The version of ESLint that we use in most places (8) now spews a warning about no longer being supported. ESLint 9 made a few changes that require us to update our plugin (which is more a shared configuration than an actual plugin): All built-in rules that enforce style have been formally deprecated in ESLint, and actually removed from `@typescript-eslint`. These now live in a new plugin, `@stylistic/eslint-plugin`. Converting to the new stylistic rules means we can actually simplify our configuration a bit. Rules that had TypeScript-specific modes now no longer require us to disable the JS rule and enable a TypeScript one, and we can just include it all in our base configuration. The `indent` rule has some known issues with TypeScript, and it seems like nobody is terribly willing to rewrite it to fix these. The impact here seems limited to type parameters for generics. I've added a couple ignored node types in order to work around this. For linting within this codebase itself, the ESLint configuration now lives in `eslint.config.mjs` rather than `.eslintrc`. This also required new dependencies for `@eslint/eslintrc`, `@eslint/js`, and `globals` While I was here, I bumped our `babel` and `typescript` dependencies, why not. Testing Done: - Ran `npm build` - Ran linting. - Set this up as a link in another package and updated that package to use eslint 9. Verified that we got correct linting output.