Add circular reference validation rules in input types

src/HotChocolate/Core/src/Types/Configuration/Validation/InputObjectTypeValidationRule.cs

@@ -2,6 +2,9 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using HotChocolate.Language;
 using HotChocolate.Types;
 using static HotChocolate.Configuration.Validation.TypeValidationHelper;
 using static HotChocolate.Utilities.ErrorHelper;
@@ -15,18 +18,104 @@
         IReadOnlySchemaOptions options,
         ICollection<ISchemaError> errors)
     {
-        if (options.StrictValidation)
+        if (!options.StrictValidation)
         {
-            List<string>? names = null;
+            return;
+        }
+
+        List<string>? names = null;
+        CycleValidationContext cycleValidationContext = new()
+        {
+            Visited = new(),
+            CycleStartIndex = new(),
+            Errors = errors,
+            FieldPath = new(),
+        };
+
+        foreach (var type in typeSystemObjects)
+        {
+            if (type is not InputObjectType inputType)
+            {
+                continue;
+            }
+
+            EnsureTypeHasFields(inputType, errors);
+            EnsureFieldNamesAreValid(inputType, errors);
+            EnsureOneOfFieldsAreValid(inputType, errors, ref names);
+            EnsureFieldDeprecationIsValid(inputType, errors);
+            TryReachCycleRecursively(cycleValidationContext, inputType);
+
+            cycleValidationContext.CycleStartIndex.Clear();
+        }
+    }
+
+    private struct CycleValidationContext
+    {
+        public HashSet<InputObjectType> Visited { get; set; }
+        public Dictionary<InputObjectType, int> CycleStartIndex { get; set; }
+        public ICollection<ISchemaError> Errors { get; set; }
+        public List<string> FieldPath { get; set; }
+    }
+
+    // https://github.com/IvanGoncharov/graphql-js/blob/408bcda9c88df85e039f5d072011b1cb465fe830/src/type/validate.js#L535
+    private static void TryReachCycleRecursively(
+        in CycleValidationContext context,
+        InputObjectType type)
+    {
+        if (!context.Visited.Add(type))
+        {
+            return;
+        }
+
+        context.CycleStartIndex[type] = context.FieldPath.Count;
+
+        foreach (var field in type.Fields)
+        {
+            var unwrappedType = UnwrapCompletelyIfRequired(field.Type);
+            if (unwrappedType is not InputObjectType inputObjectType)
+            {
+                continue;
+            }
+
+            context.FieldPath.Add(field.Name);
+            if (context.CycleStartIndex.TryGetValue(inputObjectType, out var cycleIndex))
+            {
+                var cyclePath = context.FieldPath.Skip(cycleIndex);
+                context.Errors.Add(
+                    InputObjectMustNotHaveRecursiveNonNullableReferencesToSelf(type, cyclePath));
+            }
+            else
+            {
+                TryReachCycleRecursively(context, inputObjectType);
+            }
+            context.FieldPath.Pop();
+        }
+
+        context.CycleStartIndex.Remove(type);
+    }
+
+    private static IType? UnwrapCompletelyIfRequired(IType type)
+    {
+        while (true)
+        {
+            if (type.Kind == TypeKind.NonNull)
+            {
+                type = ((NonNullType)type).Type;
+            }
+            else
+            {
+                return null;
+            }
 
-            foreach (var type in typeSystemObjects)
+            switch (type.Kind)
             {
-                if (type is InputObjectType inputType)
+                case TypeKind.List:
                 {
-                    EnsureTypeHasFields(inputType, errors);
-                    EnsureFieldNamesAreValid(inputType, errors);
-                    EnsureOneOfFieldsAreValid(inputType, errors, ref names);
-                    EnsureFieldDeprecationIsValid(inputType, errors);
+                    return null;
+                }
+                default:
+                {
+                    return type;
                 }
             }
         }
@@ -37,30 +126,33 @@
         ICollection<ISchemaError> errors,
         ref List<string>? temp)
     {
-        if (type.Directives.ContainsDirective(WellKnownDirectives.OneOf))
+        if (!type.Directives.ContainsDirective(WellKnownDirectives.OneOf))
         {
-            temp ??= new List<string>();
+            return;
+        }
 
-            foreach (var field in type.Fields)
-            {
-                if (field.Type.Kind is TypeKind.NonNull || field.DefaultValue is not null)
-                {
-                    temp.Add(field.Name);
-                }
-            }
+        temp ??= new List<string>();
 
-            if (temp.Count > 0)
+        foreach (var field in type.Fields)
+        {
+            if (field.Type.Kind is TypeKind.NonNull || field.DefaultValue is not null)
             {
-                var fieldNames = new string[temp.Count];
+                temp.Add(field.Name);
+            }
+        }
 
-                for (var i = 0; i < temp.Count; i++)
-                {
-                    fieldNames[i] = temp[i];
-                }
+        if (temp.Count == 0)
+        {
+            return;
+        }
 
-                temp.Clear();
-                errors.Add(OneofInputObjectMustHaveNullableFieldsWithoutDefaults(type, fieldNames));
-            }
+        var fieldNames = new string[temp.Count];
+        for (var i = 0; i < temp.Count; i++)
+        {
+            fieldNames[i] = temp[i];
         }
+
+        temp.Clear();
+        errors.Add(OneofInputObjectMustHaveNullableFieldsWithoutDefaults(type, fieldNames));
     }
 }