Adds metadata to rewritten aggregations (#28185)

* Adds metadata to rewritten aggregations

Previous to this change, if any filters in the filters aggregation were rewritten, the rewritten version of the FiltersAggregationBuilder would not contain the metadata form the original. This is because `AbstractAggregationBuilder.getMetadata()` returns an empty map when not metadata is set.

Closes #28170

* Always set metadata when rewritten

Author: colings86

server/src/main/java/org/elasticsearch/search/aggregations/AggregationBuilder.java

@@ -101,9 +101,7 @@ public final AggregationBuilder rewrite(QueryRewriteContext context) throws IOEx
         if (rewritten == this) {
             return rewritten;
         }
-        if (getMetaData() != null && rewritten.getMetaData() == null) {
-            rewritten.setMetaData(getMetaData());
-        }
+        rewritten.setMetaData(getMetaData());
         AggregatorFactories.Builder rewrittenSubAggs = factoriesBuilder.rewrite(context);
         rewritten.subAggregations(rewrittenSubAggs);
         return rewritten;

server/src/test/java/org/elasticsearch/search/aggregations/FiltersAggsRewriteIT.java

@@ -32,6 +32,8 @@
 import org.elasticsearch.test.ESSingleNodeTestCase;
 
 import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
 
 public class FiltersAggsRewriteIT extends ESSingleNodeTestCase {
 
@@ -58,10 +60,14 @@ public void testWrapperQueryIsRewritten() throws IOException {
         }
         FiltersAggregationBuilder builder = new FiltersAggregationBuilder("titles", new FiltersAggregator.KeyedFilter("titleterms",
                 new WrapperQueryBuilder(bytesReference)));
+        Map<String, Object> metadata = new HashMap<>();
+        metadata.put(randomAlphaOfLengthBetween(1, 20), randomAlphaOfLengthBetween(1, 20));
+        builder.setMetaData(metadata);
         SearchResponse searchResponse = client().prepareSearch("test").setSize(0).addAggregation(builder).get();
         assertEquals(3, searchResponse.getHits().getTotalHits());
         InternalFilters filters = searchResponse.getAggregations().get("titles");
         assertEquals(1, filters.getBuckets().size());
         assertEquals(2, filters.getBuckets().get(0).getDocCount());
+        assertEquals(metadata, filters.getMetaData());
     }
 }

server/src/test/java/org/elasticsearch/search/aggregations/bucket/FiltersTests.java

@@ -35,6 +35,7 @@
 import org.elasticsearch.search.aggregations.bucket.filter.FiltersAggregator.KeyedFilter;
 
 import java.io.IOException;
+import java.util.Collections;
 
 import static org.hamcrest.Matchers.instanceOf;
 
@@ -123,6 +124,7 @@ public void testOtherBucket() throws IOException {
     public void testRewrite() throws IOException {
         // test non-keyed filter that doesn't rewrite
         AggregationBuilder original = new FiltersAggregationBuilder("my-agg", new MatchAllQueryBuilder());
+        original.setMetaData(Collections.singletonMap(randomAlphaOfLengthBetween(1, 20), randomAlphaOfLengthBetween(1, 20)));
         AggregationBuilder rewritten = original.rewrite(new QueryRewriteContext(xContentRegistry(), null, null, () -> 0L));
         assertSame(original, rewritten);