Allow to raise BooleanQuery limit in gerrit.config.

Raising the limit avoids failing a query BooleanQuery.TooManyClauses,
preventing users from seeing "400 cannot create query for index" error
in the "Conflicts with" part of the change screen.

Change-Id: Ie0bf14c4a3e6c4833c064f7ac822c08aa2aaffb8

Documentation/config-gerrit.txt

@@ -1927,6 +1927,14 @@ Only used when the type is `SOLR`.
 +
 URL of the index server.
 
+[[index.defaultMaxClauseCount]]index.defaultMaxClauseCount::
++
+Only used when the type is `LUCENE`.
++
+Sets the maximum number of clauses permitted per BooleanQuery.
++
+Defaults to 1024.
+
 [[index.name.ramBufferSize]]index.name.ramBufferSize::
 +
 Only used when the type is `LUCENE`.
@@ -1976,6 +1984,7 @@ Sample index configuration:
 ----
 [index]
   type = LUCENE
+  defaultMaxClauseCount = 2048
 
 [index "changes_open"]
   ramBufferSize = 60 m

gerrit-lucene/src/main/java/com/google/gerrit/lucene/LuceneChangeIndex.java

@@ -73,6 +73,7 @@ import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.IndexWriterConfig.OpenMode;
 import org.apache.lucene.index.Term;
+import org.apache.lucene.search.BooleanQuery;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.ScoreDoc;
@@ -228,6 +229,9 @@ public class LuceneChangeIndex implements ChangeIndex {
         new StandardAnalyzer(luceneVersion, CharArraySet.EMPTY_SET);
     queryBuilder = new QueryBuilder(schema, analyzer);
 
+    BooleanQuery.setMaxClauseCount(cfg.getInt("index", "defaultMaxClauseCount",
+        BooleanQuery.getMaxClauseCount()));
+
     GerritIndexWriterConfig openConfig =
         new GerritIndexWriterConfig(luceneVersion, cfg, "changes_open");
     GerritIndexWriterConfig closedConfig =