[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 {
+
+static const char kSplitCharacters[] = " .,-_@";
+
+template <typename Char>
+struct Compare : base::CaseInsensitiveCompare<Char> {
+  explicit Compare(bool case_sensitive) : case_sensitive_(case_sensitive) {}
+  bool operator()(Char x, Char y) const {
+    return case_sensitive_ ? (x == y) : base::CaseInsensitiveCompare<Char>::
+                                        operator()(x, y);
+  }
+
+ private:
+  bool case_sensitive_;
+};
+
+}  // namespace
+
+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) {
+  const base::string16 kSplitChars = base::ASCIIToUTF16(kSplitCharacters);
+
+  // 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(

[vabr (Chromium), 2015/07/09 06:17:51]

nit: Modifying iterator in the exit condition looks like a misuse of a
for-cycle, and harms readability. Writing for (A; B; C), the iterator should
only be modified in A and C. You can also use the while cycle, if you want to
keep just one instance of the std::search call. I'd suggest something like this:

it = suggestion.begin();
do {
  it = std::search(...);
  if (/*match found*/) {
    return ...;
  }
} while (it != suggestion.end());

[Pritam Nikam, 2015/07/10 16:58:46]

Done.

This was changed to for(...) loop, originally was in while(...).
https://codereview.chromium.org/962673004/diff/620001/components/autofill/cor...

But using | do { ... } while(...); | clause we have to write addtional exit case
as std::search(...) can return suggestion.end().

[vabr (Chromium), 2015/07/13 14:04:25]

Ah, sorry about the back and forth, I did not realise that estade@ told you to
use for-cycle. While I personally like the way you wrote this with do-while
better (and view the separate exit condition as an improvement), estade@ is an
OWNER of this file, so follow his direction and feel free to revert to the
for-cycle.

[Pritam Nikam, 2015/07/14 10:30:07]

Done.

Restored to for (...) cluase.

+            it, suggestion.end(), field_contents.begin(), field_contents.end(),
+            Compare<base::string16::value_type>(case_sensitive))) !=
+           suggestion.end();
+       ++it) {
+    if (it == suggestion.begin() ||
+        kSplitChars.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