Keep quick bar slots whose record is not in the blueprint library yet

A save gets a player's blueprint library from the client some seconds
after the join. The data of a player new to the save is applied before
that, so quick bar slots pointing at library records were cleared, and
the next upload stored the quick bar without them.

The entries are now kept. They are set once the record shows up, and an
upload before that stores them again as they came.

Fixes #1219

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JyNnVzRW4jPWaoWTxCyhM7

plugins/player_sync/module/player_sync.lua

@@ -634,6 +634,7 @@ player_sync.on_nth_tick[33] = function(event)
 	player_sync.check_players_in_cutscene()
 	player_sync.check_active_downloads()
 	player_sync.check_active_uploads()
+	player_sync.check_missing_quick_bar_records()
 end
 
 player_sync.events[defines.events.on_cutscene_waypoint_reached] = function(event)
@@ -781,6 +782,20 @@ function player_sync.check_active_downloads()
 	end
 end
 
+-- Quick bar slots pointing into the blueprint library are set once the save has the player's library
+function player_sync.check_missing_quick_bar_records()
+	local script_data = get_script_data()
+	for player_name, failed in pairs(script_data.failed_deserialization) do
+		local player = failed.quick_bar and game.get_player(player_name)
+		if player and player.connected then
+			failed.quick_bar = serialize.restore_missing_quick_bar_records(player, failed.quick_bar)
+			if not next(failed) then
+				script_data.failed_deserialization[player_name] = nil
+			end
+		end
+	end
+end
+
 function player_sync.check_active_uploads()
 	local script_data = get_script_data()
 	for player_name, record in pairs(script_data.active_uploads) do

plugins/player_sync/module/serialize.lua

@@ -494,6 +494,27 @@ local function find_item_path(inventory, item_number)
 	return nil
 end
 
+--- The record a quick bar slot entry points at, if the player's library has it at that path
+--- @param player LuaPlayer
+--- @param entry QuickBarSlotEncoded.record
+--- @return LuaRecord?
+local function find_record(player, entry)
+	-- The record must still be what was stored, a shifted library must not set the wrong one
+	local records = player.blueprints
+	local record --[[@as LuaRecord?]]
+	for _, index in ipairs(entry.p) do
+		record = records[index]
+		if not (record and record.valid) then
+			return nil
+		end
+		records = record.type == "blueprint-book" and record.contents or {}
+	end
+	if record and record.type == entry.y and (record.label or "") == (entry.l or "") then
+		return record
+	end
+	return nil
+end
+
 --- @param filter ItemFilter
 --- @return QuickBarSlotEncoded
 local function serialize_filter(filter)
@@ -611,18 +632,8 @@ function serialize.deserialize_quick_bar_slot(entry, player)
 		end
 
 		if entry.t == "r" then
-			-- The record must still be what was stored, a shifted library must not set the wrong one
-			local records = player.blueprints
-			local record --[[@as LuaRecord?]]
-			for _, index in ipairs(entry.p) do
-				record = records[index]
-				if not (record and record.valid) then
-					record = nil
-					break
-				end
-				records = record.type == "blueprint-book" and record.contents or {}
-			end
-			if record and record.valid and record.type == entry.y and (record.label or "") == (entry.l or "") then
+			local record = find_record(player, entry)
+			if record then
 				return { type = "record", record = record } --[[@as QuickBarSlot]]
 			end
 
@@ -670,8 +681,9 @@ local function quick_bar_slot_count(player)
 end
 
 --- @param player LuaPlayer
+--- @param missing table<string, QuickBarSlotEncoded.record>? Entries deserialize_quick_bar could not find the record of
 --- @return table<string, QuickBarSlotEncoded>?
-function serialize.serialize_quick_bar(player)
+function serialize.serialize_quick_bar(player, missing)
 	local serialized
 	local width = v2_1_quick_bar_api and player.quick_bar_width
 
@@ -696,19 +708,63 @@ function serialize.serialize_quick_bar(player)
 		end
 	end
 
+	-- A record still missing here is stored again as it came, unless the player put something else in its slot
+	for index, entry in pairs(missing or {}) do
+		serialized = serialized or {}
+		serialized[index] = serialized[index] or entry
+	end
+
 	return serialized
 end
 
