(svn r21842) -Feature [FS#4393]: [NewGRF] Introduction dates/required types for rail types; e.g. introduce a particular rail type in 1960 (or when a vehicle using it is introduced), but also allow limiting its introduction to only happen when the required railtypes are available

src/rail.h

@@ -19,6 +19,7 @@
 #include "economy_func.h"
 #include "slope_type.h"
 #include "strings_type.h"
+#include "date_type.h"
 
 /** Railtype flags. */
 enum RailTypeFlags {
@@ -216,6 +217,21 @@ struct RailtypeInfo {
 	 */
 	byte map_colour;
 
+	/**
+	 * Introduction date.
+	 * When #INVALID_DATE or a vehicle using this railtype gets introduced earlier,
+	 * the vehicle's introduction date will be used instead for this railtype.
+	 * The introduction at this date is furthermore limited by the
+	 * #introduction_required_types.
+	 */
+	Date introduction_date;
+
+	/**
+	 * Bitmask of railtypes that are required for this railtype to be introduced
+	 * at a given #introduction_date.
+	 */
+	RailTypes introduction_required_railtypes;
+
 	/**
 	 * Bitmask of which other railtypes are introduced when this railtype is introduced.
 	 */
@@ -368,6 +384,8 @@ bool ValParamRailtype(const RailType rail);
  */
 RailType GetBestRailtype(const CompanyID company);
 
+RailTypes AddDateIntroducedRailTypes(RailTypes current, Date date);
+
 /**
  * Get the rail types the given company can build.
  * @param c the company to get the rail types for.