Function emitLegacyIndexDeprecation

lib/internal/modules/esm/resolve.js:124–151

* Emits a deprecation warning if the given URL is a module and * the package.json file does not define a "main" or "exports" field. * @param {URL} url - The URL of the module being resolved. * @param {string} path - The path of the module being resolved. * @param {string} pkgPath - The path of t

(url, path, pkgPath, base, main)

 * @param {string} [main] - The "main" field from the package.json file.
 */
function emitLegacyIndexDeprecation(url, path, pkgPath, base, main) {
  if (process.noDeprecation) {
    return;
  }
  const format = defaultGetFormatWithoutErrors(url);
  if (format !== 'module') { return; }
  const basePath = fileURLToPath(base);
  if (!main) {
    process.emitWarning(
      `No "main" or "exports" field defined in the package.json for ${pkgPath
      } resolving the main entry point "${
        StringPrototypeSlice(path, pkgPath.length)}", imported from ${basePath
      }.\nDefault "index" lookups for the main are deprecated for ES modules.`,
      'DeprecationWarning',
      'DEP0151',
    );
  } else if (resolve(pkgPath, main) !== path) {
    process.emitWarning(
      `Package ${pkgPath} has a "main" field set to "${main}", ` +
      `excluding the full filename and extension to the resolved file at "${
        StringPrototypeSlice(path, pkgPath.length)}", imported from ${
        basePath}.\n Automatic extension resolution of the "main" field is ` +
      'deprecated for ES modules.',
      'DeprecationWarning',
      'DEP0151',
    );
  }
}

const realpathCache = new SafeMap();