Fill: fix swap error found in CI (ArchipelagoMW#2397)

* Fill: add test for swap error with item rules

https://discord.com/channels/731205301247803413/731214280439103580/1167195750082560121

* Fill: fix swap error found in CI

Swap now assumes the unplaced items can be placed before the to-be-swapped item.
Unsure if that is safe or unsafe.

* Test: clarify docstring and comments in fill swap test

* Test: clarify comments in fill swap test more

Author: black-sliver

Fill.py

@@ -112,7 +112,7 @@ def fill_restrictive(world: MultiWorld, base_state: CollectionState, locations:
 
                         location.item = None
                         placed_item.location = None
-                        swap_state = sweep_from_pool(base_state, [placed_item] if unsafe else [])
+                        swap_state = sweep_from_pool(base_state, [placed_item, *item_pool] if unsafe else item_pool)
                         # unsafe means swap_state assumes we can somehow collect placed_item before item_to_place
                         # by continuing to swap, which is not guaranteed. This is unsafe because there is no mechanic
                         # to clean that up later, so there is a chance generation fails.

test/general/test_fill.py

@@ -442,6 +442,47 @@ def test_swap_to_earlier_location_with_item_rule(self):
         self.assertTrue(sphere1_loc.item, "Did not swap required item into Sphere 1")
         self.assertEqual(sphere1_loc.item, allowed_item, "Wrong item in Sphere 1")
 
+    def test_swap_to_earlier_location_with_item_rule2(self):
+        """Test that swap works before all items are placed"""
+        multi_world = generate_multi_world(1)
+        player1 = generate_player_data(multi_world, 1, 5, 5)
+        locations = player1.locations[:]  # copy required
+        items = player1.prog_items[:]  # copy required
+        # Two items provide access to sphere 2.
+        # One of them is forbidden in sphere 1, the other is first placed in sphere 4 because of placement order,
+        # requiring a swap.
+        # There are spheres in between, so for the swap to work, it'll have to assume all other items are collected.
+        one_to_two1 = items[4].name
+        one_to_two2 = items[3].name
+        three_to_four = items[2].name
+        two_to_three1 = items[1].name
+        two_to_three2 = items[0].name
+        # Sphere 4
+        set_rule(locations[0], lambda state: ((state.has(one_to_two1, player1.id) or state.has(one_to_two2, player1.id))
+                                              and state.has(two_to_three1, player1.id)
+                                              and state.has(two_to_three2, player1.id)
+                                              and state.has(three_to_four, player1.id)))
+        # Sphere 3
+        set_rule(locations[1], lambda state: ((state.has(one_to_two1, player1.id) or state.has(one_to_two2, player1.id))
+                                              and state.has(two_to_three1, player1.id)
+                                              and state.has(two_to_three2, player1.id)))
+        # Sphere 2
+        set_rule(locations[2], lambda state: state.has(one_to_two1, player1.id) or state.has(one_to_two2, player1.id))
+        # Sphere 1
+        sphere1_loc1 = locations[3]
+        sphere1_loc2 = locations[4]
+        # forbid one_to_two2 in sphere 1 to make the swap happen as described above
+        add_item_rule(sphere1_loc1, lambda item_to_place: item_to_place.name != one_to_two2)
+        add_item_rule(sphere1_loc2, lambda item_to_place: item_to_place.name != one_to_two2)
+
+        # Now fill should place one_to_two1 in sphere1_loc1 or sphere1_loc2 via swap,
+        # which it will attempt before two_to_three and three_to_four are placed, testing the behavior.
+        fill_restrictive(multi_world, multi_world.state, player1.locations, player1.prog_items)
+        # assert swap happened
+        self.assertTrue(sphere1_loc1.item and sphere1_loc2.item, "Did not swap required item into Sphere 1")
+        self.assertTrue(sphere1_loc1.item.name == one_to_two1 or
+                        sphere1_loc2.item.name == one_to_two1, "Wrong item in Sphere 1")
+
     def test_double_sweep(self):
         """Test that sweep doesn't duplicate Event items when sweeping"""
         # test for PR1114