Source-generated scan pass for SGen binary serialization

Implements a fully source-generated scan pass for duplicate/reference tracking in SGen binary serialization. The generator now emits ScanObject and ScanForDuplicates methods for each writer, handling null/depth checks, slot-based ref tracking (by Id or object hash), and recursive property scanning (strings, complex types, collections). String interning and reference tracking are feature-flagged via attributes. The runtime scan path now delegates to generated code when available, eliminating reflection and delegate overhead. Adds slot-based IdentityMap arrays to the serialization context for efficient duplicate detection. Also updates metadata, attributes, and test stubs to support these features.

AyCode.Core.Serializers.SourceGenerator/AcBinarySourceGenerator.cs

@@ -80,6 +80,7 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
                 bool hasGenWriter = false;
                 bool propTypeIsIId = false;
                 string? writerClassName = null;
+                string? propIdTypeName = null;
                 int childTypeNameHash = 0;
                 int[]? childPropertyHashes = null;
                 if (kind == PropertyTypeKind.Complex)
@@ -95,9 +96,13 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
 
                     if (hasGenWriter)
                     {
-                        propTypeIsIId = resolvedType.AllInterfaces.Any(i =>
+                        var iidIface = resolvedType.AllInterfaces.FirstOrDefault(i =>
                             i.IsGenericType &&
                             i.OriginalDefinition.ToDisplayString() == "AyCode.Core.Interfaces.IId<T>");
+                        propTypeIsIId = iidIface != null;
+                        if (iidIface != null)
+                            propIdTypeName = iidIface.TypeArguments[0].ToDisplayString();
+
                         // Writer class: {Namespace}.{FlatName}_GeneratedWriter
                         var flatName = BuildFlatName((INamedTypeSymbol)resolvedType);
                         var ns = resolvedType.ContainingNamespace.IsGlobalNamespace
@@ -118,6 +123,7 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
                 bool elemHasGenWriter = false;
                 bool elemIsIId = false;
                 string? elemWriterClassName = null;
+                string? elemIdTypeName = null;
                 string? collKind = null;
                 string? elemFullTypeName = null;
                 int elementTypeNameHash = 0;
@@ -160,9 +166,13 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
                                 a.AttributeClass?.ToDisplayString() == AttributeName);
                             if (elemHasGenWriter)
                             {
-                                elemIsIId = resolvedElem.AllInterfaces.Any(ifc =>
+                                var elemIidIface = resolvedElem.AllInterfaces.FirstOrDefault(ifc =>
                                     ifc.IsGenericType &&
                                     ifc.OriginalDefinition.ToDisplayString() == "AyCode.Core.Interfaces.IId<T>");
+                                elemIsIId = elemIidIface != null;
+                                if (elemIidIface != null)
+                                    elemIdTypeName = elemIidIface.TypeArguments[0].ToDisplayString();
+
                                 var elemFlatName = BuildFlatName((INamedTypeSymbol)resolvedElem);
                                 var ens = resolvedElem.ContainingNamespace.IsGlobalNamespace
                                     ? string.Empty : resolvedElem.ContainingNamespace.ToDisplayString();
@@ -184,17 +194,24 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
                     typeNameForTypeof,
                     kind,
                     p.Type.NullableAnnotation == NullableAnnotation.Annotated || IsNullableVT(p.Type),
-                    stringInternAttr, hasGenWriter, propTypeIsIId, writerClassName,
+                    stringInternAttr, hasGenWriter, propTypeIsIId, writerClassName, propIdTypeName,
-                    elemKind, elemHasGenWriter, elemIsIId, elemWriterClassName, collKind, elemFullTypeName,
+                    elemKind, elemHasGenWriter, elemIsIId, elemWriterClassName, elemIdTypeName, collKind, elemFullTypeName,
                     childTypeNameHash, childPropertyHashes,
                     elementTypeNameHash, elementPropertyHashes));
             }
         }
 
         // IId<T>: Id first (index 0), then alphabetical — matches runtime TypeMetadataBase ordering
-        var isIId = typeSymbol.AllInterfaces.Any(i =>
+        var isIId = false;
+        string? idTypeName = null;
+        var iidInterface = typeSymbol.AllInterfaces.FirstOrDefault(i =>
             i.IsGenericType &&
             i.OriginalDefinition.ToDisplayString() == "AyCode.Core.Interfaces.IId<T>");
+        if (iidInterface != null)
+        {
+            isIId = true;
+            idTypeName = iidInterface.TypeArguments[0].ToDisplayString();
+        }
 
         if (isIId)
             properties.Sort((a, b) =>
@@ -210,7 +227,7 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
         var className = BuildFlatName(typeSymbol);
         var typeNameHash = ComputeFnvHash(typeSymbol.Name);
         var propertyNameHashes = properties.Select(prop => ComputeFnvHash(prop.Name)).ToArray();
-        return new SerializableClassInfo(namespaceName, className, typeSymbol.ToDisplayString(), properties, typeNameHash, propertyNameHashes);
+        return new SerializableClassInfo(namespaceName, className, typeSymbol.ToDisplayString(), properties, isIId, idTypeName, typeNameHash, propertyNameHashes);
     }
 
     private static void Execute(ImmutableArray<SerializableClassInfo?> classes, SourceProductionContext context)
@@ -227,14 +244,13 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
 
