Implemented new 'unload' command in caravan script.

caravan.lua

@@ -20,6 +20,8 @@ specified, then the commands apply to all caravans on the map.
   annoying merchants, etc.). Also causes caravans to return to the depot if
   applicable.
 - ``leave [IDS]``: makes caravans pack up and leave immediately.
+- ``unload``: fixes endless unloading at the depot. Run this if merchant pack
+  animals were startled and now refuse to come to the trade depot.
 
 ]====]
 
@@ -95,6 +97,51 @@ function commands.leave(...)
     end
 end
 
+local function isDisconnectedPackAnimal(unit)
+    if unit.following then
+        local dragger = unit.following
+        return (
+            unit.relationship_ids[ df.unit_relationship_type.Dragger ] == -1 and
+            dragger.relationship_ids[ df.unit_relationship_type.Draggee ] == -1
+        )
+    end
+end
+
+local function getPrintableUnitName(unit)
+    local visible_name = dfhack.units.getVisibleName(unit)
+    local profession_name = dfhack.units.getProfessionName(unit)
+    if visible_name.has_name then
+        return ('%s (%s)'):format(dfhack.TranslateName(visible_name), profession_name)
+    end
+    return profession_name  -- for unnamed animals
+end
+
+local function rejoin_pack_animals()
+    print('Reconnecting disconnected pack animals...')
+    local found = false
+    for _, unit in pairs(df.global.world.units.active) do
+        if unit.flags1.merchant and isDisconnectedPackAnimal(unit) then
+            local dragger = unit.following
+            print(('  %s  <->  %s'):format(
+                dfhack.df2console(getPrintableUnitName(unit)),
+                dfhack.df2console(getPrintableUnitName(dragger))
+            ))
+            unit.relationship_ids[ df.unit_relationship_type.Dragger ] = dragger.id
+            dragger.relationship_ids[ df.unit_relationship_type.Draggee ] = unit.id
+            found = true
+        end
+    end
+    if (found) then
+        print('All pack animals reconnected.')
+    else
+        print('No disconnected pack animals found.')
+    end
+end
+
+function commands.unload(...)
+    rejoin_pack_animals()
+end
+
 function commands.help()
     print(dfhack.script_help())
 end

changelog.txt

@@ -28,6 +28,7 @@ that repo.
 
 ## Misc Improvements
 - `build-now`: buildings that were just designated with `buildingplan` are now handled properly instead of being skipped (as long as there are items available to build the buildings with)
+- `caravan`: new ``unload`` command, fixes endless unloading at the depot, by reconnecting merchant pack animals that were disconnected from their owners.
 - `deteriorate`: new ``now`` command immediately deteriorates all items of the specified types.
 - `list-agreements`: now displays translated Guild Names, worshiped Deity, age of petition, and "man" to race-specific professions (e.g. "Craftsman" -> "Craftsdwarf")
 - `workorder`: doesn't check for an assigned manager anymore.