module: support detection when require()ing implicit ESM

Author: joyeecheung

.eslintignore

@@ -13,3 +13,5 @@ doc/changelogs/CHANGELOG_v1*.md
 !doc/changelogs/CHANGELOG_v18.md
 !doc/api_assets/*.js
 !.eslintrc.js
+test/es-module/test-require-module-detect-entry-point.js
+test/es-module/test-require-module-detect-entry-point-aou.js

doc/api/cli.md

@@ -883,6 +883,19 @@ Supports loading a synchronous ES module graph in `require()`.
 
 See [Loading ECMAScript modules using `require()`][].
 
+### `--experimental-require-module-with-detection`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active Developement
+
+In addition to what `--experimental-require-module` supports, when the module
+being `require()`'d is not explicitly marked as an ES Module using the
+`"type": "module"` field in `package.json` or the `.mjs` extension, it will
+try to detect module type based on the syntax of the module.
+
 ### `--experimental-sea-config`
 
 <!-- YAML
@@ -2537,6 +2550,7 @@ Node.js options that are allowed are:
 * `--experimental-permission`
 * `--experimental-policy`
 * `--experimental-print-required-tla`
+* `--experimental-require-module-with-detection`
 * `--experimental-require-module`
 * `--experimental-shadow-realm`
 * `--experimental-specifier-resolution`

lib/internal/modules/cjs/loader.js

@@ -1370,6 +1370,9 @@ Module.prototype._compile = function(content, filename, loadAsESM = false) {
   if (!loadAsESM) {
     const result = wrapSafe(filename, content, this);
     compiledWrapper = result.function;
+    // If C++ land confirms it looks like ESM and we should retry here (because fallback
+    // detection is enabled), retry.
+    loadAsESM = result.retryAsESM;
   }
 
   if (loadAsESM) {

src/node_contextify.cc

@@ -1510,6 +1510,13 @@ const char* require_esm_warning =
     "or the module should use the .mjs extension.\n"
     "- If it's loaded using require(), use --experimental-require-module";
 
+static bool warned_about_require_esm_detection = false;
+const char* require_esm_warning_without_detection =
+    "The module being require()d looks like an ES module, but it is not "
+    "explicitly marked with \"type\": \"module\" in the package.json or "
+    "with a .mjs extention. To enable automatic detection of module syntax "
+    "in require(), use --experimental-require-module-with-detection.";
+
 static void CompileFunctionForCJSLoader(
     const FunctionCallbackInfo<Value>& args) {
   CHECK(args[0]->IsString());
@@ -1553,6 +1560,7 @@ static void CompileFunctionForCJSLoader(
 
   std::vector<Local<String>> params = GetCJSParameters(env->isolate_data());
 
+  bool retry_as_esm = false;
   Local<Function> fn;
 
   {
@@ -1597,13 +1605,29 @@ static void CompileFunctionForCJSLoader(
           return;
         }
 
-        if (!warned_about_require_esm) {
-          USE(ProcessEmitWarningSync(env, require_esm_warning));
-          warned_about_require_esm = true;
+        if (!env->options()->require_module) {
+          if (!warned_about_require_esm) {
+            USE(ProcessEmitWarningSync(env, require_esm_warning));
+            warned_about_require_esm = true;
+          }
+          errors::DecorateErrorStack(env, try_catch);
+          try_catch.ReThrow();
+          return;
         }
-        errors::DecorateErrorStack(env, try_catch);
-        try_catch.ReThrow();
-        return;
+
+        if (!env->options()->require_module_with_detection) {
+          if (!warned_about_require_esm_detection) {
+            USE(ProcessEmitWarningSync(env,
+                                       require_esm_warning_without_detection));
+            warned_about_require_esm_detection = true;
+          }
+          errors::DecorateErrorStack(env, try_catch);
+          try_catch.ReThrow();
+          return;
+        }
+
+        // The file being compiled is likely ESM.
+        retry_as_esm = true;
       }
     }
   }
@@ -1623,11 +1647,14 @@ static void CompileFunctionForCJSLoader(
       env->cached_data_rejected_string(),
       env->source_map_url_string(),
       env->function_string(),
+      FIXED_ONE_BYTE_STRING(isolate, "retryAsESM"),
   };
   std::vector<Local<Value>> values = {
       Boolean::New(isolate, cache_rejected),
-      fn->GetScriptOrigin().SourceMapUrl(),
-      fn.As<Value>(),
+      retry_as_esm ? v8::Undefined(isolate).As<Value>()
+                   : fn->GetScriptOrigin().SourceMapUrl(),
+      retry_as_esm ? v8::Undefined(isolate).As<Value>() : fn.As<Value>(),
+      Boolean::New(isolate, retry_as_esm),
   };
   Local<Object> result = Object::New(
       isolate, v8::Null(isolate), names.data(), values.data(), names.size());

src/node_options.cc

@@ -363,6 +363,14 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "Allow loading explicit ES Modules in require().",
             &EnvironmentOptions::require_module,
             kAllowedInEnvvar);
+  AddOption("--experimental-require-module-with-detection",
+            "Allow loading ES Modules with syntax-based detection of module "
+            "types for implicit ES modules in require().",
+            &EnvironmentOptions::require_module_with_detection,
+            kAllowedInEnvvar);
+  Implies("--experimental-require-module-with-detection",
+          "--experimental-require-module");
+
   AddOption("--diagnostic-dir",
             "set dir for all output files"
             " (default: current working directory)",

src/node_options.h

@@ -107,6 +107,7 @@ class EnvironmentOptions : public Options {
   bool detect_module = false;
   bool print_required_tla = false;
   bool require_module = false;
+  bool require_module_with_detection = false;
   std::string dns_result_order;
   bool enable_source_maps = false;
   bool experimental_fetch = true;

test/es-module/test-require-module-detect-entry-point-aou.js

@@ -0,0 +1,8 @@
+// Flags: --experimental-require-module-with-detection --abort-on-uncaught-exception
+'use strict';
+
+import { mustCall } from '../common/index.mjs';
+const fn = mustCall(() => {
+  console.log('hello');
+});
+fn();

test/es-module/test-require-module-detect-entry-point.js

@@ -0,0 +1,8 @@
+// Flags: --experimental-require-module-with-detection
+'use strict';
+
+import { mustCall } from '../common/index.mjs';
+const fn = mustCall(() => {
+  console.log('hello');
+});
+fn();

test/es-module/test-require-module-dont-detect-cjs.js

@@ -0,0 +1,11 @@
+// Flags: --experimental-require-module-with-detection
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+assert.throws(() => {
+  require('../fixtures/es-modules/es-note-unexpected-export-1.cjs');
+}, {
+  message: /Unexpected token 'export'/
+});

test/es-module/test-require-module-implicit.js

@@ -8,11 +8,12 @@ const assert = require('assert');
 
 common.expectWarning(
   'Warning',
-  'To load an ES module:\n' +
-  '- Either the nearest package.json should set "type":"module", ' +
-  'or the module should use the .mjs extension.\n' +
-  '- If it\'s loaded using require(), use --experimental-require-module'
+  'The module being require()d looks like an ES module, but it is ' +
+  'not explicitly marked with "type": "module" in the package.json ' +
+  'or with a .mjs extention. To enable automatic detection of module ' +
+  'syntax in require(), use --experimental-require-module-with-detection.'
 );
+
 common.expectWarning(
   'ExperimentalWarning',
   'Support for loading ES Module in require() is an experimental feature ' +