     private static string GenWriter(SerializableClassInfo ci)
     {
-        var sb = new StringBuilder(2048);
+        var sb = new StringBuilder(4096);
         sb.AppendLine("// <auto-generated/>");
         sb.AppendLine("#nullable enable");
         sb.AppendLine("using System.Runtime.CompilerServices;");
         sb.AppendLine("using AyCode.Core.Serializers.Binaries;");
-        // ReferenceHandlingMode is needed when any Complex/Collection property has direct object write
+        // ReferenceHandlingMode is needed for ScanObject self ref tracking and direct object write/scan
-        if (ci.Properties.Any(p => p.HasGeneratedWriter || p.ElementHasGeneratedWriter))
+        sb.AppendLine("using AyCode.Core.Serializers;");
-            sb.AppendLine("using AyCode.Core.Serializers;");
         sb.AppendLine();
         if (!string.IsNullOrEmpty(ci.Namespace))
             sb.AppendLine($"namespace {ci.Namespace};");
@@ -243,6 +259,7 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
         sb.AppendLine("{");
         sb.AppendLine($"    internal static readonly {ci.ClassName}_GeneratedWriter Instance = new();");
         sb.AppendLine($"    internal static readonly int s_metadataSlot = AcBinarySerializer.AllocateMetadataSlot();");
+        sb.AppendLine($"    internal static readonly int s_trackingSlot = AcBinarySerializer.AllocateTrackingSlot();");
         sb.AppendLine($"    internal static readonly int s_typeNameHash = {ci.TypeNameHash};");
         sb.Append(    $"    internal static readonly int[] s_propertyHashes = new int[] {{ ");
         sb.Append(string.Join(", ", ci.PropertyNameHashes));
@@ -259,10 +276,108 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
         }
 
         sb.AppendLine("    }");
+        sb.AppendLine();
+
+        // ScanObject — full scan pass (null/depth + self ref tracking + property scan)
+        GenScanProperties(sb, ci);
+
+        sb.AppendLine();
+
+        // ScanForDuplicates — instance method on IGeneratedBinaryWriter, called from Serialize
+        sb.AppendLine("    public void ScanForDuplicates<TOutput>(object value, AcBinarySerializer.BinarySerializationContext<TOutput> context)");
+        sb.AppendLine("        where TOutput : struct, IBinaryOutputBase");
+        sb.AppendLine("    {");
+        sb.AppendLine("        if (!context.HasCaching) return;");
+        sb.AppendLine("        ScanObject(value, context, 0);");
+        sb.AppendLine("        context.SortWritePlan();");
+        sb.AppendLine("    }");
+
         sb.AppendLine("}");
         return sb.ToString();
     }
 
+    /// <summary>
+    /// Generates the ScanObject method — full scan pass entry point for this type.
+    /// Includes: null/depth check, self ref tracking (IId or All mode), property scan.
+    /// Only emits code for reference properties (strings + complex types) — primitives are skipped.
+    /// </summary>
+    private static void GenScanProperties(StringBuilder sb, SerializableClassInfo ci)
+    {
+        sb.AppendLine("    public void ScanObject<TOutput>(object value, AcBinarySerializer.BinarySerializationContext<TOutput> context, int depth) where TOutput : struct, IBinaryOutputBase");
+        sb.AppendLine("    {");
+
+        // Null/depth guard — matches runtime ScanValue entry
+        sb.AppendLine("        if (value == null || depth > context.MaxDepth) return;");
+        sb.AppendLine();
+        sb.AppendLine($"        var obj = Unsafe.As<{ci.FullTypeName}>(value);");
+
+        // Self ref tracking — matches runtime ScanValue UseTypeReferenceHandling block
+        if (ci.IsIId)
+        {
+            // IId type: track when ReferenceHandling != None
+            var trackMethod = ci.IdTypeName switch
+            {
+                "int" => "ScanTrackObjectInt32",
+                "long" => "ScanTrackObjectInt64",
+                "System.Guid" => "ScanTrackObjectGuid",
+                _ => "ScanTrackObjectInt32"
+            };
+            sb.AppendLine();
+            sb.AppendLine("        if (context.ReferenceHandling != ReferenceHandlingMode.None)");
+            sb.AppendLine("        {");
+            sb.AppendLine($"            if (!context.{trackMethod}(s_trackingSlot, obj.Id))");
+            sb.AppendLine("                return;");
+            sb.AppendLine("        }");
+        }
+        else
+        {
+            // Non-IId type: track when ReferenceHandling == All
+            sb.AppendLine();
+            sb.AppendLine("        if (context.ReferenceHandling == ReferenceHandlingMode.All)");
+            sb.AppendLine("        {");
+            sb.AppendLine("            if (!context.ScanTrackObjectInt32(s_trackingSlot, System.Runtime.CompilerServices.RuntimeHelpers.GetHashCode(value)))");
+            sb.AppendLine("                return;");
+            sb.AppendLine("        }");
+        }
+
+        // Collect scannable properties
+        var scanProps = ci.Properties.Where(p =>
+            p.TypeKind == PropertyTypeKind.String ||
+            p.TypeKind == PropertyTypeKind.Complex ||
+            p.TypeKind == PropertyTypeKind.Collection).ToList();
+
+        // Hoist UseStringInterning + IsValidForInterningString checks if any string scanning needed
+        var hasStringScan = scanProps.Any(p =>
+            (p.TypeKind == PropertyTypeKind.String && p.InterningFlags != 0) ||
+            (p.TypeKind == PropertyTypeKind.Collection && p.ElementKind == PropertyTypeKind.String && p.InterningFlags != 0));
+
+        if (hasStringScan)
+        {
+            // Hoist the shift once — per-property InterningFlags check uses internBit directly.
+            // Cannot combine flags (OR) because different properties may have different flags
+            // and Attribute mode must NOT scan All-only properties.
+            sb.AppendLine();
+            sb.AppendLine("        var internBit = 1 << (int)context.Options.UseStringInterning;");
+            sb.AppendLine("        int minIntern = 0, maxIntern = 0;");
+            sb.AppendLine("        if (internBit > 1) { minIntern = context.MinStringInternLength; maxIntern = context.MaxStringInternLength; }");
+        }
+
+        var hasAnyScanProp = false;
+        foreach (var p in scanProps)
+        {
+            sb.AppendLine();
+            hasAnyScanProp = true;
+            EmitScanProp(sb, p, "        ", ci.FullTypeName);
+        }
+
+        if (!hasAnyScanProp)
+        {
+            sb.AppendLine("        // No reference properties to scan");
+        }
+
+        sb.AppendLine("    }");
+    }
+
     private static void EmitProp(StringBuilder sb, PropInfo p, string i, string fullTypeName)
     {
         var a = $"obj.{p.Name}";
@@ -396,6 +511,200 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
 
