Merge pull request #4178 from myk002/myk_retire_zone

[zone] don't count dangling references when retiring zones

docs/changelog.txt

@@ -55,6 +55,7 @@ Template for new versions:
 
 ## New Features
 - `sort`: search and sort for the "choose unit to elevate to the barony" screen. units are sorted by the number of item preferences they have and the units are annotated with the items that they have preferences for
+- `zone`: add button to location details page for retiring unused locations
 - `gui/mass-remove`: new global keybinding: Ctrl-M while on the fort map
 
 ## Fixes

plugins/lua/zone.lua

@@ -1168,12 +1168,19 @@ end
 function RetireLocationOverlay:confirm_retire()
     local details = mi.location_details
     local location = details.selected_ab
-    local num_occupations, num_zones = 0, #location.contents.building_ids
+    local num_occupations, num_zones = 0, 0
     for _, occupation in ipairs(location.occupations) do
         if occupation.histfig_id ~= -1 then
             num_occupations = num_occupations + 1
         end
     end
+    for _, zone_id in ipairs(location.contents.building_ids) do
+        -- there can be dangling references in this list; only count
+        -- "attached" zones that actually exist
+        if df.building.find(zone_id) then
+            num_zones = num_zones + 1
+        end
+    end
     if num_occupations + num_zones > 0 then
         local messages = {'Cannot retire location! Please:', ''}
         if num_occupations > 0 then