Returning useful exception when sorting on a completion field

Closes #3747

src/main/java/org/elasticsearch/index/mapper/FieldMapper.java

@@ -202,4 +202,6 @@ public interface FieldMapper<T> {
     PostingsFormatProvider postingsFormatProvider();
 
     boolean isNumeric();
+
+    boolean isSortable();
 }

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

@@ -711,4 +711,8 @@ public abstract class AbstractFieldMapper<T> implements FieldMapper<T>, Mapper {
         return false;
     }
 
+    @Override
+    public boolean isSortable() {
+        return true;
+    }
 }

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

@@ -357,6 +357,10 @@ public class CompletionFieldMapper extends AbstractFieldMapper<String> {
         return CONTENT_TYPE;
     }
 
+    @Override
+    public boolean isSortable() {
+        return false;
+    }
 
     @Override
     public FieldType defaultFieldType() {

src/main/java/org/elasticsearch/search/sort/SortParseElement.java

@@ -31,6 +31,7 @@ import org.elasticsearch.index.fielddata.IndexFieldData;
 import org.elasticsearch.index.fielddata.fieldcomparator.SortMode;
 import org.elasticsearch.index.mapper.FieldMapper;
 import org.elasticsearch.index.mapper.ObjectMappers;
+import org.elasticsearch.index.mapper.core.CompletionFieldMapper;
 import org.elasticsearch.index.mapper.core.NumberFieldMapper;
 import org.elasticsearch.index.mapper.object.ObjectMapper;
 import org.elasticsearch.index.query.ParsedFilter;
@@ -198,6 +199,10 @@ public class SortParseElement implements SearchParseElement {
                 throw new SearchParseException(context, "No mapping found for [" + fieldName + "] in order to sort on");
             }
 
+            if (!fieldMapper.isSortable()) {
+                throw new SearchParseException(context, "Sorting not supported for field[" + fieldName + "]");
+            }
+
             // Enable when we also know how to detect fields that do tokenize, but only emit one token
             /*if (fieldMapper instanceof StringFieldMapper) {
                 StringFieldMapper stringFieldMapper = (StringFieldMapper) fieldMapper;

src/test/java/org/elasticsearch/search/suggest/CompletionSuggestSearchTests.java

@@ -27,6 +27,7 @@ import org.elasticsearch.action.admin.indices.segments.IndexShardSegments;
 import org.elasticsearch.action.admin.indices.segments.ShardSegments;
 import org.elasticsearch.action.admin.indices.stats.IndicesStatsResponse;
 import org.elasticsearch.action.index.IndexRequestBuilder;
+import org.elasticsearch.action.search.SearchPhaseExecutionException;
 import org.elasticsearch.action.suggest.SuggestResponse;
 import org.elasticsearch.common.settings.ImmutableSettings;
 import org.elasticsearch.common.settings.Settings;
@@ -34,6 +35,7 @@ import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.index.mapper.MapperException;
 import org.elasticsearch.index.mapper.MapperParsingException;
 import org.elasticsearch.index.mapper.core.CompletionFieldMapper;
+import org.elasticsearch.search.sort.FieldSortBuilder;
 import org.elasticsearch.search.suggest.completion.CompletionStats;
 import org.elasticsearch.search.suggest.completion.CompletionSuggestion;
 import org.elasticsearch.search.suggest.completion.CompletionSuggestionBuilder;
@@ -556,6 +558,27 @@ public class CompletionSuggestSearchTests extends AbstractIntegrationTest {
         assertThat(regexSizeInBytes, is(totalSizeInBytes));
     }
 
+    @Test
+    public void testThatSortingOnCompletionFieldReturnsUsefulException() throws Exception {
+        createIndexAndMapping();
+
+        client().prepareIndex(INDEX, TYPE, "1").setSource(jsonBuilder()
+                .startObject().startObject(FIELD)
+                .startArray("input").value("Nirvana").endArray()
+                .endObject().endObject()
+        ).get();
+
+        refresh();
+        try {
+            client().prepareSearch(INDEX).setTypes(TYPE).addSort(new FieldSortBuilder(FIELD)).execute().actionGet();
+            fail("Expected an exception due to trying to sort on completion field, but did not happen");
+        } catch (SearchPhaseExecutionException e) {
+            assertThat(e.status().getStatus(), is(400));
+            assertThat(e.getMessage(), containsString("Sorting not supported for field[" + FIELD + "]"));
+        }
+    }
+
+
     public void assertSuggestions(String suggestion, String... suggestions) {
         String suggestionName = RandomStrings.randomAsciiOfLength(new Random(), 10);
         SuggestResponse suggestResponse = client().prepareSuggest(INDEX).addSuggestion(