     /// <summary>
     /// Emits direct object write — bypasses GetWrapper + WriteObject entirely.
+    #region Scan Pass Code Generation
+
+    /// <summary>
+    /// Emits scan pass code for a single property.
+    /// String: interning check + ScanInternString.
+    /// Complex (SGen): ref tracking via slot IdentityMap + recursive ScanProperties.
+    /// Complex (no SGen): fallback to ScanValueGenerated (runtime wrapper lookup).
+    /// Collection: iterate elements with same patterns.
+    /// </summary>
+    private static void EmitScanProp(StringBuilder sb, PropInfo p, string i, string fullTypeName)
+    {
+        var a = $"obj.{p.Name}";
+
+        // PropertyFilter: must match write pass — if filter skips property, scan must skip too
+        // Only for non-markerless properties (matching EmitProp behavior)
+        if (!IsMarkerless(p.TypeKind))
+        {
+            sb.AppendLine($"{i}if (context.HasPropertyFilter)");
+            sb.AppendLine($"{i}{{");
+            sb.AppendLine($"{i}    var fc_{p.Name} = new BinaryPropertyFilterContext(obj, typeof({fullTypeName}), \"{p.Name}\", typeof({p.TypeNameForTypeof}), static o => (({fullTypeName})o).{p.Name});");
+            sb.AppendLine($"{i}    if (!context.PropertyFilter!(in fc_{p.Name}))");
+            sb.AppendLine($"{i}        goto scanskip_{p.Name};");
+            sb.AppendLine($"{i}}}");
+        }
+
+        switch (p.TypeKind)
+        {
+            case PropertyTypeKind.String:
+                EmitScanString(sb, p, a, i);
+                break;
+
+            case PropertyTypeKind.Complex:
+                if (p.HasGeneratedWriter)
+                    EmitScanComplexSGen(sb, p, a, i);
+                else
+                    EmitScanComplexRuntime(sb, p, a, i);
+                break;
+
+            case PropertyTypeKind.Collection:
+                EmitScanCollection(sb, p, a, i);
+                break;
+        }
+
+        if (!IsMarkerless(p.TypeKind))
+            sb.AppendLine($"{i}scanskip_{p.Name}:;");
+    }
+
+    /// <summary>
+    /// Emits scan pass code for a string property: interning flags check + ScanInternString.
+    /// </summary>
+    private static void EmitScanString(StringBuilder sb, PropInfo p, string a, string i)
+    {
+        if (p.InterningFlags == 0)
+        {
+            // Never interned (explicit [AcStringIntern(false)] or no flags) — skip entirely
+            return;
+        }
+
+        // Per-property InterningFlags check with hoisted internBit (context.Options read once)
+        sb.AppendLine($"{i}if (({p.InterningFlags} & internBit) != 0)");
+        sb.AppendLine($"{i}{{");
+        sb.AppendLine($"{i}    var str_{p.Name} = {a};");
+        sb.AppendLine($"{i}    if (str_{p.Name} != null)");
+        sb.AppendLine($"{i}    {{");
+        sb.AppendLine($"{i}        var slen_{p.Name} = str_{p.Name}.Length;");
+        sb.AppendLine($"{i}        if (slen_{p.Name} >= minIntern && (maxIntern == 0 || slen_{p.Name} <= maxIntern))");
+        sb.AppendLine($"{i}            context.ScanInternString(str_{p.Name});");
+        sb.AppendLine($"{i}    }}");
+        sb.AppendLine($"{i}}}");
+    }
+
+    /// <summary>
+    /// Emits scan pass code for a Complex property with SGen writer.
+    /// No parent-side ref tracking — child ScanObject handles its own (ScanTrackObjectXxx).
+    /// </summary>
+    private static void EmitScanComplexSGen(StringBuilder sb, PropInfo p, string a, string i)
+    {
+        var writer = p.WriterClassName;
+        var childVar = $"sc_{p.Name}";
+
+        // Null check only — ScanObject handles depth + ref tracking internally
+        sb.AppendLine($"{i}var {childVar} = {a};");
+        sb.AppendLine($"{i}if ({childVar} != null)");
+        sb.AppendLine($"{i}    {writer}.Instance.ScanObject({childVar}, context, depth + 1);");
+    }
+
+    /// <summary>
+    /// Emits scan pass code for a Complex property without SGen writer (runtime fallback).
+    /// </summary>
+    private static void EmitScanComplexRuntime(StringBuilder sb, PropInfo p, string a, string i)
+    {
+        var childVar = $"sc_{p.Name}";
+        sb.AppendLine($"{i}var {childVar} = {a};");
+        sb.AppendLine($"{i}if ({childVar} != null)");
+        sb.AppendLine($"{i}    AcBinarySerializer.ScanValueGenerated({childVar}, typeof({p.TypeNameForTypeof}), context, depth + 1);");
+    }
+
+    /// <summary>
+    /// Emits scan pass code for a Collection property.
+    /// Handles string collections (interning) and complex element collections (SGen or runtime fallback).
+    /// </summary>
+    private static void EmitScanCollection(StringBuilder sb, PropInfo p, string a, string i)
+    {
+        // String element collection
+        if (p.ElementKind == PropertyTypeKind.String)
+        {
+            if (p.InterningFlags == 0) return; // never interned
+
+            sb.AppendLine($"{i}var scol_{p.Name} = {a};");
+            sb.AppendLine($"{i}if (scol_{p.Name} != null && ({p.InterningFlags} & internBit) != 0)");
+            sb.AppendLine($"{i}{{");
+
+            if (p.CollectionKind == "Array")
+            {
+                sb.AppendLine($"{i}    for (var si_{p.Name} = 0; si_{p.Name} < scol_{p.Name}.Length; si_{p.Name}++)");
