node-esm-resolve-implementation.js

// Copied from https://raw.githubusercontent.com/nodejs/node/v15.3.0/lib/internal/modules/esm/resolve.js
// Then modified to suite our needs.
// Formatting is intentionally bad to keep the diff as small as possible, to make it easier to merge
// upstream changes and understand our modifications.
//
// Github diff to easily view the changes:
//   https://github.com/TypeStrong/ts-node/compare/esm-resolver-diff..main
'use strict';

const [nodeMajor, nodeMinor, nodePatch] = process.versions.node.split('.').map(s => parseInt(s, 10))
// Test for node >14.13.1 || (>=12.20.0 && <13)
const builtinModuleProtocol = nodeMajor > 14 || (
    nodeMajor === 14 && (
      nodeMinor > 13 || (
        nodeMinor === 13 && nodePatch > 0
      )
    )
  ) || (
    nodeMajor === 12 && (
      nodeMinor > 20 || (
        nodeMinor === 20
      )
    )
  )
    ? 'node:'
    : 'nodejs:';

const {
  ArrayIsArray,
  ArrayPrototypeJoin,
  ArrayPrototypeShift,
  JSONParse,
  JSONStringify,
  ObjectFreeze,
  ObjectGetOwnPropertyNames,
  ObjectPrototypeHasOwnProperty,
  // RegExp,
  RegExpPrototypeTest,
  SafeMap,
  SafeSet,
  // String,
  StringPrototypeEndsWith,
  StringPrototypeIndexOf,
  StringPrototypeLastIndexOf,
  StringPrototypeReplace,
  StringPrototypeSlice,
  StringPrototypeSplit,
  StringPrototypeStartsWith,
  StringPrototypeSubstr,
} = require('./node-primordials');

// const internalFS = require('internal/fs/utils');
// const { NativeModule } = require('internal/bootstrap/loaders');
const Module = require('module')
const NativeModule = {
  canBeRequiredByUsers(specifier) {
    return Module.builtinModules.includes(specifier)
  }
}
const {
  realpathSync,
  statSync,
  Stats,
} = require('fs');
// const { getOptionValue } = require('internal/options');
const { getOptionValue } = require('./node-options');
// // Do not eagerly grab .manifest, it may be in TDZ
// const policy = getOptionValue('--experimental-policy') ?
//   require('internal/process/policy') :
//   null;
// disabled for now.  I am not sure if/how we should support this
const policy = null;
const { sep, relative } = require('path');
const preserveSymlinks = getOptionValue('--preserve-symlinks');
const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
const typeFlag = getOptionValue('--input-type');
// const { URL, pathToFileURL, fileURLToPath } = require('internal/url');
const { URL, pathToFileURL, fileURLToPath } = require('url');
const {
  ERR_INPUT_TYPE_NOT_ALLOWED,
  ERR_INVALID_ARG_VALUE,
  ERR_INVALID_MODULE_SPECIFIER,
  ERR_INVALID_PACKAGE_CONFIG,
  ERR_INVALID_PACKAGE_TARGET,
  ERR_MANIFEST_DEPENDENCY_MISSING,
  ERR_MODULE_NOT_FOUND,
  ERR_PACKAGE_IMPORT_NOT_DEFINED,
  ERR_PACKAGE_PATH_NOT_EXPORTED,
  ERR_UNSUPPORTED_DIR_IMPORT,
  ERR_UNSUPPORTED_ESM_URL_SCHEME,
// } = require('internal/errors').codes;
} = require('./node-errors').codes;

// const { Module: CJSModule } = require('internal/modules/cjs/loader');
const CJSModule = Module;

// const packageJsonReader = require('internal/modules/package_json_reader');
const packageJsonReader = require('./node-package-json-reader');
const userConditions = getOptionValue('--conditions');
const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import', ...userConditions]);
const DEFAULT_CONDITIONS_SET = new SafeSet(DEFAULT_CONDITIONS);

const pendingDeprecation = getOptionValue('--pending-deprecation');

function createResolve(opts) {
// TODO receive cached fs implementations here
const {tsExtensions, jsExtensions, preferTsExts} = opts;

