Fail early if there is no check at the start of the game

Catch some cases where the item randomizer won't be able to place the
first item and error out early with an actionable error message

This is not comprehensive, and might have false positives with
extra starting items due to the fairly static safety entrance
algorithm

randomizer.py

@@ -266,7 +266,15 @@ def __init__(self, seed, clean_iso_path, randomized_output_folder, options: Opti
     else:
       self.dungeons_and_caves_only_start = False
     self.logic.update_entrance_connection_macros() # Reset the entrance macros.
-
+
+    if self.dungeons_and_caves_only_start and not self.entrances.can_assign_safety_entrance():
+      msg = "No guaranteed accessible locations at the beginning of the game.\n"
+      if self.dungeons_only_start and not self.options.open_drc:
+        msg += 'Consider enabling more progression settings, adding starting items or enabling "Open DRC"'
+      else:
+        msg += "Consider enabling more progression settings or adding starting items"
+      raise TooFewProgressionLocationsError(msg)
+
     self.fully_initialized = True
 
   def get_max_progress_length(self) -> int:

randomizers/entrances.py

@@ -185,7 +185,7 @@ def __post_init__(self):
 
 
 DUNGEON_ENTRANCE_NAMES_WITH_NO_REQUIREMENTS = [
-  "Dungeon Entrance on Dragon Roost Island",
+  "Dungeon Entrance on Dragon Roost Island", # Conditional on the "Open DRC" option
 ]
 SECRET_CAVE_ENTRANCE_NAMES_WITH_NO_REQUIREMENTS = [
   "Secret Cave Entrance on Pawprint Isle",
@@ -464,7 +464,8 @@ def randomize_one_set_of_entrances(self, relevant_entrances: list[ZoneEntrance],
         e for e in relevant_entrances
         if e.entrance_name in self.entrance_names_with_no_requirements
       ]
-      self.safety_entrance = self.rng.choice(possible_safety_entrances)
+      if possible_safety_entrances:
+        self.safety_entrance = self.rng.choice(possible_safety_entrances)
 
     # We calculate which exits are terminal (the end of a nested chain) per-set instead of for all
     # entrances. This is so that, for example, Ice Ring Isle counts as terminal when its inner cave
@@ -1130,4 +1131,18 @@ def get_entrance_zone_for_boss(self, boss_name: str) -> str:
     zone_exit = ZoneExit.all[boss_arena_name]
     outermost_entrance = self.get_outermost_entrance_for_exit(zone_exit)
     return outermost_entrance.island_name
+
+  def can_assign_safety_entrance(self) -> bool:
+    # We need to be able to assign at least one safety entrance with progression
+    # in one of the sets of entrances to be randomized
+    if not self.is_enabled():
+      return True
+    for entrances, exits in self.get_all_entrance_sets_to_be_randomized():
+      if (
+        any(entr.entrance_name in self.entrance_names_with_no_requirements for entr in entrances)
+        and any(ex.unique_name in self.exit_names_with_no_requirements for ex in exits)
+      ):
+        return True
+    return False
+
   #endregion