Feature: Remember the last-used signal between games

(cherry picked from commit a9de36ad23f30d125ed495f0bd84342b594d19df)

See: https://github.com/OpenTTD/OpenTTD/pull/9792

src/rail_gui.cpp

@@ -220,6 +220,13 @@ static void PlaceRail_Station(TileIndex tile)
 	}
 }
 
+static SignalType GetDefaultSignalType()
+{
+	SignalType sigtype = _settings_client.gui.default_signal_type;
+	if (_settings_game.vehicle.train_braking_model == TBM_REALISTIC && IsSignalTypeUnsuitableForRealisticBraking(sigtype)) return SIGTYPE_PBS_ONEWAY;
+	return sigtype;
+}
+
 /**
  * Build a new signal or edit/remove a present signal, use CmdBuildSingleSignal() or CmdRemoveSingleSignal() in rail_cmd.cpp
  *
@@ -291,7 +298,7 @@ static void GenericPlaceSignals(TileIndex tile)
 	} else {
 		SB(p1, 3, 1, _ctrl_pressed);
 		SB(p1, 4, 1, (_cur_year < _settings_client.gui.semaphore_build_before ? SIG_SEMAPHORE : SIG_ELECTRIC));
-		SB(p1, 5, 3, SIGTYPE_PBS_ONEWAY);
+		SB(p1, 5, 3, GetDefaultSignalType());
 		SB(p1, 8, 1, 0);
 		SB(p1, 9, 6, cycle_types);
 	}
@@ -471,7 +478,7 @@ static void HandleAutoSignalPlacement()
 		SB(p2,  3, 1, 0);
 		SB(p2,  4, 1, (_cur_year < _settings_client.gui.semaphore_build_before ? SIG_SEMAPHORE : SIG_ELECTRIC));
 		SB(p2,  6, 1, _ctrl_pressed);
-		SB(p2,  7, 3, SIGTYPE_PBS_ONEWAY);
+		SB(p2,  7, 3, GetDefaultSignalType());
 		SB(p2, 24, 8, _settings_client.gui.drag_signals_density);
 		SB(p2, 10, 1, !_settings_client.gui.drag_signals_fixed_distance);
 	}
@@ -1977,6 +1984,9 @@ public:
 				_cur_signal_type = TypeForClick(_cur_signal_button);
 				_cur_signal_variant = widget >= WID_BS_ELECTRIC_NORM ? SIG_ELECTRIC : SIG_SEMAPHORE;
 
+				/* Update default (last-used) signal type in config file. */
+				_settings_client.gui.default_signal_type = Clamp<SignalType>(_cur_signal_type, SIGTYPE_NORMAL, SIGTYPE_PBS_ONEWAY);
+
 				/* If 'remove' button of rail build toolbar is active, disable it. */
 				ClearRemoveState();
 				break;
@@ -2457,7 +2467,7 @@ void InitializeRailGUI()
 	_convert_signal_button = false;
 	_trace_restrict_button = false;
 	_program_signal_button = false;
-	_cur_signal_type   = SIGTYPE_PBS_ONEWAY;
+	_cur_signal_type   = GetDefaultSignalType();
 	_cur_signal_button =
 		_cur_signal_type == SIGTYPE_PROG ? 4 :
 		_cur_signal_type == SIGTYPE_PBS ? 5 :

src/settings_type.h

@@ -22,6 +22,7 @@
 #include "openttd.h"
 #include "rail_gui_type.h"
 #include "station_type.h"
+#include "signal_type.h"
 
 /* Used to validate sizes of "max" value in settings. */
 const size_t MAX_SLE_UINT8 = UINT8_MAX;
@@ -192,6 +193,7 @@ struct GUISettings : public TimeSettings {
 	bool   pause_on_newgame;                 ///< whether to start new games paused or not
 	SignalGUISettings signal_gui_mode;       ///< select which signal types are shown in the signal GUI
 	SignalCycleSettings cycle_signal_types;  ///< Which signal types to cycle with the build signal tool.
+	SignalType default_signal_type;          ///< The default signal type, which is set automatically by the last signal used. Not available in Settings.
 	Year   coloured_news_year;               ///< when does newspaper become coloured?
 	bool   override_time_settings;           ///< Whether to override time display settings stored in savegame.
 	bool   timetable_in_ticks;               ///< whether to show the timetable in ticks rather than days

src/table/settings/settings.ini

@@ -4935,6 +4935,14 @@ strhelp  = STR_CONFIG_SETTING_CYCLE_SIGNAL_TYPES_HELPTEXT
 strval   = STR_CONFIG_SETTING_CYCLE_SIGNAL_PBS
 cat      = SC_ADVANCED
 
+[SDTC_VAR]
+var      = gui.default_signal_type
+type     = SLE_UINT8
+flags    = SF_NOT_IN_SAVE | SF_NO_NETWORK_SYNC
+def      = 5
+min      = 0
+max      = 5
+
 [SDTC_VAR]
 var      = gui.drag_signals_density
 type     = SLE_UINT8