Entry points proposal spec and implementation

.eslintrc.js

@@ -38,6 +38,7 @@ module.exports = {
     {
       files: [
         'doc/api/esm.md',
+        'test/es-module/test-esm-type-flag.js',
         '*.mjs',
       ],
       parserOptions: { sourceType: 'module' },

doc/api/cli.md

@@ -485,6 +485,18 @@ added: v2.4.0
 
 Track heap object allocations for heap snapshots.
 
+### `-m`, `--type=type`
+
+When using `--experimental-modules`, this informs the module resolution type
+to interpret the top-level entry into Node.js.
+
+Works with stdin, `--eval`, `--print` as well as standard execution.
+
+Valid values are `"commonjs"` and `"module"`, where the default is to infer
+from the file extension and package type boundary.
+
+`-m` is an alias for `--type=module`.
+
 ### `--use-bundled-ca`, `--use-openssl-ca`
 <!-- YAML
 added: v6.11.0

doc/api/errors.md

@@ -2196,6 +2196,27 @@ A non-specific HTTP/2 error has occurred.
 Used in the `repl` in case the old history file is used and an error occurred
 while trying to read and parse it.
 
+<a id="ERR_INVALID_REPL_TYPE"></a>
+### ERR_INVALID_REPL_TYPE
+
+> Stability: 1 - Experimental
+
+The `--type=...` flag is not compatible with the Node.js REPL.
+
+<a id="ERR_INVALID_TYPE_EXTENSION"></a>
+### ERR_INVALID_TYPE_EXTENSION
+
+> Stability: 1 - Experimental
+
+Attempted to execute a `.cjs` module with the `--type=module` flag.
+
+<a id="ERR_INVALID_TYPE_FLAG"></a>
+### ERR_INVALID_TYPE_FLAG
+
+> Stability: 1 - Experimental
+
+An invalid `--type=...` flag value was provided.
+
 <a id="ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK"></a>
 #### ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK
 
@@ -2226,7 +2247,6 @@ size.
 This `Error` is thrown when a read is attempted on a TTY `WriteStream`,
 such as `process.stdout.on('data')`.
 
-
 [`'uncaughtException'`]: process.html#process_event_uncaughtexception
 [`--force-fips`]: cli.html#cli_force_fips
 [`Class: assert.AssertionError`]: assert.html#assert_class_assert_assertionerror

doc/api/esm.md

@@ -158,8 +158,8 @@ The algorithm to load an ES module specifier is given through the
 module specifier relative to a parentURL, in addition to the unique module
 format for that resolved URL given by the **ESM_FORMAT** routine.
 
-The _"esm"_ format is returned for an ECMAScript Module, while the
-_"legacy"_ format is used to indicate loading through the legacy
+The _"module"_ format is returned for an ECMAScript Module, while the
+_"commonjs"_ format is used to indicate loading through the legacy
 CommonJS loader. Additional formats such as _"wasm"_ or _"addon"_ can be
 extended in future updates.
 
@@ -168,6 +168,12 @@ of these top-level routines.
 
 _isMain_ is **true** when resolving the Node.js application entry point.
 
+If the top-level `--type` is _"commonjs"_, then the ESM resolver is skipped
+entirely for the CommonJS loader.
+
+If the top-level `--type` is _"module"_, then the ESM resolver is used
+as described here, with the conditional `--type` check in **ESM_FORMAT**.
+
 **ESM_RESOLVE(_specifier_, _parentURL_, _isMain_)**
 > 1. Let _resolvedURL_ be **undefined**.
 > 1. If _specifier_ is a valid URL, then
@@ -234,7 +240,7 @@ PACKAGE_MAIN_RESOLVE(_packageURL_, _pjson_)
 >       _pjson.main_.
 >    1. If the file at _resolvedMain_ exists, then
 >       1. Return _resolvedMain_.
-> 1. If _pjson.type_ is equal to _"esm"_, then
+> 1. If _pjson.type_ is equal to _"module"_, then
 >    1. Throw a _Module Not Found_ error.
 > 1. Let _legacyMainURL_ be the result applying the legacy
 >    **LOAD_AS_DIRECTORY** CommonJS resolver to _packageURL_, throwing a
@@ -245,18 +251,24 @@ PACKAGE_MAIN_RESOLVE(_packageURL_, _pjson_)
 
 **ESM_FORMAT(_url_, _isMain_)**
 > 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. Return _"module"_.
 > 1. Let _pjson_ be the result of **READ_PACKAGE_BOUNDARY**(_url_).
 > 1. If _pjson_ is **null** and _isMain_ is **true**, then
->    1. Return _"legacy"_.
-> 1. If _pjson.type_ exists and is _"esm"_, then
+>    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 _"esm"_.
+>    1. Return _"module"_.
 > 1. Otherwise,
 >    1. If _url_ ends in _".mjs"_, then
->       1. Return _"esm"_.
+>       1. Return _"module"_.
 >    1. Otherwise,
->       1. Return _"legacy"_.
+>       1. Return _"commonjs"_.
 
