GRF: Add generic mechanism to observe which features have been tested

src/newgrf.cpp

@@ -9231,6 +9231,9 @@ struct GRFFeatureTest {
 		} else {
 			grfmsg(2, "Action 14 feature test: feature test: doing nothing: %u", has_feature ? 1 : 0);
 		}
+		if (this->feature != nullptr && this->feature->observation_flag != GFTOF_INVALID) {
+			SetBit(_cur.grffile->observed_feature_tests, this->feature->observation_flag);
+		}
 	}
 };
 

src/newgrf.h

@@ -358,6 +358,8 @@ struct GRFFile : ZeroedMemoryAllocator {
 	uint32 var8D_overlay;                    ///< Overlay for global variable 8D (action 0x14)
 	uint32 var9D_overlay;                    ///< Overlay for global variable 9D (action 0x14)
 
+	uint32 observed_feature_tests;           ///< Observed feature test bits (see: GRFFeatureTestObservationFlag)
+
 	const SpriteGroup *new_signals_group;    ///< New signals sprite group
 	byte new_signal_ctrl_flags;              ///< Ctrl flags for new signals
 	byte new_signal_extra_aspects;           ///< Number of extra aspects for new signals

src/newgrf_extension.h

@@ -85,20 +85,27 @@ enum Action2VariableRemapIds {
 	A2VRI_SIGNALS_SIGNAL_STYLE,
 };
 
+enum GRFFeatureTestObservationFlag : uint8 {
+	GFTOF_INVALID = 0xFF,
+};
+
 /** Action14 feature definition */
 struct GRFFeatureInfo {
 	const char *name; // nullptr indicates the end of the list
 	uint16 version;
+	GRFFeatureTestObservationFlag observation_flag;
 
 	/** Create empty object used to identify the end of a list. */
 	GRFFeatureInfo() :
 		name(nullptr),
-		version(0)
+		version(0),
+		observation_flag(GFTOF_INVALID)
 	{}
 
-	GRFFeatureInfo(const char *name, uint16 version) :
+	GRFFeatureInfo(const char *name, uint16 version, GRFFeatureTestObservationFlag observation_flag = GFTOF_INVALID) :
 		name(name),
-		version(version)
+		version(version),
+		observation_flag(observation_flag)
 	{}
 };