Random light errors on the surface

[TurkeyMcMac]

Sometimes I see light errors like this:

When I regenerate the world, the errors do not appear where they previously did (they appear elsewhere.)

I don't know what causes them, but this patch seems prevent them from cropping up:

--- surface_tunnels-old.lua
+++ surface_tunnels-new.lua
@@ -15,6 +15,7 @@
    local t_start = os.clock()

    local vm, data, data_param2, area = mapgen_helper.mapgen_vm_data_param2()
+   local data_changed = false

    local eminp = {x=minp.x, y=area.MinEdge.y, z=minp.z}
    local emaxp = {x=maxp.x, y=area.MaxEdge.y, z=maxp.z}
@@ -51,9 +52,11 @@
                local index2d = mapgen_helper.index2d(minp, maxp, x, z)
                local humidity = humiditymap[index2d]
                if previous_potential_floor_y <= maxp_y and previous_potential_floor_y >= minp_y then
+                   data_changed = true
                    df_caverns.tunnel_floor(minp, maxp, area, previous_potential_floor_vi, nvals_cracks, data, data_param2, humidity > 30)
                end
                if y <= maxp_y and y >= minp_y then
+                   data_changed = true
                    df_caverns.tunnel_ceiling(minp, maxp, area, vi, nvals_cracks, data, data_param2, humidity > 30)
                end
                previous_potential_floor_vi = nil
@@ -66,16 +69,18 @@

    end

-   --send data back to voxelmanip
-   vm:set_data(data)
-   vm:set_param2_data(data_param2)
-   --calc lighting
-   vm:set_lighting({day = 0, night = 0})
-   vm:calc_lighting()
-   
-   vm:update_liquids()
-   --write it to world
-   vm:write_to_map()
+   if data_changed then
+       --send data back to voxelmanip
+       vm:set_data(data)
+       vm:set_param2_data(data_param2)
+       --calc lighting
+       vm:set_lighting({day = 0, night = 0})
+       vm:calc_lighting()
+       
+       vm:update_liquids()
+       --write it to world
+       vm:write_to_map()
+   end

    local time_taken = os.clock() - t_start -- how long this chunk took, in seconds
    mapgen_helper.record_time("df_caverns surface tunnels", time_taken)

My Minetest version is 5.5.0-dev with LuaJIT. My operating system is Ubuntu 21.10. My computer's architecture is x86_64.

[FaceDeer]

Sorry it took so long for me to be dragged back to the modding biz. I've added your changes, even without the lighting improvement it seems like this will be a nice efficiency improvement.