Aligned to GraphQL Java Field Merging Rule

src/All.slnx

@@ -118,6 +118,7 @@
     <Project Path="HotChocolate/Core/test/Subscriptions.Redis.Tests/HotChocolate.Subscriptions.Redis.Tests.csproj" />
     <Project Path="HotChocolate/Core/test/Subscriptions.Tests/HotChocolate.Subscriptions.Tests.csproj" />
     <Project Path="HotChocolate/Core/test/Types.Analyzers.Tests/HotChocolate.Types.Analyzers.Tests.csproj" />
+    <Project Path="HotChocolate/Core/test/Types.Analyzer.Integration.Tests/HotChocolate.Types.Analyzer.Integration.Tests.csproj" />
     <Project Path="HotChocolate/Core/test/Types.CursorPagination.Tests/HotChocolate.Types.CursorPagination.Tests.csproj" />
     <Project Path="HotChocolate/Core/test/Types.Json.Tests/HotChocolate.Types.Json.Tests.csproj" />
     <Project Path="HotChocolate/Core/test/Types.Mutations.Tests/HotChocolate.Types.Mutations.Tests.csproj" />
@@ -130,9 +131,7 @@
     <Project Path="HotChocolate/Core/test/Types.Tests/HotChocolate.Types.Tests.csproj" />
     <Project Path="HotChocolate/Core/test/Utilities/HotChocolate.Tests.Utilities.csproj" />
     <Project Path="HotChocolate/Core/test/Validation.Tests/HotChocolate.Validation.Tests.csproj" />
-  </Folder>
-  <Folder Name="/HotChocolate/Core/test/Types.Analyzer.Integration.Tests/">
-    <Project Path="HotChocolate/Core/test/Types.Analyzer.Integration.Tests/HotChocolate.Types.Analyzers.Tests.csproj" />
+    <Project Path="HotChocolate/Core/test/Validation.Benchmarks/HotChocolate.Validation.Benchmarks.csproj" />
   </Folder>
   <Folder Name="/HotChocolate/CostAnalysis/" />
   <Folder Name="/HotChocolate/CostAnalysis/src/">

src/Directory.Packages.props

@@ -13,6 +13,7 @@
     <PackageVersion Include="Azure.Storage.Blobs" Version="12.23.0" />
     <PackageVersion Include="Basic.Reference.Assemblies.Net80" Version="1.7.8" />
     <PackageVersion Include="Basic.Reference.Assemblies.Net90" Version="1.7.8" />
+    <PackageVersion Include="BenchmarkDotNet" Version="0.14.0" />
     <PackageVersion Include="ChilliCream.Nitro.App" Version="$(NitroVersion)" />
     <PackageVersion Include="ChilliCream.Testing.Utilities" Version="0.2.0" />
     <PackageVersion Include="coverlet.collector" Version="6.0.2" />
@@ -132,4 +133,4 @@
     <PackageVersion Include="Roslynator.CodeAnalysis.Analyzers" Version="4.12.4" />
     <PackageVersion Include="Roslynator.Formatting.Analyzers" Version="4.12.4" />
   </ItemGroup>
-</Project>
+</Project>

src/HotChocolate/Core/HotChocolate.Core.slnx

@@ -80,8 +80,9 @@
     <Project Path="test/Types.Tests/HotChocolate.Types.Tests.csproj" />
     <Project Path="test/Utilities/HotChocolate.Tests.Utilities.csproj" />
     <Project Path="test/Validation.Tests/HotChocolate.Validation.Tests.csproj" />
+    <Project Path="test/Types.Analyzer.Integration.Tests/HotChocolate.Types.Analyzer.Integration.Tests.csproj" />
   </Folder>
-  <Folder Name="/test/Types.Analyzer.Integration.Tests/">
-    <Project Path="test/Types.Analyzer.Integration.Tests/HotChocolate.Types.Analyzers.Tests.csproj" />
+  <Folder Name="/test/Validation.Benchmarks/">
+    <Project Path="test/Validation.Benchmarks/HotChocolate.Validation.Benchmarks.csproj" />
   </Folder>
-</Solution>
+</Solution>

src/HotChocolate/Core/src/Validation/Extensions/ValidationBuilderExtensions.Rules.cs

