Bug: Flat config doesn't allow uppercase severities

[mdjermanovic]

Environment

Node version: v16.14.0
npm version: v8.3.1
Local ESLint version: v8.49.0
Global ESLint version:
Operating System: windows

What parser are you using?

Default (Espree)

What did you do?

Configuration

// eslint.config.js

module.exports = [{
    rules: {
        "no-undef": "Error"
    }
}];

foo();

What did you expect to happen?

I'd expect uppercase severities to work.

eslintrc allows severities such as "Error" or "eRRoR".

flat config validation aims to allow them too:

eslint/lib/config/flat-config-schema.js

Lines 181 to 189 in bd7a71f

	function assertIsRuleSeverity(ruleId, value) {
	const severity = typeof value === "string"
	? ruleSeverities.get(value.toLowerCase())
	: ruleSeverities.get(value);
	if (typeof severity === "undefined") {
	throw new InvalidRuleSeverityError(ruleId, value);
	}
	}

What actually happened?

Oops! Something went wrong! :(

ESLint: 8.49.0

Configuration for rule "no-undef" is invalid. Expected severity of "off", 0, "warn", 1, "error", or 2.

You passed 'undefined'.

See https://eslint.org/docs/latest/use/configure/rules#using-configuration-files for configuring rules.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/stackblitz-starters-arttsx?file=eslint.config.js

Participation

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

Additional comments

Validation works as intended, but normalizeRuleOptions, which is used while merging, returns undefined, and then the subsequent validation on the next merge fails. That's why the error message at the end says You passed 'undefined'.

[Rec0iL99]

Can reproduce 👍.

[fasttime]

The constructor option reportUnusedDisableDirectives also handles string values in a case-sensitive manner, which seems a bit inconsistent with the intent to allow uppercase severities for rules.

const { FlatESLint } = require('eslint/use-at-your-own-risk');

const eslint = new FlatESLint({
    reportUnusedDisableDirectives: 'Error' // throws ESLintInvalidOptionsError
});

[fasttime]

There is also a reportUnusedDisableDirectives severity setting in flat config. Personally, I think that a consistent handling of severity strings (either case-sensitive or case-insensitive everywhere) would be the least surprising behavior.

[nzakas]

eslintrc allows severities such as "Error" or "eRRoR".

I intentionally did not want to support these in flat config. I was trying to be more strict where possible to clean up some of the weirdness in eslintrc. So, this part isn't a bug, but the "undefined" in the error message definitely is.

My preference is to keep the severities in all places as case-sensitive.

[nzakas]

@mdjermanovic are you okay with closing this?

[mdjermanovic]

I'd like to fix flat-config-schema as in some places it treats rule severities as case-insensitive while in other places as case-sensitive, and that results in the confusing "undefined" in the error message.

Looks like the consensus is that rule severities should be case-sensitive. I'm working on this now.