Add support for inferrence of structs

src/HotChocolate/Core/src/Types/Internal/TypeDiscoveryInfo.cs

@@ -135,18 +135,38 @@ private static bool IsComplexTypeInternal(
         IExtendedType unresolvedType,
         bool isPublic)
     {
-        var isComplexType =
+        var isComplexClass =
             isPublic &&
             unresolvedType.Type.IsClass &&
             unresolvedType.Type != typeof(string);
 
-        if (!isComplexType && unresolvedType.IsGeneric)
+#if NET6_0_OR_GREATER
+        var isComplexValueType =
+            isPublic &&
+            unresolvedType.Type is
+            {
+                IsValueType: true,
+                IsPrimitive: false,
+                IsEnum: false,
+                IsByRefLike: false
+            };
+
+        if (isComplexValueType && unresolvedType.IsGeneric)
+        {
+            var typeDefinition = unresolvedType.Definition;
+            return typeDefinition == typeof(KeyValuePair<,>);
+        }
+
+        return isComplexClass || isComplexValueType;
+#else
+        if (!isComplexClass && unresolvedType.IsGeneric)
         {
             var typeDefinition = unresolvedType.Definition;
             return typeDefinition == typeof(KeyValuePair<,>);
         }
 
-        return isComplexType;
+        return isComplexClass;
+#endif
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]

src/HotChocolate/Core/test/Types.Tests/Configuration/SchemaTypeResolverTests.cs

@@ -34,6 +34,47 @@ public void InferObjectType(TypeContext context)
             });
     }
 
+    [InlineData(TypeContext.Output)]
+    [InlineData(TypeContext.None)]
+    [Theory]
+    public void InferObjectTypeFromStruct(TypeContext context)
+    {
+        // arrange
+        var descriptorContext = DescriptorContext.Create();
+        var typeReference = TypeReference.Create(TypeOf<BarStruct>(), context);
+
+        // act
+        var success = descriptorContext.TryInferSchemaType(typeReference, out var schemaTypes);
+
+        // assert
+        Assert.True(success);
+        Assert.Collection(schemaTypes,
+            type =>
+            {
+                Assert.Equal(TypeContext.Output, type.Context);
+                Assert.Equal(typeof(ObjectType<BarStruct>), ((ExtendedTypeReference)type).Type.Source);
+            });
+    }
+
+    [InlineData(TypeContext.Output)]
+    [InlineData(TypeContext.None)]
+    [Theory]
+    public void RejectRefStructAsObjectType(TypeContext context)
+    {
+        // arrange
+        var descriptorContext = DescriptorContext.Create();
+        var typeReference = TypeReference.Create(
+            _typeInspector.GetType(typeof(BarRefStruct)),
+            context);
+
+        // act
+        var success = descriptorContext.TryInferSchemaType(typeReference, out var schemaTypes);
+
+        // assert
+        Assert.False(success);
+        Assert.Null(schemaTypes);
+    }
+
     [InlineData(TypeContext.Output)]
     [InlineData(TypeContext.None)]
     [Theory]
@@ -54,7 +95,6 @@ public void InferInterfaceType(TypeContext context)
                 Assert.Equal(TypeContext.Output, type.Context);
                 Assert.Equal(typeof(InterfaceType<IBar>), ((ExtendedTypeReference)type).Type.Source);
             });
-
     }
 
     [Fact]
@@ -108,6 +148,16 @@ public class Bar
         public string Baz { get; }
     }
 
+    public struct BarStruct
+    {
+        public string Baz { get; }
+    }
+
+    public ref struct BarRefStruct
+    {
+        public string Baz { get; }
+    }
+
     public interface IBar
     {
         string Baz { get; }

src/HotChocolate/Core/test/Types.Tests/Configuration/TypeDiscoveryTests.cs

@@ -27,9 +27,20 @@ public void InferDateTimeFromModel()
             .MatchSnapshot();
     }
 
+    [Fact]
+    public void TypeDiscovery_Should_InferStructs()
+    {
+        SchemaBuilder.New()
+            .AddQueryType<QueryTypeWithStruct>()
+            .Create()
+            .Print()
+            .MatchSnapshot();
+    }
+
     public class QueryWithDateTime
     {
         public DateTimeOffset DateTimeOffset(DateTimeOffset time) => time;
+
         public DateTime DateTime(DateTime time) => time;
     }
 
@@ -50,8 +61,7 @@ protected override void Configure(IObjectTypeDescriptor descriptor)
 
     public class ModelType : ObjectType<Model>
     {
-        protected override void Configure(
-            IObjectTypeDescriptor<Model> descriptor)
+        protected override void Configure(IObjectTypeDescriptor<Model> descriptor)
         {
             descriptor.Field(t => t.Time)
                 .Type<NonNullType<DateTimeType>>();
@@ -64,9 +74,39 @@ protected override void Configure(
     public class Model
     {
         public string Foo { get; set; }
+
         public int Bar { get; set; }
+
         public bool Baz { get; set; }
+
         public DateTime Time { get; set; }
+
         public DateTime Date { get; set; }
     }
+
+    public struct InferStruct
+    {
+        public Guid Id { get; set; }
+
+        public int Number { get; set; }
+    }
+
+    public class QueryTypeWithStruct
+    {
+        public InferStruct Struct { get; set; }
+
+        public InferStruct? NullableStruct { get; set; }
+
+        public InferStruct[] StructArray { get; set; }
+
+        public InferStruct?[] NullableStructArray { get; set; }
+
+        public InferStruct[][] StructNestedArray { get; set; }
+
+        public InferStruct?[][] NullableStructNestedArray { get; set; }
+
+        public Guid ScalarGuid { get; set; }
+
+        public DateTime ScalarDateTime { get; set; }
+    }
 }

src/HotChocolate/Core/test/Types.Tests/Configuration/__snapshots__/TypeDiscoveryTests.TypeDiscovery_Should_InferStructs.snap

@@ -0,0 +1,27 @@
+schema {
+  query: QueryTypeWithStruct
+}
+
+type InferStruct {
+  id: UUID!
+  number: Int!
+}
+
+type QueryTypeWithStruct {
+  struct: InferStruct!
+  nullableStruct: InferStruct
+  structArray: [InferStruct!]
+  nullableStructArray: [InferStruct]
+  structNestedArray: [[InferStruct!]]
+  nullableStructNestedArray: [[InferStruct]]
+  scalarGuid: UUID!
+  scalarDateTime: DateTime!
+}
+
+"The `@specifiedBy` directive is used within the type system definition language to provide a URL for specifying the behavior of custom scalar definitions."
+directive @specifiedBy("The specifiedBy URL points to a human-readable specification. This field will only read a result for scalar types." url: String!) on SCALAR
+
+"The `DateTime` scalar represents an ISO-8601 compliant date time type."
+scalar DateTime @specifiedBy(url: "https:\/\/www.graphql-scalars.com\/date-time")
+
+scalar UUID @specifiedBy(url: "https:\/\/tools.ietf.org\/html\/rfc4122")