const emittedPackageWarnings = new SafeSet();
function emitFolderMapDeprecation(match, pjsonUrl, isExports, base) {
  const pjsonPath = fileURLToPath(pjsonUrl);
  if (!pendingDeprecation) {
    const nodeModulesIndex = StringPrototypeLastIndexOf(pjsonPath,
                                                        '/node_modules/');
    if (nodeModulesIndex !== -1) {
      const afterNodeModulesPath = StringPrototypeSlice(pjsonPath,
                                                        nodeModulesIndex + 14,
                                                        -13);
      try {
        const { packageSubpath } = parsePackageName(afterNodeModulesPath);
        if (packageSubpath === '.')
          return;
      } catch {}
    }
  }
  if (emittedPackageWarnings.has(pjsonPath + '|' + match))
    return;
  emittedPackageWarnings.add(pjsonPath + '|' + match);
  process.emitWarning(
    `Use of deprecated folder mapping "${match}" in the ${isExports ?
      '"exports"' : '"imports"'} field module resolution of the package at ${
      pjsonPath}${base ? ` imported from ${fileURLToPath(base)}` : ''}.\n` +
      `Update this package.json to use a subpath pattern like "${match}*".`,
    'DeprecationWarning',
    'DEP0148'
  );
}

function getConditionsSet(conditions) {
  if (conditions !== undefined && conditions !== DEFAULT_CONDITIONS) {
    if (!ArrayIsArray(conditions)) {
      throw new ERR_INVALID_ARG_VALUE('conditions', conditions,
                                      'expected an array');
    }
    return new SafeSet(conditions);
  }
  return DEFAULT_CONDITIONS_SET;
}

const realpathCache = new SafeMap();
const packageJSONCache = new SafeMap();  /* string -> PackageConfig */

function tryStatSync(path) {
  try {
    return statSync(path);
  } catch {
    return new Stats();
  }
}

function getPackageConfig(path, specifier, base) {
  const existing = packageJSONCache.get(path);
  if (existing !== undefined) {
    return existing;
  }
  const source = packageJsonReader.read(path).string;
  if (source === undefined) {
    const packageConfig = {
      pjsonPath: path,
      exists: false,
      main: undefined,
      name: undefined,
      type: 'none',
      exports: undefined,
      imports: undefined,
    };
    packageJSONCache.set(path, packageConfig);
    return packageConfig;
  }

  let packageJSON;
  try {
    packageJSON = JSONParse(source);
  } catch (error) {
    throw new ERR_INVALID_PACKAGE_CONFIG(
      path,
      (base ? `"${specifier}" from ` : '') + fileURLToPath(base || specifier),
      error.message
    );
  }

  let { imports, main, name, type } = packageJSON;
  const { exports } = packageJSON;
  if (typeof imports !== 'object' || imports === null) imports = undefined;
  if (typeof main !== 'string') main = undefined;
  if (typeof name !== 'string') name = undefined;
  // Ignore unknown types for forwards compatibility
  if (type !== 'module' && type !== 'commonjs') type = 'none';

  const packageConfig = {
    pjsonPath: path,
    exists: true,
    main,
    name,
    type,
    exports,
    imports,
  };
  packageJSONCache.set(path, packageConfig);
  return packageConfig;
}

function getPackageScopeConfig(resolved) {
  let packageJSONUrl = new URL('./package.json', resolved);
  while (true) {
    const packageJSONPath = packageJSONUrl.pathname;
    if (StringPrototypeEndsWith(packageJSONPath, 'node_modules/package.json'))
      break;
    const packageConfig = getPackageConfig(fileURLToPath(packageJSONUrl),
                                           resolved);
    if (packageConfig.exists) return packageConfig;

    const lastPackageJSONUrl = packageJSONUrl;
    packageJSONUrl = new URL('../package.json', packageJSONUrl);

    // Terminates at root where ../package.json equals ../../package.json
    // (can't just check "/package.json" for Windows support).
    if (packageJSONUrl.pathname === lastPackageJSONUrl.pathname) break;
  }
  const packageJSONPath = fileURLToPath(packageJSONUrl);
  const packageConfig = {
    pjsonPath: packageJSONPath,
    exists: false,
    main: undefined,
    name: undefined,
    type: 'none',
    exports: undefined,
    imports: undefined,
  };
  packageJSONCache.set(packageJSONPath, packageConfig);
  return packageConfig;
}

