[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 {
+
+bool IsFeatureSubstringMatchEnabled() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableSuggestionsWithSubstringMatch);
+}
+
+bool IsContentsPrefixOfSuggestionToken(const base::string16& field_suggestion,
+                                       const base::string16& field_contents,
+                                       CaseSensitivity case_sensitivity) {
+  if (field_suggestion.empty() || field_contents.empty()) {
+    return false;
+  }
+
+  bool result = false;
+  bool case_sensitive = (CASE_SENSITIVE == case_sensitivity);
+  base::string16 search_string =
+      case_sensitive ? field_contents : base::i18n::ToLower(field_contents);
+  base::string16 suggestion_string =
+      case_sensitive ? field_suggestion : base::i18n::ToLower(field_suggestion);
+  base::string16::size_type offset = suggestion_string.find(search_string);
+  if (base::string16::npos != offset) {
+    std::vector<base::string16> suggestion_tokens, search_tokens;
+    Tokenize(suggestion_string, base::ASCIIToUTF16(" .,-_@"),

[Evan Stade, 2015/03/26 18:54:38]

can we just check if the character right before offset is one of these splitting
characters?

[Pritam Nikam, 2015/03/27 14:57:42]

Acknowledged.

This seems much cleaner, I'll take care of this in next patch set (Use of
base::ContainsOnlyChars).

+             &suggestion_tokens);
+    Tokenize(search_string, base::ASCIIToUTF16(" .,-_@"), &search_tokens);

[Evan Stade, 2015/03/26 18:54:38]

why tokenize the search term?

[Pritam Nikam, 2015/03/27 14:57:42]

To handle cases where user input contains token separator as well.

For e.g.
Field's suggestion (super)list: { "foo.bar@example.com", "bar.foo@example.com",
"example@foo.com" }
User punches in: "foo@exam"
Suggestions that expected to get populate: {"bar.foo@example.com"}

But if I try to match suggestion tokens against user input (i.e. without
tokenize the search string), none suggestion would display.
IMO, if we get |search_string|'s first token matches any of the
|suggestion_string|'s token, we are safe to assume thats the suggestion we are
interested in.

+
+    // Check whether the |search_string|'s first token matches any of the
+    // |suggestion_string|'s token.
+    if (suggestion_tokens.size() != 0 && search_tokens.size() != 0) {
+      for (auto token : suggestion_tokens) {
+        result = StartsWith(token, search_tokens[0], case_sensitive);
+        if (result)
+          break;
+      }
+    }
+  }
+
+  return result;
+}
+
+base::string16::size_type ComputeRange(const base::string16& field_suggestion,
+                                       const base::string16& field_contents,
+                                       size_t* start,
+                                       size_t* end) {
+  base::string16 user_input =
+      base::i18n::ToLower(base::string16(field_contents));
+  base::string16 suggestion =
+      base::i18n::ToLower(base::string16(field_suggestion));
+  base::string16::size_type offset = suggestion.find(user_input);

[Evan Stade, 2015/03/26 18:54:37]

I wouldn't expect this to happen, but it seems like this could happen: switching
some unicode character from upper to lower case changes the number of bytes it
uses in UTF-16. Therefore |start| and |end| will be off.

This stack overflow question seems to confirm this fear (at least for utf8):
http://stackoverflow.com/questions/14792841/are-uppercase-utf8-characters-alw...

+jshin who knows if this is a problem. If it is, it seems like base::StartsWith
and base::EndsWith are also possibly broken.

+  if (base::string16::npos != offset) {
+    *start = offset + user_input.size();
+    *end = suggestion.size();
+  }
+
+  return offset;
+}
+
+}  // namespace autofill