fix IndexOutOfBoundsException on _all field without tokens and keyword analyzer

fix AllEntries to only compute boost when there are actually some Entries available for the _all field

Closes #4771

src/main/java/org/elasticsearch/common/lucene/all/AllEntries.java

@@ -145,6 +145,7 @@ public class AllEntries extends Reader {
 
     // compute the boost for a token with the given startOffset
     public float boost(int startOffset) {
+        if (!entries.isEmpty()) {
             int lo = 0, hi = entries.size() - 1;
             while (lo <= hi) {
                 final int mid = (lo + hi) >>> 1;
@@ -160,6 +161,8 @@ public class AllEntries extends Reader {
             assert index == entries.size() - 1 || entries.get(index + 1).startOffset() > startOffset;
             return entries.get(index).boost();
         }
+        return 1.0f;
+    }
 
     @Override
     public int read(char[] cbuf, int off, int len) throws IOException {

src/test/java/org/elasticsearch/common/lucene/all/SimpleAllTests.java

@@ -318,4 +318,25 @@ public class SimpleAllTests extends ElasticsearchTestCase {
 
         indexWriter.close();
     }
+
+    @Test
+    public void testNoTokensWithKeywordAnalyzer() throws Exception {
+        Directory dir = new RAMDirectory();
+        IndexWriter indexWriter = new IndexWriter(dir, new IndexWriterConfig(Lucene.VERSION, Lucene.KEYWORD_ANALYZER));
+
+        Document doc = new Document();
+        doc.add(new Field("_id", "1", StoredField.TYPE));
+        AllEntries allEntries = new AllEntries();
+        allEntries.reset();
+        doc.add(new TextField("_all", AllTokenStream.allTokenStream("_all", allEntries, Lucene.KEYWORD_ANALYZER)));
+
+        indexWriter.addDocument(doc);
+
+        IndexReader reader = DirectoryReader.open(indexWriter, true);
+        IndexSearcher searcher = new IndexSearcher(reader);
+
+        TopDocs docs = searcher.search(new MatchAllDocsQuery(), 10);
+        assertThat(docs.totalHits, equalTo(1));
+        assertThat(docs.scoreDocs[0].doc, equalTo(0));
+    }
 }

src/test/java/org/elasticsearch/search/query/SimpleQueryTests.java

@@ -2024,4 +2024,13 @@ public class SimpleQueryTests extends ElasticsearchIntegrationTest {
         assertHitCount(searchResponse, 1l);
         assertFirstHit(searchResponse, hasId("4"));
     }
+
+    @Test
+    public void testSearchEmptyDoc() {
+        prepareCreate("test").setSettings("{\"index.analysis.analyzer.default.type\":\"keyword\"}").get();
+        client().prepareIndex("test", "type1", "1").setSource("{}").get();
+        refresh();
+        assertHitCount(client().prepareSearch().setQuery(matchAllQuery()).get(), 1l);
+    }
+
 }