/*
 * Legacy CommonJS main resolution:
 * 1. let M = pkg_url + (json main field)
 * 2. TRY(M, M.js, M.json, M.node)
 * 3. TRY(M/index.js, M/index.json, M/index.node)
 * 4. TRY(pkg_url/index.js, pkg_url/index.json, pkg_url/index.node)
 * 5. NOT_FOUND
 */
function fileExists(url) {
  return tryStatSync(fileURLToPath(url)).isFile();
}

function legacyMainResolve(packageJSONUrl, packageConfig, base) {
  let guess;
  if (packageConfig.main !== undefined) {
    // Note: fs check redundances will be handled by Descriptor cache here.
    if (fileExists(guess = new URL(`./${packageConfig.main}`,
                                   packageJSONUrl))) {
      return guess;
    }
    if (fileExists(guess = new URL(`./${packageConfig.main}.js`,
                                   packageJSONUrl))) {
      return guess;
    }
    if (fileExists(guess = new URL(`./${packageConfig.main}.json`,
                                   packageJSONUrl))) {
      return guess;
    }
    if (fileExists(guess = new URL(`./${packageConfig.main}.node`,
                                   packageJSONUrl))) {
      return guess;
    }
    if (fileExists(guess = new URL(`./${packageConfig.main}/index.js`,
                                   packageJSONUrl))) {
      return guess;
    }
    if (fileExists(guess = new URL(`./${packageConfig.main}/index.json`,
                                   packageJSONUrl))) {
      return guess;
    }
    if (fileExists(guess = new URL(`./${packageConfig.main}/index.node`,
                                   packageJSONUrl))) {
      return guess;
    }
    // Fallthrough.
  }
  if (fileExists(guess = new URL('./index.js', packageJSONUrl))) {
    return guess;
  }
  // So fs.
  if (fileExists(guess = new URL('./index.json', packageJSONUrl))) {
    return guess;
  }
  if (fileExists(guess = new URL('./index.node', packageJSONUrl))) {
    return guess;
  }
  // Not found.
  throw new ERR_MODULE_NOT_FOUND(
    fileURLToPath(new URL('.', packageJSONUrl)), fileURLToPath(base));
}

function resolveExtensionsWithTryExactName(search) {
  if (fileExists(search)) return search;
  const resolvedReplacementExtension = resolveReplacementExtensions(search);
  if(resolvedReplacementExtension) return resolvedReplacementExtension;
  return resolveExtensions(search);
}

const extensions = Array.from(new Set([
  ...(preferTsExts ? tsExtensions : []),
  '.js',
  ...jsExtensions,
  '.json', '.node', '.mjs',
  ...tsExtensions
]));

function resolveExtensions(search) {
  for (let i = 0; i < extensions.length; i++) {
    const extension = extensions[i];
    const guess = new URL(`${search.pathname}${extension}`, search);
    if (fileExists(guess)) return guess;
  }
  return undefined;
}

/**
 * TS's resolver can resolve foo.js to foo.ts, by replacing .js extension with several source extensions.
 * IMPORTANT: preserve ordering according to preferTsExts; this affects resolution behavior!
 */
const replacementExtensions = extensions.filter(ext => ['.js', '.jsx', '.ts', '.tsx'].includes(ext));

function resolveReplacementExtensions(search) {
  if (search.pathname.match(/\.js$/)) {
    const pathnameWithoutExtension = search.pathname.slice(0, search.pathname.length - 3);
    for (let i = 0; i < replacementExtensions.length; i++) {
      const extension = replacementExtensions[i];
      const guess = new URL(search.toString());
      guess.pathname = `${pathnameWithoutExtension}${extension}`;
      if (fileExists(guess)) return guess;
    }
  }
  return undefined;
}

function resolveIndex(search) {
  return resolveExtensions(new URL('index', search));
}

const encodedSepRegEx = /%2F|%2C/i;
function finalizeResolution(resolved, base) {
  if (RegExpPrototypeTest(encodedSepRegEx, resolved.pathname))
    throw new ERR_INVALID_MODULE_SPECIFIER(
      resolved.pathname, 'must not include encoded "/" or "\\" characters',
      fileURLToPath(base));

  if (getOptionValue('--experimental-specifier-resolution') === 'node') {
    const path = fileURLToPath(resolved);
    let file = resolveExtensionsWithTryExactName(resolved);
    if (file !== undefined) return file;
    if (!StringPrototypeEndsWith(path, '/')) {
      file = resolveIndex(new URL(`${resolved}/`));
      if (file !== undefined) return file;
    } else {
      return resolveIndex(resolved) || resolved;
    }
    throw new ERR_MODULE_NOT_FOUND(
      resolved.pathname, fileURLToPath(base), 'module');
  }

