forbid-houses-along-roadtype.patch

diff --git a/src/road.h b/src/road.h
index 0defe74..d7bc585 100644
--- a/src/road.h
+++ b/src/road.h
@@ -25,9 +25,11 @@
 /** Roadtype flags. Starts with RO instead of R because R is used for rails */
 enum RoadTypeFlags {
 	ROTF_CATENARY = 0,                   ///< Bit number for adding catenary
+	ROTF_DISALLOW_HOUSES_ALONG,          ///< Bit number for disallowing houses along the road
 
 	ROTFB_NONE = 0,                      ///< All flags cleared.
 	ROTFB_CATENARY = 1 << ROTF_CATENARY, ///< Value for drawing a catenary.
+	ROTFB_DISALLOW_HOUSES_ALONG,         ///< Value for disallowing houses along the road.
 };
 DECLARE_ENUM_AS_BIT_SET(RoadTypeFlags)
 
diff --git a/src/table/roadtypes.h b/src/table/roadtypes.h
index 27ddd85..7f0ffd8 100644
--- a/src/table/roadtypes.h
+++ b/src/table/roadtypes.h
@@ -157,7 +157,7 @@ static const RoadtypeInfo _original_tramtypes[] = {
 		0, // TODO
 
 		/* flags */
-		ROTFB_CATENARY,
+		ROTFB_CATENARY | ROTFB_DISALLOW_HOUSES_ALONG,
 
 		/* cost multiplier */
 		16,
diff --git a/src/town_cmd.cpp b/src/town_cmd.cpp
index d8d13f0..30b899e 100644
--- a/src/town_cmd.cpp
+++ b/src/town_cmd.cpp
@@ -1120,6 +1120,42 @@ static bool GrowTownWithBridge(const Town *t, const TileIndex tile, const DiagDi
 	return false;
 }
 
+
+/**
+ * Checks whether at least one surrounding roads allows to build a house here
+ *
+ * @param t the tile where the house will be built
+ * @return true if at least one surrounding roadtype allows building houses here
+ */
+static inline bool RoadTypesAllowHouseHere(TileIndex t)
+{
+	RoadTypeIdentifier rtid;
+	RoadTypeIdentifiers rtids;
+	
+	static const TileIndexDiffC tiles[] = { {-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1} };
+	const TileIndexDiffC *ptr;
+	bool allow = false;
+
+	for (ptr = tiles; ptr != endof(tiles); ++ptr) {
+		TileIndex cur_tile = t + ToTileIndexDiff(*ptr);
+
+		if (!(IsTileType(cur_tile, MP_ROAD) || IsTileType(cur_tile, MP_STATION))) continue;
+		allow = true;
+
+		rtids = RoadTypeIdentifiers::FromTile(cur_tile);
+		FOR_EACH_SET_ROADTYPEIDENTIFIER(rtid, rtids)
+		{
+			/* Found one road which allows the type, it is enough to allow building the house here */
+			if (!HasBit(GetRoadTypeInfo(rtid)->flags, ROTF_DISALLOW_HOUSES_ALONG)) return true;
+		}
+	}
+
+	/* If no road was found surrounding the tile we can allow building the house since there is 
+	 * nothing which forbids it, if a road was found but the execution reached this point, then
+	 * all the found roads don't allow houses to be built */
+	return !allow;
+}
+
 /**
  * Grows the given town.
  * There are at the moment 3 possible way's for
@@ -1267,6 +1303,8 @@ static void GrowTownInTile(TileIndex *tile_ptr, RoadBits cur_rb, DiagDirection t
 			}
 		}
 
+		allow_house &= RoadTypesAllowHouseHere(house_tile);
+
 		if (allow_house) {
 			/* Build a house, but not if there already is a house there. */
 			if (!IsTileType(house_tile, MP_HOUSE)) {
@@ -2072,6 +2110,9 @@ static inline bool CanBuildHouseHere(TileIndex tile, TownID town, bool noslope)
 	Slope slope = GetTileSlope(tile);
 	if ((noslope && slope != SLOPE_FLAT) || IsSteepSlope(slope)) return false;
 
+	/* at least one RoadTypes allow building the house here? */
+	if (!RoadTypesAllowHouseHere(tile)) return false;
+
 	/* building under a bridge? */
 	if (IsBridgeAbove(tile)) return false;