Units walking over foundations block construction of buildings

[fabio]

Can be reproduced when a flow of traders walk on a foundation.

This is the same issue of #1406, probably reappeared after pathfinding changes. (Opening a new bug since the old one is several years old.)

[_kali]

unit refusing to move off of a foundation

[_kali]

I've noticed that this typically happens when you place a foundation over a lot of units, and typically with larger buildings like forts and civ centers. Most units move out of the way, but sometimes 1 (and it's usually only 1) gets stuck. It seems like a "retry" is needed to keep moving units off the foundation every X seconds unit construction starts.

Another option is to simply not allow foundations to be placed on units (and for units not to be allowed to travel over foundations). Since foundations have 1hp, it wouldn't be unreasonable to have an invading army destroy the foundation, or to not allow their progress over it. It would also help solve this nomad exploit: ​http://trac.wildfiregames.com/ticket/3667. And placing unconstructed buildings as obstacles wouldn't necessarily be a huge advantage since they cost everything up front. It's true that you get their money back when they're destroyed, but there could be a cliff to how much you recoup, like a max of 80% returned once you place a building and it's destroyed.

In any event, when a unit gets stuck on a foundation, the workers animate like they're working, but nothing gets built and the player doesn't get notified, so it's easy to place a building and come back a minute later to see that nothing was built. I've seen it affect the outcome of some close games.

[elexis]

refs #5500 #4278