[Fusion] Fix introspection argument list misalignment

src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Introspection/__Directive.cs

@@ -154,20 +154,23 @@ public static void Arguments(FieldContext context)
         var count = includeDeprecated
             ? directiveDef.Arguments.Count
             : directiveDef.Arguments.Count(t => !t.IsDeprecated);
-        var list = context.FieldResult.CreateListValue(count);
+        using var list = context.FieldResult.CreateListValue(count).EnumerateArray().GetEnumerator();
 
-        var index = 0;
-        foreach (var element in list.EnumerateArray())
+        foreach (var argument in directiveDef.Arguments)
         {
-            var argument = directiveDef.Arguments[index++];
-
             if (!includeDeprecated && argument.IsDeprecated)
             {
                 continue;
             }
 
+            if (!list.MoveNext())
+            {
+                Debug.Fail("Expected enumerator of list value to be able to advance");
+                break;
+            }
+
             context.AddRuntimeResult(argument);
-            element.CreateObjectValue(context.Selection, context.IncludeFlags);
+            list.Current.CreateObjectValue(context.Selection, context.IncludeFlags);
         }
     }
 

src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Introspection/__Field.cs

@@ -77,20 +77,23 @@ public static void Arguments(FieldContext context)
         var count = includeDeprecated
             ? field.Arguments.Count
             : field.Arguments.Count(t => !t.IsDeprecated);
-        var list = context.FieldResult.CreateListValue(count);
+        using var list = context.FieldResult.CreateListValue(count).EnumerateArray().GetEnumerator();
 
-        var index = 0;
-        foreach (var element in list.EnumerateArray())
+        foreach (var argument in field.Arguments)
         {
-            var argument = field.Arguments[index++];
-
             if (!includeDeprecated && argument.IsDeprecated)
             {
                 continue;
             }
 
+            if (!list.MoveNext())
+            {
+                Debug.Fail("Expected enumerator of list value to be able to advance");
+                break;
+            }
+
             context.AddRuntimeResult(argument);
-            element.CreateObjectValue(context.Selection, context.IncludeFlags);
+            list.Current.CreateObjectValue(context.Selection, context.IncludeFlags);
         }
     }
 

src/HotChocolate/Fusion/test/Fusion.Execution.Tests/Execution/Introspection/FieldArgumentsIntrospectionTests.cs

@@ -0,0 +1,75 @@
+using HotChocolate.Execution;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace HotChocolate.Fusion.Execution.Introspection;
+
+public sealed class FieldArgumentsIntrospectionTests : FusionTestBase
+{
+    // __Field.args excludes deprecated arguments by default and returns the remaining
+    // arguments without leaving gaps, even when a deprecated argument precedes a
+    // non-deprecated one.
+    [Fact]
+    public async Task Fields_Args_ExcludeDeprecatedArguments()
+    {
+        // arrange
+        var services = new ServiceCollection();
+        services.AddHttpClient();
+        services
+            .AddGraphQLGateway()
+            .AddInMemoryConfiguration(
+                ComposeSchemaDocument(
+                    """
+                    type Query {
+                        field(
+                            deprecatedArg: String @deprecated(reason: "old")
+                            normalArg: String
+                        ): String
+                    }
+                    """))
+            .UseDefaultPipeline();
+
+        var executor = await services
+            .BuildServiceProvider()
+            .GetRequestExecutorAsync(cancellationToken: TestContext.Current.CancellationToken);
+
+        // act
+        var result = await executor.ExecuteAsync(
+            OperationRequestBuilder.New()
+                .SetDocument(
+                    """
+                    {
+                        __type(name: "Query") {
+                            fields {
+                                name
+                                args {
+                                    name
+                                }
+                            }
+                        }
+                    }
+                    """)
+                .Build(),
+            TestContext.Current.CancellationToken);
+
+        // assert
+        result.MatchInlineSnapshot(
+            """
+            {
+              "data": {
+                "__type": {
+                  "fields": [
+                    {
+                      "name": "field",
+                      "args": [
+                        {
+                          "name": "normalArg"
+                        }
+                      ]
+                    }
+                  ]
+                }
+              }
+            }
+            """);
+    }
+}