Feat cloning by member visibility

README.md

@@ -239,6 +239,24 @@ if (ctx.TryClone(obj, out var cloned))
 }
 ```
 
+### Member Visibility
+
+By default, all members are eligible for cloning regardless of access modifier. Apply `[FastClonerVisibility]` to a type to restrict cloning to a specific subset:
+
+```csharp
+[FastClonerVisibility(FastClonerMemberVisibility.Public | FastClonerMemberVisibility.Internal)]
+public class Dto
+{
+    public int Id { get; set; }        // cloned
+    internal string Tag;               // cloned
+    private string _secret;            // skipped
+}
+```
+
+The policy applies to both reflection and source-generated paths; excluded members are left at their default value on the clone.
+
+The visibility filter runs before the behavior pipeline and is bypassed for any member carrying a member-level behavior attribute (`[FastClonerBehavior]`, `[FastClonerIgnore]`, `[FastClonerShallow]`, `[FastClonerReference]`), so those members are always included with their declared behavior.
+
 ### Nullability Trust
 
 The generator can be instructed to fully trust nullability annotations. When `[FastClonerTrustNullability]` attribute is applied, FastCloner will skip null checks for non-nullable reference types (e.g., `string` vs `string?`), assuming the contract is valid.

src/FastCloner.SourceGenerator/AssemblyInfo.cs

@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("FastCloner.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100bd882e7dcc8a5cfdd6e2193c66bb144ab67e83964b825035b4b05ccdc40a5a7218a497799f98f98e628c38492fa227ad1579c7d701934ea2e30459a4dabfcfa498fc9f4dc6d3e3f118e4df6615aced3da480ea45d30832ddbfd56acebc957ee6345944d2e9b82705a725276146baadf08cf7a8612fd4f3ceb8b8ec9529b975c2")]

src/FastCloner.SourceGenerator/BridgeContract.cs

@@ -0,0 +1,22 @@
+namespace FastCloner.SourceGenerator;
+
+internal sealed record BridgeMethodSpec(
+    string Name,
+    string ReturnTypeFqn,
+    EquatableArray<string> ParameterTypeFqns)
+{
+    public bool IsVoid => ReturnTypeFqn == "void";
+}
+
+internal sealed record BridgeContract(
+    string BridgeTypeMetadataName,
+    string ProxyTypeFullName,
+    EquatableArray<BridgeMethodSpec> Methods,
+    bool IsAvailable)
+{
+    public static BridgeContract Empty { get; } = new BridgeContract(
+        BridgeTypeMetadataName: string.Empty,
+        ProxyTypeFullName: string.Empty,
+        Methods: EquatableArray<BridgeMethodSpec>.Empty,
+        IsAvailable: false);
+}

src/FastCloner.SourceGenerator/BridgeContractCollector.cs

@@ -0,0 +1,64 @@
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+
+namespace FastCloner.SourceGenerator;
+
+internal static class BridgeContractCollector
+{
+    private const string BridgeTypeMetadataName = "FastCloner.FastClonerSourceGeneratorBridge";
+    private const string BridgeAttrFqn = "FastCloner.FastClonerSourceGeneratorBridgeAttribute";
+    private const string BridgeMemberAttrFqn = "FastCloner.FastClonerSourceGeneratorBridgeMemberAttribute";
+
+    public static BridgeContract Collect(Compilation compilation)
+    {
+        INamedTypeSymbol? bridge = compilation.GetTypeByMetadataName(BridgeTypeMetadataName);
+
+        AttributeData? bridgeAttr = bridge?.GetAttributes()
+            .FirstOrDefault(a => a.AttributeClass?.ToDisplayString() == BridgeAttrFqn);
+        if (bridgeAttr == null || bridgeAttr.ConstructorArguments.Length == 0 || bridgeAttr.ConstructorArguments[0].Value is not string proxyFqn || string.IsNullOrEmpty(proxyFqn))
+            return BridgeContract.Empty;
+
+        List<BridgeMethodSpec> methods = [];
+
+        foreach (ISymbol member in bridge?.GetMembers() ?? [])
+        {
+            if (member is not IMethodSymbol method)
+                continue;
+            if (method.MethodKind != MethodKind.Ordinary || !method.IsStatic)
+                continue;
+
+            bool hasMemberAttr = method.GetAttributes()
+                .Any(a => a.AttributeClass?.ToDisplayString() == BridgeMemberAttrFqn);
+            if (!hasMemberAttr)
+                continue;
+
