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>

87 files changed, 201 insertions, 209 deletions

diff --git a/src/Instance.cxx b/src/Instance.cxx
index cf25ca201..2f5261a71 100644
--- 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);
 }
diff --git a/src/LogInit.cxx b/src/LogInit.cxx
index eb2bcc3f0..ad3b8672b 100644
--- 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
diff --git a/src/command/AllCommands.cxx b/src/command/AllCommands.cxx
index ba9fc2f62..8797543a6 100644
--- 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());
 }
diff --git a/src/command/ClientCommands.cxx b/src/command/ClientCommands.cxx
index 3128b54e3..90ac993f2 100644
--- 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;
 }
diff --git a/src/command/MessageCommands.cxx b/src/command/MessageCommands.cxx
index 1478d401b..5e7f7a212 100644
--- 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());
 
diff --git a/src/command/NeighborCommands.cxx b/src/command/NeighborCommands.cxx
index 729b3c540..f4dfb5472 100644
--- 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();
diff --git a/src/command/OtherCommands.cxx b/src/command/OtherCommands.cxx
index 7b2dfe511..2bf858d90 100644
--- 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,
diff --git a/src/command/OutputCommands.cxx b/src/command/OutputCommands.cxx
index 4558f69be..298a38469 100644
--- 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());
 
diff --git a/src/command/PlayerCommands.cxx b/src/command/PlayerCommands.cxx
index 7f3b4f296..551a67905 100644
--- 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",
diff --git a/src/command/PlaylistCommands.cxx b/src/command/PlaylistCommands.cxx
index 2d80d9ded..74aa9596c 100644
--- 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());
diff --git a/src/command/QueueCommands.cxx b/src/command/QueueCommands.cxx
index 7bc1c51ad..5b099c16c 100644
--- 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);
diff --git a/src/command/StorageCommands.cxx b/src/command/StorageCommands.cxx
index 5cce791c7..8809fa995 100644
--- 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) {
diff --git a/src/db/Interface.hxx b/src/db/Interface.hxx
index 8f3a47eb0..708eb240c 100644
--- 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;
 	}
diff --git a/src/db/plugins/ProxyDatabasePlugin.cxx b/src/db/plugins/ProxyDatabasePlugin.cxx
index 703cf88af..0bc318b6e 100644
--- 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);
 
diff --git a/src/db/plugins/simple/SimpleDatabasePlugin.cxx b/src/db/plugins/simple/SimpleDatabasePlugin.cxx
index 57c4ad47e..4cd1ea892 100644
--- 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());
diff --git a/src/db/plugins/upnp/UpnpDatabasePlugin.cxx b/src/db/plugins/upnp/UpnpDatabasePlugin.cxx
index 208a0cb4c..597c67fa0 100644
--- 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);
diff --git a/src/db/update/InotifySource.cxx b/src/db/update/InotifySource.cxx
index d45764f24..e6508f463 100644
--- 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,
diff --git a/src/db/update/InotifyUpdate.cxx b/src/db/update/InotifyUpdate.cxx
index 5d0154969..8df7bad8d 100644
--- 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;
 
diff --git a/src/db/update/Walk.hxx b/src/db/update/Walk.hxx
index 0b9649a3d..3d0793e38 100644
--- 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
diff --git a/src/decoder/plugins/FlacDecoderPlugin.cxx b/src/decoder/plugins/FlacDecoderPlugin.cxx
index ca36180ad..e1c06c5a6 100644
--- 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;
 }
diff --git a/src/decoder/plugins/FlacInput.cxx b/src/decoder/plugins/FlacInput.cxx
index 94bbf9ca1..8cbab30e8 100644
--- 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;
diff --git a/src/decoder/plugins/FluidsynthDecoderPlugin.cxx b/src/decoder/plugins/FluidsynthDecoderPlugin.cxx
index 722aa44d0..9aa8e2d0d 100644
--- 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());
 }
diff --git a/src/decoder/plugins/GmeDecoderPlugin.cxx b/src/decoder/plugins/GmeDecoderPlugin.cxx
index 3ee92f877..84365fae2 100644
--- 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");
diff --git a/src/decoder/plugins/Mpg123DecoderPlugin.cxx b/src/decoder/plugins/Mpg123DecoderPlugin.cxx
index 6e85e111b..984f74928 100644
--- 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();
 
