Document rejection of PackageJsonExtras and add tip for extending PackageJson

[pting-me]

Fixes #371

Initial PR to enhance the PackageJson type. Added a new type as proposed, named PackageJsonExtras.

[voxpelli]

I'm skeptical in general.

Instead of introducing anything like this, you can simply in your own project do:

type MyPackageJson = PackageJson & { eslintConfig: import('eslint').Linter.Config };

Not sure adding it in here makes for any simpler or better implementation.

[voxpelli]

For this to work, @types/eslint would have to be a dependency rather than a dev dependency.

Though I don't like the idea of this module starting to rely on lots of other type modules. I think it should be self-contained.

We don't know if the version of eslint used in the project is 8.x, 7.x or something else. We don't even know if they use eslint at all.

[voxpelli]

There is a hack where we don't have to include the ESLint module in our dependencies:

Suggested change

	eslintConfig?: Linter.Config;
	// @ts-ignore
	eslintConfig?: import('eslint').Linter.Config;

Then it will use import('eslint').Linter.Config if it correctly finds it, else it will just fallback to any.

I used that pattern a lot through ts-ignore-import and its the one pattern I think we maybe could use to still include this here. And if we do, then we can include it in PackageJson straight away rather than in a PackageJsonExtras. Thoughts @sindresorhus?

[sindresorhus]

I don't think this is a good pattern. Falling back to any is never something I would want. It could accidentally allow specifying anything there without a warning. Maybe if it fell back to never.

[pting-me]

That's a really interesting pattern. I couldn't figure out how to override the any type with never (or anything other than any for that matter).

Side note, apparently @types/eslint is included in @typescript-eslint so I had to manually delete the package to test it. But yeah, probably best to leave versioning to the consumer.

[sindresorhus]

I think this is a very good reason not to add this:

We don't know if the version of eslint used in the project is 8.x, 7.x or something else.

[sindresorhus]

I suggest we just document:

import type {PackageJson as BasePackageJson} from 'type-fest';
import type {Linter} from 'eslint';

type PackageJson = BasePackageJson & {eslintConfig: Linter.Config};

Then it's clear to user how to support other tools too.

[pting-me]

@sindresorhus Where would that go? Under "Declined Types"?

[pting-me]

Reverted my changes and added some documentation based on the discussion.

[sindresorhus]

Thanks :)