Fix auto_date_histogram interval (#56252) (#56341)

`auto_date_histogram` was returning the incorrect `interval` because
of a combination of two things:
1. When pipeline aggregations rewrote `auto_date_histogram` we reset the
   interval to 1. Oops. Fixed that.
2. *Every* bucket aggregation was rewriting its buckets as though there
   was a pipeline aggregation even if there aren't any. This is a bit
   silly so we skip that too.

Closes #56116

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/330_auto_date_histogram.yml

@@ -25,6 +25,9 @@ setup:
 
 ---
 "basic":
+  - skip:
+      version: " - 7.8.99"
+      reason:  interval had a in bug before 7.9.0
   - do:
       search:
         rest_total_hits_as_int: true
@@ -37,6 +40,7 @@ setup:
                 buckets: 2
   - match: { hits.total: 4 }
   - length: { aggregations.histo.buckets: 2 }
+  - match: { aggregations.histo.interval: "7d" }
   - match: { aggregations.histo.buckets.0.key_as_string: "2020-03-01T00:00:00.000Z" }
   - match: { aggregations.histo.buckets.0.doc_count: 2 }
   - match: { aggregations.histo.buckets.1.key_as_string: "2020-03-08T00:00:00.000Z" }

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

@@ -152,8 +152,12 @@ public abstract class InternalMultiBucketAggregation<A extends InternalMultiBuck
     public final InternalAggregation reducePipelines(
             InternalAggregation reducedAggs, ReduceContext reduceContext, PipelineTree pipelineTree) {
         assert reduceContext.isFinalReduce();
-        List<B> materializedBuckets = reducePipelineBuckets(reduceContext, pipelineTree);
-        return super.reducePipelines(create(materializedBuckets), reduceContext, pipelineTree);
+        InternalAggregation reduced = this;
+        if (pipelineTree.hasSubTrees()) {
+            List<B> materializedBuckets = reducePipelineBuckets(reduceContext, pipelineTree);
+            reduced = create(materializedBuckets);
+        }
+        return super.reducePipelines(reduced, reduceContext, pipelineTree);
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/aggregations/bucket/InternalSingleBucketAggregation.java

@@ -121,13 +121,17 @@ public abstract class InternalSingleBucketAggregation extends InternalAggregatio
     public final InternalAggregation reducePipelines(
             InternalAggregation reducedAggs, ReduceContext reduceContext, PipelineTree pipelineTree) {
         assert reduceContext.isFinalReduce();
-        List<InternalAggregation> aggs = new ArrayList<>();
-        for (Aggregation agg : getAggregations().asList()) {
-            PipelineTree subTree = pipelineTree.subTree(agg.getName());
-            aggs.add(((InternalAggregation)agg).reducePipelines((InternalAggregation)agg, reduceContext, subTree));
+        InternalAggregation reduced = this;
+        if (pipelineTree.hasSubTrees()) {
+            List<InternalAggregation> aggs = new ArrayList<>();
+            for (Aggregation agg : getAggregations().asList()) {
+                PipelineTree subTree = pipelineTree.subTree(agg.getName());
+                aggs.add(((InternalAggregation)agg).reducePipelines((InternalAggregation)agg, reduceContext, subTree));
+            }
+            InternalAggregations reducedSubAggs = new InternalAggregations(aggs);
+            reduced = create(reducedSubAggs);
         }
-        InternalAggregations reducedSubAggs = new InternalAggregations(aggs);
-        return super.reducePipelines(create(reducedSubAggs), reduceContext, pipelineTree);
+        return super.reducePipelines(reduced, reduceContext, pipelineTree);
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalAutoDateHistogram.java

@@ -196,7 +196,10 @@ public final class InternalAutoDateHistogram extends
     private final DocValueFormat format;
     private final BucketInfo bucketInfo;
     private final int targetBuckets;
-    private long bucketInnerInterval;
+    /**
+     * The interval within the rounding that the buckets are using.
+     */
+    private final long bucketInnerInterval;
 