diff --git a/src/decoder/plugins/OpusDecoderPlugin.cxx b/src/decoder/plugins/OpusDecoderPlugin.cxx
index 37fc86b3f..1dc2d6441 100644
--- 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());
 
diff --git a/src/decoder/plugins/SndfileDecoderPlugin.cxx b/src/decoder/plugins/SndfileDecoderPlugin.cxx
index 91baf1275..6aec0825f 100644
--- 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;
diff --git a/src/decoder/plugins/VorbisDecoderPlugin.cxx b/src/decoder/plugins/VorbisDecoderPlugin.cxx
index eadd76573..b71fdd4d8 100644
--- 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());
diff --git a/src/decoder/plugins/WavpackDecoderPlugin.cxx b/src/decoder/plugins/WavpackDecoderPlugin.cxx
index 93459f311..4bb629d25 100644
--- 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 */
 }
diff --git a/src/encoder/EncoderInterface.hxx b/src/encoder/EncoderInterface.hxx
index 3730bb3d8..519cd1110 100644
--- 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) {
 	}
 
 	/**
diff --git a/src/encoder/plugins/FlacEncoderPlugin.cxx b/src/encoder/plugins/FlacEncoderPlugin.cxx
index 632a2f1ce..108aa4b00 100644
--- 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);
diff --git a/src/encoder/plugins/NullEncoderPlugin.cxx b/src/encoder/plugins/NullEncoderPlugin.cxx
index 73fac5b0c..d9405983e 100644
--- 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();
 }
diff --git a/src/encoder/plugins/WaveEncoderPlugin.cxx b/src/encoder/plugins/WaveEncoderPlugin.cxx
index 522bd7a1e..96b20885a 100644
--- 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();
 }
diff --git a/src/event/Loop.cxx b/src/event/Loop.cxx
index a7ae5c479..c83f652da 100644
--- 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());
 
diff --git a/src/event/PollGroupEpoll.hxx b/src/event/PollGroupEpoll.hxx
index ecd41a1c8..7d8bc71e0 100644
--- 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;
diff --git a/src/event/ServerSocket.cxx b/src/event/ServerSocket.cxx
index 583508d07..35407edb7 100644
--- 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;
diff --git a/src/filter/Observer.cxx b/src/filter/Observer.cxx
index e052272eb..73a6e758e 100644
--- 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;
 	}
diff --git a/src/filter/plugins/NormalizeFilterPlugin.cxx b/src/filter/plugins/NormalizeFilterPlugin.cxx
index b4e0b444b..4d3e936ee 100644
--- 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>();
 }
diff --git a/src/filter/plugins/NullFilterPlugin.cxx b/src/filter/plugins/NullFilterPlugin.cxx
index 115124179..143c104ab 100644
--- 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>();
 }
diff --git a/src/fs/io/FileOutputStream.cxx b/src/fs/io/FileOutputStream.cxx
index fb07fe438..51f73678a 100644
--- 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,
diff --git a/src/input/InputStream.cxx b/src/input/InputStream.cxx
index 1ed319466..069078e70 100644
--- 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");
 }
diff --git a/src/input/plugins/AlsaInputPlugin.cxx b/src/input/plugins/AlsaInputPlugin.cxx
index d09126d14..a5902006c 100644
--- 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();
 	}
diff --git a/src/lib/curl/Global.cxx b/src/lib/curl/Global.cxx
index 24c17798e..8b32eae97 100644
--- 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;
diff --git a/src/lib/ffmpeg/LogCallback.cxx b/src/lib/ffmpeg/LogCallback.cxx
index d88f298d0..7588ae6d7 100644
--- 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;
 
