Upgrade to ESLint 9

[fregante]

I'm opening this tracking issue for the upgrade. I found this useful thread with some tips: https://x.com/karlhorky/status/1792500811307622631, namely "Upgrade to flat config with ESLint 8, then upgrade to ESLint 9"

Some related/blocking issues:

• Move to flat config #702
• Move to eslint-stylistic (ESLint 9 dropped formatting rules) #734
• Replace eslint-plugin-import with eslint-plugin-import-x #758

[voxpelli]

Happy to help with the experience I got from updating standard to ESLint 9 / flat config in neostandard

[sindresorhus]

Help is always welcome.

[spence-s]

Some more blocking issues:

• eslint-config-prettier which does not yet support stylistic plugin

• import-resolver-webpack has peer deps that require the use of the --force flag for npm install, i don't think the import-x fork has webpack support yet? I am not totally sure

[fregante]

• i don't think the import-x fork has webpack support yet?

I see that exact resolver in its dependencies and this issue seems to suggest that it does support webpack.

So I presume eslint-plugin-import-x would require the same legacy-peer-deps setting (--force is not necessary)