Here is the log from the crash:

  12.572 Error AppManagerStates.cpp:1448: The mod Central Rails (0.18.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event central_rails::on_configuration_changed
__central_rails__/control.lua:425: attempt to index field 'collision_mask' (a nil value)
stack traceback:
        __central_rails__/control.lua:425: in function 'on_runtime_mod_setting_changed'
        __central_rails__/control.lua:464: in function <__central_rails__/control.lua:462>

The tile-unknown tile prototype appears to be missing a collision mask.

Updated code snippet:

  -- find the water tiles
  global.is_water = {}
  for k,v in pairs( game.tile_prototypes ) do
     global.is_water[k]=false
     if v.collision_mask and v.collision_mask["water-tile"] then
        global.is_water[k]=true
     end
  end

Merged. Thanks!

You're welcome. I'm still puzzled as to why there is a tile prototype with a nil value for that field.

I also suspect that this part of your code could be using game.get_filtered_tile_prototypes, though it's in initialization code and so likely shouldn't matter much. I think though that globals might be one of the things that's part of the shared state, and I don't know that your list of the waterness of all tiles needs to be there.

I couldn't get get_filtered_tile_prototypes to work correctly though, and so I confined my surgery on your mod to the change I just showed you. :-)

I'm not convinced its the best but its... ok. The real work is in the intersection code which I haven't merged in because it only made things worse and slower.

I don't know why the tile prototype changed - I can't see any mention in Wube's changelog. Is it in plain sight?

I can't see either, and nobody responded to my reply to the 0.18.37 release announcement.

Yes, I can see how the intersection code would be a mess. Personally, I just rip up the intersection and replace it with my own when it gets to the point that I need one. :-)