# HG changeset patch
# User Michael Lutz <michi@icosahedron.de>
# Date 2021-11-28 16:37:04
# Node ID f66f65c35c7426deff6abade1b8a55e5a24a150f
# Parent  15c912177c8886dcf401e532943f4b3666b64fef

Codechange: Template the command callback function type to allow unpacked arguments.

diff --git a/src/command_func.h b/src/command_func.h
--- a/src/command_func.h
+++ b/src/command_func.h
@@ -78,6 +78,20 @@ private:
 	static int _counter;
 };
 
+#if defined(__GNUC__) && !defined(__clang__)
+/*
+ * We cast specialized function pointers to a generic one, but don't use the
+ * converted value to call the function, which is safe, except that GCC
+ * helpfully thinks it is not.
+ *
+ * "Any pointer to function can be converted to a pointer to a different function type.
+ * Calling the function through a pointer to a different function type is undefined,
+ * but converting such pointer back to pointer to the original function type yields
+ * the pointer to the original function." */
+#	pragma GCC diagnostic push
+#	pragma GCC diagnostic ignored "-Wcast-function-type"
+#	define SILENCE_GCC_FUNCTION_POINTER_CAST
+#endif
 
 template<Commands TCmd, typename T, bool THasTile> struct CommandHelper;
 
@@ -148,18 +162,19 @@ public:
 	 * @param err_message Message prefix to show on error
 	 * @param args Parameters for the command
 	 */
-	static inline bool Post(StringID err_message, Targs... args) { return Post(err_message, nullptr, std::forward<Targs>(args)...); }
+	static inline bool Post(StringID err_message, Targs... args) { return Post<CommandCallback>(err_message, nullptr, std::forward<Targs>(args)...); }
 	/**
 	 * Shortcut for the long Post when not using an error message.
 	 * @param callback A callback function to call after the command is finished
 	 * @param args Parameters for the command
 	 */
-	static inline bool Post(CommandCallback *callback, Targs... args) { return Post((StringID)0, callback, std::forward<Targs>(args)...); }
+	template <typename Tcallback>
+	static inline bool Post(Tcallback *callback, Targs... args) { return Post((StringID)0, callback, std::forward<Targs>(args)...); }
 	/**
 	 * Shortcut for the long Post when not using a callback or an error message.
 	 * @param args Parameters for the command
 	 */
-	static inline bool Post(Targs... args) { return Post((StringID)0, nullptr, std::forward<Targs>(args)...); }
+	static inline bool Post(Targs... args) { return Post<CommandCallback>((StringID)0, nullptr, std::forward<Targs>(args)...); }
 
 	/**
 	 * Top-level network safe command execution for the current company.
@@ -171,7 +186,8 @@ public:
 	 * @param args Parameters for the command
 	 * @return \c true if the command succeeded, else \c false.
 	 */
-	static bool Post(StringID err_message, CommandCallback *callback, Targs... args)
+	template <typename Tcallback>
+	static bool Post(StringID err_message, Tcallback *callback, Targs... args)
 	{
 		return InternalPost(err_message, callback, true, false, std::forward_as_tuple(args...));
 	}
@@ -185,7 +201,8 @@ public:
 	 * @param args Parameters for the command
 	 * @return \c true if the command succeeded, else \c false.
 	 */
-	static bool PostFromNet(StringID err_message, CommandCallback *callback, bool my_cmd, TileIndex location, std::tuple<Targs...> args)
+	template <typename Tcallback>
+	static bool PostFromNet(StringID err_message, Tcallback *callback, bool my_cmd, TileIndex location, std::tuple<Targs...> args)
 	{
 		return InternalPost(err_message, callback, my_cmd, true, location, std::move(args));
 	}
@@ -194,11 +211,10 @@ public:
 	 * Prepare a command to be send over the network
 	 * @param cmd The command to execute (a CMD_* value)
 	 * @param err_message Message prefix to show on error
-	 * @param callback A callback function to call after the command is finished
 	 * @param company The company that wants to send the command
 	 * @param args Parameters for the command
 	 */
-	static void SendNet(StringID err_message, CommandCallback *callback, CompanyID company, Targs... args)
+	static void SendNet(StringID err_message, CompanyID company, Targs... args)
 	{
 		auto args_tuple = std::forward_as_tuple(args...);
 
