Allow individual unicode surrogate strings

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index f79106ef350f61bd64bddeba60cf73edbf78654f..bf4ec2add62afb18e9fc350f8097b5ce0683b49b 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/runtime/vm/dart_api_impl_test.cc
@@ -1107,13 +1107,22 @@ TEST_CASE(NewString) {
 
 
 TEST_CASE(MalformedStringToUTF8) {
+  // 1D11E = treble clef
+  // [0] should be high surrogate D834
+  // [1] should be low surrogate DD1E
+  // Strings are allowed to have individual or out of order surrogates, even
+  // if that doesn't make sense as renderable characters.
   const char* kScriptChars =
-      "String testMain() {"
+      "String lowSurrogate() {"
       "  return '\\u{1D11E}'[1];"
-      "}";
+      "}"
+      "String highSurrogate() {"
+      "  return '\\u{1D11E}'[0];"
+      "}"
+      "String reversed() => lowSurrogate() + highSurrogate();";
 
   Dart_Handle lib = TestCase::LoadTestScript(kScriptChars, NULL);
-  Dart_Handle str1 = Dart_Invoke(lib, NewString("testMain"), 0, NULL);
+  Dart_Handle str1 = Dart_Invoke(lib, NewString("lowSurrogate"), 0, NULL);
   EXPECT_VALID(str1);
 
   uint8_t* utf8_encoded = NULL;
@@ -1126,7 +1135,20 @@ TEST_CASE(MalformedStringToUTF8) {
   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.
+  EXPECT_VALID(str2);  // Standalone low surrogate, but still valid
+
+  Dart_Handle reversed = Dart_Invoke(lib, NewString("reversed"), 0, NULL);
+  EXPECT_VALID(reversed);  // This is also allowed.
+  uint8_t* utf8_encoded_reversed = NULL;
+  intptr_t utf8_length_reversed = 0;
+  result = Dart_StringToUTF8(reversed,
+      &utf8_encoded_reversed, &utf8_length_reversed);
+  EXPECT_VALID(result);
+  EXPECT_EQ(6, utf8_length_reversed);
+  uint8_t expected[6] = {237, 180, 158, 237, 160, 180};
+  for (int i = 0; i < 6; i++) {
+    EXPECT_EQ(expected[i], utf8_encoded_reversed[i]);
+  }
 }