feat(eslint-config): Improve ESLint v7 support by adding plugins to peerDeps

[busterc]

To better support ESLint v7 peerDep resolution.
See: #1739

When we extend open-wc/eslint-config and install it on a project, the various plugins found in dependencies are not resolved by ESLint v7:

"dependencies": {
    "eslint-plugin-babel": "^5.3.0",
    "eslint-plugin-html": "^6.0.0",
    "eslint-plugin-import": "^2.18.2",
    "eslint-plugin-lit": "^1.2.0",
    "eslint-plugin-no-only-tests": "^2.4.0",
    "eslint-plugin-wc": "^1.2.0"
  }

Therefore, we have to manually install each plugin individually as a devDependencies for each project that extends open-wc/eslint-config.

You'll notice that the airbnb-base config includes plugin-import in peerDependencies and they refer to installing peerDeps in their README and recommending install-peerdeps as a shortcut.

Like airbnb-base, it would excellent to get to use such a shortcut, but we need those plugins added as peerDependencies:

"peerDependencies": {
    "eslint-plugin-babel": "^5.3.0",
    "eslint-plugin-html": "^6.0.0",
    "eslint-plugin-import": "^2.18.2",
    "eslint-plugin-lit": "^1.2.0",
    "eslint-plugin-no-only-tests": "^2.4.0",
    "eslint-plugin-wc": "^1.2.0"
  }

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[stale]

Hi everyone! Seems like there hasn't been much going on in this issue lately. If there are still questions, comments, or bugs, please feel free to continue the discussion. Unfortunately, we don't have time to get to every issue. We are always open to contributions so please send us a pull request if you would like to help. Inactive issues will be closed after 30 days. Thanks!

[LarsDenBakker]

@busterc Sorry for the late response here. I get the general idea, but I think it's weird to have it both as dev and peer dependencies. Ideally we should be able to resolve the path before passing it to eslint, but I don't know if eslint supports that yet.

[busterc]

@busterc Sorry for the late response here. I get the general idea, but I think it's weird to have it both as dev and peer dependencies. Ideally we should be able to resolve the path before passing it to eslint, but I don't know if eslint supports that yet.

@LarsDenBakker Thanks for looking into this!

It does seem weird to have plugins as both dependencies and peerDependencies; however, for shareable configs that are extended, ESLint simply does not install plugins regardless of where they're defined. Over the years there have been many issues posted about this inconvenience and ESLint developers continue to say 'add plugins as peerDependencies' Eventually the WIP to re-implement eslint configs should resolve those complaints.

In the meantime, you'll notice that the airbnb-base config includes eslint-plugin-import in both dependencies and peerDependencies to minimize the pain when extending their configs: https://github.com/airbnb/javascript/blob/master/packages/eslint-config-airbnb-base/package.json#L62-L69

One alternative is to include the plugins only in peerDependencies; however that would require installing those peerDeps even when not extending the config. As Airbnb didn't opt for that, I guessed open-wc would prefer not too either. Otherwise, I can certainly update the PR to remove the plugin references from dependencies?

[LarsDenBakker]

Thanks for those references. Seems like it's the best option we have right now then.