repl: lazy-load acorn and defer vm context creation

Merely loading the repl builtin used to eagerly require acorn and
acorn-walk (~250KB of JS) and create an entire V8 context via
vm.runInNewContext() just to enumerate global property names, even
though both are only needed once REPL input is actually parsed or
tab-completion is used.

Require acorn and acorn-walk at their function-level use sites
instead, and wrap the global builtins set in getLazy(). The cost
moves to the first preview/completion/recoverable-error check,
where the one-time ~1ms is imperceptible.

Benchmark results (Linux x64, misc/startup-core.js, 20 runs):

  require-builtins.js: +3.12% ops/s (t=3.57, p<0.01)
  import-builtins.mjs: +2.20% ops/s (t=3.00, p<0.01)

In isolation, require('repl') drops from 4.64ms to 2.84ms (-39%)
and interactive `node -i` startup improves by ~13%.

Signed-off-by: Daijiro Wachi <daijiro.wachi@gmail.com>
PR-URL: #63879
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

Author: watilde

lib/internal/repl/completion.js

@@ -33,7 +33,7 @@ const {
 const {
   kContextId,
   getREPLResourceName,
-  globalBuiltins,
+  getGlobalBuiltins,
   getReplBuiltinLibs,
   fixReplRequire,
 } = require('internal/repl/utils');
@@ -61,13 +61,6 @@ const {
   getOwnNonIndexProperties,
 } = internalBinding('util');
 
-const {
-  isIdentifierStart,
-  isIdentifierChar,
-  parse: acornParse,
-} = require('internal/deps/acorn/acorn/dist/acorn');
-const acornWalk = require('internal/deps/acorn/acorn-walk/dist/walk');
-
 const importRE = /\bimport\s*\(\s*['"`](([\w@./:-]+\/)?(?:[\w@./:-]*))(?![^'"`])$/;
 const requireRE = /\brequire\s*\(\s*['"`](([\w@./:-]+\/)?(?:[\w@./:-]*))(?![^'"`])$/;
 const fsAutoCompleteRE = /fs(?:\.promises)?\.\s*[a-z][a-zA-Z]+\(\s*["'](.*)/;
@@ -87,6 +80,8 @@ function isIdentifier(str) {
   if (str === '') {
     return false;
   }
+  const { isIdentifierStart, isIdentifierChar } =
+    require('internal/deps/acorn/acorn/dist/acorn');
   const first = StringPrototypeCodePointAt(str, 0);
   if (!isIdentifierStart(first)) {
     return false;
@@ -374,8 +369,8 @@ function complete(line, callback) {
       if (!this.useGlobal) {
         // When the context is not `global`, builtins are not own
         // properties of it.
-        // `globalBuiltins` is a `SafeSet`, not an Array-like.
-        ArrayPrototypePush(contextOwnNames, ...globalBuiltins);
+        // `getGlobalBuiltins()` is a `SafeSet`, not an Array-like.
+        ArrayPrototypePush(contextOwnNames, ...getGlobalBuiltins());
       }
       ArrayPrototypePush(completionGroups, contextOwnNames);
       if (filter !== '') addCommonWords(completionGroups);
@@ -387,6 +382,7 @@ function complete(line, callback) {
     // so in order to make it correct we add an identifier to its end (e.g. `obj.foo.x`)
     const parsableCompleteTarget = completeTarget.endsWith('.') ? `${completeTarget}x` : completeTarget;
 
+    const { parse: acornParse } = require('internal/deps/acorn/acorn/dist/acorn');
     let completeTargetAst;
     try {
       completeTargetAst = acornParse(
@@ -551,6 +547,7 @@ function findExpressionCompleteTarget(code) {
     return !result ? result : `${result}.`;
   }
 
+  const { parse: acornParse } = require('internal/deps/acorn/acorn/dist/acorn');
   let ast;
   try {
     ast = acornParse(code, { __proto__: null, sourceType: 'module', ecmaVersion: 'latest' });
@@ -625,6 +622,7 @@ function findExpressionCompleteTarget(code) {
 
