[json] Fix error reporting when parsing an internalized one-byte string.

BUG=chromium:686010

Change-Id: I7bd4ab48f90a1013132bf037fd352ab55747189c
Reviewed-on: https://chromium-review.googlesource.com/451377
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43691}

src/json-parser.cc

@@ -720,6 +720,10 @@ Handle<String> JsonParser<seq_one_byte>::ScanJsonString() {
     // Fast path for existing internalized strings.  If the the string being
     // parsed is not a known internalized string, contains backslashes or
     // unexpectedly reaches the end of string, return with an empty handle.
+
+    // We intentionally use local variables instead of fields, compute hash
+    // while we are iterating a string and manually inline StringTable lookup
+    // here.
     uint32_t running_hash = isolate()->heap()->HashSeed();
     int position = position_;
     uc32 c0 = c0_;
@@ -731,11 +735,19 @@ Handle<String> JsonParser<seq_one_byte>::ScanJsonString() {
         return SlowScanJsonString<SeqOneByteString, uint8_t>(source_, beg_pos,
                                                              position_);
       }
-      if (c0 < 0x20) return Handle<String>::null();
+      if (c0 < 0x20) {
+        c0_ = c0;
+        position_ = position;
+        return Handle<String>::null();
+      }
       running_hash = StringHasher::AddCharacterCore(running_hash,
                                                     static_cast<uint16_t>(c0));
       position++;
-      if (position >= source_length_) return Handle<String>::null();
+      if (position >= source_length_) {
+        c0_ = kEndOfString;
+        position_ = position;
+        return Handle<String>::null();
+      }
       c0 = seq_source_->SeqOneByteStringGet(position);
     } while (c0 != '"');
     int length = position - position_;

src/objects-printer.cc

@@ -789,6 +789,9 @@ void JSMessageObject::JSMessageObjectPrint(std::ostream& os) {  // NOLINT
 
 
 void String::StringPrint(std::ostream& os) {  // NOLINT
+  if (!HasOnlyOneByteChars()) {
+    os << "u";
+  }
   if (StringShape(this).IsInternalized()) {
     os << "#";
   } else if (StringShape(this).IsCons()) {

test/mjsunit/json-errors.js

+// Copyright 2017 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.
+
+function TryParse(s, message) {
+  try {
+    JSON.parse(s);
+    assertUnreachable();
+  } catch(e) {
+    assertEquals(message, e.message);
+  }
+}
+
+var s = `{"a\\\\b `;
+TryParse(s, "Unexpected end of JSON input");
+
+var s = `{"a\\\\\u03A9 `;
+TryParse(s, "Unexpected end of JSON input");
+
+var s = `{"ab `;
+TryParse(s, "Unexpected end of JSON input");
+
+var s = `{"a\u03A9 `;
+TryParse(s, "Unexpected end of JSON input");
+
+var s = `{"a\nb":"b"}`;
+TryParse(s, "Unexpected token \n in JSON at position 3");
+
+var s = `{"a\nb":"b\u03A9"}`;
+TryParse(s, "Unexpected token \n in JSON at position 3");