feat: support for eslint v9

[yutak23]

This ought to fix #351.

ESLint v9 and seems to have moved completely to flat config. Therefore, I believe it is no longer possible to maintain backward compatibility. Therefore, i think it is better to raise the version to 5.0.0 with this modification and release 5.0.0 as supporting only ESLint v9 or higher.
I have tried to support both v8 and v9.
I believe that Node.js support is fine for 17+ to match EOL.

About mocking in rule-finder testing

In calculateConfigArray at https://github.com/eslint/eslint/blob/v9.11.1/lib/eslint/eslint.js#L444,
there is a part where it does new FlatConfigArray,
As per the implementation at https://github.com/eslint/eslint/blob/v9.11.1/lib/config/flat-config-array.js#L90:

constructor(configs, {
        basePath,
        shouldIgnore = true,
        baseConfig = defaultConfig
    } = {}) {

The baseConfig ends up being set to the default config (https://github.com/eslint/eslint/blob/v9.11.1/lib/config/default-config.js).
Therefore, in the following implementation section:

this[originalBaseConfig] = baseConfig;
Object.defineProperty(this, originalBaseConfig, { writable: false });

the following settings inevitably get included:

plugins: {
            "@": {...}
}

and it's not possible to execute calculateConfigForFile with configurations for rules that are not in ESLint.
Therefore, as a workaround, I used a mock to allow initialization with rules that are not in ESLint.
I believe that this does not prevent us from testing what needs to be tested.

[ljharb]

If this project only supports eslint 9 - and not 8 and 9 - it will disrupt the airbnb config from being able to ship eslint 9 support. Separately, I'm not sure why it must be a breaking change. I think we should try to support both simultaneously.

[yutak23]

If this project only supports eslint 9 - and not 8 and 9 - it will disrupt the airbnb config from being able to ship eslint 9 support. Separately, I'm not sure why it must be a breaking change. I think we should try to support both simultaneously.

@ljharb , thank you for your comment.
i think,
For example, many libraries have decided to support only ESMs, but I believe that users of those libraries are continuing to use the versions before ESM-only support.
In that sense, this update is not a problem, since the old version will not disappear, but will continue to be available. For that reason, I propose to raise the major version. What do you think?

As for airbnb, that is exactly what I was working on trying to migrate to 9, but was unable to complete the migration process to 9 because of its dependency on this library. The test before PR does not pass.

[ljharb]

You're correct that most users of libraries that have gone ESM-only are staying on pre-ESM-only versions - but that's not ok, that's a MASSIVE security problem for the entire JS ecosystem. It's an argument against breaking changes.

The airbnb config's next version will support both 8 and 9, and may not even ship a flat config. This tool has to work on both eslintrc and flat config, and eslint 8 and 9, simultaneously.

[yutak23]

You're correct that most users of libraries that have gone ESM-only are staying on pre-ESM-only versions - but that's not ok, that's a MASSIVE security problem for the entire JS ecosystem. It's an argument against breaking changes.

The airbnb config's next version will support both 8 and 9, and may not even ship a flat config. This tool has to work on both eslintrc and flat config, and eslint 8 and 9, simultaneously.

I understand and agree with your thinking.
Now I will try to modify it to support both 8 and 9.

[yutak23]

@ljharb , I have tried to support both v8 and v9.
I would appreciate your confirmation.

[lotmek]

Hello @yutak23,

I've tried a similar approach as yours, but I was facing some surprises in the output. Some plugins are not properly imported by the ESLint config object and I don't know why...

You can take a look at this example where I've forked your yutak23:feature/migrate-to-v9 branch in my local, run the build script and added the dependency in my project.

You can see that the eslint-find-rules -p script is not listing the plugin rules for eslint-plugin-json

I'm going to investigate another approach

[yutak23]

Hello @yutak23,

I've tried a similar approach as yours, but I was facing some surprises in the output. Some plugins are not properly imported by the ESLint config object and I don't know why...

You can take a look at this example where I've forked your yutak23:feature/migrate-to-v9 branch in my local, run the build script and added the dependency in my project.

You can see that the eslint-find-rules -p script is not listing the plugin rules for eslint-plugin-json

I'm going to investigate another approach

@lotmek , i think,
By default, eslint-find-rules tries to find ESLint rules for files with the .js extension. So if you want to target .json like eslint-plugin-json, I think you need --ext .json as follows.

study@localhost:~/workspace/eslint-find-rules-test
$ npm run test:plugins

> [email protected] test:plugins
> eslint-find-rules --ext .json -p eslint.config.js


plugin rules

json/*                                   json/colon-expected                      json/comma-expected                      json/comma-or-close-backet-expected      json/comma-or-close-brace-expected
json/comment-not-permitted               json/duplicate-key                       json/enum-value-mismatch                 json/invalid-character                   json/invalid-escape-character
json/invalid-unicode                     json/json                                json/property-expected                   json/schema-resolve-error                json/trailing-comma
json/undefined                           json/unexpected-end-of-comment           json/unexpected-end-of-number            json/unexpected-end-of-string            json/unknown
json/value-expected

My project setup is as follows.

[ljharb]

We should also be automatically looking for files with .mjs or .cjs extensions, since those are supported in node.

[ljharb]

It might be best to first add support for flat config, and then add support for eslint 9 in a separate PR.

[ljharb]

Please ensure all files end in a trailing newline.

[yutak23]

Please ensure all files end in a trailing newline.

i fixed this.

[Aluisio]

Any news on the merge of this PR? There are many other libs that are waiting for this migration to also migrate to ESLint 9

[ljharb]

Let's take this semver-major opportunity to set engines.node to '^18.18 || ^20.9 || ^22 || >= 23.1', and update CI to match.

[ljharb]

Seems good! I'll merge this after I've tested it on another project.

[niksy]

FWIW, I’ve tried it in one of my projects where config was upgraded to ESLint 9 and flat config and it seems to be working as expected.

[yutak23]

@ljharb,
Is it difficult to merge?
I would appreciate your confirmation.

[ljharb]

@yutak23

I'll merge this after I've tested it on another project.