Fix infinite recursion

src/compiler/NubLang/TypeChecking/Node/TypeNode.cs

@@ -177,19 +177,19 @@ public class StringTypeNode : ComplexTypeNode
 public class StructTypeNode(string name, IReadOnlyList<TypeNode> fields, IReadOnlyList<FuncTypeNode> functions, IReadOnlyList<InterfaceTypeNode> interfaceImplementations) : ComplexTypeNode
 {
     public string Name { get; } = name;
-    public IReadOnlyList<TypeNode> Fields { get; } = fields;
-    public IReadOnlyList<FuncTypeNode> Functions { get; } = functions;
-    public IReadOnlyList<InterfaceTypeNode> InterfaceImplementations { get; } = interfaceImplementations;
+    public IReadOnlyList<TypeNode> Fields { get; set; } = fields;
+    public IReadOnlyList<FuncTypeNode> Functions { get; set; } = functions;
+    public IReadOnlyList<InterfaceTypeNode> InterfaceImplementations { get; set; } = interfaceImplementations;
 
     public override string ToString() => Name;
     public override bool Equals(TypeNode? other) => other is StructTypeNode custom && Name == custom.Name;
     public override int GetHashCode() => HashCode.Combine(typeof(StructTypeNode), Name);
 }
 
-public class InterfaceTypeNode(string name, IReadOnlyList<FuncTypeNode> funcs) : ComplexTypeNode
+public class InterfaceTypeNode(string name, IReadOnlyList<FuncTypeNode> functions) : ComplexTypeNode
 {
     public string Name { get; } = name;
-    public IReadOnlyList<FuncTypeNode> Funcs { get; } = funcs;
+    public IReadOnlyList<FuncTypeNode> Functions { get; set; } = functions;
 
     public override string ToString() => Name;
     public override bool Equals(TypeNode? other) => other is InterfaceTypeNode custom && Name == custom.Name;

src/compiler/NubLang/TypeChecking/TypeChecker.cs

@@ -646,8 +646,15 @@ public sealed class TypeChecker
         };
     }
 
+    private readonly Dictionary<string, TypeNode> _typeCache = new();
+
     private TypeNode CheckCustomType(CustomTypeSyntax type)
     {
+        if (_typeCache.TryGetValue(type.Name, out var cachedType))
+        {
+            return cachedType;
+        }
+
         var structs = _definitionTable.LookupStruct(type.Name).ToArray();
         if (structs.Length > 0)
         {
@@ -658,6 +665,9 @@ public sealed class TypeChecker
 
             var @struct = structs[0];
 
+            var result = new StructTypeNode(type.Name, [], [], []);
+            _typeCache.Add(type.Name, result);
+
             var fields = @struct.Fields.Select(x => CheckType(x.Type)).ToList();
 
             var funcs = @struct.Functions
@@ -677,7 +687,10 @@ public sealed class TypeChecker
                 interfaceImplementations.Add(interfaceType);
             }
 
-            return new StructTypeNode(type.Name, fields, funcs, interfaceImplementations);
+            result.Fields = fields;
+            result.Functions = funcs;
+            result.InterfaceImplementations = interfaceImplementations;
+            return result;
         }
 
         var interfaces = _definitionTable.LookupInterface(type.Name).ToArray();
@@ -689,11 +702,16 @@ public sealed class TypeChecker
             }
 
             var @interface = interfaces[0];
+
+            var result = new InterfaceTypeNode(type.Name, []);
+            _typeCache.Add(type.Name, result);
+
             var functions = @interface.Functions
                 .Select(x => new FuncTypeNode(x.Signature.Parameters.Select(y => CheckType(y.Type)).ToList(), CheckType(x.Signature.ReturnType)))
                 .ToList();
 
-            return new InterfaceTypeNode(type.Name, functions);
+            result.Functions = functions;
+            return result;
         }
 
         throw new TypeCheckerException(Diagnostic.Error($"Type {type.Name} is not defined").Build());