Add optional max elements limit for Map/Set mirror iterator preview.

src/mirror-debugger.js

 // Copyright 2006-2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Handle id counters.
 var next_handle_ = 0;
 var next_transient_handle_ = -1;
 
 // Mirror cache.
 var mirror_cache_ = [];
@@ skipping 1304 matching lines @@
 function MapMirror(value) {
   %_CallFunction(this, value, MAP_TYPE, ObjectMirror);
 }
 inherits(MapMirror, ObjectMirror);
 
 
 /**
  * Returns an array of key/value pairs of a map.
  * This will keep keys alive for WeakMaps.
  *
+ * @param {number=} opt_limit Max elements to return.
  * @returns {Array.<Object>} Array of key/value pairs of a map.
  */
-MapMirror.prototype.entries = function() {
+MapMirror.prototype.entries = function(opt_limit) {
   var result = [];
 
   if (IS_WEAKMAP(this.value_)) {
-    var entries = %GetWeakMapEntries(this.value_);
+    var entries = %GetWeakMapEntries(this.value_, opt_limit || 0);
     for (var i = 0; i < entries.length; i += 2) {
       result.push({
         key: entries[i],
         value: entries[i + 1]
       });
     }
     return result;
   }
 
   var iter = %_CallFunction(this.value_, builtins.MapEntries);
   var next;
-  while (!(next = iter.next()).done) {
+  while ((!opt_limit || result.length < opt_limit) &&
+         !(next = iter.next()).done) {
     result.push({
       key: next.value[0],
       value: next.value[1]
     });
   }
   return result;
 };
 
 
 function SetMirror(value) {
   %_CallFunction(this, value, SET_TYPE, ObjectMirror);
 }
 inherits(SetMirror, ObjectMirror);
 
 
-function IteratorGetValues_(iter, next_function) {
+function IteratorGetValues_(iter, next_function, opt_limit) {
   var result = [];
   var next;
-  while (!(next = %_CallFunction(iter, next_function)).done) {
+  while ((!opt_limit || result.length < opt_limit) &&
+         !(next = %_CallFunction(iter, next_function)).done) {
     result.push(next.value);
   }
   return result;
 }
 
 
 /**
  * Returns an array of elements of a set.
  * This will keep elements alive for WeakSets.
  *
+ * @param {number=} opt_limit Max elements to return.
  * @returns {Array.<Object>} Array of elements of a set.
  */
-SetMirror.prototype.values = function() {
+SetMirror.prototype.values = function(opt_limit) {
   if (IS_WEAKSET(this.value_)) {
-    return %GetWeakSetValues(this.value_);
+    return %GetWeakSetValues(this.value_, opt_limit || 0);
   }
 
   var iter = %_CallFunction(this.value_, builtins.SetValues);
-  return IteratorGetValues_(iter, builtins.SetIteratorNextJS);
+  return IteratorGetValues_(iter, builtins.SetIteratorNextJS, opt_limit);
 };
 
 
 function IteratorMirror(value) {
   %_CallFunction(this, value, ITERATOR_TYPE, ObjectMirror);
 }
 inherits(IteratorMirror, ObjectMirror);
 
 
 /**
  * Returns a preview of elements of an iterator.
  * Does not change the backing iterator state.
  *
+ * @param {number=} opt_limit Max elements to return.
  * @returns {Array.<Object>} Array of elements of an iterator.
  */
-IteratorMirror.prototype.preview = function() {
+IteratorMirror.prototype.preview = function(opt_limit) {
   if (IS_MAP_ITERATOR(this.value_)) {
     return IteratorGetValues_(%MapIteratorClone(this.value_),
-                              builtins.MapIteratorNextJS);
+                              builtins.MapIteratorNextJS,
+                              opt_limit);
   } else if (IS_SET_ITERATOR(this.value_)) {
     return IteratorGetValues_(%SetIteratorClone(this.value_),
-                              builtins.SetIteratorNextJS);
+                              builtins.SetIteratorNextJS,
+                              opt_limit);
   }
 };
 
 
 /**
  * Mirror object for a Generator object.
  * @param {Object} data The Generator object
  * @constructor
  * @extends Mirror
  */
@@ skipping 1593 matching lines @@
   }
   if (!NUMBER_IS_FINITE(value)) {
     if (value > 0) {
       return 'Infinity';
     } else {
       return '-Infinity';
     }
   }
   return value;
 }