Fix case-insensitive searching of hashtags

The index field has always been stored lowercase, since we intended
hashtag searches to be case-insensitive. However, we never converted the
input string to lower case, with the unexpected result that searching
for [hashtag:ACamelCaseTag] would not return results for changes who
contain that exact hashtag.

Bug: Issue 10564
Change-Id: I86019d18fd0d183d857d5a91d2af20d3445c6c25
(cherry picked from commit c8d1c47f1fe2b8807850c35af5dcdb1a5ca10862)

gerrit-server/src/main/java/com/google/gerrit/server/query/change/HashtagPredicate.java

diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/query/change/HashtagPredicate.java b/gerrit-server/src/main/java/com/google/gerrit/server/query/change/HashtagPredicate.java
index bea5688..95ecf89 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/query/change/HashtagPredicate.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/query/change/HashtagPredicate.java
@@ -20,7 +20,9 @@
 
 public class HashtagPredicate extends ChangeIndexPredicate {
   public HashtagPredicate(String hashtag) {
-    super(ChangeField.HASHTAG, HashtagsUtil.cleanupHashtag(hashtag));
+    // Use toLowerCase without locale to match behavior in ChangeField.
+    // TODO(dborowitz): Change both.
+    super(ChangeField.HASHTAG, HashtagsUtil.cleanupHashtag(hashtag).toLowerCase());
   }
 
   @Override

gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java

diff --git a/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java b/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
index 934d893..36a869f 100644
--- a/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
+++ b/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
@@ -1512,7 +1512,7 @@
     in.add = ImmutableSet.of("foo");
     gApi.changes().id(change1.getId().get()).setHashtags(in);
 
-    in.add = ImmutableSet.of("foo", "bar", "a tag");
+    in.add = ImmutableSet.of("foo", "bar", "a tag", "ACamelCaseTag");
     gApi.changes().id(change2.getId().get()).setHashtags(in);
 
     return ImmutableList.of(change1, change2);
@@ -1529,6 +1529,8 @@
     assertQuery("hashtag:\" a tag \"", changes.get(1));
     assertQuery("hashtag:\"#a tag\"", changes.get(1));
     assertQuery("hashtag:\"# #a tag\"", changes.get(1));
+    assertQuery("hashtag:acamelcasetag", changes.get(1));
+    assertQuery("hashtag:ACamelCaseTAg", changes.get(1));
   }
 
   @Test