configuration.js

import { loadPartialConfig } from "@babel/core";

export function normalizeESLintConfig(options) {
  const {
    babelOptions = {},
    // ESLint sets ecmaVersion: undefined when ecmaVersion is not set in the config.
    ecmaVersion = 2020,
    sourceType = "module",
    allowImportExportEverywhere = false,
    requireConfigFile = true,
    ...otherOptions
  } = options;

  return {
    babelOptions,
    ecmaVersion,
    sourceType,
    allowImportExportEverywhere,
    requireConfigFile,
    ...otherOptions,
  };
}

/**
 * Merge user supplied estree plugin options to default estree plugin options
 *
 * @param {*} babelOptions
 * @returns {Array} Merged parser plugin descriptors
 */
function getParserPlugins(babelOptions) {
  const babelParserPlugins = babelOptions.parserOpts?.plugins ?? [];
  // todo: enable classFeatures when it is supported by ESLint
  const estreeOptions = { classFeatures: false };
  for (const plugin of babelParserPlugins) {
    if (Array.isArray(plugin) && plugin[0] === "estree") {
      Object.assign(estreeOptions, plugin[1]);
      break;
    }
  }
  // estree must be the first parser plugin to work with other parser plugins
  return [["estree", estreeOptions], ...babelParserPlugins];
}

export function normalizeBabelParseConfig(options) {
  const parseOptions = {
    sourceType: options.sourceType,
    filename: options.filePath,
    ...options.babelOptions,
    parserOpts: {
      allowImportExportEverywhere: options.allowImportExportEverywhere,
      allowReturnOutsideFunction: true,
      allowSuperOutsideMethod: true,
      ...options.babelOptions.parserOpts,
      plugins: getParserPlugins(options.babelOptions),
      ranges: true,
      tokens: true,
    },
    caller: {
      name: "@babel/eslint-parser",
      ...options.babelOptions.caller,
    },
  };

  if (options.requireConfigFile !== false) {
    const config = loadPartialConfig(parseOptions);

    if (config !== null) {
      if (!config.hasFilesystemConfig()) {
        throw new Error(
          `No Babel config file detected for ${config.options.filename}. Either disable config file checking with requireConfigFile: false, or configure Babel so that it can find the config files.`,
        );
      }

      return config.options;
    }
  }

  return parseOptions;
}