diff --git a/src/lib/nfs/Connection.cxx b/src/lib/nfs/Connection.cxx
index e51ebf509..c1dc8d18d 100644
--- 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);
diff --git a/src/lib/smbclient/Init.cxx b/src/lib/smbclient/Init.cxx
index fe2ee51b2..746b68925 100644
--- 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");
diff --git a/src/lib/sqlite/Util.hxx b/src/lib/sqlite/Util.hxx
index ba142f55a..b05b73b2f 100644
--- 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));
 }
diff --git a/src/lib/upnp/Action.hxx b/src/lib/upnp/Action.hxx
index d717f8d5d..6de060560 100644
--- 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...);
diff --git a/src/lib/xiph/FlacIOHandle.cxx b/src/lib/xiph/FlacIOHandle.cxx
index fb0079b20..13f837fd8 100644
--- 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 */
diff --git a/src/mixer/plugins/AlsaMixerPlugin.cxx b/src/mixer/plugins/AlsaMixerPlugin.cxx
index e3d774194..836989cee 100644
--- 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)
 {
diff --git a/src/mixer/plugins/HaikuMixerPlugin.cxx b/src/mixer/plugins/HaikuMixerPlugin.cxx
index af5529f9a..da2067bf3 100644
--- 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);
 }
diff --git a/src/mixer/plugins/NullMixerPlugin.cxx b/src/mixer/plugins/NullMixerPlugin.cxx
index 4f8989d50..bfb5edb34 100644
--- 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);
 }
diff --git a/src/mixer/plugins/OSXMixerPlugin.cxx b/src/mixer/plugins/OSXMixerPlugin.cxx
index ea6bdf719..2370103db 100644
--- 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);
diff --git a/src/mixer/plugins/OssMixerPlugin.cxx b/src/mixer/plugins/OssMixerPlugin.cxx
index a53559997..92896dbef 100644
--- 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)
 {
diff --git a/src/mixer/plugins/PulseMixerPlugin.cxx b/src/mixer/plugins/PulseMixerPlugin.cxx
index 428e3c4af..0104f45b1 100644
--- 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)
 {
diff --git a/src/mixer/plugins/SndioMixerPlugin.cxx b/src/mixer/plugins/SndioMixerPlugin.cxx
index c80fad411..d9776c02d 100644
--- 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);
 }
diff --git a/src/mixer/plugins/SoftwareMixerPlugin.cxx b/src/mixer/plugins/SoftwareMixerPlugin.cxx
index cb9649017..0a84fa36d 100644
--- 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);
 }
diff --git a/src/mixer/plugins/WinmmMixerPlugin.cxx b/src/mixer/plugins/WinmmMixerPlugin.cxx
index 0bf60f58b..49165b6cb 100644
--- 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);
 }
diff --git a/src/neighbor/plugins/SmbclientNeighborPlugin.cxx b/src/neighbor/plugins/SmbclientNeighborPlugin.cxx
index 0f6812ff8..b51a0b39b 100644
--- 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();
 
