Handle range query edge case

Currently when searching with an empty string as lower bound for a range query
on text-based fields we return all documents when 'gte' is used (including the
lower bound) but no documents when 'gt' is used. This might seem
counterintuitive since every value should be greate than the empty string. This
PR fixed this special edge case by implicitely setting the "lower" include flag
in this case before constructing the TermRangeQuery.

Closes elastic#63386

Author: Christoph Büscher

server/src/internalClusterTest/java/org/elasticsearch/search/simple/SimpleSearchIT.java

@@ -225,6 +225,46 @@ public void testSimpleDateRange() throws Exception {
         assertHitCount(searchResponse, 2L);
     }
 
+    public void testRangeQueryKeyword() throws Exception {
+        createIndex("test");
+
+        client().admin().indices().preparePutMapping("test").setSource("field", "type=keyword").get();
+
+        client().prepareIndex("test").setId("1").setSource("field", "A").get();
+        client().prepareIndex("test").setId("2").setSource("field", "B").get();
+        client().prepareIndex("test").setId("3").setSource("field", "C").get();
+        ensureGreen();
+        refresh();
+
+        SearchResponse searchResponse = client().prepareSearch("test").setQuery(QueryBuilders.rangeQuery("field").gte("A").lte("B")).get();
+        assertNoFailures(searchResponse);
+        assertHitCount(searchResponse, 2L);
+
+        searchResponse = client().prepareSearch("test").setQuery(QueryBuilders.rangeQuery("field").gt("A").lte("B")).get();
+        assertNoFailures(searchResponse);
+        assertHitCount(searchResponse, 1L);
+
+        searchResponse = client().prepareSearch("test").setQuery(QueryBuilders.rangeQuery("field").gte("A").lt("B")).get();
+        assertNoFailures(searchResponse);
+        assertHitCount(searchResponse, 1L);
+
+        searchResponse = client().prepareSearch("test").setQuery(QueryBuilders.rangeQuery("field").gte(null).lt("C")).get();
+        assertNoFailures(searchResponse);
+        assertHitCount(searchResponse, 2L);
+
+        searchResponse = client().prepareSearch("test").setQuery(QueryBuilders.rangeQuery("field").gte("B").lt(null)).get();
+        assertNoFailures(searchResponse);
+        assertHitCount(searchResponse, 2L);
+
+        searchResponse = client().prepareSearch("test").setQuery(QueryBuilders.rangeQuery("field").gt(null).lt(null)).get();
+        assertNoFailures(searchResponse);
+        assertHitCount(searchResponse, 3L);
+
+        searchResponse = client().prepareSearch("test").setQuery(QueryBuilders.rangeQuery("field").gt("").lt(null)).get();
+        assertNoFailures(searchResponse);
+        assertHitCount(searchResponse, 3L);
+    }
+
     public void testSimpleTerminateAfterCount() throws Exception {
         prepareCreate("test").setSettings(Settings.builder().put(SETTING_NUMBER_OF_SHARDS, 1).put(SETTING_NUMBER_OF_REPLICAS, 0)).get();
         ensureGreen();

server/src/main/java/org/elasticsearch/index/mapper/StringFieldType.java

@@ -170,8 +170,12 @@ public Query rangeQuery(Object lowerTerm, Object upperTerm, boolean includeLower
                     ALLOW_EXPENSIVE_QUERIES.getKey() + "' is set to false.");
         }
         failIfNotIndexed();
+        BytesRef indexedLower = lowerTerm == null ? null : indexedValueForSearch(lowerTerm);
+        if (indexedLower != null && indexedLower.length == 0) {
+            includeLower = true;
+        }
         return new TermRangeQuery(name(),
-            lowerTerm == null ? null : indexedValueForSearch(lowerTerm),
+            indexedLower,
             upperTerm == null ? null : indexedValueForSearch(upperTerm),
             includeLower, includeUpper);
     }

server/src/test/java/org/elasticsearch/index/mapper/TextFieldTypeTests.java

@@ -95,6 +95,13 @@ public void testRangeQuery() {
         assertEquals(new TermRangeQuery("field", BytesRefs.toBytesRef("foo"), BytesRefs.toBytesRef("bar"), true, false),
                 ft.rangeQuery("foo", "bar", true, false, null, null, null, MOCK_QSC));
 
+        // empty string lower bound should always result query with lower-include flag being set
+        assertEquals(new TermRangeQuery("field", BytesRefs.toBytesRef(""), null, true, true),
+            ft.rangeQuery("", null, true, true, null, null, null, MOCK_QSC));
+
+        assertEquals(new TermRangeQuery("field", BytesRefs.toBytesRef(""), null, true, true),
+            ft.rangeQuery("", null, false, true, null, null, null, MOCK_QSC));
+
         ElasticsearchException ee = expectThrows(ElasticsearchException.class,
                 () -> ft.rangeQuery("foo", "bar", true, false, null, null, null, MOCK_QSC_DISALLOW_EXPENSIVE));
         assertEquals("[range] queries on [text] or [keyword] fields cannot be executed when " +