+            string returnTypeFqn = method.ReturnsVoid
+                ? "void"
+                : method.ReturnType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
+
+            string[] paramFqns = new string[method.Parameters.Length];
+            for (int i = 0; i < method.Parameters.Length; i++)
+            {
+                paramFqns[i] = method.Parameters[i].Type
+                    .ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
+            }
+
+            methods.Add(new BridgeMethodSpec(
+                Name: method.Name,
+                ReturnTypeFqn: returnTypeFqn,
+                ParameterTypeFqns: new EquatableArray<string>(paramFqns)));
+        }
+
+        if (methods.Count == 0)
+            return BridgeContract.Empty;
+
+        BridgeMethodSpec[] sortedMethods = methods.OrderBy(m => m.Name, System.StringComparer.Ordinal).ToArray();
+
+        return new BridgeContract(
+            BridgeTypeMetadataName: BridgeTypeMetadataName,
+            ProxyTypeFullName: proxyFqn!,
+            Methods: new EquatableArray<BridgeMethodSpec>(sortedMethods),
+            IsAvailable: true);
+    }
+}

src/FastCloner.SourceGenerator/BridgeProxyEmitter.cs

@@ -0,0 +1,158 @@
+using System.Text;
+
+namespace FastCloner.SourceGenerator;
+
+internal static class BridgeProxyEmitter
+{
+    public const string HintName = "FastCloner_SGBridgeProxy.g.cs";
+
+    public static bool ShouldEmit(TargetFramework targetFramework, BridgeContract contract)
+    {
+        if (targetFramework >= TargetFramework.Net8)
+            return false;
+
+        return contract is { IsAvailable: true, Methods.Count: > 0 };
+    }
+
+    public static string Emit(BridgeContract contract)
+    {
+        string proxyFqn = contract.ProxyTypeFullName;
+        int lastDot = proxyFqn.LastIndexOf('.');
+        string proxyNamespace = lastDot >= 0 ? proxyFqn.Substring(0, lastDot) : string.Empty;
+        string proxyTypeName = lastDot >= 0 ? proxyFqn.Substring(lastDot + 1) : proxyFqn;
+
+        StringBuilder sb = new StringBuilder(2048);
+
+        sb.AppendLine("#nullable disable");
+        sb.AppendLine("using System;");
+        sb.AppendLine("using System.Reflection;");
+        sb.AppendLine();
+
+        bool hasNamespace = proxyNamespace.Length > 0;
+        if (hasNamespace)
+        {
+            sb.Append("namespace ").Append(proxyNamespace).AppendLine();
+            sb.AppendLine("{");
+        }
+
+        string indent = hasNamespace ? "    " : string.Empty;
+
+        sb.Append(indent).AppendLine("[global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]");
+        sb.Append(indent).AppendLine("[global::System.Runtime.CompilerServices.CompilerGenerated]");
+        sb.Append(indent).Append("internal static class ").AppendLine(proxyTypeName);
+        sb.Append(indent).AppendLine("{");
+
+        string body = hasNamespace ? indent + "    " : "    ";
+
+        sb.Append(body).Append("private const string BridgeTypeName = \"").Append(contract.BridgeTypeMetadataName).AppendLine("\";");
+        sb.AppendLine();
+        sb.Append(body).AppendLine("private static readonly Type BridgeType = ResolveBridgeType();");
+
+        foreach (BridgeMethodSpec method in contract.Methods)
+        {
+            sb.AppendLine();
+            string delegateType = BuildDelegateType(method);
+            string parameterTypeofList = BuildTypeofList(method.ParameterTypeFqns);
+
+            sb.Append(body).Append("internal static readonly ").Append(delegateType).Append(' ').Append(method.Name).AppendLine(" =");
+            sb.Append(body).Append("    (").Append(delegateType).AppendLine(")Delegate.CreateDelegate(");
+            sb.Append(body).Append("        typeof(").Append(delegateType).AppendLine("),");
+            sb.Append(body).Append("        ResolveStaticMethod(\"").Append(method.Name).Append('\"');
+            if (parameterTypeofList.Length > 0)
+            {
+                sb.Append(", ").Append(parameterTypeofList);
+            }
+            sb.AppendLine("));");
+        }
+