  const file = resolveReplacementExtensions(resolved) || resolved;
  const path = fileURLToPath(file);

  const stats = tryStatSync(StringPrototypeEndsWith(path, '/') ?
    StringPrototypeSlice(path, -1) : path);
  if (stats.isDirectory()) {
    const err = new ERR_UNSUPPORTED_DIR_IMPORT(path, fileURLToPath(base));
    err.url = String(resolved);
    throw err;
  } else if (!stats.isFile()) {
    throw new ERR_MODULE_NOT_FOUND(
      path || resolved.pathname, fileURLToPath(base), 'module');
  }

  return file;
}

function throwImportNotDefined(specifier, packageJSONUrl, base) {
  throw new ERR_PACKAGE_IMPORT_NOT_DEFINED(
    specifier, packageJSONUrl && fileURLToPath(new URL('.', packageJSONUrl)),
    fileURLToPath(base));
}

function throwExportsNotFound(subpath, packageJSONUrl, base) {
  throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
    fileURLToPath(new URL('.', packageJSONUrl)), subpath,
    base && fileURLToPath(base));
}

function throwInvalidSubpath(subpath, packageJSONUrl, internal, base) {
  const reason = `request is not a valid subpath for the "${internal ?
    'imports' : 'exports'}" resolution of ${fileURLToPath(packageJSONUrl)}`;
  throw new ERR_INVALID_MODULE_SPECIFIER(subpath, reason,
                                         base && fileURLToPath(base));
}

function throwInvalidPackageTarget(
  subpath, target, packageJSONUrl, internal, base) {
  if (typeof target === 'object' && target !== null) {
    target = JSONStringify(target, null, '');
  } else {
    target = `${target}`;
  }
  throw new ERR_INVALID_PACKAGE_TARGET(
    fileURLToPath(new URL('.', packageJSONUrl)), subpath, target,
    internal, base && fileURLToPath(base));
}

const invalidSegmentRegEx = /(^|\\|\/)(\.\.?|node_modules)(\\|\/|$)/;
const patternRegEx = /\*/g;

function resolvePackageTargetString(
  target, subpath, match, packageJSONUrl, base, pattern, internal, conditions) {
  if (subpath !== '' && !pattern && target[target.length - 1] !== '/')
    throwInvalidPackageTarget(match, target, packageJSONUrl, internal, base);

  if (!StringPrototypeStartsWith(target, './')) {
    if (internal && !StringPrototypeStartsWith(target, '../') &&
        !StringPrototypeStartsWith(target, '/')) {
      let isURL = false;
      try {
        new URL(target);
        isURL = true;
      } catch {}
      if (!isURL) {
        const exportTarget = pattern ?
          StringPrototypeReplace(target, patternRegEx, subpath) :
          target + subpath;
        return packageResolve(exportTarget, packageJSONUrl, conditions);
      }
    }
    throwInvalidPackageTarget(match, target, packageJSONUrl, internal, base);
  }

  if (RegExpPrototypeTest(invalidSegmentRegEx, StringPrototypeSlice(target, 2)))
    throwInvalidPackageTarget(match, target, packageJSONUrl, internal, base);

  const resolved = new URL(target, packageJSONUrl);
  const resolvedPath = resolved.pathname;
  const packagePath = new URL('.', packageJSONUrl).pathname;

  if (!StringPrototypeStartsWith(resolvedPath, packagePath))
    throwInvalidPackageTarget(match, target, packageJSONUrl, internal, base);

  if (subpath === '') return resolved;

  if (RegExpPrototypeTest(invalidSegmentRegEx, subpath))
    throwInvalidSubpath(match + subpath, packageJSONUrl, internal, base);

  if (pattern)
    return new URL(StringPrototypeReplace(resolved.href, patternRegEx,
                                          subpath));
  return new URL(subpath, resolved);
}

