react-native-git-upgrade should use name from app.json instead of package.json

[mike-marcacci]

• Review the documentation: https://facebook.github.io/react-native
• Search for existing issues: https://github.com/facebook/react-native/issues
• Use the latest React Native release: https://github.com/facebook/react-native/releases

Environment

  React Native Environment Info:
    System:
      OS: macOS High Sierra 10.13.6
      CPU: x64 Intel(R) Core(TM) i7-3720QM CPU @ 2.60GHz
      Memory: 82.54 MB / 16.00 GB
      Shell: 5.3 - /bin/zsh
    Binaries:
      Node: 10.9.0 - /usr/local/n/versions/node/10.9.0/bin/node
      Yarn: 1.9.4 - /usr/local/bin/yarn
      npm: 6.4.0 - /usr/local/n/versions/node/10.9.0/bin/npm
      Watchman: 4.9.0 - /usr/local/bin/watchman
    SDKs:
      iOS SDK:
        Platforms: iOS 11.4, macOS 10.13, tvOS 11.4, watchOS 4.3
    IDEs:
      Xcode: 9.4.1/9F2000 - /usr/bin/xcodebuild
    npmPackages:
      react: ^16.4.1 => 16.4.2
      react-native: ^0.56.0 => 0.56.0
    npmGlobalPackages:
      react-native-git-upgrade: 0.2.7

Description

Right now, react-native-git-upgrade gets the app name from package.json instead of app.json. This can be problematic, as NPM allows package names which don't work as iOS/Android package names, or which break the directory structure assumed by react native (for example, the package name @my-namespace/my-app).

If an app.json file exists (such as when the folder structure is generated by react-native-cli), its name field should be used instead.

[mikemorris]

Hit this issue when upgrading, can confirm that @ scoped package names are problematic when upgrading (I worked around by temporarily removing the scope, then restoring after upgrade).