+        sb.AppendLine();
+        sb.Append(body).AppendLine("private static Type ResolveBridgeType()");
+        sb.Append(body).AppendLine("{");
+        sb.Append(body).AppendLine("    Assembly runtimeAssembly = typeof(global::FastCloner.Code.FastClonerGenerator).Assembly;");
+        sb.Append(body).AppendLine("    Type type = runtimeAssembly.GetType(BridgeTypeName, throwOnError: false);");
+        sb.Append(body).AppendLine("    if (type == null)");
+        sb.Append(body).AppendLine("    {");
+        sb.Append(body).AppendLine("        throw new InvalidOperationException(");
+        sb.Append(body).AppendLine("            \"FastCloner source generator: the runtime bridge type '\" + BridgeTypeName +");
+        sb.Append(body).AppendLine("            \"' was not found in assembly '\" + runtimeAssembly.FullName +");
+        sb.Append(body).AppendLine("            \"'. The FastCloner runtime version may be incompatible with the source generator. \" +");
+        sb.Append(body).AppendLine("            \"Update the FastCloner package to a matching version.\");");
+        sb.Append(body).AppendLine("    }");
+        sb.Append(body).AppendLine("    return type;");
+        sb.Append(body).AppendLine("}");
+
+        sb.AppendLine();
+        sb.Append(body).AppendLine("private static MethodInfo ResolveStaticMethod(string name, params Type[] parameterTypes)");
+        sb.Append(body).AppendLine("{");
+        sb.Append(body).AppendLine("    const BindingFlags flags = BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public;");
+        sb.Append(body).AppendLine("    MethodInfo method = BridgeType.GetMethod(name, flags, binder: null, types: parameterTypes, modifiers: null);");
+        sb.Append(body).AppendLine("    if (method == null)");
+        sb.Append(body).AppendLine("    {");
+        sb.Append(body).AppendLine("        throw new InvalidOperationException(");
+        sb.Append(body).AppendLine("            \"FastCloner source generator: bridge method '\" + name +");
+        sb.Append(body).AppendLine("            \"' was not found on '\" + BridgeType.FullName +");
+        sb.Append(body).AppendLine("            \"'. The FastCloner runtime version may be incompatible with the source generator.\");");
+        sb.Append(body).AppendLine("    }");
+        sb.Append(body).AppendLine("    return method;");
+        sb.Append(body).AppendLine("}");
+
+        sb.Append(indent).AppendLine("}");
+
+        if (hasNamespace)
+        {
+            sb.AppendLine("}");
+        }
+
+        return sb.ToString();
+    }
+
+    private static string BuildDelegateType(BridgeMethodSpec method)
+    {
+        if (method.IsVoid)
+        {
+            if (method.ParameterTypeFqns.Count == 0)
+            {
+                return "global::System.Action";
+            }
+
+            return "global::System.Action<" + Join(method.ParameterTypeFqns) + ">";
+        }
+
+        if (method.ParameterTypeFqns.Count == 0)
+        {
+            return "global::System.Func<" + method.ReturnTypeFqn + ">";
+        }
+
+        return "global::System.Func<" + Join(method.ParameterTypeFqns) + ", " + method.ReturnTypeFqn + ">";
+    }
+
+    private static string BuildTypeofList(EquatableArray<string> parameterTypeFqns)
+    {
+        string[]? items = parameterTypeFqns.GetArray();
+        if (items is null || items.Length == 0)
+            return string.Empty;
+
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < items.Length; i++)
+        {
+            if (i > 0) sb.Append(", ");
+            sb.Append("typeof(").Append(items[i]).Append(')');
+        }
+        return sb.ToString();
+    }
+
+    private static string Join(EquatableArray<string> items)
+    {
+        string[]? array = items.GetArray();
+        if (array is null || array.Length == 0)
+            return string.Empty;
+
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < array.Length; i++)
+        {
+            if (i > 0) sb.Append(", ");
+            sb.Append(array[i]);
+        }
+        return sb.ToString();
+    }
+}