@atlaskit/eslint-plugin-ui-styling-standard/dist/es2019/rules/utils/create-rule-with-typed-config.js

The eslint plugin to enforce and educate on Atlassian's UI Styling Standard

import Ajv from 'ajv';
import { getRuleUrl } from './get-rule-url';

/**
 * A single shared Ajv instance is reused across every rule instead of constructing
 * a new one each time a default config is needed. Ajv's constructor is expensive
 * (it compiles its own meta-schemas), so we only ever want to pay for it once.
 */
const ajv = new Ajv({
  useDefaults: true
});
export const createLintRuleWithTypedConfig = rule => {
  /**
   * Lazily-computed, cached default config.
   *
   * The default config is derived purely from the rule's (static) schema, so it is
   * constant for the life of the process. Compiling the schema with Ajv involves
   * runtime code generation (`new Function`), which is expensive — previously this
   * ran on every `getDefaultConfig()` call, i.e. once per linted file. We now compute
   * it at most once per rule and reuse the result.
   */
  let defaultConfig;

  /**
   * Gets the default config by running the same validator
   * ESLint does against an empty config object with
   * `useDefaults` option enabled.
   *
   * Any properties with a `default` property set in the schema
   * will be populated with the specified default value.
   */
  function getDefaultConfig() {
    if (defaultConfig === undefined) {
      const validate = ajv.compile(rule.meta.schema);
      const config = {};
      /**
       * The `validate()` function mutates the config object.
       */
      validate(config);
      defaultConfig = config;
    }
    return defaultConfig;
  }
  return {
    ...rule,
    meta: {
      ...rule.meta,
      docs: {
        ...rule.meta.docs,
        url: getRuleUrl(rule.meta.name)
      },
      schema: [rule.meta.schema]
    },
    create(context) {
      /**
       * The config the user has passed.
       *
       * If they passed a config object, even if it is missing properties,
       * ESLint will have added any default values defined using the
       * `default` property in the schema.
       *
       * https://github.com/eslint/eslint/pull/11288
       */
      const userConfig = context.options[0];
      /**
       * If the user passed no config object at all we need to obtain
       * the default ourselves.
       */
      const config = userConfig !== null && userConfig !== void 0 ? userConfig : getDefaultConfig();
      return rule.create(context, config);
    }
  };
};