module: Allow runMain to be ESM

This follows the EPS an allows the node CLI to have ESM as an entry point.
`node ./example.mjs`. A newer V8 is needed for `import()` so that is not
included. `import.meta` is still in specification stage so that also is not
included.

PR-URL: https://github.com/nodejs/node/pull/14369
Author: Bradley Farias <bradley.meck@gmail.com>
Author: Guy Bedford <guybedford@gmail.com>
Author: Jan Krems <jan.krems@groupon.com>
Author: Timothy Gu <timothygu99@gmail.com>
Author: Michaël Zasso <targos@protonmail.com>
Author: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

1 files changed, 57 insertions, 1 deletions

diff --git a/lib/module.js b/lib/module.js
index 7bb8288f54f..0b87cf7480e 100644
--- a/lib/module.js
+++ b/lib/module.js
@@ -24,6 +24,7 @@
 const NativeModule = require('native_module');
 const util = require('util');
 const internalModule = require('internal/module');
+const { getURLFromFilePath } = require('internal/url');
 const vm = require('vm');
 const assert = require('assert').ok;
 const fs = require('fs');
@@ -32,6 +33,14 @@ const path = require('path');
 const internalModuleReadFile = process.binding('fs').internalModuleReadFile;
 const internalModuleStat = process.binding('fs').internalModuleStat;
 const preserveSymlinks = !!process.binding('config').preserveSymlinks;
+const experimentalModules = !!process.binding('config').experimentalModules;
+
+const errors = require('internal/errors');
+
+const Loader = require('internal/loader/Loader');
+const ModuleJob = require('internal/loader/ModuleJob');
+const { createDynamicModule } = require('internal/loader/ModuleWrap');
+const ESMLoader = new Loader();
 
 function stat(filename) {
   filename = path._makeLong(filename);
@@ -412,7 +421,36 @@ Module._load = function(request, parent, isMain) {
     debug('Module._load REQUEST %s parent: %s', request, parent.id);
   }
 
-  var filename = Module._resolveFilename(request, parent, isMain);
+  var filename = null;
+
+  if (isMain) {
+    let err;
+    try {
+      filename = Module._resolveFilename(request, parent, isMain);
+    } catch (e) {
+      // try to keep stack
+      e.stack;
+      err = e;
+    }
+    if (experimentalModules) {
+      if (filename === null || /\.mjs$/.test(filename)) {
+        try {
+          ESMLoader.import(request).catch((e) => {
+            console.error(e);
+            process.exit(1);
+          });
+          return;
+        } catch (e) {
+          // well, it isn't ESM
+        }
+      }
+    }
+    if (err) {
+      throw err;
+    }
+  } else {
+    filename = Module._resolveFilename(request, parent, isMain);
+  }
 
   var cachedModule = Module._cache[filename];
   if (cachedModule) {
@@ -482,6 +520,19 @@ Module.prototype.load = function(filename) {
   if (!Module._extensions[extension]) extension = '.js';
   Module._extensions[extension](this, filename);
   this.loaded = true;
+
+  if (experimentalModules) {
+    const url = getURLFromFilePath(filename);
+    if (ESMLoader.moduleMap.has(`${url}`) !== true) {
+      const ctx = createDynamicModule(['default'], url);
+      ctx.reflect.exports.default.set(this.exports);
+      ESMLoader.moduleMap.set(`${url}`,
+                              new ModuleJob(ESMLoader, ctx.module));
+    } else {
+      ESMLoader.moduleMap.get(`${url}`).moduleProvider.finish(
+        Module._cache[filename]);
+    }
+  }
 };
 
 
@@ -578,6 +629,11 @@ Module._extensions['.node'] = function(module, filename) {
   return process.dlopen(module, path._makeLong(filename));
 };
 
+if (experimentalModules) {
+  Module._extensions['.mjs'] = function(module, filename) {
+    throw new errors.Error('ERR_REQUIRE_ESM', filename);
+  };
+}
 
 // bootstrap main module.
 Module.runMain = function() {