Fast Refresh Broken on 0.66-preview.2

[chiaramooney]

Something might be broken on my personal inner dev loop, but filing issue so someone can hopefully test and confirm if issue is real.

Environment

Run the following in your terminal and copy the results here.

1. npx react-native --version: 6.0.0
2. npx react-native info:

System:
    OS: Windows 10 10.0.19042
    CPU: (8) x64 Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
    Memory: 37.46 GB / 63.84 GB
  Binaries:
    Node: 14.16.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.5 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 6.14.11 - C:\Program Files\nodejs\npm.CMD
    Watchman: Not Found
  SDKs:
    Android SDK:
      API Levels: 28, 29, 30
      Build Tools: 28.0.3, 29.0.2, 29.0.3, 30.0.3
      System Images: android-29 | Intel x86 Atom_64, android-29 | Google Play Intel x86 Atom, android-30 | Google APIs Intel x86 Atom
      Android NDK: Not Found
    Windows SDK:
      AllowDevelopmentWithoutDevLicense: Enabled
      AllowAllTrustedApps: Enabled
      Versions: 10.0.18362.0, 10.0.19041.0
  IDEs:
    Android Studio: Version  4.1.0.0 AI-201.8743.12.41.7199119
    Visual Studio: 16.9.31529.145 (Visual Studio Enterprise 2019)
  Languages:
    Java: 1.8.0_282 - C:\Program Files\OpenJDK\openjdk-8u282-b08\bin\javac.EXE
  npmPackages:
    @react-native-community/cli: Not Found
    react: 17.0.2 => 17.0.2
    react-native: 0.66.0-rc.1 => 0.66.0-rc.1
    react-native-windows: 0.66.0-preview.2 => 0.66.0-preview.2
  npmGlobalPackages:
    *react-native*: Not Found

- Target Platform Version(s): 10.0.19041
- Target Device(s): Desktop
- Visual Studio Version: 2019
- Build Configuration: Debug

Steps To Reproduce

Provide a detailed list of steps that reproduce the issue.

1. Create a fresh RNW app with react-native version 0.66.0-rc.1 and react-native-windows version 0.66.0-preview.2
2. Open App.js and make any change to the JS which should update upon saving the JS source code via Fast Refresh.
3. Updates cannot be seen.

Expected Results

Should see changes to JS appear in app upon save.

[chrisglein]

Things to investigate first:

• Is Metro picking up the changed file?
• Is it telling the app it should reload?
• Are there issues with the reload with the app

[chiaramooney]

Found commit which breaks Fast Refresh (996ed98). It's the integration from core for changes up to 8/25 which was used as the base of 0.66-stable.

When updates made to JS, metro is unresponsive and does not log that updates to the file have been made. Upon reload all changes correctly appear. @acoates-ms @NickGerleman In looking at the changes pulled in from FB in this commit do any stand out as possible sources to the problem that I could dive into?

[acoates-ms]

This one looks potentially related: facebook/react-native@f085e09