util: Fix inspection for sparse array

Fixes #1651.

lib/util.js

@@ -211,7 +211,7 @@ function formatValue(ctx, value, recurseTimes) {
     base = ' ' + value.toUTCString();
   }
 
-  if (keys.length === 0) {
+  if (keys.length === 0 && (!array || value.length == 0)) {
     return braces[0] + base + braces[1];
   }
 
@@ -225,9 +225,14 @@ function formatValue(ctx, value, recurseTimes) {
 
   ctx.seen.push(value);
 
-  var output = keys.map(function(key) {
-    return formatProperty(ctx, value, recurseTimes, visibleKeys, key, array);
-  });
+  var output;
+  if (array) {
+    output = formatArray(ctx, value, recurseTimes, visibleKeys, keys);
+  } else {
+    output = keys.map(function(key) {
+      return formatProperty(ctx, value, recurseTimes, visibleKeys, key, array);
+    });
+  }
 
   ctx.seen.pop();
 
@@ -259,6 +264,26 @@ function formatPrimitive(ctx, value) {
 }
 
 
+function formatArray(ctx, value, recurseTimes, visibleKeys, keys) {
+  var output = [];
+  for (var i = 0, l = value.length; i < l; ++i) {
+    if (Object.prototype.hasOwnProperty.call(value, String(i))) {
+      output.push(formatProperty(ctx, value, recurseTimes, visibleKeys,
+                  String(i), true));
+    } else {
+      output.push('');
+    }
+  }
+  keys.forEach(function(key) {
+    if (!key.match(/^\d+$/)) {
+      output.push(formatProperty(ctx, value, recurseTimes, visibleKeys,
+                  key, true));
+    }
+  });
+  return output;
+}
+
+
 function formatProperty(ctx, value, recurseTimes, visibleKeys, key, array) {
   var name, str;
   if (value.__lookupGetter__) {

test/simple/test-util-inspect.js

@@ -33,3 +33,11 @@ var orig = util.inspect(d);
 Date2.prototype.foo = 'bar';
 var after = util.inspect(d);
 assert.equal(orig, after);
+
+// test for sparse array
+var a = [ 'foo', 'bar', 'baz' ];
+assert.equal(util.inspect(a), "[ 'foo', 'bar', 'baz' ]");
+delete a[1];
+assert.equal(util.inspect(a), "[ 'foo', , 'baz' ]");
+assert.equal(util.inspect(a, true), "[ 'foo', , 'baz', [length]: 3 ]");
+assert.equal(util.inspect(new Array(5)), '[ , , , ,  ]');