G_MapIsSafe

Generalized safety test for maps, in an attempt to curb G_GetNextMap
producing an I_Error due to an unchecked override

src/g_game.c

@@ -4951,6 +4951,14 @@ mapnum_t G_CheckNextMap(boolean noadvancemap)
 	//boolean spec = G_IsSpecialStage(currentmap);
 	INT32 i;
 
+	// Kill nextmapoverride if it's not a safe move
+	if (!G_MapIsSafe(nextmapoverride))
+	{
+		// At least beat the programmer/host over the head for it
+		CONS_Alert(CONS_WARNING, "Overriding map ID %d is unsafe!", nextmapoverride);
+		nextmapoverride = 0;
+	}
+
 	if (nextmapoverride != 0)
 	{
 		return nextmapoverride-1;
@@ -5104,6 +5112,14 @@ mapnum_t G_CheckNextMap(boolean noadvancemap)
 	}
 }
 
+// Tests if a given map number is safe to go to. If not, this returns false.
+boolean G_MapIsSafe(mapnum_t map)
+{
+	return (map != NEXTMAP_INVALID &&
+		(map >= NEXTMAP_SPECIAL || (map < nummapheaders && mapheaderinfo[map] &&
+					    mapheaderinfo[map]->lumpnum != LUMPERROR)));
+}
+
 void G_GetNextMap(void)
 {
 	if (!server)
@@ -5222,7 +5238,7 @@ void G_GetNextMap(void)
 	}
 
 	// We are committed to this map now.
-	if (nextmap == NEXTMAP_INVALID || (nextmap < NEXTMAP_SPECIAL && (nextmap >= nummapheaders || !mapheaderinfo[nextmap] || mapheaderinfo[nextmap]->lumpnum == LUMPERROR)))
+	if (!G_MapIsSafe(nextmap))
 		I_Error("G_GetNextMap: Internal map ID %d not found (nummapheaders = %d)\n", nextmap, nummapheaders);
 
 #if 0 // This is a surprise tool that will help us later.

src/g_game.h

@@ -223,6 +223,7 @@ UINT8 G_GetGametypeColor(INT16 gt);
 void G_BeginLevelExit(void);
 void G_FinishExitLevel(void);
 void G_NextLevel(void);
+boolean G_MapIsSafe(mapnum_t map);
 mapnum_t G_CheckNextMap(boolean noadvancemap);
 void G_GetNextMap(void);
 void G_Continue(void);

src/lua_baselib.c

@@ -3502,10 +3502,11 @@ static int lib_gDoReborn(lua_State *L)
 }
 
 // Another Lua function that doesn't actually exist!
-// Sets nextmapoverride & skipstats without instantly ending the level, for instances where other sources should be exiting the level, like normal signposts.
-static int lib_gSetCustomExitVars(lua_State *L)
+// Sets nextmapoverride & skipstats without instantly ending the level, for instances where other
+// sources should be exiting the level, like normal signposts.
+static int lib_gSetCustomExitVars(lua_State* L)
 {
-	int n = lua_gettop(L); // Num arguments
+	int n = lua_gettop(L);  // Num arguments
 	NOHUD
 	INLEVEL
 
@@ -3516,15 +3517,36 @@ static int lib_gSetCustomExitVars(lua_State *L)
 	//	G_SetCustomExitVars(nil, int)	[skipstats only]
 	//	G_SetCustomExitVars(int, int)	[both of the above]
 
+	mapnum_t potential_override = 0;
+
 	nextmapoverride = 0;
 	skipstats = 0;
 
 	if (n >= 1)
 	{
-		nextmapoverride = luaL_optinteger(L, 1, 0);
+		potential_override = luaL_optinteger(L, 1, 0);
 		skipstats = (INT16)luaL_optinteger(L, 2, 0);
-		if (lua_compatmode && nextmapoverride)
-			nextmapoverride = G_KartMapToNative(nextmapoverride);
+		if (lua_compatmode && potential_override)
+			potential_override = G_KartMapToNative(potential_override);
+
+		if (potential_override != 0)
+		{
+			// Prevent crashes by making sure the override is safe
+			if (!G_MapIsSafe(potential_override))
+			{
+				// Override is very definitively NOT safe; error out
+				return luaL_error(
+				    L,
+				    "provided map override %d is invalid (nummapheaders = %d)",
+				    potential_override,
+				    nummapheaders);
+			}
+			else
+			{
+				// Allow the override
+				nextmapoverride = potential_override;
+			}
+		}
 	}
 
 	return 0;
@@ -3630,6 +3652,18 @@ static int lib_gTicsToMilliseconds(lua_State *L)
 	return 1;
 }
 
+static int lib_gMapIsSafe(lua_State *L)
+{
+	mapnum_t map = (mapnum_t)luaL_checkinteger(L, 1);
+
+	if (lua_compatmode && map)
+		map = G_KartMapToNative(map);
+
+	//HUDSAFE
+	lua_pushboolean(L, G_MapIsSafe(map));
+	return 1;
+}
+
 // K_KART
 ////////////
 
@@ -5781,6 +5815,7 @@ static luaL_Reg lib[] = {
 	{"G_AddGametype", lib_gAddGametype},
 	{"G_BuildMapName",lib_gBuildMapName},
 	{"G_MapNumber",lib_gMapNumber},
+	{"G_MapIsSafe",lib_gMapIsSafe},
 	{"G_BuildMapTitle",lib_gBuildMapTitle},
 	{"G_FindMap",lib_gFindMap},
 	{"G_FindMapByNameOrCode",lib_gFindMapByNameOrCode},