For filters aggs, make sure that rewrites preserve other_bucket. (#32921)

Author: jtibshirani

server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregationBuilder.java

@@ -209,7 +209,10 @@ protected AggregationBuilder doRewrite(QueryRewriteContext queryShardContext) th
             }
         }
         if (changed) {
-            return new FiltersAggregationBuilder(getName(), rewrittenFilters, this.keyed);
+            FiltersAggregationBuilder rewritten = new FiltersAggregationBuilder(getName(), rewrittenFilters, this.keyed);
+            rewritten.otherBucket(otherBucket);
+            rewritten.otherBucketKey(otherBucketKey);
+            return rewritten;
         } else {
             return this;
         }

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

@@ -178,4 +178,18 @@ public void testRewrite() throws IOException {
         assertSame(rewritten,
             rewritten.rewrite(new QueryRewriteContext(xContentRegistry(), null, null, () -> 0L)));
     }
+
+    public void testRewritePreservesOtherBucket() throws IOException {
+        FiltersAggregationBuilder originalFilters = new FiltersAggregationBuilder("my-agg", new BoolQueryBuilder());
+        originalFilters.otherBucket(randomBoolean());
+        originalFilters.otherBucketKey(randomAlphaOfLength(10));
+
+        AggregationBuilder rewritten = originalFilters.rewrite(new QueryRewriteContext(xContentRegistry(),
+            null, null, () -> 0L));
+        assertThat(rewritten, instanceOf(FiltersAggregationBuilder.class));
+
+        FiltersAggregationBuilder rewrittenFilters = (FiltersAggregationBuilder) rewritten;
+        assertEquals(originalFilters.otherBucket(), rewrittenFilters.otherBucket());
+        assertEquals(originalFilters.otherBucketKey(), rewrittenFilters.otherBucketKey());
+    }
 }