transform.js

const babel = require("@babel/core");
const promisify = require("util.promisify");
const LoaderError = require("./Error");

const transform = promisify(babel.transform);

module.exports = async function(source, options) {
  let result;
  try {
    result = await transform(source, injectCaller(options));
  } catch (err) {
    throw err.message && err.codeFrame ? new LoaderError(err) : err;
  }

  if (!result) return null;

  // We don't return the full result here because some entries are not
  // really serializable. For a full list of properties see here:
  // https://github.com/babel/babel/blob/master/packages/babel-core/src/transformation/index.js
  // For discussion on this topic see here:
  // https://github.com/babel/babel-loader/pull/629
  const { ast, code, map, metadata, sourceType } = result;

  if (map && (!map.sourcesContent || !map.sourcesContent.length)) {
    map.sourcesContent = [source];
  }

  return { ast, code, map, metadata, sourceType };
};

module.exports.version = babel.version;

function injectCaller(opts) {
  if (!supportsCallerOption()) return opts;

  return Object.assign({}, opts, {
    caller: Object.assign(
      {
        name: "babel-loader",

        // Webpack >= 2 supports ESM and dynamic import.
        supportsStaticESM: true,
        supportsDynamicImport: true,
      },
      opts.caller,
    ),
  });
}

// TODO: We can remove this eventually, I'm just adding it so that people have
// a little time to migrate to the newer RCs of @babel/core without getting
// hard-to-diagnose errors about unknown 'caller' options.
let supportsCallerOptionFlag = undefined;
function supportsCallerOption() {
  if (supportsCallerOptionFlag === undefined) {
    try {
      // Rather than try to match the Babel version, we just see if it throws
      // when passed a 'caller' flag, and use that to decide if it is supported.
      babel.loadPartialConfig({
        caller: undefined,
        babelrc: false,
        configFile: false,
      });
      supportsCallerOptionFlag = true;
    } catch (err) {
      supportsCallerOptionFlag = false;
    }
  }

  return supportsCallerOptionFlag;
}