Fix #8756 parse enum values in federation reference resolver

src/HotChocolate/ApolloFederation/src/ApolloFederation/Resolvers/ArgumentParser.cs

@@ -132,7 +132,26 @@ private static bool TryGetValue<T>(
             case SyntaxKind.IntValue:
             case SyntaxKind.FloatValue:
             case SyntaxKind.BooleanValue:
-                if (type.NamedType() is not ScalarType scalarType)
+                var namedType = type.NamedType();
+
+                if (namedType is EnumType stringEnumType
+                    && valueNode is StringValueNode stringValue
+                    && stringEnumType.TryGetRuntimeValue(stringValue.Value, out var enumValue))
+                {
+                    if (enumValue is T castedEnum)
+                    {
+                        value = castedEnum;
+                        return true;
+                    }
+
+                    if (DefaultTypeConverter.Default.TryConvert(typeof(T), enumValue, out var convertedEnum))
+                    {
+                        value = (T)convertedEnum;
+                        return true;
+                    }
+                }
+
+                if (namedType is not ScalarType scalarType)
                 {
                     break;
                 }

src/HotChocolate/ApolloFederation/test/ApolloFederation.Tests/Issue8756ReproTests.cs

@@ -0,0 +1,63 @@
+using HotChocolate.ApolloFederation.Resolvers;
+using HotChocolate.ApolloFederation.Types;
+using HotChocolate.Execution;
+using HotChocolate.Language;
+using Microsoft.Extensions.DependencyInjection;
+using static HotChocolate.ApolloFederation.TestHelper;
+
+namespace HotChocolate.ApolloFederation;
+
+public class Issue8756ReproTests
+{
+    [Fact]
+    public async Task Enum_Value_Is_Parsed_In_Reference_Resolver_When_Representation_Uses_String()
+    {
+        var schema = await new ServiceCollection()
+            .AddGraphQL()
+            .AddApolloFederation()
+            .AddQueryType<Issue8756Query>()
+            .BuildSchemaAsync();
+
+        var context = CreateResolverContext(schema);
+
+        var representations = new List<Representation>
+        {
+            new(
+                nameof(Issue8756Entity),
+                new ObjectValueNode(
+                    new ObjectFieldNode("id", "1"),
+                    new ObjectFieldNode("enumValue", "B")))
+        };
+
+        var result = await EntitiesResolver.ResolveAsync(schema, representations, context);
+
+        var entity = Assert.IsType<Issue8756Entity>(result[0]);
+        Assert.Equal(Issue8756Enum.B, entity.EnumValue);
+    }
+
+    public class Issue8756Query
+    {
+        public Issue8756Entity Issue8756Entity { get; set; } = null!;
+    }
+
+    [ReferenceResolver(EntityResolver = nameof(Resolve))]
+    public class Issue8756Entity
+    {
+        public string Id { get; set; } = null!;
+
+        public Issue8756Enum EnumValue { get; set; }
+
+        public static Issue8756Entity Resolve(string id, Issue8756Enum enumValue)
+            => new()
+            {
+                Id = id,
+                EnumValue = enumValue
+            };
+    }
+
+    public enum Issue8756Enum
+    {
+        A,
+        B
+    }
+}