Avoid issuing the same ID to multiple objects

When creating multiple new objects at the same time but not saving them, they would all be given the same ID since IDs were only tracked based on saved objects.

Components/ObjectList.lua

@@ -114,8 +114,6 @@ function ObjectList:New(instanceProperties)
 		-- Prevent import/export.
 		disableObjectSharing = false,
 
-
-
 		---@type function(objectId) -> boolean
 		-- Prevent creation of objects matching specific criteria.
 		disableObjectCreationFunc = nil,
@@ -177,6 +175,12 @@ function ObjectList:New(instanceProperties)
 			name = true,
 		},
 
+		---@type table<number, true>
+		-- When an ID is requested for a new object but it hasn't been saved yet,
+		-- that ID is temporarily stored here so that we won't issue the same
+		-- ID multiple times.
+		reservedObjectIds = {},
+
 		---@type table
 		-- ObjectManager instance that will be initialized when Open() is called.
 		-- DO NOT override it here -- use `<ClassInstance>:InitUi()` instead.
@@ -702,11 +706,15 @@ function ObjectList:SaveObject(objectId, objectInfo)
 	-- Filter the provided information using the template.
 	BsUtil.TableCopy(objectInfo, self.list[objectId], nil, self.objectSkeleton, BS_OBJECT_LIST_TEMPLATE_TABLE_WILDCARD)
 
+	-- Update saved date.
 	self.list[objectId].dateModified = _G.time()
 
 	-- Allow subclasses to perform operations after saving.
 	self:DoPostSaveOperations(objectId, self.list[objectId])
 
+	-- Release from pending IDs.
+	self.reservedObjectIds[objectId] = nil
+
 	-- There's been a change.
 	self:ObjectsChanged(objectId)
 end
@@ -919,7 +927,9 @@ end
 --- Obtain the next available sequential object ID.
 ---@return number
 function ObjectList:GetNewObjectId()
-	return self:GetNextId()
+	local newID = self:GetNextId()
+	self.reservedObjectIds[newID] = true
+	return newID
 end
 
 
@@ -928,16 +938,21 @@ end
 --- * Doing it this way instead of tracking the next ID in a config file since working
 ---   backwards from 1 million barely takes any time.
 --- * `table.getn()` won't work here because the tables we're using are associative, not array-type.
---- **Warning:** This requires any references to object IDs to be cleaned up when objects
+--- * An extra table is used to track IDs that have been reserved by new objects
+---   that aren't yet saved.
+--- 
+--- ⛔️ **Warning:** This requires any references to object IDs to be cleaned up when objects
 --- are deleted. Otherwise, for example, if object 4 is the last in the list and
 --- it is removed, this function will return 4 when asked for the next ID. Any
 --- leftover references to object 4 will then point to the newly created object.
 ---@param existingObjects table? Defaults to `self.list`.
+---@param reservedObjectIds table? Defaults to `self.reservedObjectIds`.
 ---@return integer
-function ObjectList:GetNextId(existingObjects)
+function ObjectList:GetNextId(existingObjects, reservedObjectIds)
 	existingObjects = existingObjects or self.list
+	reservedObjectIds = reservedObjectIds or self.reservedObjectIds
 	for i = 1000000, 1, -1 do
-		if existingObjects[i] then
+		if existingObjects[i] or reservedObjectIds[i] then
 			return i + 1
 		end
 	end