 READ_PACKAGE_BOUNDARY(_url_)
 > 1. Let _boundaryURL_ be _url_.

doc/node.1

@@ -272,6 +272,9 @@ Print stack traces for process warnings (including deprecations).
 .It Fl -track-heap-objects
 Track heap object allocations for heap snapshots.
 .
+.It Fl -type Ns = Ns Ar type
+Set the top-level module resolution type.
+.
 .It Fl -use-bundled-ca , Fl -use-openssl-ca
 Use bundled Mozilla CA store as supplied by current Node.js version or use OpenSSL's default CA store.
 The default store is selectable at build-time.

lib/internal/errors.js

@@ -780,6 +780,8 @@ E('ERR_INVALID_PROTOCOL',
   TypeError);
 E('ERR_INVALID_REPL_EVAL_CONFIG',
   'Cannot specify both "breakEvalOnSigint" and "eval" for REPL', TypeError);
+E('ERR_INVALID_REPL_TYPE',
+  'Cannot specify --type for REPL', TypeError);
 E('ERR_INVALID_RETURN_PROPERTY', (input, name, prop, value) => {
   return `Expected a valid ${input} to be returned for the "${prop}" from the` +
          ` "${name}" function but got ${value}.`;
@@ -810,6 +812,11 @@ 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',
+  TypeError);
 E('ERR_INVALID_URI', 'URI malformed', URIError);
 E('ERR_INVALID_URL', 'Invalid URL: %s', TypeError);
 E('ERR_INVALID_URL_SCHEME',
@@ -964,12 +971,10 @@ E('ERR_UNHANDLED_ERROR',
 // This should probably be a `TypeError`.
 E('ERR_UNKNOWN_CREDENTIAL', '%s identifier does not exist: %s', Error);
 E('ERR_UNKNOWN_ENCODING', 'Unknown encoding: %s', TypeError);
-
+E('ERR_UNKNOWN_FILE_EXTENSION', 'Unknown file extension: %s', TypeError);
 // This should probably be a `TypeError`.
 E('ERR_UNKNOWN_MODULE_FORMAT', 'Unknown module format: %s', RangeError);
 E('ERR_UNKNOWN_SIGNAL', 'Unknown signal: %s', TypeError);
-E('ERR_UNSUPPORTED_FILE_EXTENSION', 'Unsupported file extension: \'%s\' ' +
-  'imported from %s', Error);
 
 E('ERR_V8BREAKITERATOR',
   'Full ICU data not installed. See https://github.com/nodejs/node/wiki/Intl',

lib/internal/main/check_syntax.js

@@ -11,6 +11,8 @@ const {
   readStdin
 } = require('internal/process/execution');
 
+const { pathToFileURL } = require('url');
+
 const CJSModule = require('internal/modules/cjs/loader');
 const vm = require('vm');
 const {
@@ -32,20 +34,39 @@ if (process.argv[1] && process.argv[1] !== '-') {
   prepareMainThreadExecution();
   markBootstrapComplete();
 
-  checkScriptSyntax(source, filename);
+  checkSyntax(source, filename);
 } else {
   // TODO(joyeecheung): not every one of these are necessary
   prepareMainThreadExecution();
   markBootstrapComplete();
 
   readStdin((code) => {
-    checkScriptSyntax(code, '[stdin]');
+    checkSyntax(code, '[stdin]');
   });
 }
 
-function checkScriptSyntax(source, filename) {
+function checkSyntax(source, filename) {
   // Remove Shebang.
   source = stripShebang(source);
+
+  const experimentalModules =
+      require('internal/options').getOptionValue('--experimental-modules');
+  if (experimentalModules) {
+    let isModule = false;
+    if (filename === '[stdin]' || filename === '[eval]') {
+      isModule = require('internal/process/esm_loader').typeFlag === 'module';
+    } else {
+      const resolve = require('internal/modules/esm/default_resolve');
+      const { format } = resolve(pathToFileURL(filename).toString());
+      isModule = format === 'esm';
+    }
+    if (isModule) {
+      const { ModuleWrap } = internalBinding('module_wrap');
+      new ModuleWrap(source, filename);
+      return;
+    }
+  }
+
   // Remove BOM.
   source = stripBOM(source);
   // Wrap it.