     InternalAutoDateHistogram(String name, List<Bucket> buckets, int targetBuckets, BucketInfo emptyBucketInfo, DocValueFormat formatter,
                               Map<String, Object> metadata, long bucketInnerInterval) {
@@ -217,6 +220,7 @@ public final class InternalAutoDateHistogram extends
         format = in.readNamedWriteable(DocValueFormat.class);
         buckets = in.readList(stream -> new Bucket(stream, format));
         this.targetBuckets = in.readVInt();
+        bucketInnerInterval = 1; // Calculated on merge.
     }
 
     @Override
@@ -258,7 +262,7 @@ public final class InternalAutoDateHistogram extends
 
     @Override
     public InternalAutoDateHistogram create(List<Bucket> buckets) {
-        return new InternalAutoDateHistogram(name, buckets, targetBuckets, bucketInfo, format, metadata, 1);
+        return new InternalAutoDateHistogram(name, buckets, targetBuckets, bucketInfo, format, metadata, bucketInnerInterval);
     }
 
     @Override
@@ -593,7 +597,7 @@ public final class InternalAutoDateHistogram extends
             buckets2.add((Bucket) b);
         }
         buckets2 = Collections.unmodifiableList(buckets2);
-        return new InternalAutoDateHistogram(name, buckets2, targetBuckets, bucketInfo, format, getMetadata(), 1);
+        return new InternalAutoDateHistogram(name, buckets2, targetBuckets, bucketInfo, format, getMetadata(), bucketInnerInterval);
     }
 
     @Override

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/PipelineAggregator.java

@@ -96,6 +96,13 @@ public abstract class PipelineAggregator implements NamedWriteable {
             return subTrees.getOrDefault(name, EMPTY);
         }
 
+        /**
+         * Return {@code true} if this node in the tree has any subtrees.
+         */
+        public boolean hasSubTrees() {
+            return false == subTrees.isEmpty();
+        }
+
         @Override
         public String toString() {
             return "PipelineTree[" + aggregators + "," + subTrees + "]";

server/src/test/java/org/elasticsearch/search/aggregations/bucket/filter/InternalFilterTests.java

@@ -19,13 +19,22 @@
 
 package org.elasticsearch.search.aggregations.bucket.filter;
 
+import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.InternalSingleBucketAggregationTestCase;
 import org.elasticsearch.search.aggregations.bucket.ParsedSingleBucketAggregation;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
 
 import java.util.List;
 import java.util.Map;
 
+import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.singletonList;
+import static org.hamcrest.Matchers.sameInstance;
+
 public class InternalFilterTests extends InternalSingleBucketAggregationTestCase<InternalFilter> {
     @Override
     protected InternalFilter createTestInstance(String name, long docCount, InternalAggregations aggregations,
@@ -42,4 +51,32 @@ public class InternalFilterTests extends InternalSingleBucketAggregationTestCase
     protected Class<? extends ParsedSingleBucketAggregation> implementationClass() {
         return ParsedFilter.class;
     }
+
+    public void testReducePipelinesReturnsSameInstanceWithoutPipelines() {
+        InternalFilter test = createTestInstance();
+        assertThat(test.reducePipelines(test, emptyReduceContextBuilder().forFinalReduction(), PipelineTree.EMPTY), sameInstance(test));
+    }
+
+    public void testReducePipelinesReducesBucketPipelines() {
+        /*
+         * Tests that a pipeline buckets by creating a mock pipeline that
+         * replaces "inner" with "dummy".
+         */
+        InternalFilter dummy = createTestInstance();
+        InternalFilter inner = createTestInstance();
+
+        InternalAggregations sub = new InternalAggregations(singletonList(inner));
+        InternalFilter test = createTestInstance("test", randomNonNegativeLong(), sub, emptyMap());
+        PipelineAggregator mockPipeline = new PipelineAggregator(null, null, null) {
+            @Override
+            public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+                return dummy;
+            }
+        };
+        PipelineTree tree = new PipelineTree(
+            org.elasticsearch.common.collect.Map.of(inner.getName(), new PipelineTree(emptyMap(), singletonList(mockPipeline))),
+            emptyList());
+        InternalFilter reduced = (InternalFilter) test.reducePipelines(test, emptyReduceContextBuilder().forFinalReduction(), tree);
+        assertThat(reduced.getAggregations().get(dummy.getName()), sameInstance(dummy));
+    }
 }

server/src/test/java/org/elasticsearch/search/aggregations/bucket/filter/InternalFiltersTests.java