/**
 * @param {string} key
 * @returns {boolean}
 */
function isArrayIndex(key) {
  const keyNum = +key;
  if (`${keyNum}` !== key) return false;
  return keyNum >= 0 && keyNum < 0xFFFF_FFFF;
}

function resolvePackageTarget(packageJSONUrl, target, subpath, packageSubpath,
                              base, pattern, internal, conditions) {
  if (typeof target === 'string') {
    return resolvePackageTargetString(
      target, subpath, packageSubpath, packageJSONUrl, base, pattern, internal,
      conditions);
  } else if (ArrayIsArray(target)) {
    if (target.length === 0)
      return null;

    let lastException;
    for (let i = 0; i < target.length; i++) {
      const targetItem = target[i];
      let resolved;
      try {
        resolved = resolvePackageTarget(
          packageJSONUrl, targetItem, subpath, packageSubpath, base, pattern,
          internal, conditions);
      } catch (e) {
        lastException = e;
        if (e.code === 'ERR_INVALID_PACKAGE_TARGET')
          continue;
        throw e;
      }
      if (resolved === undefined)
        continue;
      if (resolved === null) {
        lastException = null;
        continue;
      }
      return resolved;
    }
    if (lastException === undefined || lastException === null)
      return lastException;
    throw lastException;
  } else if (typeof target === 'object' && target !== null) {
    const keys = ObjectGetOwnPropertyNames(target);
    for (let i = 0; i < keys.length; i++) {
      const key = keys[i];
      if (isArrayIndex(key)) {
        throw new ERR_INVALID_PACKAGE_CONFIG(
          fileURLToPath(packageJSONUrl), base,
          '"exports" cannot contain numeric property keys.');
      }
    }
    for (let i = 0; i < keys.length; i++) {
      const key = keys[i];
      if (key === 'default' || conditions.has(key)) {
        const conditionalTarget = target[key];
        const resolved = resolvePackageTarget(
          packageJSONUrl, conditionalTarget, subpath, packageSubpath, base,
          pattern, internal, conditions);
        if (resolved === undefined)
          continue;
        return resolved;
      }
    }
    return undefined;
  } else if (target === null) {
    return null;
  }
  throwInvalidPackageTarget(packageSubpath, target, packageJSONUrl, internal,
                            base);
}

function isConditionalExportsMainSugar(exports, packageJSONUrl, base) {
  if (typeof exports === 'string' || ArrayIsArray(exports)) return true;
  if (typeof exports !== 'object' || exports === null) return false;

  const keys = ObjectGetOwnPropertyNames(exports);
  let isConditionalSugar = false;
  let i = 0;
  for (let j = 0; j < keys.length; j++) {
    const key = keys[j];
    const curIsConditionalSugar = key === '' || key[0] !== '.';
    if (i++ === 0) {
      isConditionalSugar = curIsConditionalSugar;
    } else if (isConditionalSugar !== curIsConditionalSugar) {
      throw new ERR_INVALID_PACKAGE_CONFIG(
        fileURLToPath(packageJSONUrl), base,
        '"exports" cannot contain some keys starting with \'.\' and some not.' +
        ' The exports object must either be an object of package subpath keys' +
        ' or an object of main entry condition name keys only.');
    }
  }
  return isConditionalSugar;
}

/**
 * @param {URL} packageJSONUrl
 * @param {string} packageSubpath
 * @param {object} packageConfig
 * @param {string} base
 * @param {Set<string>} conditions
 * @returns {URL}
 */
function packageExportsResolve(
  packageJSONUrl, packageSubpath, packageConfig, base, conditions) {
  let exports = packageConfig.exports;
  if (isConditionalExportsMainSugar(exports, packageJSONUrl, base))
    exports = { '.': exports };

  if (ObjectPrototypeHasOwnProperty(exports, packageSubpath)) {
    const target = exports[packageSubpath];
    const resolved = resolvePackageTarget(
      packageJSONUrl, target, '', packageSubpath, base, false, false, conditions
    );
    if (resolved === null || resolved === undefined)
      throwExportsNotFound(packageSubpath, packageJSONUrl, base);
    return { resolved, exact: true };
  }

  let bestMatch = '';
  const keys = ObjectGetOwnPropertyNames(exports);
  for (let i = 0; i < keys.length; i++) {
    const key = keys[i];
    if (key[key.length - 1] === '*' &&
        StringPrototypeStartsWith(packageSubpath,
                                  StringPrototypeSlice(key, 0, -1)) &&
        packageSubpath.length >= key.length &&
        key.length > bestMatch.length) {
      bestMatch = key;
    } else if (key[key.length - 1] === '/' &&
      StringPrototypeStartsWith(packageSubpath, key) &&
      key.length > bestMatch.length) {
      bestMatch = key;
    }
  }

