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fix(jest-haste-map): Make watchman existence check lazy+async #12675

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Merged
merged 5 commits into from
Apr 16, 2022
Merged

fix(jest-haste-map): Make watchman existence check lazy+async #12675

merged 5 commits into from
Apr 16, 2022

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robhogan
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Summary

Currently, jest-haste-map checks for watchman existence at import time (top level) with a blocking execSync call. This has a few downsides

  • Blocking at the top level holds up main thread (by 20-200ms) at a time when there's CPU work to be done.
  • execSync spawns a shell, which isn't necessary here - execFile is more efficient.
  • The exec happens totally unnecessarily even if the consumer specifies useWatchman: false.

This PR extracts this to an async utility function, executed lazily and memoized by the core class.

Test plan

  • New unit tests cover lib/isWatchmanInstalled.ts and lazy execution

  • Behaviour of execFile when watchman is installed:

$ node -e "util.promisify(child_process.execFile)('watchman', ['--version']).then(console.log)"
{ stdout: '20220411\n', stderr: '' }
  • And when we try to exec something unavailable:
$ node -e "util.promisify(child_process.execFile)('nonexistentthing', ['--version']).then(console.log)"

node:internal/errors:464
   ErrorCaptureStackTrace(err);
   ^

Error: spawn nonexistentthing ENOENT
   at Process.ChildProcess._handle.onexit (node:internal/child_process:282:19)
   at onErrorNT (node:internal/child_process:477:16)
   at processTicksAndRejections (node:internal/process/task_queues:83:21) {
 errno: -2,
 code: 'ENOENT',
 syscall: 'spawn nonexistentthing',
 path: 'nonexistentthing',
 spawnargs: [ '--version' ],
 cmd: 'nonexistentthing --version',
 stdout: '',
 stderr: ''
}

SimenB
SimenB approved these changes Apr 16, 2022
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Ooh, great stuff! 👍

@SimenB SimenB merged commit defbc05 into jestjs:main Apr 16, 2022
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@robhogan @SimenB @facebook-github-bot