Fix composite field must have selection set rule

src/HotChocolate/Core/src/Validation/Rules/LeafFieldSelectionsRule.cs

@@ -80,7 +80,9 @@ private void ValidateField(
         FieldNode field,
         IType parentType)
     {
-        if (parentType is not IComplexTypeDefinition complex
+        var namedParentType = parentType.NamedType();
+
+        if (namedParentType is not IComplexTypeDefinition complex
             || !complex.Fields.TryGetField(field.Name.Value, out var fieldDef))
         {
             // handled by other rules like KnownFieldNames

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/FusionTestBase.cs

@@ -21,6 +21,7 @@
 using Microsoft.AspNetCore.TestHost;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Options;
 using Xunit.Sdk;
 
@@ -36,7 +37,8 @@ protected async Task<Gateway> CreateCompositeSchemaAsync(
         Action<IServiceCollection>? configureServices = null,
         Action<IApplicationBuilder>? configureApplication = null,
         Action<IFusionGatewayBuilder>? configureGatewayBuilder = null,
-        [StringSyntax("json")] string? gatewaySettings = null)
+        [StringSyntax("json")] string? gatewaySettings = null,
+        string? environmentName = "Development")
     {
         var sourceSchemas = new List<SourceSchemaText>();
         var gatewayServices = new ServiceCollection();
@@ -181,7 +183,8 @@ protected async Task<Gateway> CreateCompositeSchemaAsync(
 
                 configureServices?.Invoke(services);
             },
-            configureApplication);
+            configureApplication,
+            environmentName);
 
         return new Gateway(gatewayTestServer, sourceSchemas, interactions);
 

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/IntrospectionTests.cs

@@ -358,6 +358,76 @@ public async Task Typename_On_Introspection_Types()
         await MatchSnapshotAsync(gateway, request, result);
     }
 
+    [Fact]
+    public async Task Introspection_OfType_Without_SelectionSet()
+    {
+        // arrange
+        using var server1 = CreateSourceSchema(
+            "A",
+            TestSchema);
+
+        using var gateway = await CreateCompositeSchemaAsync(
+        [
+            ("A", server1)
+        ]);
+
+        // act
+        using var client = GraphQLHttpClient.Create(gateway.CreateClient());
+
+        var request = new OperationRequest(
+            """
+            {
+              __schema {
+                types {
+                  ofType
+                }
+              }
+            }
+            """);
+
+        using var result = await client.PostAsync(
+            request,
+            new Uri("http://localhost:5000/graphql"));
+
+        // assert
+        await MatchSnapshotAsync(gateway, request, result);
+    }
+
+    [Fact]
+    public async Task Introspection_Field_Type_Without_SelectionSet()
+    {
+        // arrange
+        using var server1 = CreateSourceSchema(
+            "A",
+            TestSchema);
+
+        using var gateway = await CreateCompositeSchemaAsync(
+        [
+            ("A", server1)
+        ]);
+
+        // act
+        using var client = GraphQLHttpClient.Create(gateway.CreateClient());
+
+        var request = new OperationRequest(
+            """
+            {
+              __type(name: "Query") {
+                fields {
+                  type
+                }
+              }
+            }
+            """);
+
+        using var result = await client.PostAsync(
+            request,
+            new Uri("http://localhost:5000/graphql"));
+
+        // assert
+        await MatchSnapshotAsync(gateway, request, result);
+    }
+
     [Theory]
     [InlineData("SchemaCapabilitiesQuery")]
     [InlineData("InputValueCapabilitiesQuery")]

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/TestServerSession.cs

@@ -13,13 +13,19 @@
 
     public TestServer CreateServer(
         Action<IServiceCollection> configureServices,
-        Action<IApplicationBuilder> configureApplication)
+        Action<IApplicationBuilder> configureApplication,
+        string? environmentName = null)
     {
         var builder = new WebHostBuilder()
             .Configure(configureApplication)
             .ConfigureServices(configureServices);
 
