Ensure index for heightmap entry is within bounds

mods/MAPGEN/mcl_villages/init.lua

@@ -80,20 +80,29 @@ end
 local mg_name = minetest.get_mapgen_setting("mg_name")
 if mg_name ~= "singlenode" then
 	mcl_mapgen_core.register_generator("villages", nil, function(minp, maxp, blockseed)
-		-- don't build settlement underground
 		if maxp.y < 0 then return end
+
 		-- randomly try to build settlements
 		if blockseed % 77 ~= 17 then return end
+		--minetest.log("Rng good. Generate attempt")
+
 		-- needed for manual and automated settlement building
 		-- don't build settlements on (too) uneven terrain
 		local n=minetest.get_node_or_nil(minp)
 		if n and n.name == "mcl_villages:structblock" then return end
+		--minetest.log("No existing village attempt here")
+
 		if villagegen[minetest.pos_to_string(minp)] ~= nil then return end
+
+		--minetest.log("Not in village gen. Put down placeholder: " .. minetest.pos_to_string(minp) .. " || " .. minetest.pos_to_string(maxp))
 		minetest.set_node(minp,{name="mcl_villages:structblock"})
 
 		local height_difference = settlements.evaluate_heightmap()
-		if height_difference > max_height_difference then return end
-
+		if not height_difference or height_difference > max_height_difference then
+			minetest.log("action", "Do not spawn village here as heightmap not good")
+			return
+		end
+		--minetest.log("Build me a village: " .. minetest.pos_to_string(minp) .. " || " .. minetest.pos_to_string(maxp))
 		villagegen[minetest.pos_to_string(minp)]={minp=vector.new(minp), maxp=vector.new(maxp), blockseed=blockseed}
 	end)
 end

mods/MAPGEN/mcl_villages/utils.lua

@@ -199,7 +199,12 @@ end
 function settlements.evaluate_heightmap()
 	local heightmap = minetest.get_mapgen_object("heightmap")
 
-	if not heightmap then return max_height_difference + 1 end
+	if not heightmap then
+		minetest.log("action", "No heightmap. That should not happen")
+		return max_height_difference + 1
+	end
+
+	--minetest.log("action", "heightmap size: " .. tostring(#heightmap))
 
 	-- max height and min height, initialize with impossible values for easier first time setting
 	local max_y = -50000
@@ -208,16 +213,32 @@ function settlements.evaluate_heightmap()
 	local square_start = 1621
 	local square_end = 1661
 	for j = 1 , 40, 1 do
+		if square_start >= #heightmap then
+			--minetest.log("action", "Heightmap size reached. Go no further outside")
+			break
+		end
 		for i = square_start, square_end, 1 do
-			-- skip buggy heightmaps, return high value
-			if heightmap[i] == -31000 or heightmap[i] == 31000 then
+			--minetest.log("action", "current hm index: " .. tostring(i) .. "current hm entry: " .. tostring(heightmap[i]))
+
+			if i >= #heightmap then
+				--minetest.log("action", "Heightmap size reached. Go no further")
+				break
+			end
+			local current_hm_entry = heightmap[i]
+			if current_hm_entry then
+				-- skip buggy heightmaps, return high value. Converted mcl5 maps can be -31007
+				if current_hm_entry == -31000 or heightmap[i] == 31000 then
+					--minetest.log("action", "incorrect heighmap values. abandon")
 					return max_height_difference + 1
 				end
-			if heightmap[i] < min_y then
-				min_y = heightmap[i]
+				if current_hm_entry < min_y then
+					min_y = current_hm_entry
 				end
-			if heightmap[i] > max_y then
-				max_y = heightmap[i]
+				if current_hm_entry > max_y then
+					max_y = current_hm_entry
+				end
+			else
+				--minetest.log("action", "Failed to get hm index: " .. tostring(i) .. "and ... " .. tostring(#heightmap))
 			end
 		end
 		-- set next line
@@ -226,10 +247,14 @@ function settlements.evaluate_heightmap()
 	end
 	-- return the difference between highest and lowest pos in chunk
 	local height_diff = max_y - min_y
+
+	--minetest.log("action", "height_diff = " .. tostring(height_diff))
+
 	-- filter buggy heightmaps
 	if height_diff <= 1 then
 		return max_height_difference + 1
 	end
+	--minetest.log("action", "return heigh diff = " .. tostring(height_diff))
 	-- debug info
 	settlements.debug("heightdiff ".. height_diff)
 	return height_diff