process: add process.features.require_module

For detecting whether `require(esm)` is supported without triggering
the experimental warning.

PR-URL: nodejs#55241
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

doc/api/modules.md

@@ -318,6 +318,8 @@ experimental and can be disabled using `--no-experimental-require-module`.
 When `require()` actually encounters an ES module for the
 first time in the process, it will emit an experimental warning. The
 warning is expected to be removed when this feature stablizes.
+This feature can be detected by checking if
+`process.features.require_module` is `true`.
 
 ## All together
 

lib/internal/bootstrap/node.js

@@ -268,6 +268,9 @@ const features = {
   get cached_builtins() {
     return binding.hasCachedBuiltins();
   },
+  get require_module() {
+    return getOptionValue('--experimental-require-module');
+  },
 };
 
 ObjectDefineProperty(process, 'features', {
@@ -299,6 +302,8 @@ ObjectDefineProperty(process, 'features', {
 }
 
 const { emitWarning, emitWarningSync } = require('internal/process/warning');
+const { getOptionValue } = require('internal/options');
+
 process.emitWarning = emitWarning;
 internalBinding('process_methods').setEmitWarningSync(emitWarningSync);
 

test/es-module/test-require-module-feature-detect.js

@@ -0,0 +1,37 @@
+'use strict';
+
+// This tests that process.features.require_module can be used to feature-detect
+// require(esm) without triggering a warning.
+
+require('../common');
+const { spawnSyncAndAssert } = require('../common/child_process');
+
+spawnSyncAndAssert(process.execPath, [
+  '--experimental-require-module',
+  '-p',
+  'process.features.require_module',
+], {
+  trim: true,
+  stdout: 'true',
+  stderr: '',  // Should not emit warnings.
+});
+
+// It is now enabled by default.
+spawnSyncAndAssert(process.execPath, [
+  '-p',
+  'process.features.require_module',
+], {
+  trim: true,
+  stdout: 'true',
+  stderr: '',  // Should not emit warnings.
+});
+
+spawnSyncAndAssert(process.execPath, [
+  '--no-experimental-require-module',
+  '-p',
+  'process.features.require_module',
+], {
+  trim: true,
+  stdout: 'false',
+  stderr: '',  // Should not emit warnings.
+});

test/parallel/test-process-features.js

@@ -10,6 +10,7 @@ assert.deepStrictEqual(keys, new Set([
   'debug',
   'uv',
   'ipv6',
+  'require_module',
   'tls_alpn',
   'tls_sni',
   'tls_ocsp',