  if (bestMatch) {
    const target = exports[bestMatch];
    const pattern = bestMatch[bestMatch.length - 1] === '*';
    const subpath = StringPrototypeSubstr(packageSubpath, bestMatch.length -
      (pattern ? 1 : 0));
    const resolved = resolvePackageTarget(packageJSONUrl, target, subpath,
                                          bestMatch, base, pattern, false,
                                          conditions);
    if (resolved === null || resolved === undefined)
      throwExportsNotFound(packageSubpath, packageJSONUrl, base);
    if (!pattern)
      emitFolderMapDeprecation(bestMatch, packageJSONUrl, true, base);
    return { resolved, exact: pattern };
  }

  throwExportsNotFound(packageSubpath, packageJSONUrl, base);
}

function packageImportsResolve(name, base, conditions) {
  if (name === '#' || StringPrototypeStartsWith(name, '#/')) {
    const reason = 'is not a valid internal imports specifier name';
    throw new ERR_INVALID_MODULE_SPECIFIER(name, reason, fileURLToPath(base));
  }
  let packageJSONUrl;
  const packageConfig = getPackageScopeConfig(base);
  if (packageConfig.exists) {
    packageJSONUrl = pathToFileURL(packageConfig.pjsonPath);
    const imports = packageConfig.imports;
    if (imports) {
      if (ObjectPrototypeHasOwnProperty(imports, name)) {
        const resolved = resolvePackageTarget(
          packageJSONUrl, imports[name], '', name, base, false, true, conditions
        );
        if (resolved !== null)
          return { resolved, exact: true };
      } else {
        let bestMatch = '';
        const keys = ObjectGetOwnPropertyNames(imports);
        for (let i = 0; i < keys.length; i++) {
          const key = keys[i];
          if (key[key.length - 1] === '*' &&
              StringPrototypeStartsWith(name,
                                        StringPrototypeSlice(key, 0, -1)) &&
              name.length >= key.length &&
              key.length > bestMatch.length) {
            bestMatch = key;
          } else if (key[key.length - 1] === '/' &&
            StringPrototypeStartsWith(name, key) &&
            key.length > bestMatch.length) {
            bestMatch = key;
          }
        }

        if (bestMatch) {
          const target = imports[bestMatch];
          const pattern = bestMatch[bestMatch.length - 1] === '*';
          const subpath = StringPrototypeSubstr(name, bestMatch.length -
            (pattern ? 1 : 0));
          const resolved = resolvePackageTarget(
            packageJSONUrl, target, subpath, bestMatch, base, pattern, true,
            conditions);
          if (resolved !== null) {
            if (!pattern)
              emitFolderMapDeprecation(bestMatch, packageJSONUrl, false, base);
            return { resolved, exact: pattern };
          }
        }
      }
    }
  }
  throwImportNotDefined(name, packageJSONUrl, base);
}

function getPackageType(url) {
  const packageConfig = getPackageScopeConfig(url);
  return packageConfig.type;
}

function parsePackageName(specifier, base) {
  let separatorIndex = StringPrototypeIndexOf(specifier, '/');
  let validPackageName = true;
  let isScoped = false;
  if (specifier[0] === '@') {
    isScoped = true;
    if (separatorIndex === -1 || specifier.length === 0) {
      validPackageName = false;
    } else {
      separatorIndex = StringPrototypeIndexOf(
        specifier, '/', separatorIndex + 1);
    }
  }

  const packageName = separatorIndex === -1 ?
    specifier : StringPrototypeSlice(specifier, 0, separatorIndex);

  // Package name cannot have leading . and cannot have percent-encoding or
  // separators.
  for (let i = 0; i < packageName.length; i++) {
    if (packageName[i] === '%' || packageName[i] === '\\') {
      validPackageName = false;
      break;
    }
  }

  if (!validPackageName) {
    throw new ERR_INVALID_MODULE_SPECIFIER(
      specifier, 'is not a valid package name', fileURLToPath(base));
  }

  const packageSubpath = '.' + (separatorIndex === -1 ? '' :
    StringPrototypeSlice(specifier, separatorIndex));

  return { packageName, packageSubpath, isScoped };
}

/**
 * @param {string} specifier
 * @param {URL} base
 * @param {Set<string>} conditions
 * @returns {URL}
 */
function packageResolve(specifier, base, conditions) {
  const { packageName, packageSubpath, isScoped } =
    parsePackageName(specifier, base);

