Store some desync messages in a ring buffer, append to log on desync

src/command.cpp

@@ -933,8 +933,10 @@ CommandCost DoCommandPInternal(TileIndex tile, uint32 p1, uint32 p2, uint32 cmd,
 	SetTownRatingTestMode(false);
 
 	if (!random_state.Check()) {
-		DEBUG(desync, 0, "Random seed changed in test command: date{%08x; %02x; %02x}; company: %02x; tile: %06x (%u x %u); p1: %08x; p2: %08x; cmd: %08x; \"%s\" %X (%s)",
-				_date, _date_fract, _tick_skip_counter, (int)_current_company, tile, TileX(tile), TileY(tile), p1, p2, cmd & ~CMD_NETWORK_COMMAND, text, binary_length, GetCommandName(cmd));
+		std::string msg = stdstr_fmt("Random seed changed in test command: company: %02x; tile: %06x (%u x %u); p1: %08x; p2: %08x; cmd: %08x; \"%s\" %X (%s)",
+				(int)_current_company, tile, TileX(tile), TileY(tile), p1, p2, cmd & ~CMD_NETWORK_COMMAND, text, binary_length, GetCommandName(cmd));
+		DEBUG(desync, 0, "msg: date{%08x; %02x; %02x}; %s", _date, _date_fract, _tick_skip_counter, msg.c_str());
+		LogDesyncMsg(std::move(msg));
 	}
 
 	/* Make sure we're not messing things up here. */

src/crashlog.cpp

@@ -459,6 +459,7 @@ char *CrashLog::FillDesyncCrashLog(char *buffer, const char *last) const
 	buffer = this->LogGamelog(buffer, last);
 	buffer = this->LogRecentNews(buffer, last);
 	buffer = this->LogCommandLog(buffer, last);
+	buffer = DumpDesyncMsgLog(buffer, last);
 
 	bool have_cache_log = false;
 	extern void CheckCaches(bool force_check, std::function<void(const char *)> log);

src/debug.cpp

@@ -16,6 +16,8 @@
 #include "string_func.h"
 #include "fileio_func.h"
 #include "settings_type.h"
+#include "date_func.h"
+#include <array>
 
 #if defined(_WIN32)
 #include "os/windows/win32.h"
@@ -305,3 +307,56 @@ const char *GetLogPrefix()
 	return _log_prefix;
 }
 
+struct DesyncMsgLogEntry {
+	Date date;
+	DateFract date_fract;
+	uint8 tick_skip_counter;
+	std::string msg;
+
+	DesyncMsgLogEntry() { }
+
+	DesyncMsgLogEntry(std::string msg)
+			: date(_date), date_fract(_date_fract), tick_skip_counter(_tick_skip_counter), msg(msg) { }
+};
+
+static std::array<DesyncMsgLogEntry, 32> desync_msg_log;
+static unsigned int desync_msg_log_count = 0;
+static unsigned int desync_msg_log_next = 0;
+
+void ClearDesyncMsgLog()
+{
+	desync_msg_log_count = 0;
+	desync_msg_log_next = 0;
+}
+
+char *DumpDesyncMsgLog(char *buffer, const char *last)
+{
+	if (!desync_msg_log_count) return buffer;
+
+	const unsigned int count = min<unsigned int>(desync_msg_log_count, desync_msg_log.size());
+	unsigned int log_index = desync_msg_log_next;
+
+	buffer += seprintf(buffer, last, "Desync Msg Log:\n Showing most recent %u of %u messages\n", count, desync_msg_log_count);
+
+	for (unsigned int i = 0 ; i < count; i++) {
+		if (log_index > 0) {
+			log_index--;
+		} else {
+			log_index = desync_msg_log.size() - 1;
+		}
+		const DesyncMsgLogEntry &entry = desync_msg_log[log_index];
+
+		YearMonthDay ymd;
+		ConvertDateToYMD(entry.date, &ymd);
+		buffer += seprintf(buffer, last, " %2u | %4i-%02i-%02i, %2i, %3i | %s\n", i, ymd.year, ymd.month + 1, ymd.day, entry.date_fract, entry.tick_skip_counter, entry.msg.c_str());
+	}
+	buffer += seprintf(buffer, last, "\n");
+	return buffer;
+}
+
+void LogDesyncMsg(std::string msg)
+{
+	desync_msg_log[desync_msg_log_next] = DesyncMsgLogEntry(std::move(msg));
+	desync_msg_log_next = (desync_msg_log_next + 1) % desync_msg_log.size();
+	desync_msg_log_count++;
+}

src/debug.h

@@ -133,4 +133,8 @@ const char *GetLogPrefix();
 /** The real time in the game. */
 extern uint32 _realtime_tick;
 
+void ClearDesyncMsgLog();
+void LogDesyncMsg(std::string msg);
+char *DumpDesyncMsgLog(char *buffer, const char *last);
+
 #endif /* DEBUG_H */

src/misc.cpp

@@ -72,6 +72,7 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 
 	ViewportMapClearTunnelCache();
 	ClearCommandLog();
+	ClearDesyncMsgLog();
 
 	_pause_mode = PM_UNPAUSED;
 	_fast_forward = 0;

src/openttd.cpp

@@ -382,6 +382,7 @@ static void ShutdownGame()
 	InvalidateVehicleTickCaches();
 	ClearVehicleTickCaches();
 	ClearCommandLog();
+	ClearDesyncMsgLog();
 
 	_game_events_since_load = (GameEventFlags) 0;
 	_game_events_overall = (GameEventFlags) 0;
@@ -1304,7 +1305,11 @@ void CheckCaches(bool force_check, std::function<void(const char *)> log)
 #define CCLOG(...) { \
 	seprintf(cclog_buffer, lastof(cclog_buffer), __VA_ARGS__); \
 	DEBUG(desync, 0, "%s", cclog_buffer); \
-	if (log) log(cclog_buffer); \
+	if (log) { \
+		log(cclog_buffer); \
+	} else { \
+		LogDesyncMsg(cclog_buffer); \
+	} \
 }
 
 	/* Check the town caches. */