PostCSS/webpack5: registering newly-created dependency causes initial dev build to hang

[bradlc]

What version of Next.js are you using?

10.0.9 / 10.0.10-canary.0

What version of Node.js are you using?

14.5.0

What browser are you using?

Chrome

What operating system are you using?

macOS 11.0.1

How are you deploying your application?

N/A

Describe the Bug

When using webpack5 (future.webpack5 = true) the Next.js dev server hangs when a PostCSS plugin registers a dependency which has just been created.

// Create a new file
fs.closeSync(fs.openSync(dependency, 'w'))

// Register that file as a dependency
result.messages.push({
  type: 'dependency',
  plugin: PLUGIN_NAME,
  parent: result.opts.from,
  file: dependency,
})

This issue does not seem to exist prior to #22737 when webpack5 was upgraded to v5.24.3. Additionally, the dev server only hangs on the initial build (i.e. when the .next folder does not exist)

Expected Behavior

The dev server should not hang.

To Reproduce

1. Clone https://github.com/bradlc/next-postcss-issue
2. Run npm install
3. Ensure that the .next folder does not exist
4. Run npm run dev

[balazsorban44]

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