Change Request: Make processors (pre/post) async or pass config to them

ESLint version

8.6.0

What problem do you want to solve?

ESLint currently calls the preprocessor and postprocessor functions synchronously. This is a problem since the ESLint class is asynchronous, thus it’s currently impossible to use it within the preprocessor.

For example, my use case is I need to know during preprocessing what type of quotes the linter will be using.

With CLIEngine it was just:

preprocess(text, filename) {
    const config = new CLIEngine({ useEslintrc: true }).getConfigForFile(path.resolve(filename));
    const quote = config.rules.quotes[1];
   /* ... */
}

However with ESLint, the equivalent function is getConfigForFile which is async. If you try to just make the processor async, like so:

async preprocess(text, filename) {
    const eslint = new ESLint();
    const config = await eslint.calculateConfigForFile(filename);
    /* ... */
}

… then it is now returning a Future instead of an array which eslint doesn’t know how to process.

What do you think is the correct solution?

Either make the the processors async as well and have eslint treat them as such, or pass the loaded config to the processor, like:

preprocess(text, filename, config) {
    const quote = config.rules.quotes;
   /* ... */
}

Participation

• I am willing to submit a pull request for this change.

Additional comments

No response

[nzakas]

Sounds like a good approach. 👍

[eladavron]

Thanks. It just occurred to me though, I can replace it with a regex pattern instead of a string - it will have effectively the same purpose as a string but I won’t have to worry about quotes. I just have to make sure it has the same length as the original expression does to avoid having errors appear on the wrong columns, and make sure it’s valid to avoid false errors.