fix #35

src/FastCloner.SourceGenerator/ContextCodeGenerator.cs

@@ -209,7 +209,7 @@ private void GenerateDispatcher()
 
     private void GenerateIsHandled()
     {
-        _sb.AppendLine("        public override bool IsHandled(Type type)");
+        _sb.AppendLine("        public override bool IsHandled(global::System.Type type)");
         _sb.AppendLine("        {");
         foreach (TypeModel? type in _model.RegisteredTypes)
         {

src/FastCloner.Tests/CollectionTests.cs

@@ -1,7 +1,41 @@
+using System.Collections;
 using System.Collections.Concurrent;
 using System.Threading.Tasks;
 
 namespace FastCloner.Tests;
+
+/// <summary>
+/// A non-generic class that implements ISet&lt;string&gt; directly.
+/// Exercises the code path where type.GetGenericArguments() returns an empty array
+/// but IsSetType() matches via the interface.
+/// </summary>
+public class StringSet : ISet<string>
+{
+    private readonly HashSet<string> _inner = new();
+
+    public int Count => _inner.Count;
+    public bool IsReadOnly => false;
+
+    public bool Add(string item) => _inner.Add(item);
+    public void Clear() => _inner.Clear();
+    public bool Contains(string item) => _inner.Contains(item);
+    public void CopyTo(string[] array, int arrayIndex) => _inner.CopyTo(array, arrayIndex);
+    public void ExceptWith(IEnumerable<string> other) => _inner.ExceptWith(other);
+    public IEnumerator<string> GetEnumerator() => _inner.GetEnumerator();
+    public void IntersectWith(IEnumerable<string> other) => _inner.IntersectWith(other);
+    public bool IsProperSubsetOf(IEnumerable<string> other) => _inner.IsProperSubsetOf(other);
+    public bool IsProperSupersetOf(IEnumerable<string> other) => _inner.IsProperSupersetOf(other);
+    public bool IsSubsetOf(IEnumerable<string> other) => _inner.IsSubsetOf(other);
+    public bool IsSupersetOf(IEnumerable<string> other) => _inner.IsSupersetOf(other);
+    public bool Overlaps(IEnumerable<string> other) => _inner.Overlaps(other);
+    public bool Remove(string item) => _inner.Remove(item);
+    public bool SetEquals(IEnumerable<string> other) => _inner.SetEquals(other);
+    public void SymmetricExceptWith(IEnumerable<string> other) => _inner.SymmetricExceptWith(other);
+    public void UnionWith(IEnumerable<string> other) => _inner.UnionWith(other);
+    void ICollection<string>.Add(string item) => _inner.Add(item);
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+}
+
 public class CollectionTests
 {
     [Test]
@@ -176,4 +210,119 @@ public async Task LinkedList_Should_Be_Deep_Cloned_Correctly()
         // Original should remain untouched
         await Assert.That(original.Count).IsEqualTo(3);
     }
+
+    [Test]
+    public async Task NonGenericSetImplementingISet_Should_Be_Deep_Cloned_Correctly()
+    {
+        StringSet original = new StringSet();
+        original.Add("alpha");
+        original.Add("beta");
+        original.Add("gamma");
+
+        StringSet clone = original.DeepClone();
+
+        await Assert.That(clone).IsNotSameReferenceAs(original);
+        await Assert.That(clone.Count).IsEqualTo(3);
+        await Assert.That(clone.Contains("alpha")).IsTrue();
+        await Assert.That(clone.Contains("beta")).IsTrue();
+        await Assert.That(clone.Contains("gamma")).IsTrue();
+
+        // Mutating clone should not affect original
+        clone.Add("delta");
+        await Assert.That(clone.Count).IsEqualTo(4);
+        await Assert.That(original.Count).IsEqualTo(3);
+    }
+
+    [Test]
+    public async Task NonGenericSetInsideObject_Should_Be_Deep_Cloned_Correctly()
+    {
+        ObjectWithNonGenericSet original = new ObjectWithNonGenericSet
