lib: remove use of Debug.MakeMirror()

This paves the way for removing `vm.runInDebugContext()`.  Inspection
of Map and Set iterators is now done through V8 instrinsics.

Fixes: https://github.com/nodejs/node/issues/11875
PR-URL: https://github.com/nodejs/node/pull/13295
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Robert Jefe Lindstaedt <robert.lindstaedt@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>

.eslintignore

@@ -1,3 +1,4 @@
+lib/internal/v8.js
 lib/internal/v8_prof_polyfill.js
 lib/punycode.js
 test/addons/??_*

lib/internal/bootstrap_node.js

@@ -27,6 +27,7 @@
     // do this good and early, since it handles errors.
     setupProcessFatal();
 
+    setupV8();
     setupProcessICUVersions();
 
     setupGlobalVariables();
@@ -414,6 +415,20 @@
     };
   }
 
+  function setupV8() {
+    // Warm up the map and set iterator preview functions.  V8 compiles
+    // functions lazily (unless --nolazy is set) so we need to do this
+    // before we turn off --allow_natives_syntax again.
+    const v8 = NativeModule.require('internal/v8');
+    v8.previewMapIterator(new Map().entries(), 1);
+    v8.previewSetIterator(new Set().entries(), 1);
+    // Disable --allow_natives_syntax again unless it was explicitly
+    // specified on the command line.
+    const re = /^--allow[-_]natives[-_]syntax$/;
+    if (!process.execArgv.some((s) => re.test(s)))
+      process.binding('v8').setFlagsFromString('--noallow_natives_syntax');
+  }
+
   function setupProcessICUVersions() {
     const icu = process.binding('config').hasIntl ?
       process.binding('icu') : undefined;

lib/internal/v8.js

@@ -0,0 +1,21 @@
+'use strict';
+
+function take(it, n) {
+  const result = [];
+  for (const e of it) {
+    if (--n < 0)
+      break;
+    result.push(e);
+  }
+  return result;
+}
+
+function previewMapIterator(it, n) {
+  return take(%MapIteratorClone(it), n);
+}
+
+function previewSetIterator(it, n) {
+  return take(%SetIteratorClone(it), n);
+}
+
+module.exports = { previewMapIterator, previewSetIterator };

lib/util.js

@@ -26,6 +26,7 @@ const { TextDecoder, TextEncoder } = require('internal/encoding');
 const { isBuffer } = require('buffer').Buffer;
 
 const { errname } = process.binding('uv');
+const { previewMapIterator, previewSetIterator } = require('internal/v8');
 
 const {
   getPromiseDetails,
@@ -77,7 +78,6 @@ const dateToISOString = Date.prototype.toISOString;
 const errorToString = Error.prototype.toString;
 
 var CIRCULAR_ERROR_MESSAGE;
-var Debug;
 
 /* eslint-disable */
 const strEscapeSequencesRegExp = /[\x00-\x1f\x27\x5c]/;
@@ -356,17 +356,6 @@ function stylizeNoColor(str, styleType) {
   return str;
 }
 
-function ensureDebugIsInitialized() {
-  if (Debug === undefined) {
-    const runInDebugContext = require('vm').runInDebugContext;
-    // a workaround till this entire method is removed
-    const originalValue = process.noDeprecation;
-    process.noDeprecation = true;
-    Debug = runInDebugContext('Debug');
-    process.noDeprecation = originalValue;
-  }
-}
-
 function formatValue(ctx, value, recurseTimes, ln) {
   // Primitive types cannot have properties
   if (typeof value !== 'object' && typeof value !== 'function') {
@@ -474,10 +463,10 @@ function formatValue(ctx, value, recurseTimes, ln) {
       formatter = formatTypedArray;
     } else if (isMapIterator(value)) {
       braces = ['MapIterator {', '}'];
-      formatter = formatCollectionIterator;
+      formatter = formatMapIterator;
     } else if (isSetIterator(value)) {
       braces = ['SetIterator {', '}'];
-      formatter = formatCollectionIterator;
+      formatter = formatSetIterator;
     } else {
       // Check for boxed strings with valueOf()
       // The .valueOf() call can fail for a multitude of reasons
@@ -782,17 +771,27 @@ function formatMap(ctx, value, recurseTimes, keys) {
   return output;
 }
 
-function formatCollectionIterator(ctx, value, recurseTimes, keys) {
-  ensureDebugIsInitialized();
-  const mirror = Debug.MakeMirror(value, true);
-  const vals = mirror.preview();
-  const output = [];
+function formatCollectionIterator(preview, ctx, value, recurseTimes,
+                                  visibleKeys, keys) {
+  var nextRecurseTimes = recurseTimes === null ? null : recurseTimes - 1;
+  var vals = preview(value, 100);
+  var output = [];
   for (const o of vals) {
-    output.push(formatValue(ctx, o, recurseTimes));
+    output.push(formatValue(ctx, o, nextRecurseTimes));
   }
   return output;
 }
 
+function formatMapIterator(ctx, value, recurseTimes, visibleKeys, keys) {
+  return formatCollectionIterator(previewMapIterator, ctx, value, recurseTimes,
+                                  visibleKeys, keys);
+}
+
+function formatSetIterator(ctx, value, recurseTimes, visibleKeys, keys) {
+  return formatCollectionIterator(previewSetIterator, ctx, value, recurseTimes,
+                                  visibleKeys, keys);
+}
+
 function formatPromise(ctx, value, recurseTimes, keys) {
   var output;
   const [state, result] = getPromiseDetails(value);

node.gyp

@@ -132,6 +132,7 @@
       'lib/internal/http2/core.js',
       'lib/internal/http2/compat.js',
       'lib/internal/http2/util.js',
+      'lib/internal/v8.js',
       'lib/internal/v8_prof_polyfill.js',
       'lib/internal/v8_prof_processor.js',
       'lib/internal/streams/lazy_transform.js',

src/node.cc

@@ -4288,6 +4288,12 @@ void Init(int* argc,
   const char no_typed_array_heap[] = "--typed_array_max_size_in_heap=0";
   V8::SetFlagsFromString(no_typed_array_heap, sizeof(no_typed_array_heap) - 1);
 
+  // Needed for access to V8 intrinsics.  Disabled again during bootstrapping,
+  // see lib/internal/bootstrap_node.js.
+  const char allow_natives_syntax[] = "--allow_natives_syntax";
+  V8::SetFlagsFromString(allow_natives_syntax,
+                         sizeof(allow_natives_syntax) - 1);
+
   // We should set node_is_initialized here instead of in node::Start,
   // otherwise embedders using node::Init to initialize everything will not be
   // able to set it and native modules will not load for them.