+        if (environmentName is not null)
+        {
+            builder.UseEnvironment(environmentName);
+        }
+
         var server = new TestServer(builder);
 
         if (!_cleanupPipeline.Writer.TryWrite(server))
         {

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/__snapshots__/IntrospectionTests.Introspection_Field_Type_Without_SelectionSet.yaml

@@ -0,0 +1,115 @@
+title: Introspection_Field_Type_Without_SelectionSet
+request:
+  document: |
+    {
+      __type(name: "Query") {
+        fields {
+          type
+        }
+      }
+    }
+response:
+  body: |
+    {
+      "errors": [
+        {
+          "message": "Field \u0022type\u0022 of type \u0022__Type!\u0022 must have a selection of subfields. Did you mean \u0022type { ... }\u0022?",
+          "locations": [
+            {
+              "line": 4,
+              "column": 7
+            }
+          ],
+          "extensions": {
+            "declaringType": "__Field",
+            "field": "type",
+            "type": "__Type!",
+            "responseName": "type",
+            "specifiedBy": "https://spec.graphql.org/September2025/#sec-Field-Selections"
+          }
+        }
+      ]
+    }
+sourceSchemas:
+  - name: A
+    schema: |
+      "Schema description"
+      schema @test(arg: "value") {
+        query: Query
+        mutation: Mutation
+        subscription: Subscription
+      }
+
+      interface Node @test(arg: "value") {
+        id: ID!
+      }
+
+      "Interface description"
+      interface Votable implements Node {
+        "Interface field description"
+        id: ID!
+      }
+
+      type Mutation @test(arg: "value") {
+        postReview(input: PostReviewInput): Review @test(arg: "value")
+      }
+
+      type Post implements Votable & Node @key(fields: "id") {
+        id: ID!
+        postKind: PostKind @shareable
+        location: String @inaccessible
+      }
+
+      "Object type description"
+      type Query @test(arg: "value") {
+        "Object field description"
+        posts(
+          "Argument description"
+          filter: PostsFilter
+          first: Int! = 5 @test(arg: "value")
+          hidden: Boolean @deprecated(reason: "No longer supported")
+        ): [Post]
+        userCreation: UserCreation
+        votables: [Votable]! @deprecated(reason: "No longer supported")
+        postById(postId: ID! @is(field: "id")): Post @lookup
+        node(id: ID!): Node @lookup
+      }
+
+      type Review implements Votable & Node @test(arg: "value") {
+        id: ID!
+      }
+
+      type Subscription @test(arg: "value") {
+        onNewReview: Review
+      }
+
+      "Union description"
+      union UserCreation @test(arg: "value") = Post | Review
+
+      input PostReviewInput @oneOf {
+        scalar: String @deprecated(reason: "No longer supported")
+        pros: [PostReviewPro]
+      }
+
+      input PostReviewPro {
+        scalar: Int!
+      }
+
+      "Input object type description"
+      input PostsFilter @test(arg: "value") {
+        "Input field description"
+        scalar: String = "test" @test(arg: "value")
+      }
+
+      "Enum description"
+      enum PostKind @test(arg: "value") {
+        "Enum value description"
+        STORY @test(arg: "value")
+        PHOTO @deprecated(reason: "No longer supported")
+      }
+
+      "The `@oneOf` directive is used within the type system definition language to indicate that an Input Object is a OneOf Input Object."
+      directive @oneOf on INPUT_OBJECT
+
+      "Directive description"
+      directive @test("Directive argument description" arg: String! = "default") repeatable on QUERY | MUTATION | SUBSCRIPTION | FIELD | FRAGMENT_DEFINITION | FRAGMENT_SPREAD | INLINE_FRAGMENT | VARIABLE_DEFINITION | SCHEMA | SCALAR | OBJECT | FIELD_DEFINITION | ARGUMENT_DEFINITION | INTERFACE | UNION | ENUM | ENUM_VALUE | INPUT_OBJECT | INPUT_FIELD_DEFINITION

