components/omnibox/browser/autocomplete_i18n.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_I18N_H_
   6 #define COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_I18N_H_
   7
   8 #include "base/strings/string16.h"
   9 #include "third_party/icu/source/common/unicode/uchar.h"
  10
  11 // Functor for a simple 16-bit Unicode case-insensitive comparison. This is
  12 // designed for the autocomplete system where we would rather get prefix lenths
  13 // correct than handle all possible case sensitivity issues.
  14 //
  15 // Any time this is used the result will be incorrect in some cases that
  16 // certain users will be able to discern. Ideally, this class would be deleted
  17 // and we would do full Unicode case-sensitivity mappings using
  18 // base::i18n::ToLower. However, ToLower can change the lenghts of strings,
  19 // making computations of offsets or prefix lengths difficult. Getting all
  20 // edge cases correct will require careful implementation and testing. In the
  21 // mean time, we use this simpler approach.
  22 //
  23 // This comparator will not handle combining accents properly since it compares
  24 // 16-bit values in isolation. If the two strings use the same sequence of
  25 // combining accents (this is the normal case) in both strings, it will work.
  26 //
  27 // Additionally, this comparator does not decode UTF sequences which is why it
  28 // is called "UCS2". UTF-16 surrogates will be compared literally (i.e. "case-
  29 // sensitively").
  30 //
  31 // There are also a few cases where the lower-case version of a character
  32 // expands to more than one code point that will not be handled properly. Such
  33 // characters will be compared case-sensitively.
  34 struct SimpleCaseInsensitiveCompareUCS2 {
  35  public:
  36   bool operator()(base::char16 x, base::char16 y) const {
  37     return u_tolower(x) == u_tolower(y);
  38   }
  39 };
  40
  41 #endif  // COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_I18N_H_