fix #2592 add unified highlighter support

src/Nest/Search/Search/Highlighting/HighlighterType.cs

@@ -12,27 +12,39 @@ public enum HighlighterType
 	{
 		/// <summary>
 		/// Plain Highlighter.
-		/// The default choice of highlighter is of type plain and uses the Lucene highlighter. 
-		/// It tries hard to reflect the query matching logic in terms of understanding word 
+		/// The default choice of highlighter is of type plain and uses the Lucene highlighter.
+		/// It tries hard to reflect the query matching logic in terms of understanding word
 		/// importance and any word positioning criteria in phrase queries.
 		/// </summary>
 		[EnumMember(Value = "plain")]
 		Plain,
 
 		/// <summary>
 		/// Postings Highlighter.
-		/// If index_options is set to offsets in the mapping the postings highlighter 
+		/// If index_options is set to offsets in the mapping the postings highlighter
 		/// will be used instead of the plain highlighter
 		/// </summary>
 		[EnumMember(Value = "postings")]
 		Postings,
 
 		/// <summary>
 		/// Fast Vector Highlighter.
-		/// If term_vector information is provided by setting term_vector to with_positions_offsets 
+		/// If term_vector information is provided by setting term_vector to with_positions_offsets
 		/// in the mapping then the fast vector highlighter will be used instead of the plain highlighter
 		/// </summary>
 		[EnumMember(Value = "fvh")]
-		Fvh
+		Fvh,
+
+
+		/// <summary>
+		/// Unified Highlighter.
+		/// The unified highlighter can extract offsets from either postings, term vectors, or via re-analyzing text.
+		/// Under the hood it uses Lucene UnifiedHighlighter which picks its strategy depending on the field and the query to highlight.
+		/// Independently of the strategy this highlighter breaks the text into sentences and scores individual sentences as if
+		/// they were documents in this corpus, using the BM25 algorithm. It supports accurate phrase and multi-term
+		/// (fuzzy, prefix, regex) highlighting
+		/// </summary>
+		[EnumMember(Value = "unified")]
+		Unified
 	}
 }

src/Tests/Search/Request/HighlightingUsageTests.cs

@@ -23,6 +23,8 @@ public class HighlightingUsageTests : SearchUsageTestBase
 	{
 		public HighlightingUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cluster, usage) { }
 
+		public string LastNameSearch { get; } = Project.Projects.First().LeadDeveloper.LastName;
+
 		protected override object ExpectJson => new
 		{
 			query = new
@@ -72,6 +74,26 @@ public HighlightingUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : ba
 							}
 						}
 					},
+					{ "leadDeveloper.lastName", new JObject
+						{
+							{ "type", "unified" },
+							{ "pre_tags", new JArray { "<name>" } },
+							{ "post_tags", new JArray { "</name>" } },
+							{ "highlight_query", new JObject
+								{
+									{ "match", new JObject
+										{
+											{ "leadDeveloper.lastName", new JObject
+												{
+													{ "query", LastNameSearch }
+												}
+											}
+										}
+									}
+								}
+							}
+						}
+					},
 					{ "state.offsets", new JObject
 						{
 							{ "type", "postings" },
@@ -122,6 +144,17 @@ public HighlightingUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : ba
 								.Query("Kurt Edgardo Naomi Dariana Justice Felton")
 							)
 						),
+					fs => fs
+						.Field(p => p.LeadDeveloper.LastName)
+						.Type(HighlighterType.Unified)
+						.PreTags("<name>")
+						.PostTags("</name>")
+						.HighlightQuery(q => q
+							.Match(m => m
+								.Field(p => p.LeadDeveloper.LastName)
+								.Query(LastNameSearch)
+							)
+						),
 					fs => fs
 						.Field(p => p.State.Suffix("offsets"))
 						.Type(HighlighterType.Postings)
@@ -175,6 +208,18 @@ public HighlightingUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : ba
 								}
 							}
 						},
+						{ "leadDeveloper.lastName", new HighlightField
+							{
+								Type = HighlighterType.Unified,
+								PreTags = new[] { "<name>"},
+								PostTags = new[] { "</name>"},
+								HighlightQuery = new MatchQuery
+								{
+									Field = "leadDeveloper.lastName",
+									Query = LastNameSearch
+								}
+							}
+						},
 						{ "state.offsets", new HighlightField
 							{
 								Type = HighlighterType.Postings,
@@ -215,6 +260,14 @@ protected override void ExpectResponse(ISearchResponse<Project> response)
 							highlight.Should().Contain("</name>");
 						}
 					}
+					else if (highlightField.Key == "leadDeveloper.lastName	")
+					{
+						foreach (var highlight in highlightField.Value.Highlights)
+						{
+							highlight.Should().Contain("<name>");
+							highlight.Should().Contain("</name>");
+						}
+					}
 					else if (highlightField.Key == "state.offsets")
 					{
 						foreach (var highlight in highlightField.Value.Highlights)