Add key inferrence for lookups

src/HotChocolate/Core/src/Types/Execution/DependencyInjection/RequestExecutorBuilderExtensions.Composite.cs

@@ -33,6 +33,7 @@ public static IRequestExecutorBuilder AddSourceSchemaDefaults(
             o.ApplyShareableToPageInfo = true;
             o.ApplyShareableToNodeFields = true;
             o.ApplySerializeAsToScalars = true;
+            o.InferKeysFromLookups = true;
         });
     }
 }

src/HotChocolate/Core/src/Types/Execution/DependencyInjection/RequestExecutorServiceCollectionExtensions.cs

@@ -9,6 +9,7 @@
 using HotChocolate.Fetching;
 using HotChocolate.Language;
 using HotChocolate.Resolvers;
+using HotChocolate.Types.Composite;
 using HotChocolate.Validation;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.ObjectPool;
@@ -144,6 +145,7 @@ private static DefaultRequestExecutorBuilder CreateBuilder(
 
         builder.TryAddTypeInterceptor<DataLoaderRootFieldTypeInterceptor>();
         builder.TryAddTypeInterceptor<RequirementsTypeInterceptor>();
+        builder.TryAddTypeInterceptor<SourceSchemaKeyInferenceTypeInterceptor>();
 
         builder.AddDocumentCache();
 

src/HotChocolate/Core/src/Types/IReadOnlySchemaOptions.cs

@@ -244,4 +244,10 @@ public interface IReadOnlySchemaOptions
     /// Applies the @serializeAs directive to scalar types that specify a serialization format.
     /// </summary>
     bool ApplySerializeAsToScalars { get; }
+
+    /// <summary>
+    /// Infers @key directives from the arguments of @lookup fields so that the published
+    /// source schema describes the entity keys that the lookups resolve.
+    /// </summary>
+    bool InferKeysFromLookups { get; }
 }

src/HotChocolate/Core/src/Types/SchemaOptions.cs

@@ -195,6 +195,9 @@ public int OperationDocumentCacheSize
     /// <inheritdoc cref="IReadOnlySchemaOptions.ApplySerializeAsToScalars"/>
     public bool ApplySerializeAsToScalars { get; set; }
 
+    /// <inheritdoc cref="IReadOnlySchemaOptions.InferKeysFromLookups"/>
+    public bool InferKeysFromLookups { get; set; }
+
     /// <summary>
     /// Creates a mutable options object from a read-only options object.
     /// </summary>
@@ -238,6 +241,7 @@ public static SchemaOptions FromOptions(IReadOnlySchemaOptions options)
             ApplyShareableToPageInfo = options.ApplyShareableToPageInfo,
             ApplyShareableToConnections = options.ApplyShareableToConnections,
             ApplyShareableToNodeFields = options.ApplyShareableToNodeFields,
-            ApplySerializeAsToScalars = options.ApplySerializeAsToScalars
+            ApplySerializeAsToScalars = options.ApplySerializeAsToScalars,
+            InferKeysFromLookups = options.InferKeysFromLookups
         };
 }

src/HotChocolate/Core/src/Types/Types/Composite/Directives/EntityKey.cs

@@ -9,7 +9,7 @@ namespace HotChocolate.Types.Composite;
 /// an entity across different source schemas.
 /// </para>
 /// <para>
-/// directive @key(fields: FieldSelectionSet!) on OBJECT | INTERFACE
+/// directive @key(fields: FieldSelectionSet!) repeatable on OBJECT | INTERFACE
 /// </para>
 /// <para>
 /// <see href="https://graphql.github.io/composite-schemas-spec/draft/#sec--key"/>
@@ -19,7 +19,7 @@ namespace HotChocolate.Types.Composite;
     DirectiveNames.Key.Name,
     DirectiveLocation.Object
     | DirectiveLocation.Interface,
-    IsRepeatable = false)]
+    IsRepeatable = true)]
 [GraphQLDescription(
     """
     The @key directive is used to designate an entity's unique key,