+                sb.AppendLine($"{i}    {{");
+                sb.AppendLine($"{i}        var se_{p.Name} = scol_{p.Name}[si_{p.Name}];");
+            }
+            else if (p.CollectionKind == "List")
+            {
+                sb.AppendLine($"{i}    for (var si_{p.Name} = 0; si_{p.Name} < scol_{p.Name}.Count; si_{p.Name}++)");
+                sb.AppendLine($"{i}    {{");
+                sb.AppendLine($"{i}        var se_{p.Name} = scol_{p.Name}[si_{p.Name}];");
+            }
+            else
+            {
+                sb.AppendLine($"{i}    foreach (var se_{p.Name} in scol_{p.Name})");
+                sb.AppendLine($"{i}    {{");
+            }
+
+            sb.AppendLine($"{i}        if (se_{p.Name} != null)");
+            sb.AppendLine($"{i}        {{");
+            sb.AppendLine($"{i}            var slen_{p.Name} = se_{p.Name}.Length;");
+            sb.AppendLine($"{i}            if (slen_{p.Name} >= minIntern && (maxIntern == 0 || slen_{p.Name} <= maxIntern))");
+            sb.AppendLine($"{i}                context.ScanInternString(se_{p.Name});");
+            sb.AppendLine($"{i}        }}");
+            sb.AppendLine($"{i}    }}");
+            sb.AppendLine($"{i}}}");
+            return;
+        }
+
+        // Complex element collection with SGen writer
+        if (p.ElementKind == PropertyTypeKind.Complex && p.ElementHasGeneratedWriter && p.CollectionKind != null)
+        {
+            var writer = p.ElementWriterClassName;
+
+            sb.AppendLine($"{i}var scol_{p.Name} = {a};");
+            sb.AppendLine($"{i}if (scol_{p.Name} != null)");
+            sb.AppendLine($"{i}{{");
+            sb.AppendLine($"{i}    var snd_{p.Name} = depth + 1;");
+
+            if (p.CollectionKind == "Array")
+            {
+                sb.AppendLine($"{i}    for (var si_{p.Name} = 0; si_{p.Name} < scol_{p.Name}.Length; si_{p.Name}++)");
+                sb.AppendLine($"{i}    {{");
+                sb.AppendLine($"{i}        var se_{p.Name} = scol_{p.Name}[si_{p.Name}];");
+            }
+            else if (p.CollectionKind == "List")
+            {
+                sb.AppendLine($"{i}    for (var si_{p.Name} = 0; si_{p.Name} < scol_{p.Name}.Count; si_{p.Name}++)");
+                sb.AppendLine($"{i}    {{");
+                sb.AppendLine($"{i}        var se_{p.Name} = scol_{p.Name}[si_{p.Name}];");
+            }
+            else // Counted (foreach)
+            {
+                sb.AppendLine($"{i}    foreach (var se_{p.Name} in scol_{p.Name})");
+                sb.AppendLine($"{i}    {{");
+            }
+
+            var e = $"se_{p.Name}";
+            // Null check only — ScanObject handles depth + ref tracking internally
+            sb.AppendLine($"{i}        if ({e} == null) continue;");
+            sb.AppendLine($"{i}        {writer}.Instance.ScanObject({e}, context, snd_{p.Name});");
+            sb.AppendLine($"{i}    }}");
+            sb.AppendLine($"{i}}}");
+            return;
+        }
+
+        // Complex element collection without SGen writer — runtime fallback
+        if (p.ElementKind == PropertyTypeKind.Complex)
+        {
+            sb.AppendLine($"{i}var scol_{p.Name} = {a};");
+            sb.AppendLine($"{i}if (scol_{p.Name} != null)");
+            sb.AppendLine($"{i}    AcBinarySerializer.ScanValueGenerated(scol_{p.Name}, typeof({p.TypeNameForTypeof}), context, depth);");
+            return;
+        }
+
+        // Primitive element collection — no scanning needed
+    }
+
+    #endregion
+
+    /// <summary>
+    /// Emits inline object write for a Complex property that has a generated writer.
     /// Writes marker bytes + inline metadata (UseMetadata) + calls child GeneratedWriter.WriteProperties.
     /// IId types: guard ReferenceHandling != None (tracked in OnlyId + All).
     /// Non-IId types: guard ReferenceHandling == All (tracked only in All mode).
@@ -888,12 +1197,16 @@ internal sealed class SerializableClassInfo
     public string ClassName { get; }
     public string FullTypeName { get; }
     public List<PropInfo> Properties { get; }
+    /// <summary>True if this type implements IId&lt;T&gt;</summary>
+    public bool IsIId { get; }
+    /// <summary>The Id type name ("int", "long", "System.Guid") if IsIId, null otherwise</summary>
+    public string? IdTypeName { get; }
     /// <summary>FNV-1a hash of ClassName (matches runtime SourceType.Name hash)</summary>
     public int TypeNameHash { get; }
     /// <summary>FNV-1a hash of each property name, in property order</summary>
     public int[] PropertyNameHashes { get; }
-    public SerializableClassInfo(string ns, string cn, string ftn, List<PropInfo> p, int typeNameHash, int[] propertyNameHashes)
+    public SerializableClassInfo(string ns, string cn, string ftn, List<PropInfo> p, bool isIId, string? idTypeName, int typeNameHash, int[] propertyNameHashes)
-    { Namespace = ns; ClassName = cn; FullTypeName = ftn; Properties = p; TypeNameHash = typeNameHash; PropertyNameHashes = propertyNameHashes; }
+    { Namespace = ns; ClassName = cn; FullTypeName = ftn; Properties = p; IsIId = isIId; IdTypeName = idTypeName; TypeNameHash = typeNameHash; PropertyNameHashes = propertyNameHashes; }
 }
 