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/__snapshots__/IntrospectionTests.Introspection_OfType_Without_SelectionSet.yaml

@@ -0,0 +1,115 @@
+title: Introspection_OfType_Without_SelectionSet
+request:
+  document: |
+    {
+      __schema {
+        types {
+          ofType
+        }
+      }
+    }
+response:
+  body: |
+    {
+      "errors": [
+        {
+          "message": "Field \u0022ofType\u0022 of type \u0022__Type\u0022 must have a selection of subfields. Did you mean \u0022ofType { ... }\u0022?",
+          "locations": [
+            {
+              "line": 4,
+              "column": 7
+            }
+          ],
+          "extensions": {
+            "declaringType": "__Type",
+            "field": "ofType",
+            "type": "__Type",
+            "responseName": "ofType",
+            "specifiedBy": "https://spec.graphql.org/September2025/#sec-Field-Selections"
+          }
+        }
+      ]
+    }
+sourceSchemas:
+  - name: A
+    schema: |
+      "Schema description"
+      schema @test(arg: "value") {
+        query: Query
+        mutation: Mutation
+        subscription: Subscription
+      }
+
+      interface Node @test(arg: "value") {
+        id: ID!
+      }
+
+      "Interface description"
+      interface Votable implements Node {
+        "Interface field description"
+        id: ID!
+      }
+
+      type Mutation @test(arg: "value") {
+        postReview(input: PostReviewInput): Review @test(arg: "value")
+      }
+
+      type Post implements Votable & Node @key(fields: "id") {
+        id: ID!
+        postKind: PostKind @shareable
+        location: String @inaccessible
+      }
+
+      "Object type description"
+      type Query @test(arg: "value") {
+        "Object field description"
+        posts(
+          "Argument description"
+          filter: PostsFilter
+          first: Int! = 5 @test(arg: "value")
+          hidden: Boolean @deprecated(reason: "No longer supported")
+        ): [Post]
+        userCreation: UserCreation
+        votables: [Votable]! @deprecated(reason: "No longer supported")
+        postById(postId: ID! @is(field: "id")): Post @lookup
+        node(id: ID!): Node @lookup
+      }
+
+      type Review implements Votable & Node @test(arg: "value") {
+        id: ID!
+      }
+
+      type Subscription @test(arg: "value") {
+        onNewReview: Review
+      }
+
+      "Union description"
+      union UserCreation @test(arg: "value") = Post | Review
+
+      input PostReviewInput @oneOf {
+        scalar: String @deprecated(reason: "No longer supported")
+        pros: [PostReviewPro]
+      }
+
+      input PostReviewPro {
+        scalar: Int!
+      }
+
+      "Input object type description"
+      input PostsFilter @test(arg: "value") {
+        "Input field description"
+        scalar: String = "test" @test(arg: "value")
+      }
+
+      "Enum description"
+      enum PostKind @test(arg: "value") {
+        "Enum value description"
+        STORY @test(arg: "value")
+        PHOTO @deprecated(reason: "No longer supported")
+      }
+
+      "The `@oneOf` directive is used within the type system definition language to indicate that an Input Object is a OneOf Input Object."
+      directive @oneOf on INPUT_OBJECT
+
+      "Directive description"
+      directive @test("Directive argument description" arg: String! = "default") repeatable on QUERY | MUTATION | SUBSCRIPTION | FIELD | FRAGMENT_DEFINITION | FRAGMENT_SPREAD | INLINE_FRAGMENT | VARIABLE_DEFINITION | SCHEMA | SCALAR | OBJECT | FIELD_DEFINITION | ARGUMENT_DEFINITION | INTERFACE | UNION | ENUM | ENUM_VALUE | INPUT_OBJECT | INPUT_FIELD_DEFINITION