[Autofill/Autocomplete Feature] Substring matching instead of prefix matching.

components/autofill/core/common/autofill_util.cc

+// Copyright 2015 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.
+
+#include "components/autofill/core/common/autofill_util.h"
+
+#include <algorithm>
+#include <vector>
+
+#include "base/command_line.h"
+#include "base/i18n/case_conversion.h"
+#include "base/strings/string_piece.h"
+#include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
+#include "base/strings/utf_string_conversions.h"
+#include "components/autofill/core/common/autofill_switches.h"
+
+namespace autofill {
+
+namespace {
+
+template <typename Char>
+struct Compare {
+  Compare(bool case_sensitive) : case_sensitive_(case_sensitive) {}
+  bool operator()(Char x, Char y) const {
+    return case_sensitive_ ? (x == y) : (tolower(x) == tolower(y));
+  }
+
+ private:
+  bool case_sensitive_;
+};
+
+}  // namespace
+
+static const char kSplitCharacters[] = " .,-_@";
+
+bool IsFeatureSubstringMatchEnabled() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableSuggestionsWithSubstringMatch);
+}
+
+bool ContainsTokenThatStartsWith(const base::string16& suggestion,
+                                 const base::string16& field_contents,
+                                 bool case_sensitive) {
+  return IsFeatureSubstringMatchEnabled() &&
+         suggestion.length() >= field_contents.length() &&
+         GetTextSelectionStart(suggestion, field_contents, case_sensitive) !=
+             base::string16::npos;
+}
+
+size_t GetTextSelectionStart(const base::string16& suggestion,
+                             const base::string16& field_contents,
+                             bool case_sensitive) {
+  // Loop until we find either the |field_contents| is a prefix of |suggestion|
+  // or character right before the match is one of the splitting characters.
+  for (base::string16::const_iterator it = suggestion.begin();
+       (it = std::search(
+            it, suggestion.end(), field_contents.begin(), field_contents.end(),
+            Compare<base::string16::value_type>(case_sensitive))) !=

[please use gerrit instead, 2015/07/03 02:05:43]

case_sensitive ? Compare<...>() : base::CaseInsensitiveCompare<...>()

(IMHO, base::CaseInsensitiveCompare is not doing the right thing, because it's
using to lower(), which works only for the current locale. For example, if your
locale is en-US, then Ё will not be changed to ё. Let's go with it for now..)

[Pritam Nikam, 2015/07/03 16:21:27]

This will not compile.

In that case, how about:

template <typename Char>
struct Compare : public base::CaseInsensitiveCompare<Char> {
  ...
  bool operator()(Char x, Char y) const {
    return case_sensitive_ ? (x == y) : base::CaseInsensitiveCompare<Char>::
                                        operator()(x, y);
  }
}

[please use gerrit instead, 2015/07/03 22:05:47]

Looks good.

+           suggestion.end();
+       ++it) {
+    static const base::string16 split_chars(

[please use gerrit instead, 2015/07/03 02:05:43]

1) No need to make it static.
2) Constants are named kLikeThis (kSplitChars).
3) Put this outside of the loop.

[Pritam Nikam, 2015/07/03 16:21:27]

Done.

+        base::ASCIIToUTF16(kSplitCharacters));
+    if (it == suggestion.begin() ||
+        split_chars.find(*(it - 1)) != std::string::npos) {
+      // Returns the character position right after the |field_contents| within
+      // |suggestion| text as a caret position for text selection.
+      return it - suggestion.begin() + field_contents.size();
+    }
+  }
+
+  // Unable to find the |field_contents| in |suggestion| text.
+  return base::string16::npos;
+}
+
+}  // namespace autofill