game/scripts/main.gd

@@ -25,6 +25,9 @@ var hud: Hud
 
 var _player_key: PackedByteArray
 var _next_dig_tick := 0
+## True while an unusable save could not be set aside. Saving is refused
+## then, so that the unusable save is never overwritten.
+var _save_blocked := false
 
 
 func _ready() -> void:
@@ -72,7 +75,8 @@ func _unhandled_input(event: InputEvent) -> void:
 
 func _notification(what: int) -> void:
 	if what == NOTIFICATION_WM_CLOSE_REQUEST and session != null:
-		save_game()
+		if not save_game():
+			push_warning("the game could not be saved on close")
 		_write_recording()
 
 
@@ -90,9 +94,14 @@ func _start_from_save() -> bool:
 	var loaded := GwSession.new()
 	if not loaded.start_loaded(store.read_save()):
 		var aside := store.set_aside_save()
+		if aside.is_empty():
+			_save_blocked = true
+			push_warning("save not usable (%s) and could not be set aside; saving is off" % loaded.last_error())
+		else:
 			push_warning("save not usable (%s), kept as %s" % [loaded.last_error(), aside])
 		hud.flash("LOAD_FAILED")
 		return false
+	_save_blocked = false
 	_enter(loaded)
 	return true
 
@@ -112,8 +121,9 @@ func _enter(next: GwSession) -> void:
 
 func _run_tick() -> void:
 	_apply(session.step())
-	if session.tick() % AUTOSAVE_TICKS == 0:
+	if session.tick() % AUTOSAVE_TICKS == 0 and not save_game():
-		save_game()
+		hud.flash("SAVE_FAILED")
+		push_warning("the automatic save failed")
 
 
 func _apply(events: Array[Dictionary]) -> void:
@@ -153,8 +163,11 @@ func dig_at(tile: Vector2i) -> void:
 	_next_dig_tick = session.tick() + GwSession.DIG_COOLDOWN_TICKS
 
 
-## Writes the running world as the save. Returns false if nothing was written.
+## Writes the running world as the save. Returns false if nothing was
+## written, also while an unusable save could not be set aside.
 func save_game() -> bool:
+	if _save_blocked:
+		return false
 	return store.write_save(session.save())
 
 

game/tests/test_main.gd

@@ -58,3 +58,19 @@ func test_an_unusable_save_is_set_aside_and_a_new_world_starts() -> void:
 	check_eq(main.hud.message(), tr("LOAD_FAILED"), "the player is told")
 	_stop_main(main)
 	TestFiles.remove_dir(directory)
+
+
+func test_an_unusable_save_that_cannot_be_set_aside_is_never_overwritten() -> void:
+	var directory := TestFiles.temporary_dir("stuck")
+	var store := SaveStore.new(directory)
+	store.write_save(PackedByteArray([1, 2, 3]))
+	# A folder under the set-aside name keeps the unusable save from moving.
+	DirAccess.make_dir_absolute(directory.path_join(SaveStore.SAVE_FILE + ".broken"))
+	var main := _start_main(directory)
+	await tree.process_frame
+	check(main.session.is_running(), "a new world runs")
+	check(not main.save_game(), "saving is refused")
+	check_eq(store.read_save(), PackedByteArray([1, 2, 3]), "the unusable save is untouched")
+	check_eq(main.hud.message(), tr("LOAD_FAILED"), "the player is told")
+	_stop_main(main)
+	TestFiles.remove_dir(directory)