Fix bad canonicalization for strings whose utf32->utf16 conversion is lossy.

runtime/vm/object.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 "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 20079 matching lines @@
   for (intptr_t i = 0; i < len; i++) {
     if (this->CharAt(i) != utf16_array[i]) {
       return false;
     }
   }
   return true;
 }
 
 
 bool String::Equals(const int32_t* utf32_array, intptr_t len) const {
-  CodePointIterator it(*this);
-  intptr_t i = 0;
-  bool has_more = it.Next();
-  while (has_more && (i < len)) {
-    if ((it.Current() != static_cast<int32_t>(utf32_array[i]))) {
-      return false;
+  if (len < 0) return false;
+  intptr_t j = 0;
+  for (intptr_t i = 0; i < len; ++i) {
+    if (Utf::IsSupplementary(utf32_array[i])) {
+      uint16_t encoded[2];
+      Utf16::Encode(utf32_array[i], &encoded[0]);
+      if (j + 1 >= Length()) return false;

[siva, 2016/10/06 23:37:23]

((j + 1) >= ... to maintain our style.

+      if (CharAt(j++) != encoded[0]) return false;
+      if (CharAt(j++) != encoded[1]) return false;
+    } else {
+      if (j >= Length()) return false;
+      if (CharAt(j++) != utf32_array[i]) return false;
     }
-    // Advance both streams forward.
-    ++i;
-    has_more = it.Next();
   }
-  // Strings are only true iff we reached the end in both streams.
-  return (i == len) && !has_more;
+  return j == Length();

[siva, 2016/10/06 23:37:23]

The compiler maybe doing this optimization but I was wondering it it might make
sense to cache Length() in a local variable at the top
and also would this check at the start be valid?
if ((len < 0) || (len > Length())) return false;

 }
 
 
 bool String::EqualsConcat(const String& str1, const String& str2) const {
   return (Length() == str1.Length() + str2.Length()) &&
     str1.Equals(*this, 0, str1.Length()) &&
     str2.Equals(*this, str1.Length(), str2.Length());
 }
 
 
@@ skipping 2880 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart