@redocly/openapi-core/src/config/rules.ts

See https://github.com/Redocly/redocly-cli

import { RuleSet, SpecVersion } from '../oas-types';
import { StyleguideConfig } from './config';
import { isDefined } from '../utils';
import type { ProblemSeverity } from '../walk';

type InitializedRule = {
  severity: ProblemSeverity;
  ruleId: string;
  visitor: any;
};

export function initRules<T extends Function, P extends RuleSet<T>>(
  rules: P[],
  config: StyleguideConfig,
  type: 'rules' | 'preprocessors' | 'decorators',
  oasVersion: SpecVersion
): InitializedRule[] {
  return rules
    .flatMap((ruleset) =>
      Object.keys(ruleset).map((ruleId) => {
        const rule = ruleset[ruleId];

        const ruleSettings =
          type === 'rules'
            ? config.getRuleSettings(ruleId, oasVersion)
            : type === 'preprocessors'
            ? config.getPreprocessorSettings(ruleId, oasVersion)
            : config.getDecoratorSettings(ruleId, oasVersion);

        if (ruleSettings.severity === 'off') {
          return undefined;
        }
        const severity: ProblemSeverity = ruleSettings.severity;

        const visitors = rule(ruleSettings);

        if (Array.isArray(visitors)) {
          return visitors.map((visitor: any) => ({
            severity,
            ruleId,
            visitor: visitor,
          }));
        }

        return {
          severity,
          ruleId,
          visitor: visitors, // note: actually it is only one visitor object
        };
      })
    )
    .flatMap((visitor) => visitor)
    .filter(isDefined);
}