 internal sealed class PropInfo
@@ -920,6 +1233,8 @@ internal sealed class PropInfo
     public bool IsIId { get; }
     /// <summary>Generated writer class name, e.g. "SharedTag_GeneratedWriter". Only set when HasGeneratedWriter.</summary>
     public string? WriterClassName { get; }
+    /// <summary>Id type name ("int", "long", "System.Guid") for IId child types. Null if not IId.</summary>
+    public string? IdTypeName { get; }
 
     // Collection element metadata — set when TypeKind == Collection and element type is Complex with generated writer
     /// <summary>Element type kind for collection properties. Only meaningful when TypeKind == Collection.</summary>
@@ -930,6 +1245,8 @@ internal sealed class PropInfo
     public bool ElementIsIId { get; }
     /// <summary>Generated writer class name for collection element type.</summary>
     public string? ElementWriterClassName { get; }
+    /// <summary>Id type name for collection element IId types. Null if not IId.</summary>
+    public string? ElementIdTypeName { get; }
     /// <summary>Collection type: "List", "Array", or null (unknown — fallback to runtime).</summary>
     public string? CollectionKind { get; }
     /// <summary>Full element type name for generated code (e.g. "SharedTag").</summary>
@@ -946,9 +1263,9 @@ internal sealed class PropInfo
     public int[]? ElementPropertyHashes { get; }
 
     public PropInfo(string n, string tn, string tnForTypeof, PropertyTypeKind tk, bool nullable,
-        bool? stringInternAttr = null, bool hasGeneratedWriter = false, bool isIId = false, string? writerClassName = null,
+        bool? stringInternAttr = null, bool hasGeneratedWriter = false, bool isIId = false, string? writerClassName = null, string? idTypeName = null,
         PropertyTypeKind elementKind = PropertyTypeKind.Unknown, bool elementHasGenWriter = false, bool elementIsIId = false,
-        string? elementWriterClassName = null, string? collectionKind = null, string? elementFullTypeName = null,
+        string? elementWriterClassName = null, string? elementIdTypeName = null, string? collectionKind = null, string? elementFullTypeName = null,
         int childTypeNameHash = 0, int[]? childPropertyHashes = null,
         int elementTypeNameHash = 0, int[]? elementPropertyHashes = null)
     {
@@ -960,10 +1277,12 @@ internal sealed class PropInfo
         HasGeneratedWriter = hasGeneratedWriter;
         IsIId = isIId;
         WriterClassName = writerClassName;
+        IdTypeName = idTypeName;
         ElementKind = elementKind;
         ElementHasGeneratedWriter = elementHasGenWriter;
         ElementIsIId = elementIsIId;
         ElementWriterClassName = elementWriterClassName;
+        ElementIdTypeName = elementIdTypeName;
         CollectionKind = collectionKind;
         ElementFullTypeName = elementFullTypeName;
         ChildTypeNameHash = childTypeNameHash;

AyCode.Core.Tests/GeneratedWriters/TestOrderWriter.cs

@@ -90,6 +90,18 @@ internal sealed class TestOrderWriter : IGeneratedBinaryWriter
         context.WriteDecimalBits(obj.TotalAmount);
     }
 
+    public void ScanObject<TOutput>(object value, AcBinarySerializer.BinarySerializationContext<TOutput> context, int depth) where TOutput : struct, IBinaryOutputBase
+    {
+        throw new NotImplementedException();
+    }
+
+    public void ScanForDuplicates<TOutput>(object value, AcBinarySerializer.BinarySerializationContext<TOutput> context) where TOutput : struct, IBinaryOutputBase
+    {
+        if (!context.HasCaching) return;
+        ScanObject(value, context, 0);
+        context.SortWritePlan();
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static void WriteComplexOrNull<TOutput>(object? value, AcBinarySerializer.BinarySerializationContext<TOutput> context, int depth)
         where TOutput : struct, IBinaryOutputBase

AyCode.Core/Serializers/AcSerializerOptions.cs

@@ -19,7 +19,7 @@ public abstract class AcSerializerOptions
         set => _referenceHandling = value;
     }
 
-    private ReferenceHandlingMode _referenceHandling = ReferenceHandlingMode.All;
+    private ReferenceHandlingMode _referenceHandling = ReferenceHandlingMode.OnlyId;
 
     private readonly byte _maxDepth = byte.MaxValue;
     private readonly bool _throwOnCircularReference = true;

AyCode.Core/Serializers/Attributes/AcBinarySerializableAttribute.cs

@@ -14,4 +14,28 @@ namespace AyCode.Core.Serializers.Attributes;
 [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, Inherited = false, AllowMultiple = false)]
 public sealed class AcBinarySerializableAttribute : Attribute
 {
+    public bool EnableMetadataFeature { get; }
+    public bool EnableIdTrackingFeature { get; }
+    public bool EnableRefHandlingFeature { get; }
+    public bool EnableInternStringFeature { get; }
+
+    public AcBinarySerializableAttribute() : this(true)
+    {
+    }
+
+    public AcBinarySerializableAttribute(bool enableAllFeatures)
+    {
+        EnableMetadataFeature = enableAllFeatures;
+        EnableIdTrackingFeature = enableAllFeatures;
+        EnableRefHandlingFeature = enableAllFeatures;
+        EnableInternStringFeature = enableAllFeatures;
+    }
+
+    public AcBinarySerializableAttribute(bool enableMetadataFeature, bool enableIdTrackingFeature, bool enableRefHandlingFeature, bool enableInternStringFeature)
+    {
+        EnableMetadataFeature = enableMetadataFeature;
+        EnableIdTrackingFeature = enableIdTrackingFeature;
+        EnableRefHandlingFeature = enableRefHandlingFeature;
+        EnableInternStringFeature = enableInternStringFeature;
+    }
 }

AyCode.Core/Serializers/Binaries/AcBinarySerializer.BinarySerializationContext.cs

@@ -94,6 +94,14 @@ public static partial class AcBinarySerializer
         private int _nextCacheIndex;    // Next dense cache index to assign (starts at 0, uses ++_nextCacheIndex)
         public int NextFirstIndex;    // Next first occurrence index for scan pass. Direct access for performance.
 
