Empty homes draw settlers: growth follows housing

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -35,7 +35,8 @@ Alpha. One season, bandit raids plus two friendly events, six buildings.
   Construction also saws planks, which higher building levels need, and
   builds fittings from them: one-off upgrades a building takes once it's high
   enough (shelving, a well pump, weapon racks, enchanted chests…). Population eats food,
-  pays taxes, and grows up to the housing cap; it promotes the settlement
+  pays taxes, and fills the houses (empty homes draw settlers, about a
+  quarter of all homes a day, plus slow family growth); it promotes the settlement
   (hamlet, village at 40, town at 90, city at 150), which raises building
   level caps and gives everyone bank slots.
 - **Prayer:** enemies drop bones; burying them gives prayer points and

game.py

@@ -482,7 +482,10 @@ TIERS = [
     {"name": "City", "pop": 150, "cap": 99, "houses": 8},
 ]
 TIER_SLOTS = 2
-GROWTH_PER_DAY = 0.12
+# Growth: empty homes draw settlers (a share of all the homes, every day, while
+# any stand empty), and families grow a little on their own.
+SETTLERS_PER_HOME = 0.25
+FAMILY_GROWTH = 0.05
 
 RAID_GROUPS = ["the Red Hand", "the Hollow Crows", "the Blackwater gang", "the Ashen Wolves",
                "the Gallows Men", "the Thornback raiders"]
@@ -1431,6 +1434,13 @@ def _start_next(world: dict, now: float) -> None:
         log(world, now, "build", f"{verb} the {BUILDINGS[key]['name'].lower()} began")
 
 
+def growth_per_day(world: dict) -> float:
+    """New townsfolk a day while there's room: settlers for the homes, plus families."""
+    pop = world["city"]["population"]
+    growth = SETTLERS_PER_HOME * housing(world) + FAMILY_GROWTH * pop
+    return growth * city_rate(world, "growth") * (1.25 if fitted(world, "furniture") else 1)
+
+
 def population_view(world: dict) -> dict:
     """Population, food and tier, with the numbers that explain them."""
     city = world["city"]
@@ -1439,7 +1449,7 @@ def population_view(world: dict) -> dict:
     if city["starving"]:
         growth = -pop * 0.04
     elif pop < room - 0.01:
-        growth = max(0.5, pop * GROWTH_PER_DAY)
+        growth = growth_per_day(world)
     elif pop > room:
         growth = -pop * 0.05
     else:
@@ -1619,8 +1629,7 @@ def _city_hour(world: dict, now: float) -> None:
     else:
         room = housing(world)
         if pop < room:
-            growth = max(0.5, pop * GROWTH_PER_DAY) * city_rate(world, "growth") * (1.25 if fitted(world, "furniture") else 1)
-            city["population"] = min(room, pop + growth / 24)
+            city["population"] = min(room, pop + growth_per_day(world) / 24)
         elif pop > room:
             city["population"] = max(room, pop - pop * 0.05 / 24)
         city["treasury"] += pop * 0.5 / 24

tests/test_game.py

@@ -302,11 +302,26 @@ class CityTest(unittest.TestCase):
         world = world_with()
         city = world["city"]
         city["stockpile"] = {"bread": 5}
+        city["population"] = 25.0  # a full town, so nobody new arrives
         world["next_fortune_at"] = None  # no lucky wagon of bread
         game.tick(world, T0 + 4 * game.DAY, random.Random(1))
         self.assertTrue(city["starving"])
         self.assertNotIn("bread", city["stockpile"])
-        self.assertLess(city["population"], 20)
+        self.assertLess(city["population"], 25)
+
+    def test_empty_homes_draw_settlers(self):
+        world = world_with()
+        city = world["city"]
+        city["population"] = 22.0
+        city["buildings"]["houses"]["level"] = 2
+        city["stockpile"] = {"bread": 10_000}
+        self.assertAlmostEqual(game.growth_per_day(world), 0.25 * 65 + 0.05 * 22)
+        for _hour in range(24):
+            game._city_hour(world, T0)
+        self.assertGreater(city["population"], 38)
+        for _hour in range(48):
+            game._city_hour(world, T0)
+        self.assertEqual(city["population"], 65)
 
     def test_fed_city_grows_to_housing_and_pays_tax(self):
         world = world_with()
@@ -899,8 +914,9 @@ class ConstructionTest(unittest.TestCase):
 
     def test_townsfolk_trickle_and_levels_help(self):
         world = self.site()
+        world["city"]["population"] = 25.0  # houses full, so the workforce stays put
         game.tick(world, T0 + 10 * game.HOUR, random.Random(1))
-        self.assertAlmostEqual(world["city"]["construction"]["labour"], 10 * 20 * game.TOWNSFOLK_LABOUR, delta=5)
+        self.assertAlmostEqual(world["city"]["construction"]["labour"], 10 * 25 * game.TOWNSFOLK_LABOUR, delta=5)
         p = world["players"]["bob"]
         self.assertEqual(game.labour_per_action(p), 1)
         p["xp"]["construction"] = game.XP_TABLE[40]