mapt build --single: honour node_keys / way_keys

[cldellow]

If you write two slices:

node_keys = {"amenity"}

function node_function()
  Layer("amenity")
end

and

node_keys = {"tourism"}

function node_function()
  Layer("tourism")
end

and do mapt build, you will get two layers who each contain only amenity or tourism nodes.

If you do mapt build --single, you will get two layers who contain all nodes. This is because the merged driver file does not attempt to express your node_keys (or way_keys) to tilemaker, or filter on them before calling you.

So users need to write their functions defensively, e.g.:

node_keys = {"amenity"}

function node_function()
  if Find("amenity") == "" then return end
  Layer("amenity")
end

This is OK for a v1, but it'd be nicer if:

• the driver enforced node_keys/way_keys before delegating to your function
• the driver (when possible) expressed node_keys/way_keys to tilemaker, to allow it to optimize reading
  • it's not generally possible to do this for all permutations, but if your keys were all positive (i.e. no ~building entries), we could just union them all together