Switch to flat config

[fregante]

I'm opening this tracking issue to collect related tickets.

This change blocks:

• Suggestion on slimming down dependencies #2151
• npm audit security vulnerability in semver <= 7.5.2 #2163

[silverwind]

Does it have to be a "switch"? There are a number of plugins that support both configs at the same time and I think it would ease the migration.

[fregante]

I think the flat config is already supported:

• Support ESLint new config system #1886

So this issue is to drop support for the old config. It's not something that will happen anytime soon, I suppose.

[philsherry]

ESLint v8.x end of life was October 5, 2024, so Flat config is the only way forward now.

[sindresorhus]

@fisker What do you think about doing this now? (Asking for your opinion, not for you to do the work)

[fisker]

I'm fine with it, but should we wait for XO to get ready first?

[sindresorhus]

No, I don't want this blocked on XO.

[sindresorhus]

I'm working on this now.

[silverwind]

ESLint v8.x end of life was October 5, 2024, so Flat config is the only way forward now.

FWIW, eslint v9 still supports the deprecated config format. It will be removed only in v10.

[sindresorhus]

Ok, I manually migrated to ESM and flat config now. Took almost 5 hours...

[sindresorhus]

CI is failing because snapshot test binaries differ. I suspect it's a difference since I'm on macOS and tests run on Linux. Same Node.js version though. Anyone on Linux and Windows and can try updating the snapshots with Node.js 23.6.0 locally?

[fregante]

GitHub Codespaces might be an option