Add skip_duplicates to completion suggester (#3140)

Closes #3130

Author: russcam

src/Nest/Search/Suggesters/BaseSuggest.cs

@@ -6,12 +6,18 @@ namespace Nest
 {
 	public interface ISuggester
 	{
+		/// <summary>
+		/// The name of the field on which to run the query
+		/// </summary>
 		[JsonProperty("field")]
 		Field Field { get; set; }
 
 		[JsonProperty("analyzer")]
 		string Analyzer { get; set; }
 
+		/// <summary>
+		/// The number of suggestions to return. Defaults to 5
+		/// </summary>
 		[JsonProperty("size")]
 		int? Size { get; set; }
 }

src/Nest/Search/Suggesters/CompletionSuggester/CompletionSuggester.cs

@@ -9,50 +9,89 @@ namespace Nest
 	[JsonConverter(typeof(ReadAsTypeJsonConverter<CompletionSuggester>))]
 	public interface ICompletionSuggester : ISuggester
 	{
+		/// <summary>
+		/// Prefix used to search for suggestions
+		/// </summary>
 		[JsonIgnore]
 		string Prefix { get; set; }
 
+		/// <summary>
+		/// Prefix as a regular expression used to search for suggestions
+		/// </summary>
 		[JsonIgnore]
 		string Regex { get; set; }
 
+		/// <summary>
+		/// Support fuzziness for the suggestions
+		/// </summary>
 		[JsonProperty("fuzzy")]
 		IFuzzySuggester Fuzzy { get; set; }
 
+		/// <summary>
+		/// Context mappings used to filter and/or boost suggestions
+		/// </summary>
 		[JsonProperty("contexts")]
 		IDictionary<string, IList<ISuggestContextQuery>> Contexts { get; set; }
+
+		/// <summary>
+		/// Whether duplicate suggestions should be filtered out. Defaults to <c>false</c>
+		/// </summary>
+		[JsonProperty("skip_duplicates")]
+		bool? SkipDuplicates { get; set; }
 	}
 
 	public class CompletionSuggester : SuggesterBase, ICompletionSuggester
 	{
+		/// <inheritdoc />
 		public IFuzzySuggester Fuzzy { get; set; }
 
+		/// <inheritdoc />
 		public IDictionary<string, IList<ISuggestContextQuery>> Contexts { get; set; }
 
+		/// <inheritdoc />
 		public string Prefix { get; set; }
 
+		/// <inheritdoc />
 		public string Regex { get; set; }
+
+		/// <inheritdoc />
+		public bool? SkipDuplicates { get; set; }
 	}
 
 	public class CompletionSuggesterDescriptor<T> : SuggestDescriptorBase<CompletionSuggesterDescriptor<T>, ICompletionSuggester, T>, ICompletionSuggester
 		where T : class
 	{
 		IFuzzySuggester ICompletionSuggester.Fuzzy { get; set; }
-
 		IDictionary<string, IList<ISuggestContextQuery>> ICompletionSuggester.Contexts { get; set; }
-
 		string ICompletionSuggester.Prefix { get; set; }
-
 		string ICompletionSuggester.Regex { get; set; }
+		bool? ICompletionSuggester.SkipDuplicates { get; set; }
 
+		/// <summary>
+		/// Prefix used to search for suggestions
+		/// </summary>
 		public CompletionSuggesterDescriptor<T> Prefix(string prefix) => Assign(a => a.Prefix = prefix);
 
+		/// <summary>
+		/// Prefix as a regular expression used to search for suggestions
+		/// </summary>
 		public CompletionSuggesterDescriptor<T> Regex(string regex) => Assign(a => a.Regex = regex);
 
+		/// <summary>
+		/// Support fuzziness for the suggestions
+		/// </summary>
 		public CompletionSuggesterDescriptor<T> Fuzzy(Func<FuzzySuggestDescriptor<T>, IFuzzySuggester> selector = null) =>
 			Assign(a => a.Fuzzy = selector.InvokeOrDefault(new FuzzySuggestDescriptor<T>()));
 
+		/// <summary>
+		/// Context mappings used to filter and/or boost suggestions
+		/// </summary>
 		public CompletionSuggesterDescriptor<T> Contexts(Func<SuggestContextQueriesDescriptor<T>, IPromise<IDictionary<string, IList<ISuggestContextQuery>>>> contexts) =>
 			Assign(a => a.Contexts = contexts?.Invoke(new SuggestContextQueriesDescriptor<T>()).Value);
 
+		/// <summary>
+		/// Whether duplicate suggestions should be filtered out. Defaults to <c>false</c>
+		/// </summary>
+		public CompletionSuggesterDescriptor<T> SkipDuplicates(bool? skipDuplicates = true) => Assign(a => a.SkipDuplicates = skipDuplicates);
 	}
 }

src/Tests/Search/Request/SuggestUsageTests.cs

@@ -42,6 +42,7 @@ public SuggestUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cl
 						  unicode_aware = false
 						},
 						size = 8,
+						skip_duplicates = true
 					  },
 					  prefix = Project.Instance.Name
 					} },
@@ -121,6 +122,7 @@ public SuggestUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cl
 					.Field(p => p.Suggest)
 					.Size(8)
 					.Prefix(Project.Instance.Name)
+					.SkipDuplicates()
 				)
 				.Phrase("my-phrase-suggest", ph => ph
 					.Collate(c => c
@@ -186,6 +188,7 @@ public SuggestUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cl
 							Analyzer = "simple",
 							Field = Field<Project>(p=>p.Suggest),
 							Size = 8,
+							SkipDuplicates = true
 						}
 					} },
 					{ "my-phrase-suggest", new SuggestBucket