-m alias; determine type based for symlinks based on targets; error on mismatched type flag and package scope

.eslintrc.js

@@ -39,6 +39,7 @@ module.exports = {
       files: [
         'doc/api/esm.md',
         'test/es-module/test-esm-type-flag.js',
+        'test/es-module/test-esm-type-flag-alias.js',
         '*.mjs',
       ],
       parserOptions: { sourceType: 'module' },

doc/api/errors.md

@@ -1270,6 +1270,11 @@ An invalid or unexpected value was passed in an options object.
 
 An invalid or unknown file encoding was passed.
 
+<a id="ERR_INVALID_PACKAGE_CONFIG"></a>
+### ERR_INVALID_PACKAGE_CONFIG
+
+An invalid `package.json` file was found which failed parsing.
+
 <a id="ERR_INVALID_PERFORMANCE_MARK"></a>
 ### ERR_INVALID_PERFORMANCE_MARK
 
@@ -2213,12 +2218,17 @@ while trying to read and parse it.
 
 The `--type=...` flag is not compatible with the Node.js REPL.
 
-<a id="ERR_INVALID_TYPE_EXTENSION"></a>
-### ERR_INVALID_TYPE_EXTENSION
+<a id="ERR_TYPE_MISMATCH"></a>
+### ERR_TYPE_MISMATCH
 
 > Stability: 1 - Experimental
 
-Attempted to execute a `.cjs` module with the `--type=module` flag.
+The `--type=commonjs` flag was used to attempt to execute an `.mjs` file or
+a `.js` file where the nearest parent `package.json` contains
+`"type": "module"`; or
+the `--type=module` flag was used to attempt to execute a `.cjs` file or
+a `.js` file where the nearest parent `package.json` either lacks a `"type"`
+field or contains `"type": "commonjs"`.
 
 <a id="ERR_INVALID_TYPE_FLAG"></a>
 ### ERR_INVALID_TYPE_FLAG

doc/api/esm.md

@@ -190,7 +190,8 @@ as described here, with the conditional `--type` check in **ESM_FORMAT**.
 >       **PACKAGE_RESOLVE**(_specifier_, _parentURL_).
 > 1. If the file at _resolvedURL_ does not exist, then
 >    1. Throw a _Module Not Found_ error.
-> 1. Let _format_ be the result of **ESM_FORMAT**(_url_, _isMain_).
+> 1. Set _resolvedURL_ to the real path of _resolvedURL_.
+> 1. Let _format_ be the result of **ESM_FORMAT**(_resolvedURL_, _isMain_).
 > 1. Load _resolvedURL_ as module format, _format_.
 
 PACKAGE_RESOLVE(_packageSpecifier_, _parentURL_)
@@ -253,22 +254,23 @@ PACKAGE_MAIN_RESOLVE(_packageURL_, _pjson_)
 > 1. Assert: _url_ corresponds to an existing file.
 > 1. If _isMain_ is **true** and the `--type` flag is _"module"_, then
 >    1. If _url_ ends with _".cjs"_, then
->       1. Throw an _Invalid File Extension_ error.
+>       1. Throw a _Type Mismatch_ error.
 >    1. Return _"module"_.
 > 1. Let _pjson_ be the result of **READ_PACKAGE_BOUNDARY**(_url_).
 > 1. If _pjson_ is **null** and _isMain_ is **true**, then
+>    1. If _url_ ends in _".mjs"_, then
+>       1. Return _"module"_.
 >    1. Return _"commonjs"_.
 > 1. If _pjson.type_ exists and is _"module"_, then
 >    1. If _url_ ends in _".cjs"_, then
 >       1. Return _"commonjs"_.
->    1. If _url_ does not end in _".js"_ or _".mjs"_, then
->       1. Throw an _Unsupported File Extension_ error.
 >    1. Return _"module"_.
 > 1. Otherwise,
 >    1. If _url_ ends in _".mjs"_, then
 >       1. Return _"module"_.
->    1. Otherwise,
->       1. Return _"commonjs"_.
+>    1. If _url_ does not end in _".js"_, then
+>       1. Throw an _Unsupported File Extension_ error.
+>    1. Return _"commonjs"_.
 