@@ -207,7 +223,7 @@ public:
 			tile = std::get<0>(args_tuple);
 		}
 
-		::NetworkSendCommand(Tcmd, err_message, callback, _current_company, tile, EndianBufferWriter<CommandDataBuffer>::FromValue(args_tuple));
+		::NetworkSendCommand(Tcmd, err_message, nullptr, _current_company, tile, EndianBufferWriter<CommandDataBuffer>::FromValue(args_tuple));
 	}
 
 	/**
@@ -220,9 +236,10 @@ public:
 	 * @param args Parameters for the command
 	 * @return the command cost of this function.
 	 */
-	static CommandCost Unsafe(StringID err_message, CommandCallback *callback, bool my_cmd, bool estimate_only, TileIndex location, std::tuple<Targs...> args)
+	template <typename Tcallback>
+	static CommandCost Unsafe(StringID err_message, Tcallback *callback, bool my_cmd, bool estimate_only, TileIndex location, std::tuple<Targs...> args)
 	{
-		return Execute(err_message, callback, my_cmd, estimate_only, false, location, std::move(args));
+		return Execute(err_message, reinterpret_cast<CommandCallback *>(callback), my_cmd, estimate_only, false, location, std::move(args));
 	}
 
 protected:
@@ -242,7 +259,8 @@ protected:
 		((SetClientIdHelper(std::get<Tindices>(values))), ...);
 	}
 
-	static bool InternalPost(StringID err_message, CommandCallback *callback, bool my_cmd, bool network_command, std::tuple<Targs...> args)
+	template <typename Tcallback>
+	static bool InternalPost(StringID err_message, Tcallback *callback, bool my_cmd, bool network_command, std::tuple<Targs...> args)
 	{
 		/* Where to show the message? */
 		TileIndex tile{};
@@ -253,7 +271,8 @@ protected:
 		return InternalPost(err_message, callback, my_cmd, network_command, tile, std::move(args));
 	}
 
-	static bool InternalPost(StringID err_message, CommandCallback *callback, bool my_cmd, bool network_command, TileIndex tile, std::tuple<Targs...> args)
+	template <typename Tcallback>
+	static bool InternalPost(StringID err_message, Tcallback *callback, bool my_cmd, bool network_command, TileIndex tile, std::tuple<Targs...> args)
 	{
 		auto [err, estimate_only, only_sending] = InternalPostBefore(Tcmd, GetCommandFlags<Tcmd>(), tile, err_message, network_command);
 		if (err) return false;
@@ -261,7 +280,7 @@ protected:
 		/* Only set client IDs when the command does not come from the network. */
 		if (!network_command && GetCommandFlags<Tcmd>() & CMD_CLIENT_ID) SetClientIds(args, std::index_sequence_for<Targs...>{});
 
-		CommandCost res = Execute(err_message, callback, my_cmd, estimate_only, network_command, tile, args);
+		CommandCost res = Execute(err_message, reinterpret_cast<CommandCallback *>(callback), my_cmd, estimate_only, network_command, tile, args);
 		InternalPostResult(res, tile, estimate_only, only_sending, err_message, my_cmd);
 
 		if (!estimate_only && !only_sending && callback != nullptr) {
@@ -360,20 +379,21 @@ struct CommandHelper<Tcmd, CommandCost(*
 	 * @param location Tile location for user feedback.
 	 * @param args Parameters for the command
 	 */
-	static inline bool Post(StringID err_message, TileIndex location, Targs... args) { return Post(err_message, nullptr, location, std::forward<Targs>(args)...); }
+	static inline bool Post(StringID err_message, TileIndex location, Targs... args) { return Post<CommandCallback>(err_message, nullptr, location, std::forward<Targs>(args)...); }
 	/**
 	 * Shortcut for Post when not using a callback.
 	 * @param callback A callback function to call after the command is finished
 	 * @param location Tile location for user feedback.
 	 * @param args Parameters for the command
 	 */
-	static inline bool Post(CommandCallback *callback, TileIndex location, Targs... args) { return Post((StringID)0, callback, location, std::forward<Targs>(args)...); }
+	template <typename Tcallback>
+	static inline bool Post(Tcallback *callback, TileIndex location, Targs... args) { return Post((StringID)0, callback, location, std::forward<Targs>(args)...); }
 	/**
 	 * Shortcut for Post when not using a callback or an error message.
 	 * @param location Tile location for user feedback.
 	 * @param args Parameters for the command*
 	 */
-	static inline bool Post(TileIndex location, Targs... args) { return Post((StringID)0, nullptr, location, std::forward<Targs>(args)...); }
+	static inline bool Post(TileIndex location, Targs... args) { return Post<CommandCallback>((StringID)0, nullptr, location, std::forward<Targs>(args)...); }
 