diff --git a/src/neighbor/plugins/UdisksNeighborPlugin.cxx b/src/neighbor/plugins/UdisksNeighborPlugin.cxx
index 820271d67..4ff406f2c 100644
--- 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);
 }
diff --git a/src/neighbor/plugins/UpnpNeighborPlugin.cxx b/src/neighbor/plugins/UpnpNeighborPlugin.cxx
index e04f5011a..281b9b534 100644
--- 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);
 }
diff --git a/src/output/Interface.cxx b/src/output/Interface.cxx
index 99c200978..9f7250408 100644
--- 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");
 }
diff --git a/src/output/SharedPipeConsumer.hxx b/src/output/SharedPipeConsumer.hxx
index 814ddeadf..ee4078bed 100644
--- 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;
diff --git a/src/output/plugins/HaikuOutputPlugin.cxx b/src/output/plugins/HaikuOutputPlugin.cxx
index 952fb0c2f..e00df46eb 100644
--- 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;
diff --git a/src/output/plugins/NullOutputPlugin.cxx b/src/output/plugins/NullOutputPlugin.cxx
index 11572be5f..4e33f3461 100644
--- 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();
diff --git a/src/output/plugins/OSXOutputPlugin.cxx b/src/output/plugins/OSXOutputPlugin.cxx
index 312d16965..5dfe23641 100644
--- 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)
 {
diff --git a/src/output/plugins/PipeOutputPlugin.cxx b/src/output/plugins/PipeOutputPlugin.cxx
index 62e01be1e..45fbecdfd 100644
--- 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)
diff --git a/src/output/plugins/PulseOutputPlugin.cxx b/src/output/plugins/PulseOutputPlugin.cxx
index 0220423bf..6558232d0 100644
--- 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;
diff --git a/src/output/plugins/httpd/HttpdOutputPlugin.cxx b/src/output/plugins/httpd/HttpdOutputPlugin.cxx
index ef4b7eaae..b34c1dedf 100644
--- 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 */
diff --git a/src/output/plugins/sles/SlesOutputPlugin.cxx b/src/output/plugins/sles/SlesOutputPlugin.cxx
index b0bcbe7be..ad216e7fc 100644
--- 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;
diff --git a/src/playlist/plugins/EmbeddedCuePlaylistPlugin.cxx b/src/playlist/plugins/EmbeddedCuePlaylistPlugin.cxx
index 343f29845..f6fe530de 100644
--- 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 */
diff --git a/src/playlist/plugins/XspfPlaylistPlugin.cxx b/src/playlist/plugins/XspfPlaylistPlugin.cxx
index b8d2da61d..504c3720f 100644
--- 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();
diff --git a/src/storage/MemoryDirectoryReader.cxx b/src/storage/MemoryDirectoryReader.cxx
index 4220c237e..3ac286633 100644
--- 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());
diff --git a/src/storage/StorageInterface.cxx b/src/storage/StorageInterface.cxx
index 2a51f8d5f..821c18251 100644
--- 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;
 }
diff --git a/src/storage/plugins/CurlStorage.cxx b/src/storage/plugins/CurlStorage.cxx
index 98f6de247..5cabd379c 100644
--- 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
 
diff --git a/src/storage/plugins/NfsStorage.cxx b/src/storage/plugins/NfsStorage.cxx
index f6d4a5dcb..ffcbe13a0 100644
--- 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;
 
diff --git a/src/storage/plugins/SmbclientStorage.cxx b/src/storage/plugins/SmbclientStorage.cxx
index f86542383..a0c662f54 100644
--- 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;
diff --git a/src/system/EventFD.cxx b/src/system/EventFD.cxx
index 80c722953..ebf8f84c3 100644
--- 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));
 }
diff --git a/src/system/EventPipe.cxx b/src/system/EventPipe.cxx
index 981832b8c..462cc4a1c 100644
--- 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
 }
 
diff --git a/src/tag/Handler.cxx b/src/tag/Handler.cxx
index 467a93517..56c0a53cd 100644
--- 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
 {
 }
 
diff --git a/src/tag/Handler.hxx b/src/tag/Handler.hxx
index d5d4396bc..30bab72be 100644
--- 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;
diff --git a/src/thread/Name.hxx b/src/thread/Name.hxx
index 091cbb5ac..2313f291e 100644
--- 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...));
diff --git a/src/util/Compiler.h b/src/util/Compiler.h
index cdfcc1db0..4b7b22269 100644
--- 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
diff --git a/src/util/UTF8.cxx b/src/util/UTF8.cxx
index 9dbcb3260..608843a87 100644
--- 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;
 	}
 };
diff --git a/src/win32/Win32Main.cxx b/src/win32/Win32Main.cxx
index e812cc435..782554121 100644
--- 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,
diff --git a/src/zeroconf/ZeroconfAvahi.cxx b/src/zeroconf/ZeroconfAvahi.cxx
index a5465f5fb..8f983bc93 100644
--- 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);
 
diff --git a/src/zeroconf/ZeroconfBonjour.cxx b/src/zeroconf/ZeroconfBonjour.cxx
index 80b41b4ff..44fcb6d90 100644
--- 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,
diff --git a/src/zeroconf/ZeroconfGlue.cxx b/src/zeroconf/ZeroconfGlue.cxx
index 5fe6eff1d..bad174ec7 100644
--- 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;