fix: Sort Processor does not have proper behavior with targetField

to specify a `targetField`. This results in some interesting behavior that was missed in the review.
This processor sorts in-place, so there is a side-effect in both the original field and the target field.
Another bug was that the targetField was not being set if the list being sorted was fewer than two elements.

The new behavior works like this: If targetField and fieldName are not the same, we copy the list.

Author: talevy

modules/ingest-common/src/main/java/org/elasticsearch/ingest/common/SortProcessor.java

@@ -24,6 +24,7 @@
 import org.elasticsearch.ingest.IngestDocument;
 import org.elasticsearch.ingest.Processor;
 
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -99,17 +100,15 @@ public void execute(IngestDocument document) {
             throw new IllegalArgumentException("field [" + field + "] is null, cannot sort.");
         }
 
-        if (list.size() <= 1) {
-            return;
-        }
+        List<? extends Comparable> copy = new ArrayList<>(list);
 
         if (order.equals(SortOrder.ASCENDING)) {
-            Collections.sort(list);
+            Collections.sort(copy);
         } else {
-            Collections.sort(list, Collections.reverseOrder());
+            Collections.sort(copy, Collections.reverseOrder());
         }
 
-        document.setFieldValue(targetField, list);
+        document.setFieldValue(targetField, copy);
     }
 
     @Override

modules/ingest-common/src/test/java/org/elasticsearch/ingest/common/SortProcessorTests.java

@@ -275,7 +275,7 @@ public void testSortNullValue() throws Exception {
         }
     }
 
-    public void testSortWithTargetField() throws Exception {
+    public void testDescendingSortWithTargetField() throws Exception {
         IngestDocument ingestDocument = RandomDocumentPicks.randomIngestDocument(random());
         int numItems = randomIntBetween(1, 10);
         List<String> fieldValue = new ArrayList<>(numItems);
@@ -285,18 +285,54 @@ public void testSortWithTargetField() throws Exception {
             fieldValue.add(value);
             expectedResult.add(value);
         }
+
+        Collections.sort(expectedResult, Collections.reverseOrder());
+
+        String fieldName = RandomDocumentPicks.addRandomField(random(), ingestDocument, fieldValue);
+        String targetFieldName = RandomDocumentPicks.randomFieldName(random());
+        Processor processor = new SortProcessor(randomAlphaOfLength(10), fieldName,
+            SortOrder.DESCENDING, targetFieldName);
+        processor.execute(ingestDocument);
+        assertEquals(ingestDocument.getFieldValue(targetFieldName, List.class), expectedResult);
+    }
+
+    public void testAscendingSortWithTargetField() throws Exception {
+        IngestDocument ingestDocument = RandomDocumentPicks.randomIngestDocument(random());
+        int numItems = randomIntBetween(1, 10);
+        List<String> fieldValue = new ArrayList<>(numItems);
+        List<String> expectedResult = new ArrayList<>(numItems);
+        for (int j = 0; j < numItems; j++) {
+            String value = randomAlphaOfLengthBetween(1, 10);
+            fieldValue.add(value);
+            expectedResult.add(value);
+        }
+
+        Collections.sort(expectedResult);
+
+        String fieldName = RandomDocumentPicks.addRandomField(random(), ingestDocument, fieldValue);
+        String targetFieldName = RandomDocumentPicks.randomFieldName(random());
+        Processor processor = new SortProcessor(randomAlphaOfLength(10), fieldName,
+            SortOrder.ASCENDING, targetFieldName);
+        processor.execute(ingestDocument);
+        assertEquals(ingestDocument.getFieldValue(targetFieldName, List.class), expectedResult);
+    }
+
+    public void testSortWithTargetFieldLeavesOriginalUntouched() throws Exception {
+        IngestDocument ingestDocument = RandomDocumentPicks.randomIngestDocument(random());
+        List<Integer> fieldValue = Arrays.asList(1, 5, 4);
+        List<Integer> expectedResult = new ArrayList<>(fieldValue);
         Collections.sort(expectedResult);
 
         SortOrder order = randomBoolean() ? SortOrder.ASCENDING : SortOrder.DESCENDING;
         if (order.equals(SortOrder.DESCENDING)) {
             Collections.reverse(expectedResult);
         }
 
-        String fieldName = RandomDocumentPicks.addRandomField(random(), ingestDocument, fieldValue);
-        String targetFieldName = RandomDocumentPicks.randomFieldName(random());
+        String fieldName = RandomDocumentPicks.addRandomField(random(), ingestDocument, new ArrayList<>(fieldValue));
+        String targetFieldName = fieldName + "foo";
         Processor processor = new SortProcessor(randomAlphaOfLength(10), fieldName, order, targetFieldName);
         processor.execute(ingestDocument);
         assertEquals(ingestDocument.getFieldValue(targetFieldName, List.class), expectedResult);
+        assertEquals(ingestDocument.getFieldValue(fieldName, List.class), fieldValue);
     }
-
 }