feat: Add support for config comments

[mdjermanovic]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Adds support for rule configuration comments and disable directives.

What changes did you make? (Give an overview)

Added getInlineConfigNodes(), getDisableDirectives() and applyInlineConfig() methods to the JSONSourceCode class.

Related Issues

Fixes #21

Is there anything you'd like reviewers to focus on?

Unlike the JS language implementation (SourceCode in eslint/eslint), in this implementation rule configs, eslint-disable and eslint-enable can be Line comments. We wanted to implemented this in the JS language as well (eslint/rfcs#34), and eventually did but reverted the change due to backwards compatibility reasons (eslint/eslint#14960). Since there were no backwards compatibility concerns here, it seemed fine to allow this, but let me know if it would be better to have the same behavior as in the JS language (e.g., ignore comments like // eslint rule).

[mdjermanovic]

I inserted if (parseResult.ok === false) here because I was getting this TypeScript error without it (with just else):

error TS2339: Property 'error' does not exist on type '{ ok: true; config: RulesConfig; } | { ok: false; error: { message: string; }; }'.
  Property 'error' does not exist on type '{ ok: true; config: RulesConfig; }'.

229       message: parseResult.error.message,

It seems that TypeScript doesn't infer that in else of if (parseResult.ok), parseResult must be { ok: false; error: { message: string; }; }. Please let me know if there's a better solution.

[fasttime]

I think this is happening because we don't use the strictNullChecks option in tsconfig.json. Without that option, TypeScript assumes that the ok field in parseResult could be possibly nullish in both alternatives of the union type, so it cannot infer that the error property exists from the fact that ok is falsy.

You could add a JSDoc annotation like /** @type {*} */ above the line where parseResult is declared to disable type checking in this case, but maybe there's an even better solution.

[nzakas]

Another way to do this is with a type guard, something like:

/**
 * @param {ParseResult} result
 * @returns {result is OkParseResult}
 */
function isOkParseResult(result) {
    return result.ok;
}

Then you can use isOkParseResult() and TypeScript can know that you're positively identifying the type.

[mdjermanovic]

Okay, I fixed this with casting.