module: remove underscore modules from builtinModules and isBuiltin

lib/internal/bootstrap/realm.js

@@ -310,21 +310,46 @@ class BuiltinModule {
   }
 
   static isBuiltin(id) {
-    return BuiltinModule.canBeRequiredWithoutScheme(id) || (
-      typeof id === 'string' &&
-        StringPrototypeStartsWith(id, 'node:') &&
+    if (typeof id !== 'string') {
+      return false;
+    }
+
+    // Modules starting with underscore (e.g. `_http_agent`) can be required
+    // by users but those are discouraged and should not be exposed as proper
+    // public ones, so if `id` starts with `_` (or `node:_`) return `false` right away
+    if (StringPrototypeStartsWith(id, '_') || StringPrototypeStartsWith(id, 'node:_')) {
+      return false;
+    }
+
+    // Check if `id` matches a builtin module without the `node:` prefix
+    if (BuiltinModule.canBeRequiredWithoutScheme(id)) {
+      return true;
+    }
+
+    // Check if `id` matches a builtin module with the `node:` prefix
+    if (
+      StringPrototypeStartsWith(id, 'node:') &&
         BuiltinModule.canBeRequiredByUsers(StringPrototypeSlice(id, 5))
-    );
+    ) {
+      return true;
+    }
+
+    return false;
   }
 
   static getSchemeOnlyModuleNames() {
     return ArrayFrom(schemelessBlockList);
   }
 
-  static getAllBuiltinModuleIds() {
+  static getAllPublicBuiltinModuleIds() {
     const allBuiltins = ArrayFrom(canBeRequiredByUsersWithoutSchemeList);
     ArrayPrototypePushApply(allBuiltins, ArrayFrom(schemelessBlockList, (x) => `node:${x}`));
-    return allBuiltins;
+    return ArrayPrototypeFilter(allBuiltins, (id) => {
+      // Modules starting with an underscore (e.g. `_http_agent`) can be
+      // required by users because of historical reasons, but they are not
+      // proper documented public modules, so they need to be filtered out
+      return id[0] !== '_';
+    });
   }
 
   // Used by user-land module loaders to compile and load builtins.

lib/internal/modules/cjs/loader.js

@@ -439,7 +439,7 @@ Module.isBuiltin = BuiltinModule.isBuiltin;
 function initializeCJS() {
   // This need to be done at runtime in case --expose-internals is set.
 
-  let modules = Module.builtinModules = BuiltinModule.getAllBuiltinModuleIds();
+  let modules = Module.builtinModules = BuiltinModule.getAllPublicBuiltinModuleIds();
   if (!getOptionValue('--experimental-quic')) {
     modules = modules.filter((i) => i !== 'node:quic');
   }

test/parallel/test-module-builtin.js

@@ -12,3 +12,10 @@ assert.deepStrictEqual(
   builtinModules.filter((mod) => mod.startsWith('internal/')),
   []
 );
+
+// Does not include modules starting with an underscore
+// (these are exposed to users but not proper public documented modules)
+assert.deepStrictEqual(
+  builtinModules.filter((mod) => mod.startsWith('_')),
+  []
+);

test/parallel/test-module-isBuiltin.js

@@ -14,3 +14,28 @@ assert(!isBuiltin('internal/errors'));
 assert(!isBuiltin('test'));
 assert(!isBuiltin(''));
 assert(!isBuiltin(undefined));
+
+const underscoreModules = [
+  '_http_agent',
+  '_http_client',
+  '_http_common',
+  '_http_incoming',
+  '_http_outgoing',
+  '_http_server',
+  '_stream_duplex',
+  '_stream_passthrough',
+  '_stream_readable',
+  '_stream_transform',
+  '_stream_wrap',
+  '_stream_writable',
+  '_tls_common',
+  '_tls_wrap',
+];
+
+// Does not include modules starting with underscore
+// (these can be required for historical reasons but
+// are not proper documented public modules)
+for (const module of underscoreModules) {
+  assert(!isBuiltin(module));
+  assert(!isBuiltin(`node:${module}`));
+}