title: Flutter stopped suddenly with error Dart:core is missing
body: <p>My flutter sdk on Android studio suddenly stopped working without any changes made. I am using mac book pro and the error is:</p>
  
  <blockquote>
    <p>Required library 'dat:core' is missing.</p>
  </blockquote>
  
  <p>I have tried downloading new flutter sdk and also update Android studio but still the same problem</p>
  
  <p>I tried the fix using git clean -xfd</p>
  
  <p>did not work ,, here is the flutter doctor log </p>
  
  <pre><code>[✓] Flutter (Channel stable, v1.2.1, on Mac OS X 10.14.3 18D109, locale en-OM)
  • Flutter version 1.2.1 at /Users/pocketcarage/Desktop/fluttersdk/flutter-3
  • Framework revision 8661d8aecd (4 weeks ago), 2019-02-14 19:19:53 -0800
  • Engine revision 3757390fa4
  • Dart version 2.1.2 (build 2.1.2-dev.0.0 0a7dcf17eb)
  
  [✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
  • Android SDK at /Users/pocketcarage/Library/Android/sdk
  • Android NDK location not configured (optional; useful for native profiling support)
  • Platform android-28, build-tools 28.0.3
  • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
  • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1248-b01)
  • All Android licenses accepted.
  
  [!] iOS toolchain - develop for iOS devices
  ✗ Xcode installation is incomplete; a full installation is necessary for iOS development.
    Download at: https://developer.apple.com/xcode/download/
    Or install Xcode via the App Store.
    Once installed, run:
      sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
  ✗ libimobiledevice and ideviceinstaller are not installed. To install with Brew, run:
      brew update
      brew install --HEAD usbmuxd
      brew link usbmuxd
      brew install --HEAD libimobiledevice
      brew install ideviceinstaller
  ✗ ios-deploy not installed. To install:
      brew install ios-deploy
  • CocoaPods version 1.5.3
  
  [✓] Android Studio (version 3.3)
  • Android Studio at /Applications/Android Studio.app/Contents
  • Flutter plugin version 33.4.1
  • Dart plugin version 182.5215
  • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1248-b01)
  
  [!] Connected device
  ! No devices available
  
     ! Doctor found issues in 2 categories.
     PocketCarages-MacBook-Pro:pocketcarage_official pocketcarage$   flutter doctor -v
  [✓] Flutter (Channel stable, v1.2.1, on Mac OS X 10.14.3 18D109, locale en-OM)
  • Flutter version 1.2.1 at /Users/pocketcarage/Desktop/fluttersdk/flutter-3
  • Framework revision 8661d8aecd (4 weeks ago), 2019-02-14 19:19:53 -0800
  • Engine revision 3757390fa4
  • Dart version 2.1.2 (build 2.1.2-dev.0.0 0a7dcf17eb)
  
   [✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
  • Android SDK at /Users/pocketcarage/Library/Android/sdk
  • Android NDK location not configured (optional; useful for native profiling support)
  • Platform android-28, build-tools 28.0.3
  • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
  • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1248-b01)
  • All Android licenses accepted.
  
   [!] iOS toolchain - develop for iOS devices
  ✗ Xcode installation is incomplete; a full installation is necessary for iOS development.
    Download at: https://developer.apple.com/xcode/download/
    Or install Xcode via the App Store.
    Once installed, run:
      sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
  ✗ libimobiledevice and ideviceinstaller are not installed. To install with Brew, run:
      brew update
      brew install --HEAD usbmuxd
      brew link usbmuxd
      brew install --HEAD libimobiledevice
      brew install ideviceinstaller
  ✗ ios-deploy not installed. To install:
      brew install ios-deploy
  • CocoaPods version 1.5.3
  
   [✓] Android Studio (version 3.3)
  • Android Studio at /Applications/Android Studio.app/Contents
  • Flutter plugin version 33.4.1
  • Dart plugin version 182.5215
  • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1248-b01)
  
  [!] Connected device
  ! No devices available
  
  ! Doctor found issues in 2 categories.
  </code></pre>