lib/internal/main/eval_stdin.js

@@ -7,6 +7,7 @@ const {
 } = require('internal/bootstrap/pre_execution');
 
 const {
+  evalModule,
   evalScript,
   readStdin
 } = require('internal/process/execution');
@@ -16,5 +17,8 @@ markBootstrapComplete();
 
 readStdin((code) => {
   process._eval = code;
-  evalScript('[stdin]', process._eval, process._breakFirstLine);
+  if (require('internal/process/esm_loader').typeFlag === 'module')
+    evalModule(process._eval);
+  else
+    evalScript('[stdin]', process._eval, process._breakFirstLine);
 });

lib/internal/main/eval_string.js

@@ -6,11 +6,14 @@
 const {
   prepareMainThreadExecution
 } = require('internal/bootstrap/pre_execution');
-const { evalScript } = require('internal/process/execution');
+const { evalModule, evalScript } = require('internal/process/execution');
 const { addBuiltinLibsToObject } = require('internal/modules/cjs/helpers');
 
 const source = require('internal/options').getOptionValue('--eval');
 prepareMainThreadExecution();
 addBuiltinLibsToObject(global);
 markBootstrapComplete();
-evalScript('[eval]', source, process._breakFirstLine);
+if (require('internal/process/esm_loader').typeFlag === 'module')
+  evalModule(source);
+else
+  evalScript('[eval]', source, process._breakFirstLine);

lib/internal/main/repl.js

@@ -11,8 +11,15 @@ const {
   evalScript
 } = require('internal/process/execution');
 
+const { ERR_INVALID_REPL_TYPE } = require('internal/errors').codes;
+
 prepareMainThreadExecution();
 
+// --type flag not supported in REPL
+if (require('internal/process/esm_loader').typeFlag) {
+  throw ERR_INVALID_REPL_TYPE();
+}
+
 const cliRepl = require('internal/repl');
 cliRepl.createInternalRepl(process.env, (err, repl) => {
   if (err) {

lib/internal/modules/cjs/loader.js

@@ -786,21 +786,21 @@ if (experimentalModules) {
 // bootstrap main module.
 Module.runMain = function() {
   // Load the main module--the command line argument.
-  const base = path.basename(process.argv[1]);
-  const ext = path.extname(base);
-  const isESM = ext === '.mjs';
-
-  if (experimentalModules && isESM) {
+  if (experimentalModules) {
     if (asyncESM === undefined) lazyLoadESM();
-    asyncESM.loaderPromise.then((loader) => {
-      return loader.import(pathToFileURL(process.argv[1]).pathname);
-    })
-    .catch((e) => {
-      internalBinding('util').triggerFatalException(e);
-    });
-  } else {
-    Module._load(process.argv[1], null, true);
+    if (asyncESM.typeFlag !== 'commonjs') {
+      asyncESM.loaderPromise.then((loader) => {
+        return loader.import(pathToFileURL(process.argv[1]).pathname);
+      })
+      .catch((e) => {
+        internalBinding('util').triggerFatalException(e);
+      });
+      // Handle any nextTicks added in the first tick of the program
+      process._tickCallback();
+      return;
+    }
   }
+  Module._load(process.argv[1], null, true);
   // Handle any nextTicks added in the first tick of the program
   process._tickCallback();
 };

lib/internal/modules/esm/default_resolve.js

@@ -7,20 +7,23 @@ const { realpathSync } = require('fs');
 const { getOptionValue } = require('internal/options');
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
-const { ERR_UNSUPPORTED_FILE_EXTENSION } = require('internal/errors').codes;
+const { 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 realpathCache = new Map();
 
 const extensionFormatMap = {
   '__proto__': null,
-  '.mjs': 'esm',
-  '.js': 'esm'
+  '.cjs': 'cjs',
+  '.js': 'esm',
+  '.mjs': 'esm'
 };
 
 const legacyExtensionFormatMap = {
   '__proto__': null,
+  '.cjs': 'cjs',
   '.js': 'cjs',
   '.json': 'cjs',
   '.mjs': 'esm',
@@ -39,7 +42,10 @@ function resolve(specifier, parentURL) {
   if (isMain)
     parentURL = pathToFileURL(`${process.cwd()}/`).href;
 
-  const resolved = moduleWrapResolve(specifier, parentURL, isMain);
+  const resolved = moduleWrapResolve(specifier,
+                                     parentURL,
+                                     isMain,
+                                     typeFlag === 'module');
 
   let url = resolved.url;
   const legacy = resolved.legacy;
@@ -61,8 +67,8 @@ function resolve(specifier, parentURL) {
     if (isMain)
       format = legacy ? 'cjs' : 'esm';
     else
-      throw new ERR_UNSUPPORTED_FILE_EXTENSION(fileURLToPath(url),
-                                               fileURLToPath(parentURL));
+      throw new ERR_UNKNOWN_FILE_EXTENSION(fileURLToPath(url),
+                                           fileURLToPath(parentURL));
   }
 
   return { url: `${url}`, format };