Make amendments following feedback.

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/PreMergeValidation/Rules/ExternalArgumentDefaultMismatchRule.cs

@@ -1,5 +1,6 @@
 using System.Collections.Immutable;
 using HotChocolate.Fusion.Events;
+using HotChocolate.Language;
 using static HotChocolate.Fusion.Logging.LogEntryHelper;
 
 namespace HotChocolate.Fusion.PreMergeValidation.Rules;
@@ -29,28 +30,19 @@ public void Handle(OutputFieldGroupEvent @event, CompositionContext context)
 
         var argumentNames = fieldGroup
             .SelectMany(i => i.Field.Arguments, (_, arg) => arg.Name)
-            .ToHashSet();
+            .ToImmutableHashSet();
 
         foreach (var argumentName in argumentNames)
         {
             var arguments = fieldGroup
-                .Select(i => i.Field.Arguments[argumentName])
+                .SelectMany(i => i.Field.Arguments.Where(a => a.Name == argumentName))
                 .ToImmutableArray();
 
             var defaultValue = arguments[0].DefaultValue;
 
             foreach (var argument in arguments)
             {
-                var currentDefaultValue = argument.DefaultValue;
-                var match = (currentDefaultValue, defaultValue) switch
-                {
-                    (null, null) => true,
-                    (not null, null) => false,
-                    (null, not null) => false,
-                    _ => currentDefaultValue.Value!.Equals(defaultValue.Value)
-                };
-
-                if (!match)
+                if (!SyntaxComparer.BySyntax.Equals(argument.DefaultValue, defaultValue))
                 {
                     context.Log.Write(
                         ExternalArgumentDefaultMismatch(argumentName, fieldName, typeName));

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/Properties/CompositionResources.resx

@@ -1,8 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <root>
-  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
-              xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
     <xsd:element name="root" msdata:IsDataSet="true">
 
     </xsd:element>
@@ -14,14 +13,10 @@
     <value>1.3</value>
   </resheader>
   <resheader name="reader">
-    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=2.0.0.0, Culture=neutral,
-      PublicKeyToken=b77a5c561934e089
-    </value>
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
   </resheader>
   <resheader name="writer">
-    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=2.0.0.0, Culture=neutral,
-      PublicKeyToken=b77a5c561934e089
-    </value>
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
   </resheader>
   <data name="ErrorHelper_PreMergeValidationFailed" xml:space="preserve">
     <value>Pre-merge validation failed. View the composition log for details.</value>

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/SourceSchemaMerger.cs

@@ -47,6 +47,7 @@ private CompositionResult<SchemaDefinition> MergeSchemaDefinitions(CompositionCo
     private static readonly List<object> _preMergeValidationRules =
     [
         new DisallowedInaccessibleElementsRule(),
+        new ExternalArgumentDefaultMismatchRule(),
         new ExternalMissingOnBaseRule(),
         new OutputFieldTypesMergeableRule()
     ];