esm: experimental wasm modules

This is a first pass at a loader for wasm modules.

It offers support for both named imports as well as deafult.
It may be possible to move some of this logic down to C++, but
I think the current implementation might be good enough. It doesn't
currently use the ESM cache, but AFAICT it isn't currently exposed.

Will dig in more with tests / examples / cache after initial
implementation gets feedback.

lib/internal/modules/esm/default_resolve.js

@@ -7,6 +7,7 @@ const { realpathSync } = require('fs');
 const { getOptionValue } = require('internal/options');
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
+const experimentalWasmModules = getOptionValue('--experimental-wasm-modules');
 const { ERR_UNKNOWN_FILE_EXTENSION } = require('internal/errors').codes;
 const { resolve: moduleWrapResolve } = internalBinding('module_wrap');
 const { pathToFileURL, fileURLToPath } = require('internal/url');
@@ -30,6 +31,16 @@ const legacyExtensionFormatMap = {
   '.node': 'cjs'
 };
 
+if (experimentalWasmModules) {
+  // This is a total hack
+  Object.assign(extensionFormatMap, {
+    '.wasm': 'wasm'
+  });
+  Object.assign(legacyExtensionFormatMap, {
+    '.wasm': 'wasm'
+  });
+}
+
 function resolve(specifier, parentURL) {
   if (NativeModule.canBeRequiredByUsers(specifier)) {
     return {

lib/internal/modules/esm/translators.js

@@ -13,7 +13,7 @@ const fs = require('fs');
 const {
   SafeMap,
 } = primordials;
-const { URL } = require('url');
+const { fileURLToPath, URL } = require('url');
 const { debuglog, promisify } = require('util');
 const esmLoader = require('internal/process/esm_loader');
 
@@ -94,3 +94,24 @@ translators.set('builtin', async function(url) {
       reflect.exports.default.set(module.exports);
     });
 });
+
+// Strategy for loading a wasm module
+translators.set('wasm', async function(url) {
+  const pathname = fileURLToPath(url);
+  const buffer = await readFileAsync(pathname);
+  debug(`Translating WASMModule ${url}`);
+  let result, keys;
+  try {
+    WebAssembly.validate(buffer);
+    result = await WebAssembly.instantiate(buffer, {});
+    keys = Object.keys(result.instance.exports);
+  } catch (err) {
+    err.message = pathname + ': ' + err.message;
+    throw err;
+  }
+  return createDynamicModule([...keys, 'default'], url, (reflect) => {
+    for (const key of keys)
+      reflect.exports[key].set(result.instance.exports[key]);
+    reflect.exports.default.set(result.instance.exports);
+  });
+});

src/node_options.cc

@@ -164,6 +164,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "experimental ES Module support and caching modules",
             &EnvironmentOptions::experimental_modules,
             kAllowedInEnvironment);
+  AddOption("--experimental-wasm-modules",
+            "experimental ES Module support for webassembly modules",
+            &EnvironmentOptions::experimental_wasm_modules,
+            kAllowedInEnvironment);
   AddOption("--experimental-policy",
             "use the specified file as a "
             "security policy",

src/node_options.h

@@ -86,6 +86,7 @@ class EnvironmentOptions : public Options {
  public:
   bool abort_on_uncaught_exception = false;
   bool experimental_modules = false;
+  bool experimental_wasm_modules = false;
   std::string module_type;
   std::string experimental_policy;
   bool experimental_repl_await = false;

test/es-module/test-esm-wasm.mjs

@@ -0,0 +1,9 @@
+// Flags: --experimental-modules --experimental-wasm-modules
+/* eslint-disable node-core/required-modules */
+import wasmMod from '../fixtures/simple.wasm'
+import {add} from '../fixtures/simple.wasm';
+import {strictEqual} from 'assert';
+
+strictEqual(wasmMod.add(10, 20), 30);
+strictEqual(add(10, 20), 30);
+strictEqual(wasmMod.add, add);