 	/**
 	 * Post variant that takes a TileIndex (for error window location and text effects) for
@@ -384,12 +404,16 @@ struct CommandHelper<Tcmd, CommandCost(*
 	 * @param args Parameters for the command
 	 * @return \c true if the command succeeded, else \c false.
 	 */
-	static inline bool Post(StringID err_message, CommandCallback *callback, TileIndex location, Targs... args)
+	template <typename Tcallback>
+	static inline bool Post(StringID err_message, Tcallback *callback, TileIndex location, Targs... args)
 	{
 		return CommandHelper<Tcmd, CommandCost(*)(DoCommandFlag, Targs...), true>::InternalPost(err_message, callback, true, false, location, std::forward_as_tuple(args...));
 	}
 };
 
+#ifdef SILENCE_GCC_FUNCTION_POINTER_CAST
+#	pragma GCC diagnostic pop
+#endif
 
 template <Commands Tcmd>
 using Command = CommandHelper<Tcmd, typename CommandTraits<Tcmd>::ProcType, std::is_same_v<TileIndex, std::tuple_element_t<0, typename CommandTraits<Tcmd>::Args>>>;
diff --git a/src/network/network_client.cpp b/src/network/network_client.cpp
--- a/src/network/network_client.cpp
+++ b/src/network/network_client.cpp
@@ -840,7 +840,7 @@ NetworkRecvStatus ClientNetworkGameSocke
 			 * the server will give us a client-id and let us in */
 			_network_join_status = NETWORK_JOIN_STATUS_REGISTERING;
 			ShowJoinStatusWindow();
-			Command<CMD_COMPANY_CTRL>::SendNet(STR_NULL, nullptr, _local_company, CCA_NEW, INVALID_COMPANY, CRR_NONE, INVALID_CLIENT_ID);
+			Command<CMD_COMPANY_CTRL>::SendNet(STR_NULL, _local_company, CCA_NEW, INVALID_COMPANY, CRR_NONE, INVALID_CLIENT_ID);
 		}
 	} else {
 		/* take control over an existing company */
diff --git a/src/network/network_command.cpp b/src/network/network_command.cpp
--- a/src/network/network_command.cpp
+++ b/src/network/network_command.cpp
@@ -53,55 +53,95 @@
 
 #include "../safeguards.h"
 
