Rewrite portal removal to avoid stack overflow

This solves a problem were nether portal removal would trigger deep
recursion through node callbacks.  For large portals this could result
in stack overflow crashes on LuaJIT.  The issue is solved by rewriting
the portal removal to avoid recursion and removing the portal in one
operation using minetest.bulk_set_node.

mods/ITEMS/mcl_portals/portal_nether.lua

@@ -204,37 +204,52 @@ local function get_target(p)
 	end
 end
 
--- Destroy portal if pos (portal frame or portal node) got destroyed
+-- Destroy a nether portal.  Connected portal nodes are searched and removed
+-- using 'bulk_set_node'.  This function is called from 'after_destruct' of
+-- nether portal nodes.  The flag 'destroying_portal' is used to avoid this
+-- function being called recursively through callbacks in 'bulk_set_node'.
+local destroying_portal = false
 local function destroy_nether_portal(pos, node)
-	if not node then return end
-	local nn, orientation = node.name, node.param2
-	local obsidian = nn == OBSIDIAN
-
-	local function check_remove(pos, orientation)
-		local node = get_node(pos)
-		if node and (node.name == PORTAL and (orientation == nil or (node.param2 == orientation))) then
-			minetest.remove_node(pos)
-			remove_exit(pos)
-		end
-	end
-	if obsidian then -- check each of 6 sides of it and destroy every portal:
-		check_remove({x = pos.x - 1, y = pos.y, z = pos.z}, 0)
-		check_remove({x = pos.x + 1, y = pos.y, z = pos.z}, 0)
-		check_remove({x = pos.x, y = pos.y, z = pos.z - 1}, 1)
-		check_remove({x = pos.x, y = pos.y, z = pos.z + 1}, 1)
-		check_remove({x = pos.x, y = pos.y - 1, z = pos.z})
-		check_remove({x = pos.x, y = pos.y + 1, z = pos.z})
+	if destroying_portal then
 		return
 	end
+	destroying_portal = true
+
+	local orientation = node.param2
+	local checked_tab = { [minetest.hash_node_position(pos)] = true }
+	local nodes = { pos }
+
+	local function check_remove(pos)
+		local h = minetest.hash_node_position(pos)
+		if checked_tab[h] then
+			return
+		end
+
+		local node = minetest.get_node(pos)
+		if node and node.name == PORTAL and (orientation == nil or node.param2 == orientation) then
+			table.insert(nodes, pos)
+			checked_tab[h] = true
+		end
+	end
+
+	local i = 1
+	while i <= #nodes do
+		pos = nodes[i]
 		if orientation == 0 then
-		check_remove({x = pos.x - 1, y = pos.y, z = pos.z}, 0)
-		check_remove({x = pos.x + 1, y = pos.y, z = pos.z}, 0)
+			check_remove({x = pos.x - 1, y = pos.y, z = pos.z})
+			check_remove({x = pos.x + 1, y = pos.y, z = pos.z})
 		else
-		check_remove({x = pos.x, y = pos.y, z = pos.z - 1}, 1)
-		check_remove({x = pos.x, y = pos.y, z = pos.z + 1}, 1)
+			check_remove({x = pos.x, y = pos.y, z = pos.z - 1})
+			check_remove({x = pos.x, y = pos.y, z = pos.z + 1})
 		end
 		check_remove({x = pos.x, y = pos.y - 1, z = pos.z})
 		check_remove({x = pos.x, y = pos.y + 1, z = pos.z})
+		remove_exit(pos)
+		i = i + 1
+	end
+
+	minetest.bulk_set_node(nodes, { name = "air" })
+	destroying_portal = false
 end
 
 local on_rotate
@@ -817,7 +832,23 @@ local usagehelp = S("To open a Nether portal, place an upright frame of obsidian
 minetest.override_item(OBSIDIAN, {
 	_doc_items_longdesc = longdesc,
 	_doc_items_usagehelp = usagehelp,
-	after_destruct = destroy_nether_portal,
+	after_destruct = function(pos, node)
+		local function check_remove(pos, orientation)
+			local node = get_node(pos)
+			if node and node.name == PORTAL then
+				minetest.remove_node(pos)
+			end
+		end
+
+		-- check each of 6 sides of it and destroy every portal
+		check_remove({x = pos.x - 1, y = pos.y, z = pos.z})
+		check_remove({x = pos.x + 1, y = pos.y, z = pos.z})
+		check_remove({x = pos.x, y = pos.y, z = pos.z - 1})
+		check_remove({x = pos.x, y = pos.y, z = pos.z + 1})
+		check_remove({x = pos.x, y = pos.y - 1, z = pos.z})
+		check_remove({x = pos.x, y = pos.y + 1, z = pos.z})
+	end,
+
 	_on_ignite = function(user, pointed_thing)
 		local x, y, z = pointed_thing.under.x, pointed_thing.under.y, pointed_thing.under.z
 		-- Check empty spaces around obsidian and light all frames found: