Unsupported Swift Version

[DevX143]

Problem: The target "flutter_document_picker" contains source code developed with Swift 2.x. Xcode 9 does not support building or migrating to Swift 2.x targets.

Additional Information: BUILD FAILED Xcode's output: ↳ The “Swift Language Version” (SWIFT_VERSION) build setting must be set to a supported value for targets which use Swift. Supported values are: 3.0, 4.0, 4.2. This setting can be set in the build settings editor. The “Swift Language Version” (SWIFT_VERSION) build setting must be set to a supported value for targets which use Swift. Supported values are: 3.0, 4.0, 4.2. This setting can be set in the build settings editor. Could not build the precompiled application for the device.

Details ( where the problem exist):

• Xcode version 10.0 with Swift 4.2 pre-installed.
• Flutter 0.9.2 • channel dev • https://github.com/flutter/flutter.git Framework • revision 85b4670b2a (11 days ago) • 2018-09-19 14:59:23 -0700 Engine • revision 2e8e96fad1 Tools • Dart 2.1.0-dev.4.0.flutter-4eb879133a
  • flutter doctor Doctor summary (to see all details, run flutter doctor -v): [✓] Flutter (Channel dev, v0.9.2, on Mac OS X 10.13.6 17G65, locale en-SG) [✓] Android toolchain - develop for Android devices (Android SDK 28.0.2) [✓] iOS toolchain - develop for iOS devices (Xcode 10.0) [✓] Android Studio (version 3.1) [✓] IntelliJ IDEA Community Edition (version 2018.1.5) [!] Connected devices ! No devices available

[sidlatau]

It looks like an issue registered in flutter repo, when trying to add swift plugin to objective-c project. Check this comment for possible fix: https://github.com/flutter/flutter/issues/16049#issuecomment-382629492