  // ResolveSelf
  const packageConfig = getPackageScopeConfig(base);
  if (packageConfig.exists) {
    const packageJSONUrl = pathToFileURL(packageConfig.pjsonPath);
    if (packageConfig.name === packageName &&
        packageConfig.exports !== undefined && packageConfig.exports !== null) {
      return packageExportsResolve(
        packageJSONUrl, packageSubpath, packageConfig, base, conditions
      ).resolved;
    }
  }

  let packageJSONUrl =
    new URL('./node_modules/' + packageName + '/package.json', base);
  let packageJSONPath = fileURLToPath(packageJSONUrl);
  let lastPath;
  do {
    const stat = tryStatSync(StringPrototypeSlice(packageJSONPath, 0,
                                                  packageJSONPath.length - 13));
    if (!stat.isDirectory()) {
      lastPath = packageJSONPath;
      packageJSONUrl = new URL((isScoped ?
        '../../../../node_modules/' : '../../../node_modules/') +
        packageName + '/package.json', packageJSONUrl);
      packageJSONPath = fileURLToPath(packageJSONUrl);
      continue;
    }

    // Package match.
    const packageConfig = getPackageConfig(packageJSONPath, specifier, base);
    if (packageConfig.exports !== undefined && packageConfig.exports !== null)
      return packageExportsResolve(
        packageJSONUrl, packageSubpath, packageConfig, base, conditions
      ).resolved;
    if (packageSubpath === '.')
      return legacyMainResolve(packageJSONUrl, packageConfig, base);
    return new URL(packageSubpath, packageJSONUrl);
    // Cross-platform root check.
  } while (packageJSONPath.length !== lastPath.length);

  // eslint can't handle the above code.
  // eslint-disable-next-line no-unreachable
  throw new ERR_MODULE_NOT_FOUND(packageName, fileURLToPath(base));
}

function isBareSpecifier(specifier) {
  return specifier[0] && specifier[0] !== '/' && specifier[0] !== '.';
}

function isRelativeSpecifier(specifier) {
  if (specifier[0] === '.') {
    if (specifier.length === 1 || specifier[1] === '/') return true;
    if (specifier[1] === '.') {
      if (specifier.length === 2 || specifier[2] === '/') return true;
    }
  }
  return false;
}

function shouldBeTreatedAsRelativeOrAbsolutePath(specifier) {
  if (specifier === '') return false;
  if (specifier[0] === '/') return true;
  return isRelativeSpecifier(specifier);
}

/**
 * @param {string} specifier
 * @param {URL} base
 * @param {Set<string>} conditions
 * @returns {URL}
 */
function moduleResolve(specifier, base, conditions) {
  // Order swapped from spec for minor perf gain.
  // Ok since relative URLs cannot parse as URLs.
  let resolved;
  if (shouldBeTreatedAsRelativeOrAbsolutePath(specifier)) {
    resolved = new URL(specifier, base);
  } else if (specifier[0] === '#') {
    ({ resolved } = packageImportsResolve(specifier, base, conditions));
  } else {
    try {
      resolved = new URL(specifier);
    } catch {
      resolved = packageResolve(specifier, base, conditions);
    }
  }
  return finalizeResolution(resolved, base);
}

/**
 * Try to resolve an import as a CommonJS module
 * @param {string} specifier
 * @param {string} parentURL
 * @returns {boolean|string}
 */
function resolveAsCommonJS(specifier, parentURL) {
  try {
    const parent = fileURLToPath(parentURL);
    const tmpModule = new CJSModule(parent, null);
    tmpModule.paths = CJSModule._nodeModulePaths(parent);

    let found = CJSModule._resolveFilename(specifier, tmpModule, false);

