Add matched_fields to field highlighting options

Author: gmarz

src/Nest/DSL/Search/HighlightFieldDescriptor.cs

@@ -54,6 +54,9 @@ public interface IHighlightField
 
 		[JsonProperty("force_source")]
 		bool? ForceSource { get; set; }
+
+		[JsonProperty("matched_fields")]
+		IEnumerable<PropertyPathMarker> MatchedFields { get; set; }
 	}
 
 	public class HighlightField : IHighlightField
@@ -73,6 +76,7 @@ public class HighlightField : IHighlightField
 		public string BoundaryChars { get; set; }
 		public string Type { get; set; }
 		public bool? ForceSource { get; set; }
+		public IEnumerable<PropertyPathMarker> MatchedFields { get; set; }
 	}
 
 	public class HighlightFieldDescriptor<T> : IHighlightField where T : class
@@ -108,6 +112,8 @@ public class HighlightFieldDescriptor<T> : IHighlightField where T : class
 		string IHighlightField.Type { get; set; }
 
 		bool? IHighlightField.ForceSource { get; set; }
+
+		IEnumerable<PropertyPathMarker> IHighlightField.MatchedFields { get; set; }
 
 		public HighlightFieldDescriptor<T> OnField(string field)
 		{
@@ -208,5 +214,15 @@ public HighlightFieldDescriptor<T> BoundaryMaxSize(int boundaryMaxSize)
 			Self.BoundaryMaxSize = boundaryMaxSize;
 			return this;
 		}
+		public HighlightFieldDescriptor<T> MatchedFields(IEnumerable<string> fields)
+		{
+			Self.MatchedFields = fields.Select(f => (PropertyPathMarker)f);
+			return this;
+		}
+		public HighlightFieldDescriptor<T> MatchedFields(params Expression<Func<T, object>>[] objectPaths)
+		{
+			Self.MatchedFields = objectPaths.Select(f => (PropertyPathMarker)f);
+			return this;
+		}
 	}
 }

src/Tests/Nest.Tests.Unit/Search/Highlight/HighlightTests.cs

@@ -32,10 +32,14 @@ public void TestHighlight()
 					.OnFields(
 					f => f
 						.OnAll()
-                        .NoMatchSize(200)
+						.NoMatchSize(200)
 						.PreTags("<em>")
 						.PostTags("</em>")
-						.Type(HighlighterType.Plain)
+						.Type(HighlighterType.Plain),
+					f => f
+						.OnField(p => p.Name)
+						.Type(HighlighterType.Postings)
+						.MatchedFields(mf => mf.Country, mf => mf.Content)
 					)
 				);
 			var json = TestElasticClient.Serialize(s);
@@ -57,6 +61,10 @@ public void TestHighlight()
 				post_tags: [""</em>""],
 				no_match_size: 200,
 				type: ""plain""
+			  },
+			  name: {
+				type: ""postings"",
+				matched_fields: [ ""country"", ""content"" ]
 			  }
 			},
 			require_field_match: true,