   // Walk the AST for the current block of code, and check whether it contains any
   // statement or expression type that would potentially have side effects if evaluated.
+  const acornWalk = require('internal/deps/acorn/acorn-walk/dist/walk');
   let isAllowed = true;
   const disallow = () => isAllowed = false;
   acornWalk.simple(lastBodyStatement, {

lib/internal/repl/utils.js

@@ -20,10 +20,8 @@ const {
   Symbol,
 } = primordials;
 
-const { tokTypes: tt, Parser: AcornParser } =
-  require('internal/deps/acorn/acorn/dist/acorn');
-
 const { sendInspectorCommand } = require('internal/util/inspector');
+const { getLazy } = require('internal/util');
 
 const {
   ERR_INSPECTOR_NOT_AVAILABLE,
@@ -80,6 +78,9 @@ function isRecoverableError(e, code) {
       isRecoverableError(e, `(${code}`))
     return true;
 
+  const { tokTypes: tt, Parser: AcornParser } =
+    require('internal/deps/acorn/acorn/dist/acorn');
+
   let recoverable = false;
 
   // Determine if the point of any error raised is at the end of the input.
@@ -756,6 +757,8 @@ function setupReverseSearch(repl) {
 const startsWithBraceRegExp = /^\s*{/;
 const endsWithSemicolonRegExp = /;\s*$/;
 function isValidSyntax(input) {
+  const { Parser: AcornParser } =
+    require('internal/deps/acorn/acorn/dist/acorn');
   try {
     AcornParser.parse(input, {
       ecmaVersion: 'latest',
@@ -815,8 +818,9 @@ function getREPLResourceName() {
   return `REPL${nextREPLResourceNumber++}`;
 }
 
-const globalBuiltins =
-  new SafeSet(vm.runInNewContext('Object.getOwnPropertyNames(globalThis)'));
+// Creating a new context is expensive, so only do it on first use.
+const getGlobalBuiltins = getLazy(() =>
+  new SafeSet(vm.runInNewContext('Object.getOwnPropertyNames(globalThis)')));
 
 let _builtinLibs = ArrayPrototypeFilter(
   CJSModule.builtinModules,
@@ -848,7 +852,7 @@ module.exports = {
   isValidSyntax,
   kContextId,
   getREPLResourceName,
-  globalBuiltins,
+  getGlobalBuiltins,
   getReplBuiltinLibs,
   setReplBuiltinLibs,
   fixReplRequire,

lib/repl.js

@@ -89,10 +89,6 @@ const {
   makeRequireFunction,
   addBuiltinLibsToObject,
 } = require('internal/modules/helpers');
-const {
-  parse: acornParse,
-} = require('internal/deps/acorn/acorn/dist/acorn');
-const acornWalk = require('internal/deps/acorn/acorn-walk/dist/walk');
 const {
   decorateErrorStack,
   isError,
@@ -153,7 +149,7 @@ const {
   isValidSyntax,
   kContextId,
   getREPLResourceName,
-  globalBuiltins,
+  getGlobalBuiltins,
   getReplBuiltinLibs,
   setReplBuiltinLibs,
   fixReplRequire,
@@ -249,6 +245,8 @@ writer.options = { ...inspect.defaultOptions, showProxy: true };
 
 // Converts static import statement to dynamic import statement
 const toDynamicImport = (codeLine) => {
+  const { parse: acornParse } = require('internal/deps/acorn/acorn/dist/acorn');
+  const acornWalk = require('internal/deps/acorn/acorn-walk/dist/walk');
   let dynamicImportStatement = '';
   const ast = acornParse(codeLine, { __proto__: null, sourceType: 'module', ecmaVersion: 'latest' });
   acornWalk.ancestor(ast, {
@@ -1139,7 +1137,7 @@ class REPLServer extends Interface {
       });
       ArrayPrototypeForEach(ObjectGetOwnPropertyNames(globalThis), (name) => {
         // Only set properties that do not already exist as a global builtin.
-        if (!globalBuiltins.has(name)) {
+        if (!getGlobalBuiltins().has(name)) {
           ObjectDefineProperty(context, name,
                                {
                                  __proto__: null,