Add support for loading custom formatter from package

[meriouma]

Which issue, if any, is this issue related to?

Closes #6100

Is there anything in the PR that needs further explanation?

No, it's self-explanatory.

[JounQin]

@meriouma Don't do squash and force push locally, keep the commits' history, that's fine. We'll merge with squash.

[ybiquitous]

The change looks good to me. I've left a suggestion for testing.

[ybiquitous]

[suggest] Sorry, I missed one point. Could you make single exporting consistent with other modules?

[ybiquitous]

[suggest] I think it's good to improve the CLI help and the doc about the --custom-formatter option. It will support a package name, not only a relative/absolute file path.

Could you update also the following files?

stylelint/lib/cli.js

Lines 178 to 180 in 743030d

	--custom-formatter
	Path to a JS file exporting a custom formatting function.

stylelint/docs/user-guide/usage/options.md

Line 91 in 743030d

The `formatter` Node.js API option can also accept a function, whereas the `--custom-formatter` CLI flag accepts a path to a JS file exporting one. The function in both cases must fit the signature described in the [Developer Guide](../../developer-guide/formatters.md).

[JounQin]

@meriouma Are you still working on this?

[meriouma]

@JounQin Yes, I will apply the changes. I stopped pushing changes yesterday so we were not two persons pushing in the branch at the same time.

[JounQin]

@JounQin Yes, I will apply the changes. I stopped pushing changes yesterday so we were not two persons pushing in the branch at the same time.

You'll only need to pull the latest codes and then continue the work. 🍺

[ybiquitous]

@meriouma Thank you for addressing the requested changes! The PR looks almost good to me.

I got an idea to test a custom formatter dependency in the repository: to install a private internal dependency. For example:

package.json:

{
  "devDependencies": {
    "stylelint-test-custom-formatter": "file:packages/stylelint-test-custom-formatter"
  }
}

packages/:

$ tree packages
packages/
└── stylelint-test-custom-formatter/
    ├── index.js
    └── package.json

1 directory, 2 files

Run a test:

$ bin/stylelint.js --config=scripts/visual-config.json --custom-formatter=stylelint-test-custom-formatter scripts/*.css
Custom formatter reports 1 warning(s).%

What do you think about this idea?

[JounQin]

@ybiquitous jest.mock can also be used in cli.test.js to cover this?

[ybiquitous]

@JounQin I thought about how to test the dependency behavior without mocking. But mocking dependency resolution in cli.test.js may be enough and straightforward.

[JounQin]

@JounQin I thought about how to test the dependency behavior without mocking. But mocking dependency resolution in cli.test.js may be enough and straightforward.

Yeah, a mock module like https://github.com/stylelint/stylelint/blob/main/lib/__tests__/__mocks__/get-stdin.js is fine IMO.

(Besides, https://github.com/stylelint/stylelint/blob/main/lib/__tests__/__mocks__/get-stdin.js seems can be deleted safely in favor of #6182, see #6233

[ybiquitous]

Great! LGTM 👍🏼

[JounQin]

@meriouma Thanks for your contribution!

[ybiquitous]

Changelog entry added:

• Added: support for loading custom formatter from package (#6228).