-/** Table with all the callbacks we'll use for conversion*/
-static CommandCallback * const _callback_table[] = {
-	/* 0x00 */ nullptr,
-	/* 0x01 */ CcBuildPrimaryVehicle,
-	/* 0x02 */ CcBuildAirport,
-	/* 0x03 */ CcBuildBridge,
-	/* 0x04 */ CcPlaySound_CONSTRUCTION_WATER,
-	/* 0x05 */ CcBuildDocks,
-	/* 0x06 */ CcFoundTown,
-	/* 0x07 */ CcBuildRoadTunnel,
-	/* 0x08 */ CcBuildRailTunnel,
-	/* 0x09 */ CcBuildWagon,
-	/* 0x0A */ CcRoadDepot,
-	/* 0x0B */ CcRailDepot,
-	/* 0x0C */ CcPlaceSign,
-	/* 0x0D */ CcPlaySound_EXPLOSION,
-	/* 0x0E */ CcPlaySound_CONSTRUCTION_OTHER,
-	/* 0x0F */ CcPlaySound_CONSTRUCTION_RAIL,
-	/* 0x10 */ CcStation,
-	/* 0x11 */ CcTerraform,
-	/* 0x12 */ CcAI,
-	/* 0x13 */ CcCloneVehicle,
-	/* 0x14 */ nullptr,
-	/* 0x15 */ CcCreateGroup,
-	/* 0x16 */ CcFoundRandomTown,
-	/* 0x17 */ CcRoadStop,
-	/* 0x18 */ CcBuildIndustry,
-	/* 0x19 */ CcStartStopVehicle,
-	/* 0x1A */ CcGame,
-	/* 0x1B */ CcAddVehicleNewGroup,
-};
+/** Typed list of all possible callbacks. */
+static constexpr auto _callback_tuple = std::make_tuple(
+	(CommandCallback *)nullptr, // Make sure this is actually a pointer-to-function.
+	&CcBuildPrimaryVehicle,
+	&CcBuildAirport,
+	&CcBuildBridge,
+	&CcPlaySound_CONSTRUCTION_WATER,
+	&CcBuildDocks,
+	&CcFoundTown,
+	&CcBuildRoadTunnel,
+	&CcBuildRailTunnel,
+	&CcBuildWagon,
+	&CcRoadDepot,
+	&CcRailDepot,
+	&CcPlaceSign,
+	&CcPlaySound_EXPLOSION,
+	&CcPlaySound_CONSTRUCTION_OTHER,
+	&CcPlaySound_CONSTRUCTION_RAIL,
+	&CcStation,
+	&CcTerraform,
+	&CcAI,
+	&CcCloneVehicle,
+	&CcCreateGroup,
+	&CcFoundRandomTown,
+	&CcRoadStop,
+	&CcBuildIndustry,
+	&CcStartStopVehicle,
+	&CcGame,
+	&CcAddVehicleNewGroup
+);
+
+#ifdef SILENCE_GCC_FUNCTION_POINTER_CAST
+/*
+ * We cast specialized function pointers to a generic one, but don't use the
+ * converted value to call the function, which is safe, except that GCC
+ * helpfully thinks it is not.
+ *
+ * "Any pointer to function can be converted to a pointer to a different function type.
+ * Calling the function through a pointer to a different function type is undefined,
+ * but converting such pointer back to pointer to the original function type yields
+ * the pointer to the original function." */
+#	pragma GCC diagnostic push
+#	pragma GCC diagnostic ignored "-Wcast-function-type"
+#endif
+
+/* Helpers to generate the callback table from the callback list. */
+
+inline constexpr size_t _callback_tuple_size = std::tuple_size_v<decltype(_callback_tuple)>;
+
+template <size_t... i>
+inline auto MakeCallbackTable(std::index_sequence<i...>) noexcept
+{
+	return std::array<CommandCallback *, sizeof...(i)>{{ reinterpret_cast<CommandCallback *>(reinterpret_cast<void(*)()>(std::get<i>(_callback_tuple)))... }}; // MingW64 fails linking when casting a pointer to its own type. To work around, cast it to some other type first.
+}
+
+/** Type-erased table of callbacks. */
+static auto _callback_table = MakeCallbackTable(std::make_index_sequence<_callback_tuple_size>{});
+
 
 /* Helpers to generate the command dispatch table from the command traits. */
 
 template <Commands Tcmd> static CommandDataBuffer SanitizeCmdStrings(const CommandDataBuffer &data);
-template <Commands Tcmd> static void UnpackNetworkCommand(const CommandPacket *cp);
+template <Commands Tcmd, size_t cb> static void UnpackNetworkCommand(const CommandPacket *cp);
 template <Commands Tcmd> static void NetworkReplaceCommandClientId(CommandPacket &cp, ClientID client_id);
+using UnpackNetworkCommandProc = void (*)(const CommandPacket *);
+using UnpackDispatchT = std::array<UnpackNetworkCommandProc, _callback_tuple_size>;
 struct CommandDispatch {
 	CommandDataBuffer(*Sanitize)(const CommandDataBuffer &);
 	void (*ReplaceClientId)(CommandPacket &, ClientID);
-	void (*Unpack)(const CommandPacket *);
+	UnpackDispatchT Unpack;
 };
 
