module: support Wasm without file extension within module scope

lib/internal/modules/esm/formats.js

@@ -2,9 +2,12 @@
 
 const {
   RegExpPrototypeExec,
+  Uint8Array,
 } = primordials;
 const { getOptionValue } = require('internal/options');
 
+const { closeSync, openSync, readSync } = require('fs');
+
 const experimentalWasmModules = getOptionValue('--experimental-wasm-modules');
 
 const extensionFormatMap = {
@@ -35,7 +38,27 @@ function mimeToFormat(mime) {
   return null;
 }
 
+function guessExtensionlessModule(url) {
+  if (!experimentalWasmModules)
+    return 'module';
+
+  const magic = new Uint8Array(4);
+  let fd;
+  try {
+    fd = openSync(url);
+    readSync(fd, magic);
+    if (magic[0] === 0x00 && magic[1] === 0x61 && magic[2] === 0x73 && magic[3] === 0x6d) {
+      return 'wasm';
+    }
+  } finally {
+    if (fd) closeSync(fd);
+  }
+
+  return 'module';
+}
+
 module.exports = {
   extensionFormatMap,
+  guessExtensionlessModule,
   mimeToFormat,
 };

lib/internal/modules/esm/get_format.js

@@ -10,6 +10,7 @@ const {
 const { getOptionValue } = require('internal/options');
 const {
   extensionFormatMap,
+  guessExtensionlessModule,
   mimeToFormat,
 } = require('internal/modules/esm/formats');
 
@@ -73,10 +74,17 @@ function extname(url) {
  */
 function getFileProtocolModuleFormat(url, context, ignoreErrors) {
   const ext = extname(url);
-  if (ext === '.js' || ext === '') {
+  if (ext === '.js') {
     return getPackageType(url) === 'module' ? 'module' : 'commonjs';
   }
 
+  if (ext === '') {
+    if (getPackageType(url) === 'module') {
+      return guessExtensionlessModule(url);
+    }
+    return 'commonjs';
+  }
+
   const format = extensionFormatMap[ext];
   if (format) return format;
 

test/fixtures/es-modules/package-type-module/wasm-dep.mjs

@@ -0,0 +1,13 @@
+import { strictEqual } from 'assert';
+
+export function jsFn () {
+  state = 'WASM JS Function Executed';
+  return 42;
+}
+
+export let state = 'JS Function Executed';
+
+export function jsInitFn () {
+  strictEqual(state, 'JS Function Executed');
+  state = 'WASM Start Executed';
+}

test/parallel/test-esm-wasm.mjs

@@ -0,0 +1,25 @@
+// Flags: --experimental-wasm-modules
+import { mustCall } from '../common/index.mjs';
+import { path } from '../common/fixtures.mjs';
+import { strictEqual } from 'assert';
+import { spawn } from 'child_process';
+
+{
+  const entry = path('/es-modules/package-type-module/noext-wasm');
+
+  // Run a module that does not have extension.
+  // This is to ensure that "type": "module" applies to extensionless files.
+
+  const child = spawn(process.execPath, ['--experimental-wasm-modules', entry]);
+
+  let stdout = '';
+  child.stdout.setEncoding('utf8');
+  child.stdout.on('data', (data) => {
+    stdout += data;
+  });
+  child.on('close', mustCall((code, signal) => {
+    strictEqual(code, 0);
+    strictEqual(signal, null);
+    strictEqual(stdout, '');
+  }));
+}