@@ -121,6 +121,14 @@ public static IValidationBuilder AddDocumentRules(
     /// </summary>
     public static IValidationBuilder AddFieldRules(
         this IValidationBuilder builder)
+    {
+        return builder
+            .TryAddValidationRule<LeafFieldSelectionsRule>()
+            .TryAddValidationRule<OverlappingFieldsCanBeMergedRule>();
+    }
+
+    public static IValidationBuilder AddFieldRulesLegacy(
+        this IValidationBuilder builder)
     {
         return builder.TryAddValidationVisitor<FieldVisitor>();
     }

src/HotChocolate/Core/src/Validation/HotChocolate.Validation.csproj

@@ -4,7 +4,6 @@
     <PackageId>HotChocolate.Validation</PackageId>
     <AssemblyName>HotChocolate.Validation</AssemblyName>
     <RootNamespace>HotChocolate.Validation</RootNamespace>
-    <Description></Description>
   </PropertyGroup>
 
   <ItemGroup>
@@ -13,6 +12,7 @@
 
   <ItemGroup>
     <InternalsVisibleTo Include="HotChocolate.Validation.Tests" />
+    <InternalsVisibleTo Include="HotChocolate.Validation.Benchmarks" />
   </ItemGroup>
 
   <ItemGroup>

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

@@ -0,0 +1,94 @@
+using HotChocolate.Language;
+using HotChocolate.Types;
+
+namespace HotChocolate.Validation.Rules;
+
+internal sealed class LeafFieldSelectionsRule : IDocumentValidatorRule
+{
+    public ushort Priority => ushort.MaxValue;
+
+    public bool IsCacheable => true;
+
+    public void Validate(IDocumentValidatorContext context, DocumentNode document)
+    {
+        foreach (var operation in document.Definitions)
+        {
+            if(operation is not OperationDefinitionNode operationDef)
+            {
+                continue;
+            }
+
+            if (context.Schema.GetOperationType(operationDef.Operation) is { } rootType)
+            {
+                ValidateSelectionSet(context, operationDef.SelectionSet, rootType);
+            }
+        }
+    }
+
+    private void ValidateSelectionSet(IDocumentValidatorContext context, SelectionSetNode selectionSet, IType type)
+    {
+        foreach (var selection in selectionSet.Selections)
+        {
+            if (selection is FieldNode field)
+            {
+                ValidateField(context, field, type);
+            }
+            else if (selection is InlineFragmentNode inlineFrag)
+            {
+                var typeCondition = inlineFrag.TypeCondition is null
+                    ? type
+                    : context.Schema.GetType<INamedType>(inlineFrag.TypeCondition.Name.Value);
+                ValidateSelectionSet(context, inlineFrag.SelectionSet, typeCondition);
+            }
+            else if (selection is FragmentSpreadNode spread
+                && context.Fragments.TryGetValue(spread.Name.Value, out var frag))
+            {
+                if (context.VisitedFragments.Add(spread.Name.Value))
+                {
+                    var typeCondition = context.Schema.GetType<INamedType>(frag.TypeCondition.Name.Value);
+                    ValidateSelectionSet(context, frag.SelectionSet, typeCondition);
+                    context.VisitedFragments.Remove(spread.Name.Value);
+                }
+            }
+        }
+    }
+
+    private void ValidateField(IDocumentValidatorContext context, FieldNode field, IType parentType)
+    {
+        if (parentType is not IComplexOutputType complex ||
+            !complex.Fields.TryGetField(field.Name.Value, out var fieldDef))
+        {
+            // handled by other rules like KnownFieldNames
+            return;
+        }
+
+        var namedType = fieldDef.Type.NamedType();
+
+        if (namedType.IsLeafType())
+        {
+            if (field.SelectionSet is not null)
+            {
+                context.ReportError(
+                    ErrorBuilder.New()
+                        .SetMessage($"Field \"{field.Name.Value}\" must not have a selection since type \"{namedType.Name}\" has no subfields.")
+                        .AddLocation(field)
+                        .Build());
+            }
+        }
+        else
+        {
+            if (field.SelectionSet is null)
+            {
+                context.ReportError(
+                    ErrorBuilder.New()
+                        .SetMessage($"Field \"{field.Name.Value}\" of type \"{namedType.Name}\" must have a selection of subfields. Did you mean \"{field.Name.Value} {{ ... }}\"?")
+                        .AddLocation(field)
+                        .Build());
+            }
+            else
+            {
+                ValidateSelectionSet(context, field.SelectionSet, fieldDef.Type);
+            }
+        }
+    }
+}