0009643: Removal of up/down staircase causes pathing through non existent tile above - Dwarf Fortress Bug Tracker

ID	Project	Category	View Status	Date Submitted	Last Update

0009643	Dwarf Fortress	Dwarf Mode -- Jobs, Building Construction and Destruction	public	2016-03-20 02:01	2016-03-20 14:30

Reporter	PatrikLundell	Assigned To
Priority	normal	Severity	minor	Reproducibility	have not tried
Status	new	Resolution	open
Platform	PC	OS	Windows	OS Version	10
Product Version	0.42.05

Summary	0009643: Removal of up/down staircase causes pathing through non existent tile above
Description	I've recently had three instances of rather strange pathing along non existent paths. Two of the instances happened along the same path, so there were two locations affected. In the first case I removed an up/down staircase at level Z-1, and after that had been done I got two builders who climbed in the always empty space above the removed staircase, cancelled their jobs due to a dangerous path, and then proceeded to climb sideways to strand themselves on an isolated ledge. The second arrived a minute or two later than the first one, so it's not a case of the staircse being removed beneath their feet. The haulers had no business there at any time, since the staircase was to the side of the path if they were hauling to level Z-1 (there's a perfectly good ramp down which provides a shorter path). I think, however, the hauler were using a shortcut through the space above the removed staircase (that would be a shorter route, cutting a corner on level Z). In the second case a builder paths on level Z towards a recently removed up/down staircase at level Z-1 with a single tile gap above it (again, there's never been anything in the gap at level Z), cancelling the job with a dangerous terrain message. I didn't see the builder go over the edge and back, but it might have done so. Every other builder have taken the much longer (but actually existing) path around the gap both before and after the incident. I've also had 3 other up/down staircases along/below the gap that might have provoked similar pathing when removed, but without doing so. It seems removal of an up/down staircase somehow briefly generates pathable terrain on the level above it, and if the timing is right a dorf may select that "path", only to discover it isn't valid when reaching that never actually existing pathable tile.
Additional Information	Using the Lazy Newb Pack r01 with Dwarf Therapist, the Phoebus tile set, and DFHack Performance Tweaks. The Crimson Crops mod has been used and removed. Gremlins have been doubled in size mid game to allow them to wear kobold clothes.
Tags	No tags attached.

Loci 2016-03-20 11:32 viewer ~0034883	Dwarves will repath using jump/climb pathing if their previously-chosen path is blocked (by deconstructing stairs in this instance). As the name suggests, the path can include climbing and/or jumping.

PatrikLundell 2016-03-20 14:30 reporter ~0034887	The explanation explains why dorfs sometimes pass over dangerous terrain when something has been removed, which is useful info. However, it does not explain why they do so in my cases, since there was never a legal path there in the first place, and nobody used/tried to use those paths before the deconstruction of the up/down staircases on the level below the "paths".

Date Modified	Username	Field	Change
2016-03-20 02:01	PatrikLundell	New Issue
2016-03-20 11:32	Loci	Note Added: 0034883
2016-03-20 14:30	PatrikLundell	Note Added: 0034887