Fix saved version being reset to latest migration version on server w…

…hen saved version is ahead and backwards compatible

src/Collection.lua

@@ -110,6 +110,8 @@ function Collection:load(key, defaultUserIds)
 				return "retry", "Could not acquire lock"
 			end
 
+			local savedVersion = value.migrationVersion
+
 			local migrationOk, migrated, lastCompatibleVersion = Migration.migrate(self.options.migrations, value)
 			if not migrationOk then
 				return "fail", migrated
@@ -125,7 +127,7 @@ function Collection:load(key, defaultUserIds)
 			end
 
 			local data = {
-				migrationVersion = #self.options.migrations,
+				migrationVersion = math.max(savedVersion, #self.options.migrations),
 				lastCompatibleVersion = lastCompatibleVersion,
 				lockId = lockId,
 				data = migrated,

src/init.test.lua

@@ -550,6 +550,31 @@ return function(x)
 				-- This shouldn't error because v3 is backwards compatible with v1.
 				collectionWithV1:load("document"):expect()
 			end)
+
+			x.test("keeps saved version", function(context)
+				local collection = context.lapis.createCollection("collection", {
+					defaultData = "a",
+				})
+
+				local dataStore = context.dataStoreService.dataStores.collection.global
+				dataStore:write("document", {
+					lastCompatibleVersion = 0,
+					migrationVersion = 1,
+					data = "b",
+				})
+
+				local document = collection:load("document"):expect()
+
+				assertEqual(context.read("collection", "document").migrationVersion, 1)
+
+				document:save("document"):expect()
+
+				assertEqual(context.read("collection", "document").migrationVersion, 1)
+
+				document:close("document"):expect()
+
+				assertEqual(context.read("collection", "document").migrationVersion, 1)
+			end)
 		end)
 	end)