+--- Slot index to page and slot on it
+--- @param player LuaPlayer
+--- @param i integer
+local function quick_bar_location(player, i)
+	local width = player.quick_bar_width
+	return math.floor((i - 1) / width) + 1, ((i - 1) % width) + 1
+end
+
+--- Set the slots whose records were not in the player's library when the data was applied. A save gets the library
+--- of a player from the client some seconds after the join, later than the data of a player new to it is applied.
+--- @param player LuaPlayer
+--- @param missing table<string, QuickBarSlotEncoded.record>
+--- @return table<string, QuickBarSlotEncoded.record>? missing Entries whose record is still not there
+function serialize.restore_missing_quick_bar_records(player, missing)
+	for index, entry in pairs(missing) do
+		local page, page_slot = quick_bar_location(player, tonumber(index) --[[@as integer]])
+		if player.get_quick_bar_slot(page, page_slot) ~= nil then
+			-- The player put something else there
+			missing[index] = nil
+		else
+			local record = find_record(player, entry)
+			if record then
+				player.set_quick_bar_slot(page, page_slot, { type = "record", record = record })
+				missing[index] = nil
+			end
+		end
+	end
+	return next(missing) and missing or nil
+end
+
 --- @param player LuaPlayer
 --- @param serialized table<string, string | QuickBarSlotEncoded>?
+--- @return table<string, QuickBarSlotEncoded.record>? missing Entries whose record is not in the player's library
 function serialize.deserialize_quick_bar(player, serialized)
 	-- Every slot is set, and the ones not in the data are cleared, so a slot moved or cleared on the
 	-- previous server does not come back from this server's old copy
 	serialized = serialized or {}
 	local width = v2_1_quick_bar_api and player.quick_bar_width
+	local missing
 	for i = 1, quick_bar_slot_count(player) do
 		local entry = serialized[tostring(i)]
 		local slot = entry ~= nil and serialize.deserialize_quick_bar_slot(entry, player) or nil
+		if slot == nil and v2_1_quick_bar_api and type(entry) == "table" and entry.t == "r" then
+			-- ponytail: kept until the record shows up or the slot is used for something else, so the entry of a
+			-- record deleted from the library is carried along. Drop them by age if that ever matters.
+			missing = missing or {}
+			missing[tostring(i)] = entry
+		end
 		if v2_1_quick_bar_api then
 			local page = math.floor((i - 1) / width) + 1
 			local page_slot = ((i - 1) % width) + 1
@@ -718,6 +774,7 @@ function serialize.deserialize_quick_bar(player, serialized)
 			player.set_quick_bar_slot(i, slot)
 		end
 	end
+	return missing
 end
 
 --- Quick bar page shown on each quick bar row of the screen, kept by every save on its own
@@ -1212,7 +1269,7 @@ function serialize.serialize_player(player, failed_deserialization, components)
 
 	-- Serialize quick bar
 	if syncs(components, "quick_bar") then
-		serialized.quick_bar = serialize.serialize_quick_bar(player)
+		serialized.quick_bar = serialize.serialize_quick_bar(player, failed_deserialization.quick_bar)
 		serialized.quick_bar_pages = serialize.serialize_quick_bar_pages(player)
 	end
 
@@ -1333,6 +1390,7 @@ end
 
 --- @class FailedDeserializationPlayerData
 --- @field recipe_notifications string[]?
+--- @field quick_bar table<string, QuickBarSlotEncoded.record>? Slots whose record is not in the library (yet)
 
 --- @param player LuaPlayer
 --- @param serialized SerializedPlayerData
@@ -1495,7 +1553,9 @@ function serialize.deserialize_player(player, serialized, components, local_cont
 
 	-- Deserialize quick bar (named hotbar in old data)
 	if syncs(components, "quick_bar") then
-		serialize.deserialize_quick_bar(player, serialized.quick_bar or serialized.hotbar)
+		failed_deserialization.quick_bar = serialize.deserialize_quick_bar(
+			player, serialized.quick_bar or serialized.hotbar
+		)
 		serialize.deserialize_quick_bar_pages(player, serialized.quick_bar_pages)
 	end