Fix stylelint config usage

[webschik]

There was a comment in lib/standalone.js:312 that stylelint._options.config might be undefined, but
invalidScopeDisables.js function always expected an object as 2nd parameter.

For me there were 2 ways to fix that:

• adding a conditional expression to stylelint._options.config || {} for invalidScopeDisables call, or
• changinginvalidScopeDisables interface to accept undefined as 2nd parameter.

I've chosen 2nd option, to prevent adding more conditions in the future in we need to call invalidScopeDisables somewhere else with the optional config param.

Closes #4479

[hudochenkov]

I think test should look like this:

it('invalidScopeDisables without config', () => {
	return standalone({
		config: {},
		code: 'a {}',
		ignoreDisables: true,
	}).then((linted) => {
		expect(invalidScopeDisables(linted.results)).toEqual([]);
	});
});

Because we want to test when config is empty, and code doesn't have any stylelint-disable comments. (I'm not sure about expect part).

[webschik]

Make sense, but then it should look like

return standalone({
    config: {
        rules: {}
    },
    code: 'a {}',
    ignoreDisables: true,
}).then((linted) => {
    expect(invalidScopeDisables(linted.results)).toEqual([]);
});

because there is a check for config.rules param in lib/augmentConfig.js:88

[hudochenkov]

Suggested change

	* @param {import('stylelint').StylelintConfig|undefined} config
	* @param {import('stylelint').StylelintConfig} config

It works without undefined.

[webschik]

In this case type annotation in JSDoc is not correct, it means the function accepts config only with StylelintConfig type, but it's not true. I think it's more correct to specify in type that function may accept undefined. Also, we can describe config as optional - https://jsdoc.app/tags-param.html#optional-parameters-and-default-values, but I think it's a worse approach.

[hudochenkov]

By default null and undefined are subtypes of all other types. That means you can assign null and undefined to something like number.

http://www.typescriptlang.org/docs/handbook/basic-types.html#null-and-undefined

While explicitly specifying undefined is correct, it's not necessary.

If you want to keep, it's ok.

[hudochenkov]

• Fixed: --report-invalid-scope-disables crash when no rules specified (#4498).