README.md

• Start Date: 2019-12-09
• RFC PR:
• Authors: @manuth

Public ConfigArray API

Summary

Allow 3rd-party developers to determine which configuration-files are considered by eslint.

Motivation

In some cases people might want to automatically trigger a new linting process as soon as the configuration of eslint has changed. This is a key feature for language servers which provide warnings and fixes to IDEs.

Therefore the language-server needs to know which config-files are considered by eslint.

Detailed Design

A method called getConfigArrayForFile() shall be added to the CLIEngine class. By providing such a feature people can easily watch the correct files for changes as soon as the configuration changes.

Example:

import fs = require("fs");

let engine = new CLIEngine({});
let file = "./App/src/index.ts";
let configArray = engine.getConfigArrayForFile(file);

for (let config of configArray) {
    if (config.filePath.length > 0) {
        fs.watchFile(
            conig.filePath,
            () =>
            {
                lint();
            });
    }
}

function lint() {
    engine.executeOnFiles([file]);
}

lint();

Documentation

I think it might be a good idea to blog about this new feature as this is a key feature for writing language servers for IDEs. That way the integration of eslint in all sorts of text-editors can be improved to its best.

Drawbacks

The only downside I can think of is that on every change to the ConfigArray or CascadingConfigArray API either a new major version has to be released or a separate implementation of said classes has to be added for the public API.

Backwards Compatibility Analysis

Adding this feature provides full backwards compatibility.

Alternatives

Add a method which only returns filepaths and a value indicating whether said filepath is root.
That way the drawbacks could be fixed but the developers don't have the benefit to further analyze the config-array.

A similar method already exists: The CLIEngine#getConfigForFile-method. Though this method does not indicate which files are considered by eslint which draws developers of language-servers unable to hot-reload eslint as soon as a config-file changes.

Open Questions

• Is it reasonable to return the whole config-array or should such a method only return the filePaths?
• Does it make sense to also return the root-directory in order to let language-servers run eslint with root as its cwd?
• Is there some more key information other than filePath which should be returned? (Such as name, for instance)

Help Needed

I think it should be pretty easy to implement such a feature as the only thing that is required is a simple call to CascadingConfigArrayFactory#getConfigArrayForFile and, if required, some data extraction/manipulation.

Frequently Asked Questions

Related Discussions

• eslint/eslint#12631