Add test for the index_options on a keyword field. #16990

This found a bug in the validation, which was checking the wrong IndexOptions.

core/src/main/java/org/elasticsearch/index/mapper/core/KeywordFieldMapper.java

@@ -85,9 +85,9 @@ public final class KeywordFieldMapper extends FieldMapper implements AllFieldMap
 
         @Override
         public Builder indexOptions(IndexOptions indexOptions) {
-            if (fieldType.indexOptions().compareTo(IndexOptions.DOCS_AND_FREQS) > 0) {
+            if (indexOptions.compareTo(IndexOptions.DOCS_AND_FREQS) > 0) {
                 throw new IllegalArgumentException("The [keyword] field does not support positions, got [index_options]="
-                        + indexOptionToString(fieldType.indexOptions()));
+                        + indexOptionToString(indexOptions));
             }
             return super.indexOptions(indexOptions);
         }

core/src/test/java/org/elasticsearch/index/mapper/core/KeywordFieldMapperTests.java

@@ -34,6 +34,7 @@ import org.elasticsearch.test.ESSingleNodeTestCase;
 import org.junit.Before;
 
 import java.io.IOException;
+import java.util.Arrays;
 
 import static org.hamcrest.Matchers.equalTo;
 
@@ -200,4 +201,35 @@ public class KeywordFieldMapperTests extends ESSingleNodeTestCase {
         assertEquals(1, fields.length);
         assertEquals(DocValuesType.NONE, fields[0].fieldType().docValuesType());
     }
+
+    public void testIndexOptions() throws IOException {
+        String mapping = XContentFactory.jsonBuilder().startObject().startObject("type")
+                .startObject("properties").startObject("field").field("type", "keyword")
+                .field("index_options", "freqs").endObject().endObject()
+                .endObject().endObject().string();
+
+        DocumentMapper mapper = parser.parse("type", new CompressedXContent(mapping));
+
+        assertEquals(mapping, mapper.mappingSource().toString());
+
+        ParsedDocument doc = mapper.parse("test", "type", "1", XContentFactory.jsonBuilder()
+                .startObject()
+                .field("field", "1234")
+                .endObject()
+                .bytes());
+
+        IndexableField[] fields = doc.rootDoc().getFields("field");
+        assertEquals(2, fields.length);
+        assertEquals(IndexOptions.DOCS_AND_FREQS, fields[0].fieldType().indexOptions());
+
+        for (String indexOptions : Arrays.asList("positions", "offsets")) {
+            final String mapping2 = XContentFactory.jsonBuilder().startObject().startObject("type")
+                    .startObject("properties").startObject("field").field("type", "keyword")
+                    .field("index_options", indexOptions).endObject().endObject()
+                    .endObject().endObject().string();
+            IllegalArgumentException e = expectThrows(IllegalArgumentException.class,
+                    () -> parser.parse("type", new CompressedXContent(mapping2)));
+            assertEquals("The [keyword] field does not support positions, got [index_options]=" + indexOptions, e.getMessage());
+        }
+    }
 }