---
title: Xcode 10.2.1 Release Notes
framework: xcode-release-notes
role: article
role_heading: Article
path: xcode-release-notes/xcode-10_2_1-release-notes
---

# Xcode 10.2.1 Release Notes

Update your apps to use new features, and test your apps against API changes.

## Overview

Overview Xcode 10.2.1 includes SDKs for iOS 12.2, watchOS 5.2, macOS 10.14.4, and tvOS 12.2. Xcode 10.2.1 supports on-device debugging for iOS 8 and later, tvOS 9 and later, and watchOS 2 and later. Xcode 10.2.1 requires a Mac running macOS 10.14.3 or later. Apple Clang Compiler Resolved Issues Simulator builds of watchOS projects that emit bitcode no longer fail with the error message: “GNU-style inline assembly is disabled.” (48903352) Build System Resolved Issues Resolved an issue that would produce a spurious “ignoring build task” warning when building localized Siri Intents. (49649474) LLDB Resolved Issues When importing Swift modules, LLDB now applies the target.source-map and the DBGSourcePathRemapping dictionary in the .dSYM bundle to the -fmodule-map-file option. This impacted alternative build systems that rely on path-remapping to access debug information. (49539481) Localization Resolved Issues Fixed a crash that could occur when modernizing localized content. (49575302) Simulator Known Issues Simulators for iOS 9.3 and earlier might fail to launch Swift apps with the message: “dyld: Library not loaded: /usr/lib/libauto.dylib”. (49326587) Workaround: Run the following command in Terminal for the relevant version of iOS: sudo mkdir '/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 9.3.simruntime/Contents/Resources/RuntimeRoot/usr/lib/swift' Swift Compiler Known Issues In some cases, compilation may fail without emitting a specific error. (49303574) Workaround: Disable batch mode by adding the SWIFT_ENABLE_BATCH_MODE custom build setting and setting it to NO. If you’re invoking swift directly, include -disable-batch-mode on the command line. If you set the Reflection Metadata Level build setting to None, you might get a linker error about a missing nominal type descriptor when building a Swift project. (49710077) Workaround: Change the setting to All. Using an @objc designated initializer as a protocol witness always creates an instance of the base class, even if the protocol requirement is called on the metatype of a subclass. (49560721) For example, the following code should create an instance of DerivedClass, but actually creates an instance of BaseClass: protocol Initable {     init() }

class BaseClass: NSObject, Initable {     required override init() {         super.init()     } }

class DerivedClass: BaseClass {}

let type: Initable.Type = DerivedClass.self print(type.init()) Workaround: Either declare the initializer as @nonobjc, or replace the protocol’s initializer requirement with a static method, as follows: protocol Initable {     static func construct() -> Self }

class BaseClass: NSObject, Initable {     required override init() {         super.init()     }

static func construct() -> Self {         return self.init()     } }

class DerivedClass: BaseClass {} Resolved Issues A build time regression associated with Swift files that define a large number of types has been resolved. (49022293) The Swift compiler now applies the -fdebug-prefix-map to path names in Clang module import debug information records. (49539327) Indexing an invalid class that has circular inheritance during a debug build no longer hangs the compiler. (SR-10236, 49539370) Resolved a memory usage issue associated with whole module optimization mode. (49586719) Resolved a build-time crash that occurred when the Thread Sanitizer was enabled. (49539420) Checking validity of the conditional requirements associated with constrained type extensions, such as when using synthesized protocol conformance code, now completes correctly. (49539169) When you declare enumerations that contain a single case with an associated value and multiple cases without an associated value, the compiler now properly distinguishes the cases without associated values. (SR-10221, 49539226) enum SomeEnum {     case payloadCase(defaultUnknownInnerValue: Int),     nonPayloadCase1,     nonPayloadCase2

var isNonPayloadCase1: Bool {         switch self {         case .nonPayloadCase1:             return true         default:             return false         }     } } The compiler now properly distinguishes between .nonPayloadCase1 and .nonPayloadCase2. Swift Package Manager Resolved Issues The swift package generate-xcodeproj command now handles submodules in the top-level package. (49535554)

## See Also

### Xcode 10

- [Xcode 10.3 Release Notes](xcode-release-notes/xcode-10_3-release-notes.md)
- [Xcode 10.2 Release Notes](xcode-release-notes/xcode-10_2-release-notes.md)
- [Xcode 10.1 Release Notes](xcode-release-notes/xcode-10_1-release-notes.md)
- [Xcode 10 Release Notes](xcode-release-notes/xcode-10-release-notes.md)