How can I throw an error from a plugin to prevent a build?

❔ Question

How can I throw an error in a plugin that will prevent the build from continuing?

🔦 Context

I am developing a one-liner plugin whose only job is to run execSync('tsc --noEmit') before every build. It throws an error, and a warning is printed to the console, but the build continues on anyway. I can manually call process.exit(1) but that’ll kill the whole parcel process watching my files. Is it possible for a plugin to indicate that the build has failed?

💻 Code Sample

const { execSync } = require('child_process')
const path = require('path')

const cwd = process.cwd()
const binPath = execSync('yarn bin', { cwd, encoding: 'utf8' }).trim()
const tscCommand = `${path.join(binPath, 'tsc')} --noEmit`

module.exports = () => {
  // Will throw if tsc reports any issues
  execSync(tscCommand, { cwd, encoding: 'utf8', stdio: 'inherit' })
}

[mischnic]

This makes it on every rebuild (“before”/“when”), but you can’t abort a build.

module.exports = (bundler) => {
  bundler.on('buildStart', entryPoints => {
	  execSync(tscCommand, { cwd, encoding: 'utf8', stdio: 'inherit' })
  });
}

[mmiller42]

buildStart worked perfectly, thanks!

If anyone happens to be looking for a full list of events, they’re all very neatly defined at https://github.com/parcel-bundler/parcel/blob/23ba2cc54f3286f60e2cab63eb358660c916139d/packages/core/types/index.js