-template<typename T, T... i>
-inline constexpr auto MakeDispatchTable(std::integer_sequence<T, i...>) noexcept
+template <Commands Tcmd, size_t... i>
+constexpr UnpackDispatchT MakeUnpackNetworkCommand(std::index_sequence<i...>) noexcept
+{
+	return UnpackDispatchT{{ {&UnpackNetworkCommand<Tcmd, i>}... }};
+}
+
+template <typename T, T... i, size_t... j>
+inline constexpr auto MakeDispatchTable(std::integer_sequence<T, i...>, std::index_sequence<j...>) noexcept
 {
-	return std::array<CommandDispatch, sizeof...(i)>{{ { &SanitizeCmdStrings<static_cast<Commands>(i)>, &NetworkReplaceCommandClientId<static_cast<Commands>(i)>, &UnpackNetworkCommand<static_cast<Commands>(i)> }... }};
+	return std::array<CommandDispatch, sizeof...(i)>{{ { &SanitizeCmdStrings<static_cast<Commands>(i)>, &NetworkReplaceCommandClientId<static_cast<Commands>(i)>, MakeUnpackNetworkCommand<static_cast<Commands>(i)>(std::make_index_sequence<_callback_tuple_size>{}) }... }};
 }
-static constexpr auto _cmd_dispatch = MakeDispatchTable(std::make_integer_sequence<std::underlying_type_t<Commands>, CMD_END>{});
+/** Command dispatch table. */
+static constexpr auto _cmd_dispatch = MakeDispatchTable(std::make_integer_sequence<std::underlying_type_t<Commands>, CMD_END>{}, std::make_index_sequence<_callback_tuple_size>{});
+
+#ifdef SILENCE_GCC_FUNCTION_POINTER_CAST
+#	pragma GCC diagnostic pop
+#endif
 
 
 /**
@@ -180,6 +220,20 @@ static CommandQueue _local_execution_que
 
 
 /**
+ * Find the callback index of a callback pointer.
+ * @param callback Address of callback to search for.
+ * @return Callback index or std::numeric_limits<size_t>::max() if the function wasn't found in the callback list.
+ */
+static size_t FindCallbackIndex(CommandCallback *callback)
+{
+	if (auto it = std::find(std::cbegin(_callback_table), std::cend(_callback_table), callback); it != std::cend(_callback_table)) {
+		return static_cast<size_t>(std::distance(std::cbegin(_callback_table), it));
+	}
+
+	return std::numeric_limits<size_t>::max();
+}
+
+/**
  * Prepare a DoCommand to be send over the network
  * @param cmd The command to execute (a CMD_* value)
  * @param err_message Message prefix to show on error
@@ -259,7 +313,9 @@ void NetworkExecuteLocalCommandQueue()
 
 		/* We can execute this command */
 		_current_company = cp->company;
-		_cmd_dispatch[cp->cmd].Unpack(cp);
+		size_t cb_index = FindCallbackIndex(cp->callback);
+		assert(cb_index < _callback_tuple_size);
+		_cmd_dispatch[cp->cmd].Unpack[cb_index](cp);
 
 		queue.Pop();
 		delete cp;
@@ -354,7 +410,7 @@ const char *NetworkGameSocketHandler::Re
 	cp->data    = _cmd_dispatch[cp->cmd].Sanitize(p->Recv_buffer());
 
 	byte callback = p->Recv_uint8();
-	if (callback >= lengthof(_callback_table))  return "invalid callback";
+	if (callback >= _callback_table.size())  return "invalid callback";
 
 	cp->callback = _callback_table[callback];
 	return nullptr;
@@ -373,16 +429,12 @@ void NetworkGameSocketHandler::SendComma
 	p->Send_uint32(cp->tile);
 	p->Send_buffer(cp->data);
 
-	byte callback = 0;
-	while (callback < lengthof(_callback_table) && _callback_table[callback] != cp->callback) {
-		callback++;
-	}
-
-	if (callback == lengthof(_callback_table)) {
+	size_t callback = FindCallbackIndex(cp->callback);
+	if (callback > UINT8_MAX) {
 		Debug(net, 0, "Unknown callback for command; no callback sent (command: {})", cp->cmd);
 		callback = 0; // _callback_table[0] == nullptr
 	}
-	p->Send_uint8 (callback);
+	p->Send_uint8 ((uint8)callback);
 }
 
 /** Helper to process a single ClientID argument. */
@@ -455,9 +507,15 @@ CommandDataBuffer SanitizeCmdStrings(con
 	return EndianBufferWriter<CommandDataBuffer>::FromValue(args);
 }
 
