[Backport 7.x] Support case_insensitive on term-based queries

src/Nest/QueryDsl/Span/Term/SpanTermQuery.cs

@@ -9,18 +9,33 @@ namespace Nest
 {
 	[InterfaceDataContract]
 	[JsonFormatter(typeof(FieldNameQueryFormatter<SpanTermQuery, ISpanTermQuery>))]
-	public interface ISpanTermQuery : ITermQuery, ISpanSubQuery { }
+	public interface ISpanTermQuery : ISpanSubQuery, IFieldNameQuery
+	{
+		[DataMember(Name = "value")]
+		[JsonFormatter(typeof(SourceWriteFormatter<object>))]
+		object Value { get; set; }
+	}
 
 	[DataContract]
 	public class SpanTermQuery : FieldNameQueryBase, ISpanTermQuery
 	{
 		public object Value { get; set; }
-
-		protected override bool Conditionless => TermQuery.IsConditionless(this);
+		
+		protected override bool Conditionless => IsConditionless(this);
 
 		internal override void InternalWrapInContainer(IQueryContainer c) => c.SpanTerm = this;
+
+		internal static bool IsConditionless(ISpanTermQuery q) => q.Value == null || q.Value.ToString().IsNullOrEmpty() || q.Field.IsConditionless();
 	}
 
-	public class SpanTermQueryDescriptor<T> : TermQueryDescriptorBase<SpanTermQueryDescriptor<T>, ISpanTermQuery, T>, ISpanTermQuery
-		where T : class { }
+	public class SpanTermQueryDescriptor<T> : FieldNameQueryDescriptorBase<SpanTermQueryDescriptor<T>, ISpanTermQuery, T>, ISpanTermQuery
+		where T : class
+	{
+		protected override bool Conditionless => SpanTermQuery.IsConditionless(this);
+
+		object ISpanTermQuery.Value { get; set; }
+
+		public SpanTermQueryDescriptor<T> Value(object value) =>
+			Assign(value, (a, v) => a.Value = v);
+	}
 }

src/Nest/QueryDsl/TermLevel/Prefix/PrefixQuery.cs

@@ -20,6 +20,7 @@ public class PrefixQuery : FieldNameQueryBase, IPrefixQuery
 	{
 		public MultiTermQueryRewrite Rewrite { get; set; }
 		public object Value { get; set; }
+		public bool? CaseInsensitive { get; set; }
 		protected override bool Conditionless => TermQuery.IsConditionless(this);
 
 		internal override void InternalWrapInContainer(IQueryContainer c) => c.Prefix = this;

src/Nest/QueryDsl/TermLevel/Term/TermQuery.cs

@@ -14,12 +14,17 @@ public interface ITermQuery : IFieldNameQuery
 		[DataMember(Name = "value")]
 		[JsonFormatter(typeof(SourceWriteFormatter<object>))]
 		object Value { get; set; }
+
+		[DataMember(Name = "case_insensitive")]
+		bool? CaseInsensitive { get; set; }
 	}
 
 	[DataContract]
 	public class TermQuery : FieldNameQueryBase, ITermQuery
 	{
 		public object Value { get; set; }
+
+		public bool? CaseInsensitive { get; set; }
 
 		protected override bool Conditionless => IsConditionless(this);
 
@@ -37,12 +42,19 @@ public abstract class TermQueryDescriptorBase<TDescriptor, TInterface, T>
 	{
 		protected override bool Conditionless => TermQuery.IsConditionless(this);
 		object ITermQuery.Value { get; set; }
+		bool? ITermQuery.CaseInsensitive { get; set; }
 
 		public TDescriptor Value(object value)
 		{
 			Self.Value = value;
 			return (TDescriptor)this;
 		}
+
+		public TDescriptor CaseInsensitive(bool? caseInsensitive = true)
+		{
+			Self.CaseInsensitive = caseInsensitive;
+			return (TDescriptor)this;
+		}
 	}
 
 	public class TermQueryDescriptor<T> : TermQueryDescriptorBase<TermQueryDescriptor<T>, ITermQuery, T>

src/Nest/QueryDsl/TermLevel/Wildcard/WildcardQuery.cs

@@ -27,6 +27,7 @@ public class WildcardQuery : FieldNameQueryBase, IWildcardQuery
 	{
 		public MultiTermQueryRewrite Rewrite { get; set; }
 		public object Value { get; set; }
+		public bool? CaseInsensitive { get; set; }
 		protected override bool Conditionless => TermQuery.IsConditionless(this);
 
 		internal override void InternalWrapInContainer(IQueryContainer c) => c.Wildcard = this;

tests/Tests/QueryDsl/TermLevel/Term/TermQueryUsageTests.cs

@@ -104,4 +104,61 @@ protected override QueryContainer QueryFluent(QueryContainerDescriptor<Project>
 				.Value(string.Empty)
 			);
 	}
+
+	//hide
+	[SkipVersion("<7.10.0", "Case insensitive flag added in 7.10.0")]
+	public class TermQueryWithCaseInsensitiveUsageTests : QueryDslUsageTestsBase
+	{
+		public TermQueryWithCaseInsensitiveUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cluster, usage) { }
+
+		protected override ConditionlessWhen ConditionlessWhen => new ConditionlessWhen<ITermQuery>(q => q.Term)
+		{
+			q => q.Field = null,
+			q => q.Value = "  ",
+			q => q.Value = null
+		};
+
+		protected override QueryContainer QueryInitializer => new TermQuery
+		{
+			Name = "named_query",
+			Boost = 1.1,
+			Field = "description",
+			Value = "project description",
+			CaseInsensitive = true
+		};
+
+		protected override object QueryJson => new
+		{
+			term = new
+			{
+				description = new
+				{
+					_name = "named_query",
+					boost = 1.1,
+					value = "project description",
+					case_insensitive = true
+				}
+			}
+		};
+
+		protected override QueryContainer QueryFluent(QueryContainerDescriptor<Project> q) => q
+			.Term(c => c
+				.Name("named_query")
+				.Boost(1.1)
+				.Field(p => p.Description)
+				.Value("project description")
+				.CaseInsensitive(true)
+			);
+
+		//hide
+		[U]
+		public void DeserializeShortForm()
+		{
+			using var stream = new MemoryStream(ShortFormQuery);
+			var query = Client.RequestResponseSerializer.Deserialize<ITermQuery>(stream);
+			query.Should().NotBeNull();
+			query.Field.Should().Be(new Field("description"));
+			query.Value.Should().Be("project description");
+		}
+	}
 }