    // If it is a relative specifier return the relative path
    // to the parent
    if (isRelativeSpecifier(specifier)) {
      found = relative(parent, found);
      // Add '.separator if the path does not start with '..separator'
      // This should be a safe assumption because when loading
      // esm modules there should be always a file specified so
      // there should not be a specifier like '..' or '.'
      if (!StringPrototypeStartsWith(found, `..${sep}`)) {
        found = `.${sep}${found}`;
      }
    } else if (isBareSpecifier(specifier)) {
      // If it is a bare specifier return the relative path within the
      // module
      const pkg = StringPrototypeSplit(specifier, '/')[0];
      const index = StringPrototypeIndexOf(found, pkg);
      if (index !== -1) {
        found = StringPrototypeSlice(found, index);
      }
    }
    // Normalize the path separator to give a valid suggestion
    // on Windows
    if (process.platform === 'win32') {
      found = StringPrototypeReplace(found, new RegExp(`\\${sep}`, 'g'), '/');
    }
    return found;
  } catch {
    return false;
  }
}

function defaultResolve(specifier, context = {}, defaultResolveUnused) {
  let { parentURL, conditions } = context;
  if (parentURL && policy != null && policy.manifest) {
    const redirects = policy.manifest.getDependencyMapper(parentURL);
    if (redirects) {
      const { resolve, reaction } = redirects;
      const destination = resolve(specifier, new SafeSet(conditions));
      let missing = true;
      if (destination === true) {
        missing = false;
      } else if (destination) {
        const href = destination.href;
        return { url: href };
      }
      if (missing) {
        reaction(new ERR_MANIFEST_DEPENDENCY_MISSING(
          parentURL,
          specifier,
          ArrayPrototypeJoin([...conditions], ', '))
        );
      }
    }
  }
  let parsed;
  try {
    parsed = new URL(specifier);
    if (parsed.protocol === 'data:') {
      return {
        url: specifier
      };
    }
  } catch {}
  if (parsed && parsed.protocol === builtinModuleProtocol)
    return { url: specifier };
  if (parsed && parsed.protocol !== 'file:' && parsed.protocol !== 'data:')
    throw new ERR_UNSUPPORTED_ESM_URL_SCHEME(parsed);
  if (NativeModule.canBeRequiredByUsers(specifier)) {
    return {
      url: builtinModuleProtocol + specifier
    };
  }
  if (parentURL && StringPrototypeStartsWith(parentURL, 'data:')) {
    // This is gonna blow up, we want the error
    new URL(specifier, parentURL);
  }

  const isMain = parentURL === undefined;
  if (isMain) {
    parentURL = pathToFileURL(`${process.cwd()}/`).href;

    // This is the initial entry point to the program, and --input-type has
    // been passed as an option; but --input-type can only be used with
    // --eval, --print or STDIN string input. It is not allowed with file
    // input, to avoid user confusion over how expansive the effect of the
    // flag should be (i.e. entry point only, package scope surrounding the
    // entry point, etc.).
    if (typeFlag)
      throw new ERR_INPUT_TYPE_NOT_ALLOWED();
  }

  conditions = getConditionsSet(conditions);
  let url;
  try {
    url = moduleResolve(specifier, parentURL, conditions);
  } catch (error) {
    // Try to give the user a hint of what would have been the
    // resolved CommonJS module
    if (error.code === 'ERR_MODULE_NOT_FOUND' ||
        error.code === 'ERR_UNSUPPORTED_DIR_IMPORT') {
      if (StringPrototypeStartsWith(specifier, 'file://')) {
        specifier = fileURLToPath(specifier);
      }
      const found = resolveAsCommonJS(specifier, parentURL);
      if (found) {
        // Modify the stack and message string to include the hint
        const lines = StringPrototypeSplit(error.stack, '\n');
        const hint = `Did you mean to import ${found}?`;
        error.stack =
          ArrayPrototypeShift(lines) + '\n' +
          hint + '\n' +
          ArrayPrototypeJoin(lines, '\n');
        error.message += `\n${hint}`;
      }
    }
    throw error;
  }

  if (isMain ? !preserveSymlinksMain : !preserveSymlinks) {
    const urlPath = fileURLToPath(url);
    const real = realpathSync(urlPath, {
      // [internalFS.realpathCacheKey]: realpathCache
    });
    const old = url;
    url = pathToFileURL(
      real + (StringPrototypeEndsWith(urlPath, sep) ? '/' : ''));
    url.search = old.search;
    url.hash = old.hash;
  }

  return { url: `${url}` };
}

return {
  DEFAULT_CONDITIONS,
  defaultResolve,
  encodedSepRegEx,
  getPackageType,
  packageExportsResolve,
  packageImportsResolve
};
}
module.exports = {
  createResolve
};