@@ -19,9 +19,13 @@
 
 package org.elasticsearch.search.aggregations.bucket.filter;
 
+import org.elasticsearch.search.aggregations.InternalAggregation;
+import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 import org.elasticsearch.search.aggregations.InternalAggregations;
 import org.elasticsearch.search.aggregations.ParsedMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.bucket.filter.InternalFilters.InternalBucket;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
 import org.elasticsearch.test.InternalMultiBucketAggregationTestCase;
 
 import java.util.ArrayList;
@@ -30,6 +34,11 @@ import java.util.List;
 import java.util.Map;
 import java.util.TreeMap;
 
+import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.singletonList;
+import static org.hamcrest.Matchers.sameInstance;
+
 public class InternalFiltersTests extends InternalMultiBucketAggregationTestCase<InternalFilters> {
 
     private boolean keyed;
@@ -109,4 +118,34 @@ public class InternalFiltersTests extends InternalMultiBucketAggregationTestCase
         }
         return new InternalFilters(name, buckets, keyed, metadata);
     }
+
+    public void testReducePipelinesReturnsSameInstanceWithoutPipelines() {
+        InternalFilters test = createTestInstance();
+        assertThat(test.reducePipelines(test, emptyReduceContextBuilder().forFinalReduction(), PipelineTree.EMPTY), sameInstance(test));
+    }
+
+    public void testReducePipelinesReducesBucketPipelines() {
+        /*
+         * Tests that a pipeline buckets by creating a mock pipeline that
+         * replaces "inner" with "dummy".
+         */
+        InternalFilters dummy = createTestInstance();
+        InternalFilters inner = createTestInstance();
+
+        InternalAggregations sub = new InternalAggregations(singletonList(inner));
+        InternalFilters test = createTestInstance("test", emptyMap(), sub);
+        PipelineAggregator mockPipeline = new PipelineAggregator(null, null, null) {
+            @Override
+            public InternalAggregation reduce(InternalAggregation aggregation, ReduceContext reduceContext) {
+                return dummy;
+            }
+        };
+        PipelineTree tree = new PipelineTree(
+            org.elasticsearch.common.collect.Map.of(inner.getName(), new PipelineTree(emptyMap(), singletonList(mockPipeline))),
+            emptyList());
+        InternalFilters reduced = (InternalFilters) test.reducePipelines(test, emptyReduceContextBuilder().forFinalReduction(), tree);
+        for (InternalFilters.InternalBucket bucket : reduced.getBuckets()) {
+            assertThat(bucket.getAggregations().get(dummy.getName()), sameInstance(dummy));
+        }
+    }
 }

server/src/test/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalAutoDateHistogramTests.java

@@ -50,6 +50,7 @@ import static java.util.stream.Collectors.toList;
 import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
+import static org.hamcrest.Matchers.hasSize;
 
 public class InternalAutoDateHistogramTests extends InternalMultiBucketAggregationTestCase<InternalAutoDateHistogram> {
 
@@ -376,4 +377,18 @@ public class InternalAutoDateHistogramTests extends InternalMultiBucketAggregati
     private List<Integer> docCounts(InternalAutoDateHistogram h) {
         return h.getBuckets().stream().map(b -> (int) b.getDocCount()).collect(toList());
     }
+
+    public void testCreateWithReplacementBuckets() {
+        InternalAutoDateHistogram noInterval = createTestInstance();
+        InternalAutoDateHistogram orig = new InternalAutoDateHistogram(
+            noInterval.getName(), noInterval.getBuckets(), noInterval.getTargetBuckets(), noInterval.getBucketInfo(),
+            noInterval.getFormatter(), noInterval.getMetadata(), randomLong());
+        InternalAutoDateHistogram copy = orig.create(emptyList());
+        assertThat(copy.getName(), equalTo(orig.getName()));
+        assertThat(copy.getBuckets(), hasSize(0));
+        assertThat(copy.getTargetBuckets(), equalTo(orig.getTargetBuckets()));
+        assertThat(copy.getBucketInfo(), equalTo(orig.getBucketInfo()));
+        assertThat(copy.getFormatter(), equalTo(orig.getFormatter()));
+        assertThat(copy.getInterval(), equalTo(orig.getInterval()));
+    }
 }