
+	[[maybe_unused]] ssize_t nbytes = write(STDOUT_FILENO, data, datalen);
 	return GetCommand();
 }

 DecoderCommand
-DumpDecoderClient::SubmitTag(gcc_unused InputStream *is,
+DumpDecoderClient::SubmitTag([[maybe_unused]] InputStream *is,
 			     Tag &&tag) noexcept
 {
 	fprintf(stderr, "TAG: duration=%f\n", tag.duration.ToDoubleS());
@@ -139,7 +139,7 @@ DumpDecoderClient::SubmitReplayGain(const ReplayGainInfo *rgi) noexcept
 }

 void
-DumpDecoderClient::SubmitMixRamp(gcc_unused MixRampInfo &&mix_ramp) noexcept
+DumpDecoderClient::SubmitMixRamp([[maybe_unused]] MixRampInfo &&mix_ramp) noexcept
 {
 	fprintf(stderr, "MixRamp: start='%s' end='%s'\n",
 		mix_ramp.GetStart(), mix_ramp.GetEnd());

--- a/test/MakeTag.hxx
+++ b/test/MakeTag.hxx
@@ -22,7 +22,7 @@
 #include "util/Compiler.h"

 inline void
-BuildTag(gcc_unused TagBuilder &tag) noexcept
+BuildTag([[maybe_unused]] TagBuilder &tag) noexcept
 {
 }


--- a/test/ReadApeTags.cxx
+++ b/test/ReadApeTags.cxx
@@ -34,7 +34,7 @@
 #endif

 static bool
-MyApeTagCallback(gcc_unused unsigned long flags,
+MyApeTagCallback([[maybe_unused]] unsigned long flags,
 		 const char *key, StringView value)
 {
 	if ((flags & (0x3 << 1)) == 0)

--- a/test/read_mixer.cxx
+++ b/test/read_mixer.cxx
@@ -30,13 +30,13 @@
 #include <stdlib.h>

 const FilterPlugin *
-filter_plugin_by_name(gcc_unused const char *name) noexcept
+filter_plugin_by_name([[maybe_unused]] const char *name) noexcept
 {
 	assert(false);
 	return nullptr;
 }

-int main(int argc, gcc_unused char **argv)
+int main(int argc, [[maybe_unused]] char **argv)
 try {
 	int volume;


--- a/test/run_avahi.cxx
+++ b/test/run_avahi.cxx
@@ -26,7 +26,7 @@
 unsigned listen_port = 1234;

 int
-main(gcc_unused int argc, gcc_unused char **argv)
+main([[maybe_unused]] int argc, [[maybe_unused]] char **argv)
 {
 	EventLoop event_loop;
 	const ShutdownHandler shutdown_handler(event_loop);

--- a/test/run_convert.cxx
+++ b/test/run_convert.cxx
@@ -137,7 +137,7 @@ try {

 		auto output = state.Convert({src.data, src.size});

-		gcc_unused ssize_t ignored = write(1, output.data,
+		[[maybe_unused]] ssize_t ignored = write(1, output.data,
 						   output.size);
 	}

@@ -146,7 +146,7 @@ try {
 		if (output.IsNull())
 			break;

-		gcc_unused ssize_t ignored = write(1, output.data,
+		[[maybe_unused]] ssize_t ignored = write(1, output.data,
 						   output.size);
 	}


--- a/test/run_filter.cxx
+++ b/test/run_filter.cxx
@@ -42,8 +42,8 @@
 #include <stdio.h>

 void
-mixer_set_volume(gcc_unused Mixer *mixer,
-		 gcc_unused unsigned volume)
+mixer_set_volume([[maybe_unused]] Mixer *mixer,
+		 [[maybe_unused]] unsigned volume)
 {
 }


--- a/test/run_gunzip.cxx
+++ b/test/run_gunzip.cxx
@@ -55,7 +55,7 @@ CopyGunzip(FILE *_dest, Path src_path)
 }

 int
-main(int argc, gcc_unused char **argv)
+main(int argc, [[maybe_unused]] char **argv)
 try {
 	if (argc != 2) {
 		fprintf(stderr, "Usage: run_gunzip PATH\n");

--- a/test/run_gzip.cxx
+++ b/test/run_gzip.cxx
@@ -59,7 +59,7 @@ CopyGzip(FILE *_dest, int src)
 }

 int
-main(int argc, gcc_unused char **argv)
+main(int argc, [[maybe_unused]] char **argv)
 try {
 	if (argc != 1) {
 		fprintf(stderr, "Usage: run_gzip\n");

--- a/test/run_inotify.cxx
+++ b/test/run_inotify.cxx
@@ -34,8 +34,8 @@ static constexpr unsigned IN_MASK =
 	|IN_MOVE|IN_MOVE_SELF;

 static void
-my_inotify_callback(gcc_unused int wd, unsigned mask,
-		    const char *name, gcc_unused void *ctx)
+my_inotify_callback([[maybe_unused]] int wd, unsigned mask,
+		    const char *name, [[maybe_unused]] void *ctx)
 {
 	printf("mask=0x%x name='%s'\n", mask, name);
 }

--- a/test/run_normalize.cxx
+++ b/test/run_normalize.cxx
@@ -57,7 +57,7 @@ try {
 		Compressor_Process_int16(compressor,
 					 (int16_t *)buffer, nbytes / 2);

-		gcc_unused ssize_t ignored = write(1, buffer, nbytes);
+		[[maybe_unused]] ssize_t ignored = write(1, buffer, nbytes);
 	}

 	Compressor_delete(compressor);

--- a/test/software_volume.cxx
+++ b/test/software_volume.cxx
@@ -58,7 +58,7 @@ try {

 	while ((nbytes = read(0, buffer, sizeof(buffer))) > 0) {
 		auto dest = pv.Apply({buffer, size_t(nbytes)});
-		gcc_unused ssize_t ignored = write(1, dest.data, dest.size);
+		[[maybe_unused]] ssize_t ignored = write(1, dest.data, dest.size);
 	}

 	pv.Close();

--- a/test/test_translate_song.cxx
+++ b/test/test_translate_song.cxx
@@ -85,8 +85,8 @@ static const char *uri1 = "/foo/bar.ogg";
 static const char *uri2 = "foo/bar.ogg";

 DetachedSong
-DatabaseDetachSong(gcc_unused const Database &db,
-		   gcc_unused const Storage *_storage,
+DatabaseDetachSong([[maybe_unused]] const Database &db,
+		   [[maybe_unused]] const Storage *_storage,
 		   const char *uri)
 {
 	if (strcmp(uri, uri2) == 0)
@@ -119,7 +119,7 @@ Client::GetStorage() const noexcept
 }

 void
-Client::AllowFile(gcc_unused Path path_fs) const
+Client::AllowFile([[maybe_unused]] Path path_fs) const
 {
 	/* always fail, so a SongLoader with a non-nullptr
 	   Client pointer will be regarded "insecure", while one with

--- a/test/test_vorbis_encoder.cxx
+++ b/test/test_vorbis_encoder.cxx