-template <Commands Tcmd>
-void UnpackNetworkCommand(const CommandPacket *cp)
+/**
+ * Unpack a generic command packet into its actual typed components.
+ * @tparam Tcmd Command type to be unpacked.
+ * @tparam Tcb Index into the callback list.
+ * @param cp Command packet to unpack.
+ */
+template <Commands Tcmd, size_t Tcb>
+void UnpackNetworkCommand(const CommandPacket* cp)
 {
 	auto args = EndianBufferReader::ToValue<typename CommandTraits<Tcmd>::Args>(cp->data);
-	Command<Tcmd>::PostFromNet(cp->err_msg, cp->callback, cp->my_cmd, cp->tile, args);
+	Command<Tcmd>::PostFromNet(cp->err_msg, std::get<Tcb>(_callback_tuple), cp->my_cmd, cp->tile, args);
 }
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -1538,7 +1538,7 @@ private:
 		if (_network_server) {
 			Command<CMD_COMPANY_CTRL>::Post(CCA_NEW, INVALID_COMPANY, CRR_NONE, _network_own_client_id);
 		} else {
-			Command<CMD_COMPANY_CTRL>::SendNet(STR_NULL, nullptr, _local_company, CCA_NEW, INVALID_COMPANY, CRR_NONE, INVALID_CLIENT_ID);
+			Command<CMD_COMPANY_CTRL>::SendNet(STR_NULL, _local_company, CCA_NEW, INVALID_COMPANY, CRR_NONE, INVALID_CLIENT_ID);
 		}
 	}
 
diff --git a/src/network/network_server.cpp b/src/network/network_server.cpp
--- a/src/network/network_server.cpp
+++ b/src/network/network_server.cpp
@@ -2081,7 +2081,7 @@ void NetworkServerNewCompany(const Compa
 		/* ci is nullptr when replaying, or for AIs. In neither case there is a client. */
 		ci->client_playas = c->index;
 		NetworkUpdateClientInfo(ci->client_id);
-		Command<CMD_RENAME_PRESIDENT>::SendNet(STR_NULL, nullptr, c->index, ci->client_name);
+		Command<CMD_RENAME_PRESIDENT>::SendNet(STR_NULL, c->index, ci->client_name);
 	}
 
 	/* Announce new company on network. */
diff --git a/src/order_backup.cpp b/src/order_backup.cpp
--- a/src/order_backup.cpp
+++ b/src/order_backup.cpp
@@ -198,7 +198,7 @@ CommandCost CmdClearOrderBackup(DoComman
 			/* We need to circumvent the "prevention" from this command being executed
 			 * while the game is paused, so use the internal method. Nor do we want
 			 * this command to get its cost estimated when shift is pressed. */
-			Command<CMD_CLEAR_ORDER_BACKUP>::Unsafe(STR_NULL, nullptr, true, false, ob->tile, CommandTraits<CMD_CLEAR_ORDER_BACKUP>::Args{ ob->tile, static_cast<ClientID>(user) });
+			Command<CMD_CLEAR_ORDER_BACKUP>::Unsafe<CommandCallback>(STR_NULL, nullptr, true, false, ob->tile, CommandTraits<CMD_CLEAR_ORDER_BACKUP>::Args{ ob->tile, static_cast<ClientID>(user) });
 		} else {
 			/* The command came from the game logic, i.e. the clearing of a tile.
 			 * In that case we have no need to actually sync this, just do it. */
diff --git a/src/settings.cpp b/src/settings.cpp
--- a/src/settings.cpp
+++ b/src/settings.cpp
@@ -1600,7 +1600,7 @@ void SyncCompanySettings()
 		const SettingDesc *sd = GetSettingDesc(desc);
 		uint32 old_value = (uint32)sd->AsIntSetting()->Read(new_object);
 		uint32 new_value = (uint32)sd->AsIntSetting()->Read(old_object);
-		if (old_value != new_value) Command<CMD_CHANGE_COMPANY_SETTING>::SendNet(STR_NULL, nullptr, _local_company, sd->GetName(), new_value);
+		if (old_value != new_value) Command<CMD_CHANGE_COMPANY_SETTING>::SendNet(STR_NULL, _local_company, sd->GetName(), new_value);
 	}
 }