[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 <vector>
+
+#include "base/command_line.h"
+#include "base/i18n/case_conversion.h"
+#include "base/strings/string_piece.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 {
+
+const base::string16 kSplitCharacters = base::ASCIIToUTF16(" .,-_@");
+
+}  // namespace
+
+bool IsFeatureSubstringMatchEnabled() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableSuggestionsWithSubstringMatch);
+}
+
+bool IsContentsPrefixOfSuggestionToken(const base::string16& suggestion,
+                                       const base::string16& field_contents,
+                                       bool case_sensitive) {
+  if (!IsFeatureSubstringMatchEnabled()) {
+    return false;
+  }

[Evan Stade, 2015/04/27 19:25:21]

no curlies

[Pritam Nikam, 2015/04/28 14:45:55]

Done.

+
+  bool result = false;
+  std::vector<base::string16> suggestion_tokens;
+  Tokenize(suggestion, kSplitCharacters, &suggestion_tokens);
+
+  // Check whether the |field_contents| prefixes any of the |suggestion|'s
+  // token.
+  for (const base::string16& token : suggestion_tokens) {
+    result = StartsWith(token, field_contents, case_sensitive);
+    if (result)
+      break;
+  }
+
+  return result;
+}
+
+size_t GetTextSelectionStart(const base::string16& suggestion,
+                             const base::string16& field_contents) {
+  size_t offset = 0;
+  base::string16::const_iterator it = suggestion.end();
+  // Loop until we find either the |field_contents| begins with the |suggestion|
+  // or character right before |offset| is one of the splitting characters.
+  while ((it = std::search(
+              offset + suggestion.begin(), suggestion.end(),
+              field_contents.begin(), field_contents.end(),
+              base::CaseInsensitiveCompare<base::string16::value_type>())) !=
+         suggestion.end()) {
+    offset = it - suggestion.begin();
+    if ((it == suggestion.begin()) ||

[Evan Stade, 2015/04/27 19:25:21]

offset == 0

[Pritam Nikam, 2015/04/28 14:45:55]

Done.

+        ContainsOnlyChars(suggestion.substr(offset - 1, 1), kSplitCharacters)) {
+      offset += field_contents.size();
+      break;
+    }
+
+    ++offset;

[Evan Stade, 2015/04/27 19:25:21]

what is the purpose of this?

[Pritam Nikam, 2015/04/28 14:45:55]

It will advance the suggestion iterator (or first1 in the range) in search() so
that we could find next occurrence of pattern (contents prefix) in the text
(suggestion).

   ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1,
                            ForwardIterator2 first2, ForwardIterator2 last2,
                            BinaryPredicate pred);

e.g. 
Let suggestion text: "texample@example.com", and user input: "example", after
first search(), will return iterator & offset will be at "1". To make sure,
we'll get next occurrence we've increment our search text iterator by one i.e.
++offset, this will advance suggestion iterator first1 to "xample@example.com"
so that the next search() will return iterator at offset as "9".

+  }
+
+  return (it != suggestion.end()) ? offset : base::string16::npos;

[Evan Stade, 2015/04/27 19:25:21]

is it valid if it == suggestion.end()? It seems like this should not happen.

[Pritam Nikam, 2015/04/28 14:45:55]

it == suggestion.end() is equivalent to std::search() unable to find the
field_contents in suggestion text.

[Evan Stade, 2015/05/11 19:07:12]

in which case you probably shouldn't have called GetTextSelectionStart on these
inputs then, right?

[Pritam Nikam, 2015/05/21 10:58:22]

Yes, thats right.
But there is no restriction on doing so.

[Evan Stade, 2015/05/22 18:26:48]

then you should DCHECK and not attempt to handle this misuse

+}
+
+}  // namespace autofill