Omnibox - HistoryQuick Provider - Don't Run Duplicate Searches

components/omnibox/browser/url_index_private_data.cc

Index: components/omnibox/browser/url_index_private_data.cc
diff --git a/components/omnibox/browser/url_index_private_data.cc b/components/omnibox/browser/url_index_private_data.cc
index b9f2a93ea945bc2e73e33afdb396d0bd0ef8a975..659828c27181492f2d26dd6f7edfe1645b3922f3 100644
--- a/components/omnibox/browser/url_index_private_data.cc
+++ b/components/omnibox/browser/url_index_private_data.cc
@@ -153,9 +153,12 @@ ScoredHistoryMatches URLIndexPrivateData::HistoryItemsForTerms(
   search_strings.push_back(original_search_string);
   if ((cursor_position != base::string16::npos) &&
       (cursor_position < original_search_string.length()) &&
-      (cursor_position > 0)) {
+      (cursor_position > 0) &&
+      (original_search_string[cursor_position - 1] != L' ') &&
+      (original_search_string[cursor_position] != L' ')) {

[Peter Kasting, 2017/04/26 01:43:02]

What about other kinds of whitespace/word breaks?  Will the tokenizer only
tokenize the search string on spaces, or will it use ICU to word break?  It
seems like we should match that, ideally by calling the same tokenizer and
checking if there's a break point here (maybe we can avoid duplicate effort by
then passing the tokenized search string).

Nit: I think L' ' is basically correct on Windows but wrong on other platforms,
since L means "wide character literal" and string16 is not a wide string on all
platforms.  I would just use ' ' (the narrow value should always upconvert
correctly).  I don't think this can make any correctness difference anywhere.

[Mark P, 2017/04/26 22:24:44]

It uses ICU via the call to String16VectorFromString16() below.
We could check whether the vector returned is identical to a previous vector
returned.  That seemed like more code and complexity than is worth it.  (It
would mean keep a map of vectors of previous search words.)  I can do that if
you prefer.

     // The original search_string broken at cursor position. This is one type of
-    // transformation.
+    // transformation.  There is no need to break the cursor position at a space
+    // if there is already a space adjacent to the cursor.
     base::string16 transformed_search_string(original_search_string);
     transformed_search_string.insert(cursor_position, base::ASCIIToUTF16(" "));
     search_strings.push_back(transformed_search_string);