Core: Add guard to start of fill to early exit if it is impossible to create a beatable game.

Fill.py

@@ -508,6 +508,32 @@ def distribute_items_restrictive(multiworld: MultiWorld,
         f"{[(item.location, item) for item in multiworld.itempool if item.location is not None]}"
     )
 
+    # cheap quick guard against unreachable goals to avoid wasting fill and progression balancing time
+    # collect all items and sweep pre_fill advancements because fill doesn't catch when they're unreachable
+    guard_state = multiworld.state.copy()
+    # super metroid can fail this check because of maxdiff, which it corrects in post fill, so we set maxdiff to max in
+    # our state to prevent a false warning.
+    smbm = getattr(guard_state, "smbm", None)
+    if smbm is not None:
+        for p in multiworld.player_ids:
+            if multiworld.game[p] == "Super Metroid" and p in smbm:
+                smbm[p].maxDiff = 8675309
+
+    for item in multiworld.itempool:
+        if item.advancement:
+            guard_state.collect(item, True)
+    pre_fill_advancements = [
+        location for location in multiworld.get_locations()
+        if location.item is not None and location.item.advancement
+    ]
+    guard_state.sweep_for_advancements(locations=pre_fill_advancements)
+    unreachable_goals = [
+        multiworld.player_name[player] for player in multiworld.player_ids
+        if not multiworld.has_beaten_game(guard_state, player)
+    ]
+    if unreachable_goals:
+        logging.warning(f"Prefill check failed for the following players. Generation may fail: {unreachable_goals}")
+
     fill_locations = sorted(multiworld.get_unfilled_locations())
     multiworld.random.shuffle(fill_locations)
     # get items to distribute
@@ -900,7 +926,7 @@ def item_percentage(player: int, num: int) -> float:
                     items_to_replace.sort()
                     multiworld.random.shuffle(items_to_replace)
 
-                    # Start swapping items. Since we swap into earlier spheres, no need for accessibility checks. 
+                    # Start swapping items. Since we swap into earlier spheres, no need for accessibility checks.
                     while replacement_locations and items_to_replace:
                         old_location = items_to_replace.pop()
                         for i, new_location in enumerate(replacement_locations):