Units::setPathGoal check for NULL unit.

docs/changelog.txt

@@ -33,6 +33,7 @@ Template for new versions:
 ## New Features
 
 ## Fixes
+- ``Units::setPathGoal``: no longer crashes when passed NULL as a unit.  Also fixes ``dfhack.units.setPathGoal()``.
 
 ## Misc Improvements
 

library/modules/Units.cpp

@@ -1029,6 +1029,7 @@ void Units::setAutomaticProfessions(df::unit* unit) {
 // functionality reverse-engineered from DF's unitst::set_goal
 void Units::setPathGoal(df::unit *unit, df::coord pos, df::unit_path_goal goal)
 {
+    CHECK_NULL_POINTER(unit);
     if (unit->path.dest != pos || unit->path.goal != goal)
     {
         unit->path.dest = pos;

test/modules/units_fortress.lua

@@ -1,10 +1,18 @@
 config.mode = 'fortress'
 config.target = 'core'
 
+local utils = require('utils')
+
+---TODO when we get LuaLS integrated, declare coord in just one place.
+---@alias coord { x:integer, y:integer, z:integer } | df.coord
+
+---@param pos coord
+---@return df.tile_occupancy
 local function tile_occupancy(pos)
     return select(2, dfhack.maps.getTileFlags(pos))
 end
 
+---@return df.unit, df.unit
 local function two_citizens()
     local a, b
     for _, unit in ipairs(df.global.world.units.active) do
@@ -21,6 +29,9 @@ local function two_citizens()
 end
 
 -- find an allocated, walkable tile with no unit occupancy near pos
+---@param pos coord
+---@return coord?
+---@return string?
 local function free_tile_near(pos)
     for dx = -4, 4 do for dy = -4, 4 do
         if dx ~= 0 or dy ~= 0 then
@@ -40,6 +51,8 @@ end
 
 -- recompute the unit occupancy flags of the given tiles from the given
 -- units, so fabricated flag states do not leak into later tests
+---@param tiles coord[]
+---@param units df.unit[]
 local function resync_occupancy(tiles, units)
     for _, pos in ipairs(tiles) do
         local occ = tile_occupancy(pos)
@@ -138,3 +151,34 @@ function test.teleport_keeps_unit_flag_with_other_standing_unit()
         expect.false_(tile_occupancy(shared).unit)
     end)
 end
+
+function test.setPathGoal()
+    -- catch regression of issue #5978, setPathGoal() is missing CHECK_NULL_POINTER(unit)
+    expect.error(function()
+            ---@diagnostic disable-next-line: param-type-mismatch
+            dfhack.units.setPathGoal(nil, xyz2pos(1, 2, 3), df.unit_path_goal.None)
+        end,
+        "dfhack.units.setPathGoal should have thrown an error.")
+
+    local unit
+    for _,u in ipairs(dfhack.units.getCitizens()) do
+        if #u.path.path.x > 0 then
+            unit = u
+            break
+        end
+    end
+    expect.ne(unit, nil)
+
+    local oldpath = utils.clone(unit.path, true)
+
+    local retval = dfhack.units.setPathGoal(unit, xyz2pos(1, 2, 3), df.unit_path_goal.None)
+    expect.nil_(retval)
+    expect.eq(df.unit_path_goal.None, unit.path.goal)
+    expect.table_eq(xyz2pos(1, 2, 3), utils.clone(unit.path.dest, true))
+    expect.table_eq({ x = {}, y = {}, z = {} }, utils.clone(unit.path.path, true))
+
+    unit.path:assign(oldpath)
+    expect.eq(oldpath.goal, unit.path.goal)
+    expect.table_eq(oldpath.dest, utils.clone(unit.path.dest, true))
+    expect.table_eq(oldpath.path, utils.clone(unit.path.path, true))
+end