From 7d4c6a16adb16b3efa88079b11be66ae90758380 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Sat, 7 Sep 2024 10:26:49 +0100
Subject: [PATCH] Avoid unnecessary reservations when editing track under
 trains loading in stations

---
 src/rail_cmd.cpp  | 30 +++++++++++++++++-------------
 src/train.h       |  2 ++
 src/train_cmd.cpp |  8 ++++++++
 3 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/src/rail_cmd.cpp b/src/rail_cmd.cpp
index 8fcf2ecf8d..c3582df32c 100644
--- a/src/rail_cmd.cpp
+++ b/src/rail_cmd.cpp
@@ -647,6 +647,19 @@ static inline bool ValParamTrackOrientation(Track track)
 	return IsValidTrack(track);
 }
 
+static void ReReserveTrainPath(Train *v)
+{
+	const bool consider_stopped = (((v->vehstatus & VS_STOPPED) && v->cur_speed == 0) || v->current_order.IsType(OT_LOADING));
+	const bool at_safe_waiting_position = IsSafeWaitingPosition(v, v->tile, v->GetVehicleTrackdir(), true, _settings_game.pf.forbid_90_deg);
+
+	/* Don't extend the train's path if it's stopped or loading, and at a safe position. */
+	if (consider_stopped && at_safe_waiting_position) return;
+
+	if (!at_safe_waiting_position || (v->UsingRealisticBraking() && !v->StopFoundAtVehiclePosition())) {
+		TryPathReserve(v, true);
+	}
+}
+
 /**
  * Build a single piece of rail
  * @param tile tile  to build on
@@ -1141,7 +1154,7 @@ CommandCost CmdRemoveSingleRail(TileIndex tile, DoCommandFlag flags, uint32_t p1
 			YapfNotifyTrackLayoutChange(tile, track);
 		}
 
-		if (v != nullptr) TryPathReserve(v, true);
+		if (v != nullptr) ReReserveTrainPath(v);
 	}
 
 	_rail_track_endtile = tile;
@@ -1461,15 +1474,6 @@ static void SetupBridgeTunnelSignalSimulation(TileIndex entrance, TileIndex exit
 	}
 }
 
-static void ReReserveTrainPath(Train *v)
-{
-	/* Extend the train's path if it's not stopped or loading, or not at a safe position. */
-	if (!(((v->vehstatus & VS_STOPPED) && v->cur_speed == 0) || v->current_order.IsType(OT_LOADING)) ||
-			!IsSafeWaitingPosition(v, v->tile, v->GetVehicleTrackdir(), true, _settings_game.pf.forbid_90_deg)) {
-		TryPathReserve(v, true);
-	}
-}
-
 /**
  * Build signals, alternate between double/single, signal/semaphore,
  * pre/exit/combo-signals, and what-else not. If the rail piece does not
@@ -2719,7 +2723,7 @@ CommandCost CmdConvertRail(TileIndex tile, DoCommandFlag flags, uint32_t p1, uin
 		}
 
 		for (uint i = 0; i < vehicles_affected.size(); ++i) {
-			TryPathReserve(vehicles_affected[i], true);
+			ReReserveTrainPath(vehicles_affected[i]);
 		}
 	}
 
@@ -3036,7 +3040,7 @@ CommandCost CmdConvertRailTrack(TileIndex tile, DoCommandFlag flags, uint32_t p1
 		}
 
 		for (uint i = 0; i < vehicles_affected.size(); ++i) {
-			TryPathReserve(vehicles_affected[i], true);
+			ReReserveTrainPath(vehicles_affected[i]);
 		}
 	} while (advance_tile());
 
@@ -3085,7 +3089,7 @@ static CommandCost RemoveTrainDepot(TileIndex tile, DoCommandFlag flags)
 		DoClearSquare(tile);
 		AddSideToSignalBuffer(tile, dir, owner);
 		YapfNotifyTrackLayoutChange(tile, DiagDirToDiagTrack(dir));
-		if (v != nullptr) TryPathReserve(v, true);
+		if (v != nullptr) ReReserveTrainPath(v);
 		DeleteNewGRFInspectWindow(GSF_RAILTYPES, tile);
 	}
 
diff --git a/src/train.h b/src/train.h
index eaf081a8fe..98ccc11298 100644
--- a/src/train.h
+++ b/src/train.h
@@ -527,6 +527,8 @@ public:
 	{
 		if (speed != this->signal_speed_restriction) this->UpdateTrainSpeedAdaptationLimitInternal(speed);
 	}
+
+	bool StopFoundAtVehiclePosition() const;
 };
 
 struct TrainDecelerationStats {
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index 559a04a02a..92bbc0413f 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -7816,3 +7816,11 @@ CommandCost CmdSetTrainSpeedRestriction(TileIndex tile, DoCommandFlag flags, uin
 	}
 	return CommandCost();
 }
+
+bool Train::StopFoundAtVehiclePosition() const
+{
+	ChooseTrainTrackLookAheadState lookahead_state;
+	VehicleOrderSaver orders(const_cast<Train *>(this));
+	orders.AdvanceOrdersFromVehiclePosition(lookahead_state);
+	return HasBit(lookahead_state.flags, CTTLASF_STOP_FOUND);
+}