Don't crash when generating error messages with malformed strings.

runtime/vm/dart_api_impl_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/builtin.h"
 #include "include/dart_api.h"
 #include "include/dart_debugger_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 #include "platform/assert.h"
@@ skipping 1022 matching lines @@
   EXPECT_VALID(utf8_str);
   EXPECT(Dart_IsString(utf8_str));
 
   uint8_t invalid[] = { 0xE4, 0xBA };  // underflow.
   Dart_Handle invalid_str = Dart_NewStringFromUTF8(invalid,
                                                    ARRAY_SIZE(invalid));
   EXPECT(Dart_IsError(invalid_str));
 }
 
 
+TEST_CASE(MalformedStringToUTF8) {
+  const char* kScriptChars =
+      "String testMain() {"
+      "  return '\\u{1D11E}'[1];"
+      "}";
+
+  Dart_Handle lib = TestCase::LoadTestScript(kScriptChars, NULL);
+  Dart_Handle str1 = Dart_Invoke(lib, NewString("testMain"), 0, NULL);
+  EXPECT_VALID(str1);
+
+  uint8_t* utf8_encoded = NULL;
+  intptr_t utf8_length = 0;
+  Dart_Handle result = Dart_StringToUTF8(str1, &utf8_encoded, &utf8_length);
+  EXPECT_VALID(result);
+  EXPECT_EQ(3, utf8_length);
+  EXPECT_EQ(237, static_cast<intptr_t>(utf8_encoded[0]));
+  EXPECT_EQ(180, static_cast<intptr_t>(utf8_encoded[1]));
+  EXPECT_EQ(158, static_cast<intptr_t>(utf8_encoded[2]));
+
+  Dart_Handle str2 = Dart_NewStringFromUTF8(utf8_encoded, utf8_length);
+  EXPECT(Dart_IsError(str2));  // Invalid UTF-8.
+}
+
+
 static void ExternalStringCallbackFinalizer(void* peer) {
   *static_cast<int*>(peer) *= 2;
 }
 
 
 TEST_CASE(ExternalStringCallback) {
   int peer8 = 40;
   int peer16 = 41;
 
   {
@@ skipping 7613 matching lines @@
                                    NewString("main"),
                                    1,
                                    dart_args);
   int64_t value = 0;
   result = Dart_IntegerToInt64(result, &value);
   EXPECT_VALID(result);
   EXPECT_EQ(6, value);
 }
 
 }  // namespace dart