metro-file-map: Got unexpected null error (in onTimeout)

[renchap]

Do you want to request a feature or report a bug?
Bug report

What is the current behavior?
This started to happen after updating from RN 0.71 to 0.72.

Metro crashes with the following error:

/Users/renchap/dev/notos/node_modules/.pnpm/nullthrows@1.1.1/node_modules/nullthrows/nullthrows.js:9
  throw error;
  ^

Error: Got unexpected null
    at nullthrows (/Users/renchap/dev/notos/node_modules/.pnpm/nullthrows@1.1.1/node_modules/nullthrows/nullthrows.js:7:15)
    at Timeout.emitChange [as _onTimeout] (/Users/renchap/dev/notos/node_modules/.pnpm/metro-file-map@0.76.5/node_modules/metro-file-map/src/index.js:823:48)
    at listOnTimeout (node:internal/timers:569:17)
    at process.processTimers (node:internal/timers:512:7) {
  framesToPop: 1
}

This seems to be happening what I start a build, or when I run pnpm.

This was not happening when running RN 0.71 (Metro 0.73.9).

If the current behavior is a bug, please provide the steps to reproduce and a minimal repository on GitHub that we can yarn install and yarn test.
I do not have a repro, this happens randomly

What is the expected behavior?
Metro does not crash

Please provide your exact Metro configuration and mention your Metro, node, yarn/npm version and operating system.
Metro 0.76.5 in a pnpm monorepo

• Standard RN configuration, but using unstable_enableSymlinks: true, due to pnpm
• Node 18.16.0
• pnpm 8.6.2
• macOS 13.4.1

[robhogan]

Thanks for the report. I've seen this a very intermittently as well - just noting for now that the offending assertion is this one

metro/packages/metro-file-map/src/index.js

Line 921 in 6d46078

hmrPerfLogger.start({timestamp: nullthrows(eventStartTimestamp)});

So eventStartTimestamp is null for some reason, possibly a parallel Fast Refresh race - pretty sure it's unrelated to unstable_enableSymlinks or PNPM. We'll backport a fix once we pin this down.

[angusryer]

I have this issue consistently since upgrading to 0.72.4 from 0.71.6. I also have unstable_enableSymlinks = true, and have watchman configured to watch folders outside the yarn workspace my RN project is in.

I use a custom bash script that detects existing instances of metro and launches a new instance if necessary before building and running the Android and iOS emulator/sim (in that order, by chance). This error always occurs while the Android emulator is connected and building on-device.

It doesn't happen if I launch the sims manually.

I'm running metro v0.76.7.

Here's the output from npx react-native info:

System:
  OS: macOS 13.5.1
  CPU: (8) arm64 Apple M1
  Memory: 135.63 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 18.16.1
    path: ~/.nvm/versions/node/v18.16.1/bin/node
  Yarn:
    version: 3.2.2
    path: ~/.yarn/bin/yarn
  npm:
    version: 9.5.1
    path: ~/.nvm/versions/node/v18.16.1/bin/npm
  Watchman:
    version: 2023.07.10.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.12.1
    path: /Users/angusryer/.rvm/gems/ruby-2.7.5/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 22.1
      - iOS 16.1
      - macOS 13.0
      - tvOS 16.1
      - watchOS 9.1
  Android SDK:
    Android NDK: 22.1.7171670
IDEs:
  Android Studio: 2022.3 AI-223.8836.35.2231.10671973
  Xcode:
    version: 14.1/14B47b
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 11.0.19
    path: /usr/bin/javac
  Ruby:
    version: 2.7.5
    path: /Users/angusryer/.rvm/rubies/ruby-2.7.5/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 18.2.0
    wanted: 18.2.0
  react-native:
    installed: 0.72.4
    wanted: 0.72.4
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: false
iOS:
  hermesEnabled: true
  newArchEnabled: false

[yangm97]

In my case this bug seems to be triggered by operations in node_modules such as when you yarn add something.

[robhogan]

Confirmed that this is an intermittent race crash caused when dealing with many overlapping file change events (eg, a yarn operation, or native build). #1083 should fix it, and I'll backport that for supported RN versions.

[siddarthkay]

Hi @robhogan : Thanks for this fix!
I see this fix is already a part of react-native 0.73, Can you please let me know when this fix is planned to land in 0.72?
our project is currently using react-native 0.72.5