 READ_PACKAGE_BOUNDARY(_url_)
 > 1. Let _boundaryURL_ be _url_.

lib/internal/errors.js

@@ -774,6 +774,8 @@ E('ERR_INVALID_OPT_VALUE', (name, value) =>
   RangeError);
 E('ERR_INVALID_OPT_VALUE_ENCODING',
   'The value "%s" is invalid for option "encoding"', TypeError);
+E('ERR_INVALID_PACKAGE_CONFIG',
+  'Invalid package config in \'%s\' imported from %s', Error);
 E('ERR_INVALID_PERFORMANCE_MARK',
   'The "%s" performance mark has not been set', Error);
 E('ERR_INVALID_PROTOCOL',
@@ -813,10 +815,8 @@ E('ERR_INVALID_SYNC_FORK_INPUT',
   TypeError);
 E('ERR_INVALID_THIS', 'Value of "this" must be of type %s', TypeError);
 E('ERR_INVALID_TUPLE', '%s must be an iterable %s tuple', TypeError);
-E('ERR_INVALID_TYPE_EXTENSION', '%s extension is not supported for --type=%s',
-  TypeError);
 E('ERR_INVALID_TYPE_FLAG',
-  'Type flag must be one of "esm", "commonjs". Received --type=%s',
+  'Type flag must be one of "module", "commonjs". Received --type=%s',
   TypeError);
 E('ERR_INVALID_URI', 'URI malformed', URIError);
 E('ERR_INVALID_URL', 'Invalid URL: %s', TypeError);
@@ -956,6 +956,20 @@ E('ERR_TRANSFORM_ALREADY_TRANSFORMING',
 E('ERR_TRANSFORM_WITH_LENGTH_0',
   'Calling transform done when writableState.length != 0', Error);
 E('ERR_TTY_INIT_FAILED', 'TTY initialization failed', SystemError);
+E('ERR_TYPE_MISMATCH', (filename, ext, typeFlag, conflict) => {
+  const typeString =
+    typeFlag === 'module' ? '--type=module or -m' : '--type=commonjs';
+  // --type mismatches file extension
+  if (conflict === 'extension')
+    return `Extension ${ext} is not supported for ` +
+      `${typeString} loading ${filename}`;
+  // --type mismatches package.json "type"
+  else if (conflict === 'scope')
+    return `Cannot use ${typeString} because nearest parent package.json ` +
+      ((typeFlag === 'module') ?
+        'includes "type": "commonjs"' : 'includes "type": "module",') +
+      ` which controls the type to use for ${filename}`;
+}, TypeError);
 E('ERR_UNCAUGHT_EXCEPTION_CAPTURE_ALREADY_SET',
   '`process.setupUncaughtExceptionCapture()` was called while a capture ' +
     'callback was already active',

lib/internal/main/check_syntax.js

@@ -60,7 +60,7 @@ function checkSyntax(source, filename) {
     } else {
       const resolve = require('internal/modules/esm/default_resolve');
       const { format } = resolve(pathToFileURL(filename).toString());
-      isModule = format === 'esm';
+      isModule = format === 'module';
     }
     if (isModule) {
       const { ModuleWrap } = internalBinding('module_wrap');

lib/internal/modules/esm/default_resolve.js

@@ -3,33 +3,106 @@
 const internalFS = require('internal/fs/utils');
 const { NativeModule } = require('internal/bootstrap/loaders');
 const { extname } = require('path');
-const { realpathSync } = require('fs');
+const { realpathSync, readFileSync } = require('fs');
 const { getOptionValue } = require('internal/options');
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
-const { ERR_UNKNOWN_FILE_EXTENSION } = require('internal/errors').codes;
+const { ERR_INVALID_PACKAGE_CONFIG,
+        ERR_TYPE_MISMATCH,
+        ERR_UNKNOWN_FILE_EXTENSION } = require('internal/errors').codes;
 const { resolve: moduleWrapResolve } = internalBinding('module_wrap');
-const { pathToFileURL, fileURLToPath } = require('internal/url');
-const { typeFlag } = require('internal/process/esm_loader');
+const { pathToFileURL, fileURLToPath, URL } = require('internal/url');
+const asyncESM = require('internal/process/esm_loader');
 
 const realpathCache = new Map();
+// TOOD(@guybedford): Shared cache with C++
+const pjsonCache = new Map();
 
 const extensionFormatMap = {
   '__proto__': null,
-  '.cjs': 'cjs',
-  '.js': 'esm',
-  '.mjs': 'esm'
+  '.cjs': 'commonjs',
+  '.js': 'module',
+  '.mjs': 'module'
 };
 
 const legacyExtensionFormatMap = {
   '__proto__': null,
-  '.cjs': 'cjs',
-  '.js': 'cjs',
-  '.json': 'cjs',
-  '.mjs': 'esm',
-  '.node': 'cjs'
+  '.cjs': 'commonjs',
+  '.js': 'commonjs',
+  '.json': 'commonjs',
+  '.mjs': 'module',
+  '.node': 'commonjs'
 };
 