+        #region Slot-based IdentityMaps for SGen scan pass (replaces wrapper-based tracking)
+
+        private IdentityMap<int, InternEntry>?[]? _slottedIdMapsInt32;
+        private IdentityMap<long, InternEntry>?[]? _slottedIdMapsInt64;
+        private IdentityMap<Guid, InternEntry>?[]? _slottedIdMapsGuid;
+
+        #endregion
+
         #region WriteDuplicateEntry — scan pass output for write pass cursor
 
         private WriteDuplicateEntry[]? _writePlan;
@@ -281,6 +289,9 @@ public static partial class AcBinarySerializer
             _stringInternMap?.Reset();
             _metadataSeenBits.AsSpan().Clear();
             _metadataSeenOverflow?.Clear();
+            ResetSlottedMaps(_slottedIdMapsInt32);
+            ResetSlottedMaps(_slottedIdMapsInt64);
+            ResetSlottedMaps(_slottedIdMapsGuid);
             _nextCacheIndex = 0;
             NextFirstIndex = 0;
             ScanVisitIndex = 0;
@@ -769,6 +780,140 @@ public static partial class AcBinarySerializer
 
         #endregion
 
+        #region Slot-based Scan Pass Ref Tracking (SGen)
+
+        /// <summary>
+        /// SGen scan pass: tracks an object by Int32 Id (IId or RuntimeHelpers.GetHashCode for non-IId).
+        /// Increments ScanVisitIndex, manages IdentityMap via slot, and builds WriteDuplicateEntry on duplicates.
+        /// Returns true if first occurrence (caller should scan children), false if duplicate (skip children).
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool ScanTrackObjectInt32(int slot, int id)
+        {
+            var visitIndex = ScanVisitIndex++;
+
+            if (id == 0) return true; // default Id — no tracking
+
+            ref var maps = ref _slottedIdMapsInt32;
+            if (maps == null || maps.Length <= slot)
+                GrowSlottedMaps(ref maps, slot);
+
+            var map = maps[slot] ??= new IdentityMap<int, InternEntry>();
+
+            if (!map.TryAdd(id, out var si))
+            {
+                ref var entry = ref map.GetValueRef(si);
+                if (entry.CacheIndex == -1)
+                {
+                    entry.CacheIndex = ++_nextCacheIndex;
+                    entry.IsFirstWrite = true;
+                    AddWriteDuplicateEntry(entry.FirstIndex, entry.CacheIndex, isFirst: true, value: null);
+                }
+                AddWriteDuplicateEntry(visitIndex, entry.CacheIndex, isFirst: false, value: null);
+                return false;
+            }
+
+            ref var ne = ref map.GetValueRef(si);
+            ne.FirstIndex = visitIndex;
+            ne.CacheIndex = -1;
+            return true;
+        }
+
+        /// <summary>
+        /// SGen scan pass: tracks an object by Int64 Id.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool ScanTrackObjectInt64(int slot, long id)
+        {
+            var visitIndex = ScanVisitIndex++;
+
+            if (id == 0) return true;
+
+            ref var maps = ref _slottedIdMapsInt64;
+            if (maps == null || maps.Length <= slot)
+                GrowSlottedMaps(ref maps, slot);
+
+            var map = maps[slot] ??= new IdentityMap<long, InternEntry>();
+
+            if (!map.TryAdd(id, out var si))
+            {
+                ref var entry = ref map.GetValueRef(si);
+                if (entry.CacheIndex == -1)
+                {
+                    entry.CacheIndex = ++_nextCacheIndex;
+                    entry.IsFirstWrite = true;
+                    AddWriteDuplicateEntry(entry.FirstIndex, entry.CacheIndex, isFirst: true, value: null);
+                }
+                AddWriteDuplicateEntry(visitIndex, entry.CacheIndex, isFirst: false, value: null);
+                return false;
+            }
+
+            ref var ne = ref map.GetValueRef(si);
+            ne.FirstIndex = visitIndex;
+            ne.CacheIndex = -1;
+            return true;
+        }
+
+        /// <summary>
+        /// SGen scan pass: tracks an object by Guid Id.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool ScanTrackObjectGuid(int slot, Guid id)
+        {
+            var visitIndex = ScanVisitIndex++;
+
+            if (id == Guid.Empty) return true;
+
+            ref var maps = ref _slottedIdMapsGuid;
+            if (maps == null || maps.Length <= slot)
+                GrowSlottedMaps(ref maps, slot);
+
+            var map = maps[slot] ??= new IdentityMap<Guid, InternEntry>();
+
+            if (!map.TryAdd(id, out var si))
+            {
+                ref var entry = ref map.GetValueRef(si);
+                if (entry.CacheIndex == -1)
+                {
+                    entry.CacheIndex = ++_nextCacheIndex;
+                    entry.IsFirstWrite = true;
+                    AddWriteDuplicateEntry(entry.FirstIndex, entry.CacheIndex, isFirst: true, value: null);
+                }
+                AddWriteDuplicateEntry(visitIndex, entry.CacheIndex, isFirst: false, value: null);
+                return false;
+            }
+
+            ref var ne = ref map.GetValueRef(si);
+            ne.FirstIndex = visitIndex;
+            ne.CacheIndex = -1;
+            return true;
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private static void GrowSlottedMaps<TMap>(ref TMap?[]? maps, int slot) where TMap : class
+        {
+            var newSize = Math.Max(slot + 1, 16);
+            if (maps == null)
+            {
+                maps = new TMap?[newSize];
+                return;
+            }
+            var newMaps = new TMap?[newSize];
+            maps.AsSpan().CopyTo(newMaps);
+            maps = newMaps;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void ResetSlottedMaps<TKey, TValue>(IdentityMap<TKey, TValue>?[]? maps)
+            where TKey : notnull where TValue : struct
+        {
+            if (maps == null) return;
+            for (var i = 0; i < maps.Length; i++)
+                maps[i]?.Reset();
+        }
+
+        #endregion
+
         #region UseMetadata Type Tracking
 
