don't warn for units on unwalkable tiles

if an adjacent tile is walkable. this avoids warning for, for example,
units walking under waterfalls or through variable depth water

changelog.txt

@@ -34,6 +34,7 @@ Template for new versions:
 - `gui/unit-syndromes`: show the syndrome names properly in the UI
 
 ## Misc Improvements
+- `warn-stranded`: don't warn for units that are temporarily on unwalkable tiles (e.g. as they pass under a waterfall)
 
 ## Removed
 

warn-stranded.lua

@@ -4,7 +4,6 @@
 --@module = true
 
 local gui = require 'gui'
-local utils = require 'utils'
 local widgets = require 'gui.widgets'
 local argparse = require 'argparse'
 local args = {...}
@@ -266,7 +265,7 @@ function WarningWindow:onClear()
 end
 
 function WarningWindow:onZoom()
-    local index, choice = self.subviews.list:getSelected()
+    local _, choice = self.subviews.list:getSelected()
     local unit = choice.data['unit']
 
     local target = xyz2pos(dfhack.units.getPosition(unit))
@@ -299,6 +298,11 @@ local function compareGroups(group_one, group_two)
     return #group_one['units'] < #group_two['units']
 end
 
+local function getWalkGroup(pos)
+    local block = dfhack.maps.getTileBlock(pos)
+    return block and block.walkable[pos.x % 16][pos.y % 16]
+end
+
 local function getStrandedUnits()
     local groupCount = 0
     local grouped = {}
@@ -310,9 +314,22 @@ local function getStrandedUnits()
 
     -- Pathability group calculation is from gui/pathable
     for _, unit in ipairs(citizens) do
-        local target = xyz2pos(dfhack.units.getPosition(unit))
-        local block = dfhack.maps.getTileBlock(target)
-        local walkGroup = block and block.walkable[target.x % 16][target.y % 16] or 0
+        local unitPos = xyz2pos(dfhack.units.getPosition(unit))
+        local walkGroup = getWalkGroup(unitPos) or 0
+
+        -- if on an unpathable tile, use the walkGroup of an adjacent tile. this prevents
+        -- warnings for units that are walking under falling water, which sometimes makes
+        -- a tile unwalkable while the unit is standing on it
+        if walkGroup == 0 then
+            walkGroup = getWalkGroup(xyz2pos(unitPos.x-1, unitPos.y-1, unitPos.z))
+                or getWalkGroup(xyz2pos(unitPos.x, unitPos.y-1, unitPos.z))
+                or getWalkGroup(xyz2pos(unitPos.x+1, unitPos.y-1, unitPos.z))
+                or getWalkGroup(xyz2pos(unitPos.x-1, unitPos.y, unitPos.z))
+                or getWalkGroup(xyz2pos(unitPos.x+1, unitPos.y, unitPos.z))
+                or getWalkGroup(xyz2pos(unitPos.x-1, unitPos.y+1, unitPos.z))
+                or getWalkGroup(xyz2pos(unitPos.x, unitPos.y+1, unitPos.z))
+                or getWalkGroup(xyz2pos(unitPos.x+1, unitPos.y+1, unitPos.z))
+        end
 
         if unitIgnored(unit) then
             table.insert(ensure_key(ignoredGroup, walkGroup), unit)