preflightCheck.js

import * as babel from '@babel/core';

import { INLINE, RUNTIME, EXTERNAL, BUNDLED } from './constants';
import { addBabelPlugin } from './utils';

const MODULE_ERROR =
  'Rollup requires that your Babel configuration keeps ES6 module syntax intact. ' +
  'Unfortunately it looks like your configuration specifies a module transformer ' +
  'to replace ES6 modules with another module format. To continue you have to disable it.' +
  '\n\n' +
  "Most commonly it's a CommonJS transform added by @babel/preset-env - " +
  'in such case you should disable it by adding `modules: false` option to that preset ' +
  '(described in more detail here - https://github.com/rollup/plugins/tree/master/packages/babel#modules ).';

const UNEXPECTED_ERROR =
  'An unexpected situation arose. Please raise an issue at ' +
  'https://github.com/rollup/plugins/issues. Thanks!';

const PREFLIGHT_TEST_STRING = '__ROLLUP__PREFLIGHT_CHECK_DO_NOT_TOUCH__';
const PREFLIGHT_INPUT = `export default "${PREFLIGHT_TEST_STRING}";`;

function helpersTestTransform() {
  return {
    visitor: {
      StringLiteral(path, state) {
        if (path.node.value === PREFLIGHT_TEST_STRING) {
          path.replaceWith(state.file.addHelper('inherits'));
        }
      }
    }
  };
}

const mismatchError = (actual, expected, filename) =>
  `You have declared using "${expected}" babelHelpers, but transforming ${filename} resulted in "${actual}". Please check your configuration.`;

const inheritsHelperRe = /\/helpers\/(esm\/)?inherits/;

export default async function preflightCheck(ctx, babelHelpers, transformOptions) {
  const finalOptions = addBabelPlugin(transformOptions, helpersTestTransform);
  const check = (await babel.transformAsync(PREFLIGHT_INPUT, finalOptions)).code;

  // Babel sometimes splits ExportDefaultDeclaration into 2 statements, so we also check for ExportNamedDeclaration
  if (!/export (d|{)/.test(check)) {
    ctx.error(MODULE_ERROR);
  }

  if (inheritsHelperRe.test(check)) {
    if (babelHelpers === RUNTIME) {
      return;
    }
    ctx.error(mismatchError(RUNTIME, babelHelpers, transformOptions.filename));
  }

  if (check.includes('babelHelpers.inherits')) {
    if (babelHelpers === EXTERNAL) {
      return;
    }
    ctx.error(mismatchError(EXTERNAL, babelHelpers, transformOptions.filename));
  }

  // test unminifiable string content
  if (check.includes('Super expression must either be null or a function')) {
    if (babelHelpers === INLINE || babelHelpers === BUNDLED) {
      return;
    }
    if (babelHelpers === RUNTIME && !transformOptions.plugins.length) {
      ctx.error(
        `You must use the \`@babel/plugin-transform-runtime\` plugin when \`babelHelpers\` is "${RUNTIME}".\n`
      );
    }
    ctx.error(mismatchError(INLINE, babelHelpers, transformOptions.filename));
  }

  ctx.error(UNEXPECTED_ERROR);
}