         /// <summary>

AyCode.Core/Serializers/Binaries/AcBinarySerializer.BinarySerializeTypeMetadata.cs

@@ -24,6 +24,8 @@ public static partial class AcBinarySerializer
         /// </summary>
         public Type? GeneratedSerializerType { get; }
 
+        public bool EnableInternString { get; }
+        
         /// <summary>
         /// Lazy-computed FNV-1a hash of the type name (SourceType.Name).
         /// Only computed once per type, on first access when UseMetadata=true.
@@ -78,7 +80,7 @@ public static partial class AcBinarySerializer
             for (var i = 0; i < Properties.Length; i++)
             {
                 var prop = Properties[i];
-                if (prop.IsComplexType || prop.AccessorType == PropertyAccessorType.String)
+                if (prop.IsComplexType || (EnableInternString && prop.AccessorType == PropertyAccessorType.String))
                     list.Add(prop);
             }
 
@@ -120,12 +122,16 @@ public static partial class AcBinarySerializer
             // Use pre-computed WritableProperties directly - no method call overhead!
             var orderedProperties = WritableProperties;
 
+            // Read [AcBinarySerializable] once per type — passed to property accessors
+            var serializableAttr = type.GetCustomAttribute<AcBinarySerializableAttribute>(inherit: false);
+            EnableInternString = serializableAttr == null || serializableAttr.EnableInternStringFeature;
+
             Properties = new BinaryPropertyAccessor[orderedProperties.Length];
             var complexCount = 0;
 
             for (var i = 0; i < orderedProperties.Length; i++)
             {
-                var accessor = new BinaryPropertyAccessor(orderedProperties[i], type);
+                var accessor = new BinaryPropertyAccessor(orderedProperties[i], type, EnableInternString);
                 accessor.PropertyIndex = i;
                 Properties[i] = accessor;
 
@@ -176,8 +182,8 @@ public static partial class AcBinarySerializer
     /// </summary>
     internal sealed class BinaryPropertyAccessor : BinaryPropertyAccessorBase
     {
-        public BinaryPropertyAccessor(PropertyInfo prop, Type declaringType) 
+        public BinaryPropertyAccessor(PropertyInfo prop, Type declaringType, bool enableInternString) 
-            : base(prop, declaringType)
+            : base(prop, declaringType, enableInternString)
         {
         }
     }

AyCode.Core/Serializers/Binaries/AcBinarySerializer.ScanPass.cs

@@ -14,6 +14,9 @@ public static partial class AcBinarySerializer
     /// - Consistent with write pass which writes ObjectRef (no children) for 2nd occurrence
     /// - Strings/objects skipped here are never written anyway (parent is ObjectRef)
     /// CacheIndex is assigned immediately on 2nd occurrence (no post-processing needed).
+    /// Uses wrapper.GeneratedWriter when available — the wrapper is already cached,
+    /// so no dictionary lookup overhead. SGen types call generated ScanForDuplicates
+    /// which bypasses the entire runtime scan path.
     /// </summary>
     private static void ScanForDuplicates<TOutput>(object value, Type type, BinarySerializationContext<TOutput> context)
         where TOutput : struct, IBinaryOutputBase
@@ -22,8 +25,18 @@ public static partial class AcBinarySerializer
             return;
 
         var wrapper = context.GetWrapper(type);
-        ScanValue(value, wrapper, context, 0);
 
+        // SGen path: wrapper.GeneratedWriter is cached (no registry lookup per call).
+        // Generated ScanForDuplicates handles HasCaching + ScanObject + SortWritePlan.
+        var genWriter = wrapper.GeneratedWriter;
+        if (genWriter != null && context.Options.UseGeneratedCode)
+        {
+            genWriter.ScanObject(value, context, 0);
+            context.SortWritePlan();
+            return;
+        }
+
+        ScanValue(value, wrapper, context, 0);
         context.SortWritePlan();
     }
 
@@ -86,6 +99,15 @@ public static partial class AcBinarySerializer
 
         // Object → ref tracking + recursive scan
 
+        // SGen path: ScanObject handles its own ref tracking (ScanTrackObjectXxx)
+        // Must be checked BEFORE runtime ref tracking to avoid double ScanVisitIndex++
+        var genWriter = wrapper.GeneratedWriter;
+        if (genWriter != null && context.Options.UseGeneratedCode)
+        {
+            genWriter.ScanObject(value, context, depth);
+            return;
+        }
+
         // Reference tracking for IId types (or all types when ReferenceHandling == All)
         // 2nd occurrence → skip children because:
         // 1. Write pass writes ObjectRef (no children) → strings/objects here are never in output
@@ -135,8 +157,7 @@ public static partial class AcBinarySerializer
             }
         }
 
-        // Recursive scan on reference properties only
+        // Fallback: runtime property loop (no SGen writer for this type)
-        // Use typed getter for strings (much faster than reflection GetValue)
         var refProperties = metadata.ReferenceProperties;
         var hasPropertyFilter = context.HasPropertyFilter;
         var nextDepth2 = depth + 1;
@@ -144,7 +165,6 @@ public static partial class AcBinarySerializer
         for (var i = 0; i < refProperties.Length; i++)
         {
             var prop = refProperties[i];
-            //context.CurrentProperty = prop;
 
