ValueSerializer: Distinguish between 'undefined' and an absent property.

test/unittests/value-serializer-unittest.cc

 // Copyright 2016 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.
 
 #include "src/value-serializer.h"
 
 #include <algorithm>
 #include <string>
 
 #include "include/v8.h"
@@ skipping 1227 matching lines @@
       [this](Local<Value> value) {
         ASSERT_TRUE(value->IsArray());
         EXPECT_EQ(2u, Array::Cast(*value)->Length());
         EXPECT_TRUE(EvaluateScriptForResultBool("!(0 in result)"));
         EXPECT_TRUE(EvaluateScriptForResultBool("result[1] instanceof Array"));
         EXPECT_TRUE(EvaluateScriptForResultBool("!(0 in result[1])"));
         EXPECT_TRUE(EvaluateScriptForResultBool("result[1][1] === true"));
       });
 }
 
+TEST_F(ValueSerializerTest, RoundTripDenseArrayContainingUndefined) {
+  // In previous serialization versions, this would be interpreted as an absent
+  // property.
+  RoundTripTest("[undefined]", [this](Local<Value> value) {
+    ASSERT_TRUE(value->IsArray());
+    EXPECT_EQ(1u, Array::Cast(*value)->Length());
+    EXPECT_TRUE(EvaluateScriptForResultBool("result.hasOwnProperty(0)"));
+    EXPECT_TRUE(EvaluateScriptForResultBool("result[0] === undefined"));
+  });
+}
+
+TEST_F(ValueSerializerTest, DecodeDenseArrayContainingUndefined) {
+  // In previous versions, "undefined" in a dense array signified absence of the
+  // element (for compatibility). In new versions, it has a separate encoding.
+  DecodeTest({0xff, 0x09, 0x41, 0x01, 0x5f, 0x24, 0x00, 0x01},
+             [this](Local<Value> value) {
+               EXPECT_TRUE(EvaluateScriptForResultBool("!(0 in result)"));
+             });
+  DecodeTest(
+      {0xff, 0x0b, 0x41, 0x01, 0x5f, 0x24, 0x00, 0x01},
+      [this](Local<Value> value) {
+        EXPECT_TRUE(EvaluateScriptForResultBool("0 in result"));
+        EXPECT_TRUE(EvaluateScriptForResultBool("result[0] === undefined"));
+      });
+  DecodeTest({0xff, 0x0b, 0x41, 0x01, 0x2d, 0x24, 0x00, 0x01},
+             [this](Local<Value> value) {
+               EXPECT_TRUE(EvaluateScriptForResultBool("!(0 in result)"));
+             });
+}
+
 TEST_F(ValueSerializerTest, RoundTripDate) {
   RoundTripTest("new Date(1e6)", [](Local<Value> value) {
     ASSERT_TRUE(value->IsDate());
     EXPECT_EQ(1e6, Date::Cast(*value)->ValueOf());
     EXPECT_TRUE("Object.getPrototypeOf(result) === Date.prototype");
   });
   RoundTripTest("new Date(Date.UTC(1867, 6, 1))", [](Local<Value> value) {
     ASSERT_TRUE(value->IsDate());
     EXPECT_TRUE("result.toISOString() === '1867-07-01T00:00:00.000Z'");
   });
@@ skipping 1376 matching lines @@
   InvalidDecodeTest(raw);
 }
 
 TEST_F(ValueSerializerTestWithWasm, DecodeWasmModuleWithInvalidDataLength) {
   InvalidDecodeTest({0xff, 0x09, 0x3f, 0x00, 0x57, 0x79, 0x7f, 0x00});
   InvalidDecodeTest({0xff, 0x09, 0x3f, 0x00, 0x57, 0x79, 0x00, 0x7f});
 }
 
 }  // namespace
 }  // namespace v8