+function readPackageConfig(path, parentURL) {
+  const existing = pjsonCache.get(path);
+  if (existing !== undefined)
+    return existing;
+  try {
+    return JSON.parse(readFileSync(path).toString());
+  } catch (e) {
+    if (e.code === 'ENOENT') {
+      pjsonCache.set(path, null);
+      return null;
+    } else if (e instanceof SyntaxError) {
+      throw new ERR_INVALID_PACKAGE_CONFIG(path, fileURLToPath(parentURL));
+    }
+    throw e;
+  }
+}
+
+function getPackageBoundaryConfig(url, parentURL) {
+  let pjsonURL = new URL('package.json', url);
+  while (true) {
+    const pcfg = readPackageConfig(fileURLToPath(pjsonURL), parentURL);
+    if (pcfg)
+      return pcfg;
+
+    const lastPjsonURL = pjsonURL;
+    pjsonURL = new URL('../package.json', pjsonURL);
+
+    // Terminates at root where ../package.json equals ../../package.json
+    // (can't just check "/package.json" for Windows support).
+    if (pjsonURL.pathname === lastPjsonURL.pathname)
+      return;
+  }
+}
+
+function getModuleFormat(url, isMain, parentURL) {
+  const pcfg = getPackageBoundaryConfig(url, parentURL);
+
+  const legacy = !pcfg || pcfg.type !== 'module';
+
+  const ext = extname(url.pathname);
+
+  let format = (legacy ? legacyExtensionFormatMap : extensionFormatMap)[ext];
+
+  if (!format) {
+    if (isMain)
+      format = legacy ? 'commonjs' : 'module';
+    else
+      throw new ERR_UNKNOWN_FILE_EXTENSION(fileURLToPath(url),
+                                           fileURLToPath(parentURL));
+  }
+
+  // Check for mismatch between --type and file extension,
+  // and between --type and the "type" field in package.json.
+  if (isMain && format !== 'module' && asyncESM.typeFlag === 'module') {
+    // Conflict between package scope type and --type
+    if (ext === '.js') {
+      if (pcfg && pcfg.type)
+        throw new ERR_TYPE_MISMATCH(
+          fileURLToPath(url), ext, asyncESM.typeFlag, 'scope');
+    // Conflict between explicit extension (.mjs, .cjs) and --type
+    } else {
+      throw new ERR_TYPE_MISMATCH(
+        fileURLToPath(url), ext, asyncESM.typeFlag, 'extension');
+    }
+  }
+
+  return format;
+}
+
 function resolve(specifier, parentURL) {
   if (NativeModule.canBeRequiredByUsers(specifier)) {
     return {
@@ -42,13 +115,7 @@ function resolve(specifier, parentURL) {
   if (isMain)
     parentURL = pathToFileURL(`${process.cwd()}/`).href;
 
-  const resolved = moduleWrapResolve(specifier,
-                                     parentURL,
-                                     isMain,
-                                     typeFlag === 'module');
-
-  let url = resolved.url;
-  const legacy = resolved.legacy;
+  let url = moduleWrapResolve(specifier, parentURL);
 
   if (isMain ? !preserveSymlinksMain : !preserveSymlinks) {
     const real = realpathSync(fileURLToPath(url), {
@@ -60,16 +127,7 @@ function resolve(specifier, parentURL) {
     url.hash = old.hash;
   }
 
-  const ext = extname(url.pathname);
-  let format = (legacy ? legacyExtensionFormatMap : extensionFormatMap)[ext];
-
-  if (!format) {
-    if (isMain)
-      format = legacy ? 'cjs' : 'esm';
-    else
-      throw new ERR_UNKNOWN_FILE_EXTENSION(fileURLToPath(url),
-                                           fileURLToPath(parentURL));
-  }
+  const format = getModuleFormat(url, isMain, parentURL);
 
   return { url: `${url}`, format };
 }

lib/internal/modules/esm/translators.js

@@ -35,7 +35,7 @@ async function importModuleDynamically(specifier, { url }) {
 }
 
 // Strategy for loading a standard JavaScript module
-translators.set('esm', async function(url) {
+translators.set('module', async function(url) {
   const source = `${await readFileAsync(new URL(url))}`;
   debug(`Translating StandardModule ${url}`);
   const module = new ModuleWrap(stripShebang(source), url);
@@ -52,7 +52,7 @@ translators.set('esm', async function(url) {
 // Strategy for loading a node-style CommonJS module
 const isWindows = process.platform === 'win32';
 const winSepRegEx = /\//g;
-translators.set('cjs', async function(url, isMain) {
+translators.set('commonjs', async function(url, isMain) {
   debug(`Translating CJSModule ${url}`);
   const pathname = internalURLModule.fileURLToPath(new URL(url));
   const cached = this.cjsCache.get(url);