             // Must match write pass: filtered properties write PropertySkip (no value) →
             // scanning them would assign CacheIndex for strings/objects never in output
@@ -155,14 +175,12 @@ public static partial class AcBinarySerializer
             {
                 if (!prop.UseStringPropertyInterning(context.Options.UseStringInterning)) continue;
 
-                // Fast path: typed getter for string
                 var str2 = prop.GetString(value);
                 if (str2 != null && context.IsValidForInterningString(str2.Length))
                     context.ScanInternString(str2);
             }
             else if (prop.IsStringCollectionProperty)
             {
-                // String collection: per-property interning control, no GetWrapper needed
                 if (!prop.UseStringPropertyInterning(context.Options.UseStringInterning)) continue;
 
                 var propValue = prop.GetValue(value);
@@ -171,7 +189,6 @@ public static partial class AcBinarySerializer
             }
             else
             {
-                // Object property: use pre-cached wrapper, fallback to GetWrapper on miss/polymorphism
                 var propValue = prop.GetValue(value);
                 if (propValue != null)
                 {
@@ -188,6 +205,17 @@ public static partial class AcBinarySerializer
         }
     }
 
+    /// <summary>
+    /// Public entry point for SGen-generated ScanProperties to call back into runtime ScanValue
+    /// for child types that don't have a generated writer (fallback to runtime path with wrapper lookup).
+    /// </summary>
+    internal static void ScanValueGenerated<TOutput>(object value, Type type, BinarySerializationContext<TOutput> context, int depth)
+        where TOutput : struct, IBinaryOutputBase
+    {
+        var wrapper = context.GetWrapper(type);
+        ScanValue(value, wrapper, context, depth);
+    }
+
     /// <summary>
     /// Scans string elements of a collection for interning. Uses IList fast path when available.
     /// </summary>

AyCode.Core/Serializers/Binaries/AcBinarySerializer.cs

@@ -264,6 +264,19 @@ public static partial class AcBinarySerializer
 
     #endregion
 
+    #region Scan Pass Tracking Slot Allocation
+
+    private static int s_nextTrackingSlot;
+
+    /// <summary>
+    /// Allocates a unique slot index for SGen scan pass ref tracking IdentityMaps.
+    /// Called once per SGen type at startup (ModuleInitializer). Thread-safe.
+    /// Slot indexes the per-context IdentityMap arrays in BinarySerializationContext.
+    /// </summary>
+    internal static int AllocateTrackingSlot() => Interlocked.Increment(ref s_nextTrackingSlot) - 1;
+
+    #endregion
+
     /// <summary>
     /// Thread-safe registry for generated writers. Looked up once per TypeMetadataWrapper creation.
     /// </summary>

AyCode.Core/Serializers/Binaries/BinaryPropertyAccessorBase.cs

@@ -1,5 +1,6 @@
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using AyCode.Core.Serializers.Attributes;
 using static AyCode.Core.Helpers.JsonUtilities;
 
 namespace AyCode.Core.Serializers.Binaries;
@@ -53,13 +54,13 @@ public abstract class BinaryPropertyAccessorBase : PropertyAccessorBase
     /// </summary>
     public byte? ExpectedTypeCode { get; }
 
-    protected BinaryPropertyAccessorBase(PropertyInfo prop, Type declaringType)
+    protected BinaryPropertyAccessorBase(PropertyInfo prop, Type declaringType, bool enableInternString)
         : base(prop, declaringType)
     {
         IsStringCollectionProperty = IsStringCollection(prop.PropertyType);
 
         // All typed getters are initialized in PropertyAccessorBase
-        if (AccessorType == PropertyAccessorType.String || IsStringCollectionProperty)
+        if (enableInternString && (AccessorType == PropertyAccessorType.String || IsStringCollectionProperty))
         {
             // Cache [AcStringIntern] attribute (inherit: true to check base class properties)
             var internAttr = prop.GetCustomAttribute<AcStringInternAttribute>(inherit: true);
@@ -67,7 +68,7 @@ public abstract class BinaryPropertyAccessorBase : PropertyAccessorBase
             var stringInternAttributeValue = internAttr?.Enabled;
 
             byte flags = 0;
-            if (stringInternAttributeValue == true)  flags |= (1 << (int)StringInterningMode.Attribute);
+            if (stringInternAttributeValue == true) flags |= (1 << (int)StringInterningMode.Attribute);
             if (stringInternAttributeValue != false) flags |= (1 << (int)StringInterningMode.All);
             _interningFlags = flags;
         }

AyCode.Core/Serializers/Binaries/IGeneratedBinaryWriter.cs

@@ -26,4 +26,20 @@ internal interface IGeneratedBinaryWriter
     /// <typeparam name="TOutput">Output strategy (ArrayBinaryOutput or BufferWriterBinaryOutput).</typeparam>
     void WriteProperties<TOutput>(object value, AcBinarySerializer.BinarySerializationContext<TOutput> context, int depth)
         where TOutput : struct, IBinaryOutputBase;
+
+    /// <summary>
+    /// Full scan pass for this type: null/depth check, ref tracking (slot-based IdentityMap),
+    /// and recursive property scan (strings + complex types).
+    /// Replaces the entire runtime ScanValue for SGen types — no GetWrapper, no delegate invoke.
+    /// Called from ScanForDuplicates or from parent SGen ScanObject (child).
+    /// </summary>
+    void ScanObject<TOutput>(object value, AcBinarySerializer.BinarySerializationContext<TOutput> context, int depth)
+        where TOutput : struct, IBinaryOutputBase;
+
+    /// <summary>
+    /// SGen scan pass entry point. Called from Serialize instead of runtime ScanForDuplicates.
+    /// HasCaching check + ScanObject + SortWritePlan — eliminates GetWrapper for the root type.
+    /// </summary>
+    void ScanForDuplicates<TOutput>(object value, AcBinarySerializer.BinarySerializationContext<TOutput> context)
+        where TOutput : struct, IBinaryOutputBase;
 }