Reintroduce password support to NativeTextfieldViews

base/utf_offset_string_conversions.cc

Index: base/utf_offset_string_conversions.cc
diff --git a/base/utf_offset_string_conversions.cc b/base/utf_offset_string_conversions.cc
index 8405303fd9d95bd5fb8fe3ef0a0bcdb70102cd80..3e468b554ab29a89114f756c5ed8a4666fb40a04 100644
--- a/base/utf_offset_string_conversions.cc
+++ b/base/utf_offset_string_conversions.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -6,8 +6,10 @@
 
 #include <algorithm>
 
+#include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/string_piece.h"
+#include "base/third_party/icu/icu_utf.h"
 #include "base/utf_string_conversion_utils.h"
 
 using base::PrepareForUTF16Or32Output;
@@ -15,6 +17,8 @@ using base::PrepareForUTF8Output;
 using base::ReadUnicodeCharacter;
 using base::WriteUnicodeCharacter;
 
+namespace {
+
 // Converts the given source Unicode character type to the given destination
 // Unicode character type as a STL string. The given input buffer and size
 // determine the source, and the given output STL string will be replaced by
@@ -56,6 +60,41 @@ bool ConvertUnicode(const SrcChar* src,
   return success;
 }
 
+}  // namespace
+
+bool IsValidCodePointIndex(const string16& s, size_t index) {
+  return index == 0 || index == s.length() ||
+    !(CBU16_IS_TRAIL(s[index]) && CBU16_IS_LEAD(s[index - 1]));
+}
+
+ptrdiff_t Utf16IndexToOffset(const string16& s, size_t base, size_t pos) {
+  DCHECK_LE(base, s.length());
+  DCHECK_LE(pos, s.length());
+  ptrdiff_t delta = 0;
+  while (base < pos)
+    delta += IsValidCodePointIndex(s, base++) ? 1 : 0;
+  while (pos < base)
+    delta -= IsValidCodePointIndex(s, pos++) ? 1 : 0;
+  return delta;
+}
+
+size_t Utf16OffsetToIndex(const string16& s, size_t pos, ptrdiff_t offset) {

[msw, 2012/03/01 22:48:54]

s/pos/base/ to match decl and for clarity.

[benrg, 2012/03/02 00:06:08]

Done.

+  DCHECK_LE(pos, s.length());

[msw, 2012/03/01 22:48:54]

Should you DCHECK_LE(pos + offset, s.length())?
Maybe also DCHECK_GE(pos + offset, 0)?
Maybe the DCHECK_EQ(offset, 0) after covers these cases?

[benrg, 2012/03/02 00:06:08]

It covers those cases.

+  while (offset > 0 && pos < s.length())
+    offset -= IsValidCodePointIndex(s, pos++) ? 1 : 0;
+  while (offset < 0 && pos > 0)
+    offset += IsValidCodePointIndex(s, --pos) ? 1 : 0;
+  // If offset != 0 then we ran off the edge of the string, which shouldn't
+  // happen but is handled anyway for safety.

[msw, 2012/03/01 22:48:54]

It seems like this should happen with garbage input, so it's worth doing to
alert the user of improper usage, maybe the comment should reflect that or omit
"which shouldn't happen".

[benrg, 2012/03/02 00:06:08]

Rewritten.

+  DCHECK_EQ(offset, 0);
+  // Since the second half of a surrogate pair has "length" zero, there is an
+  // ambiguity in the returned position. Resolve it by always returning a valid
+  // index.
+  if (!IsValidCodePointIndex(s, pos))
+    ++pos;
+  return pos;
+}
+
 bool UTF8ToUTF16AndAdjustOffset(const char* src,
                                 size_t src_len,
                                 string16* output,