Support geotile_grid aggregation in composite agg sources.

src/Nest/Aggregations/Bucket/Composite/CompositeAggregationSource.cs

@@ -98,6 +98,12 @@ public CompositeAggregationSourcesDescriptor<T> DateHistogram(string name,
 			Func<DateHistogramCompositeAggregationSourceDescriptor<T>, IDateHistogramCompositeAggregationSource> selector
 		) =>
 			Assign(selector?.Invoke(new DateHistogramCompositeAggregationSourceDescriptor<T>(name)), (a, v) => a.Add(v));
+
+		/// <inheritdoc cref="IGeoTileGridCompositeAggregationSource" />
+		public CompositeAggregationSourcesDescriptor<T> GeoTileGrid(string name,
+			Func<GeoTileGridCompositeAggregationSourceDescriptor<T>, IGeoTileGridCompositeAggregationSource> selector
+		) =>
+			Assign(selector?.Invoke(new GeoTileGridCompositeAggregationSourceDescriptor<T>(name)), (a, v) => a.Add(v));
 	}
 
 	/// <inheritdoc cref="ICompositeAggregationSource" />
@@ -154,6 +160,9 @@ public void Serialize(ref JsonWriter writer, ICompositeAggregationSource value,
 				case IHistogramCompositeAggregationSource histogramCompositeAggregationSource:
 					Serialize(ref writer, histogramCompositeAggregationSource, formatterResolver);
 					break;
+				case IGeoTileGridCompositeAggregationSource geoTileGridCompositeAggregationSource:
+					Serialize(ref writer, geoTileGridCompositeAggregationSource, formatterResolver);
+					break;
 				default:
 					Serialize(ref writer, value, formatterResolver);
 					break;
@@ -176,6 +185,7 @@ IJsonFormatterResolver formatterResolver
 			{ "terms", 0 },
 			{ "date_histogram", 1 },
 			{ "histogram", 2 },
+			{ "geotile_grid", 3 },
 		};
 
 		public ICompositeAggregationSource Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver)
@@ -208,6 +218,10 @@ public ICompositeAggregationSource Deserialize(ref JsonReader reader, IJsonForma
 						compositeAggregationSource = formatterResolver.GetFormatter<HistogramCompositeAggregationSource>()
 							.Deserialize(ref reader, formatterResolver);
 						break;
+					case 3:
+						compositeAggregationSource = formatterResolver.GetFormatter<GeoTileGridCompositeAggregationSource>()
+							.Deserialize(ref reader, formatterResolver);
+						break;
 				}
 			}
 			else

src/Nest/Aggregations/Bucket/Composite/GeoTileGridCompositeAggregationSource.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Runtime.Serialization;
+
+namespace Nest
+{
+	/// <summary>
+	/// A values source that is equivalent to a simple Geo aggregation.
+	/// </summary>
+	public interface IGeoTileGridCompositeAggregationSource : ICompositeAggregationSource
+	{
+		/// <summary>
+		/// The zoom of the key used to define cells/buckets in the results.
+		/// </summary>
+		[DataMember(Name ="precision")]
+		GeoTilePrecision? Precision { get; set; }
+	}
+
+	/// <inheritdoc cref="IGeoTileGridCompositeAggregationSource" />
+	public class GeoTileGridCompositeAggregationSource : CompositeAggregationSourceBase, IGeoTileGridCompositeAggregationSource
+	{
+		public GeoTileGridCompositeAggregationSource(string name) : base(name) { }
+
+		/// <inheritdoc />
+		public GeoTilePrecision? Precision { get; set; }
+
+		/// <inheritdoc />
+		protected override string SourceType => "geotile_grid";
+	}
+
+	/// <inheritdoc cref="IGeoTileGridCompositeAggregationSource" />
+	public class GeoTileGridCompositeAggregationSourceDescriptor<T>
+		: CompositeAggregationSourceDescriptorBase<GeoTileGridCompositeAggregationSourceDescriptor<T>, IGeoTileGridCompositeAggregationSource, T>,
+			IGeoTileGridCompositeAggregationSource
+	{
+		public GeoTileGridCompositeAggregationSourceDescriptor(string name) : base(name, "geotile_grid") { }
+
+		GeoTilePrecision? IGeoTileGridCompositeAggregationSource.Precision { get; set; }
+
+		/// <inheritdoc cref="IGeoTileGridCompositeAggregationSource.Precision" />
+		public GeoTileGridCompositeAggregationSourceDescriptor<T> Precision(GeoTilePrecision? precision) =>
+			Assign(precision, (a, v) => a.Precision = v);
+	}
+}

src/Tests/Tests/Aggregations/Bucket/Composite/CompositeAggregationUsageTests.cs

@@ -28,7 +28,7 @@ namespace Tests.Aggregations.Bucket.Composite
 	 *
 	 * Be sure to read the Elasticsearch documentation on {ref_current}/search-aggregations-bucket-composite-aggregation.html[Composite Aggregation].
 	*/
-	[SkipVersion("<6.1.0", "Composite Aggregation is only available in Elasticsearch 6.1.0+")]
+	[SkipVersion("<7.5.0", "Geo tile grid composite agg added in 7.5.0, rest available in 6.1.0+")]
 	public class CompositeAggregationUsageTests : ProjectsOnlyAggregationUsageTestBase
 	{
 		public CompositeAggregationUsageTests(ReadOnlyCluster i, EndpointUsage usage) : base(i, usage) { }
@@ -73,6 +73,17 @@ public CompositeAggregationUsageTests(ReadOnlyCluster i, EndpointUsage usage) :
 								}
 							}
 						},
+						new
+						{
+							geo = new
+							{
+								geotile_grid = new
+								{
+									field = "locationPoint",
+									precision = 12
+								}
+							}
+						},
 					}
 				},
 				aggs = new
@@ -109,6 +120,10 @@ public CompositeAggregationUsageTests(ReadOnlyCluster i, EndpointUsage usage) :
 						.Field(f => f.RequiredBranches)
 						.Interval(1)
 					)
+					.GeoTileGrid("geo", h => h
+						.Field(f => f.LocationPoint)
+						.Precision(GeoTilePrecision.Precision12)
+					)
 				)
 				.Aggregations(childAggs => childAggs
 					.Nested("project_tags", n => n
@@ -138,6 +153,11 @@ public CompositeAggregationUsageTests(ReadOnlyCluster i, EndpointUsage usage) :
 					{
 						Field = Field<Project>(f => f.RequiredBranches),
 						Interval = 1
+					},
+					new GeoTileGridCompositeAggregationSource("geo")
+					{
+						Field = Field<Project>(f => f.LocationPoint),
+						Precision = GeoTilePrecision.Precision12
 					}
 				},
 				Aggregations = new NestedAggregation("project_tags")
@@ -164,8 +184,8 @@ protected override void ExpectResponse(ISearchResponse<Project> response)
 			composite.AfterKey.Should().NotBeNull();
 			if (TestConfiguration.Instance.InRange(">=6.3.0"))
 				composite.AfterKey.Should()
-					.HaveCount(3)
-					.And.ContainKeys("branches", "started", "branch_count");
+					.HaveCount(4)
+					.And.ContainKeys("branches", "started", "branch_count", "geo");
 			foreach (var item in composite.Buckets)
 			{
 				var key = item.Key;