Is this a bug report?

Yes. Although this may not be RN specific -- it's more of a problem with flow in RN.

Have you read the Contributing Guidelines?

Yes

Environment

Environment:
OS: macOS High Sierra 10.13.1
Node: 9.2.0
Yarn: 1.2.1
npm: 5.5.1
Watchman: 4.9.0
Xcode: Xcode 9.1 Build version 9B55
Android Studio: Not Found

Packages: (wanted => installed)
react: 16.0.0 => 16.0.0
react-native: 0.50.3 => 0.50.3
flow-bin: 0.56.0 => 0.56.0

Target Platform: iOS (10.3)

Steps to Reproduce

Run flow in a RN project

Expected Behavior

Should pass flow checks.

Actual Behavior

Flow errors are being reported from both the metro-bundler package and react-native.

Full list of errors can be found here.

They seem to all be Promise related, but I can't quite work out why. This has only been an issue since upgrading RN@0.50.3.

Reproducible Demo

n/a, not a visual bug.