Add fmt-based Debug macro for upstream

src/debug.cpp

@@ -139,7 +139,7 @@ char *DumpDebugFacilityNames(char *buf, char *last)
  * @param dbg Debug category.
  * @param buf Text line to output.
  */
-static void debug_print(const char *dbg, const char *buf)
+void debug_print(const char *dbg, const char *buf)
 {
 	if (_debug_socket != INVALID_SOCKET) {
 		char buf2[1024 + 32];

src/debug.h

@@ -64,6 +64,7 @@ extern bool _save_DBGC_data;
 extern std::string _loadgame_DBGC_data;
 
 void CDECL debug(const char *dbg, const char *format, ...) WARN_FORMAT(2, 3);
+void debug_print(const char *dbg, const char *buf);
 
 char *DumpDebugFacilityNames(char *buf, char *last);
 void SetDebugString(const char *s, void (*error_func)(const char *));

src/debug_fmt.h

@@ -0,0 +1,24 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file debug_fmt.h Functions related to debugging. */
+
+#ifndef DEBUG_FMT_H
+#define DEBUG_FMT_H
+
+#include "debug.h"
+#include "3rdparty/fmt/format.h"
+
+/**
+ * Ouptut a line of debugging information.
+ * @param name The category of debug information.
+ * @param level The maximum debug level this message should be shown at. When the debug level for this category is set lower, then the message will not be shown.
+ * @param format_string The formatting string of the message.
+ */
+#define Debug(name, level, format_string, ...) if ((level) == 0 || _debug_ ## name ## _level >= (level)) debug_print(#name, fmt::format(FMT_STRING(format_string), ## __VA_ARGS__).c_str())
+
+#endif /* DEBUG_FMT_H */