module: add submodules builtins in addBuiltinLibsToObject

doc/api/repl.md

@@ -147,6 +147,13 @@ global or scoped variable, the input `fs` will be evaluated on-demand as
 > fs.createReadStream('./some/file');
 ```
 
+Node.js core submodules are exposed in parent module object,
+for example, `stream/consumers` would be accessible in `stream.consumers`.
+
+```console
+> stream.consumers.text(process.stdin);
+```
+
 #### Global uncaught exceptions
 <!-- YAML
 changes:

lib/internal/modules/cjs/helpers.js

@@ -9,7 +9,7 @@ const {
   SafeMap,
   SafeSet,
   StringPrototypeCharCodeAt,
-  StringPrototypeIncludes,
+  StringPrototypeSplit,
   StringPrototypeSlice,
   StringPrototypeStartsWith,
 } = primordials;
@@ -145,52 +145,62 @@ function addBuiltinLibsToObject(object, dummyModuleName) {
   const { builtinModules } = Module;
 
   // To require built-in modules in user-land and ignore modules whose
-  // `canBeRequiredByUsers` is false. So we create a dummy module object and not
-  // use `require()` directly.
+  // `canBeRequiredByUsers` is false. So we create a dummy module object and
+  // not use `require()` directly.
   const dummyModule = new Module(dummyModuleName);
 
-  ArrayPrototypeForEach(builtinModules, (name) => {
-    // Neither add underscored modules, nor ones that contain slashes (e.g.,
-    // 'fs/promises') or ones that are already defined.
-    if (StringPrototypeStartsWith(name, '_') ||
-        StringPrototypeIncludes(name, '/') ||
-        ObjectPrototypeHasOwnProperty(object, name)) {
-      return;
-    }
-    // Goals of this mechanism are:
-    // - Lazy loading of built-in modules
-    // - Having all built-in modules available as non-enumerable properties
-    // - Allowing the user to re-assign these variables as if there were no
-    //   pre-existing globals with the same name.
-
-    const setReal = (val) => {
-      // Deleting the property before re-assigning it disables the
-      // getter/setter mechanism.
-      delete object[name];
-      object[name] = val;
-    };
+  // Goals of this mechanism are:
+  // - Lazy loading of built-in modules or submodules
+  // - Having all built-in modules or submodules available as
+  //   non-enumerable properties
+  // - Allowing the user to re-assign these variables as if there were no
+  //   pre-existing globals with the same name.
+
+  function attachModulesWrapper(object, parent, modules) {
+    ArrayPrototypeForEach(modules, (mod) => {
+      const name = parent ? StringPrototypeSplit(mod, '/')[1] : mod;
+
+      // Neither add underscored modules/submodules or ones that
+      // are already defined.
+      if (StringPrototypeStartsWith(name, '_') ||
+          ObjectPrototypeHasOwnProperty(object, name)) {
+        return;
+      }
 
-    ObjectDefineProperty(object, name, {
-      get: () => {
-        const lib = dummyModule.require(name);
-
-        // Disable the current getter/setter and set up a new
-        // non-enumerable property.
-        delete object[name];
-        ObjectDefineProperty(object, name, {
-          get: () => lib,
-          set: setReal,
-          configurable: true,
-          enumerable: false
-        });
-
-        return lib;
-      },
-      set: setReal,
-      configurable: true,
-      enumerable: false
+      ObjectDefineProperty(object, name, {
+        get() {
+          const lib = dummyModule.require(mod);
+
+          const submodules = builtinModules
+            .filter((module) => module.startsWith(`${mod}/`));
+          if (submodules.length > 0)
+            attachModulesWrapper(lib, mod, submodules);
+
+          // Disable the current getter/setter and set up a new
+          // non-enumerable property.
+          delete object[name];
+          ObjectDefineProperty(object, name, {
+            value: lib,
+            writable: true,
+            configurable: true,
+            enumerable: false,
+          });
+          return lib;
+        },
+
+        set(val) {
+          // Deleting the property before re-assigning it disables the
+          // getter/setter mechanism.
+          delete object[name];
+          object[name] = val;
+        },
+        configurable: true,
+        enumerable: false,
+      });
     });
-  });
+  }
+
+  attachModulesWrapper(object, '', builtinModules);
 }
 
 function normalizeReferrerURL(referrer) {

test/parallel/test-repl-autolibs.js

@@ -36,7 +36,6 @@ function test1() {
   putIn.write = function(data) {
     gotWrite = true;
     if (data.length) {
-
       // Inspect output matches repl output
       assert.strictEqual(data,
                          `${util.inspect(require('fs'), null, 2, false)}\n`);
@@ -59,6 +58,7 @@ function test2() {
       assert.strictEqual(data, '{}\n');
       // Original value wasn't overwritten
       assert.strictEqual(val, global.url);
+      test3();
     }
   };
   const val = {};
@@ -68,3 +68,20 @@ function test2() {
   putIn.run(['url']);
   assert(gotWrite);
 }
+
+function test3() {
+  let gotWrite = false;
+  putIn.write = function(data) {
+    gotWrite = true;
+    if (data.length) {
+      // Inspect output matches repl output
+      assert.strictEqual(data,
+                         `${util.inspect(require('stream/consumers'), null, 2, false)}\n`);
+      // Globally added lib matches required lib
+      assert.strictEqual(global.stream.consumers, require('stream/consumers'));
+    }
+  };
+  assert(!gotWrite);
+  putIn.run(['stream.consumers']);
+  assert(gotWrite);
+}