Asymmetric inter-shard portals

[late patrol]

I noticed when I was running some whole-world offline map analysis a while back that a small number of the inter-shard portals in highway intersections are asymmetric - there's a portal going one direction, but unlike most cases, there's no return portal going the other direction back to the original shard. This seems likely unintended or a bug with the tools managing portals for MMO that's persisted for a while.

The portals without an associated return portal are:

from shard2 E0N10 to shard3 E0N10
from shard1 W10S40 to shard0 W10S80
from shard1 W10S50 to shard0 W10S90
from shard1 W20N10 to shard0 W30N10

[lavish tulip]

I checked into this for the first example and see it may be an intended quirk.

• This is a "double highway" intersection
• that there is a portal 1 room left in W0N10, that goes from Shard 3 to shard2.
• Good chance the doublehighway is splitting these paths intentionally.
  https://screeps.com/a/#!/room/shard3/E0N10
  https://screeps.com/a/#!/room/shard3/W0N10

[late patrol]

Fair, but all other double-highways in the game have portals in both rooms, which made me lean toward it being likely unintended

[crimson loom]

On shard0 there are portals (not inter-shard) leading to disabled rooms. Maybe it's somehow related.
For example, W60N70 in a disabled W40N70:
https://screeps.com/a/#!/room/shard0/W60N70

[heavy swan]

Okay, this is actually pretty interesting. It seems like a bug to me.

Double lane highways are intentional. Highways occur on any room where the E/W and/or N/S coord is 0, so that part is fine.

The weird part is that https://screeps.com/a/#!/room/shard2/E0N10 has a portal to https://screeps.com/a/#!/room/shard3/E0N10, but there's no matching portal in shard3.

[lavish ermine]

it's here: https://screeps.com/a/#!/room/shard3/W0N10

I think the portals around dual-highways are laid out to make a "room loop" or something?