+        {
+            Name = "test",
+            Tags = new StringSet()
+        };
+        original.Tags.Add("a");
+        original.Tags.Add("b");
+
+        ObjectWithNonGenericSet clone = original.DeepClone();
+
+        await Assert.That(clone).IsNotSameReferenceAs(original);
+        await Assert.That(clone.Tags).IsNotSameReferenceAs(original.Tags);
+        await Assert.That(clone.Tags.Count).IsEqualTo(2);
+        await Assert.That(clone.Tags.Contains("a")).IsTrue();
+        await Assert.That(clone.Tags.Contains("b")).IsTrue();
+
+        clone.Tags.Add("c");
+        await Assert.That(clone.Tags.Count).IsEqualTo(3);
+        await Assert.That(original.Tags.Count).IsEqualTo(2);
+    }
+
+    [Test]
+    public async Task GenericSetWhereElementIsNotFirstTypeArg_Should_Be_Deep_Cloned_Correctly()
+    {
+        // TTag=List<int> (mutable, no stable hash semantics) forces the iterate-and-clone
+        // path rather than the memberwise fast path, exposing the wrong element type.
+        TaggedSet<List<int>, string> original = new TaggedSet<List<int>, string>
+        {
+            Tag = new List<int> { 1, 2, 3 }
+        };
+        original.Add("one");
+        original.Add("two");
+        original.Add("three");
+
+        TaggedSet<List<int>, string> clone = original.DeepClone();
+
+        await Assert.That(clone).IsNotSameReferenceAs(original);
+        await Assert.That(clone.Tag).IsNotSameReferenceAs(original.Tag);
+        await Assert.That(clone.Tag).IsEquivalentTo(original.Tag);
+        await Assert.That(clone.Count).IsEqualTo(3);
+        await Assert.That(clone.Contains("one")).IsTrue();
+        await Assert.That(clone.Contains("two")).IsTrue();
+        await Assert.That(clone.Contains("three")).IsTrue();
+
+        // Mutating clone should not affect original
+        clone.Add("four");
+        clone.Tag = new List<int> { 99 };
+        await Assert.That(clone.Count).IsEqualTo(4);
+        await Assert.That(original.Count).IsEqualTo(3);
+        await Assert.That(original.Tag).IsEquivalentTo(new List<int> { 1, 2, 3 });
+    }
+}
+
+public class ObjectWithNonGenericSet
+{
+    public string Name { get; set; } = "";
+    public StringSet Tags { get; set; } = new();
+}
+
+/// <summary>
+/// A generic set where the ISet element type is NOT the first generic parameter.
+/// Exercises the case where type.GetGenericArguments()[0] != the ISet&lt;T&gt; element type.
+/// </summary>
+public class TaggedSet<TTag, TElement> : ISet<TElement>
+{
+    private readonly HashSet<TElement> _inner = new();
+    public TTag? Tag { get; set; }
+
+    public int Count => _inner.Count;
+    public bool IsReadOnly => false;
+
+    public bool Add(TElement item) => _inner.Add(item);
+    public void Clear() => _inner.Clear();
+    public bool Contains(TElement item) => _inner.Contains(item);
+    public void CopyTo(TElement[] array, int arrayIndex) => _inner.CopyTo(array, arrayIndex);
+    public void ExceptWith(IEnumerable<TElement> other) => _inner.ExceptWith(other);
+    public IEnumerator<TElement> GetEnumerator() => _inner.GetEnumerator();
+    public void IntersectWith(IEnumerable<TElement> other) => _inner.IntersectWith(other);
+    public bool IsProperSubsetOf(IEnumerable<TElement> other) => _inner.IsProperSubsetOf(other);
+    public bool IsProperSupersetOf(IEnumerable<TElement> other) => _inner.IsProperSupersetOf(other);
+    public bool IsSubsetOf(IEnumerable<TElement> other) => _inner.IsSubsetOf(other);
+    public bool IsSupersetOf(IEnumerable<TElement> other) => _inner.IsSupersetOf(other);
+    public bool Overlaps(IEnumerable<TElement> other) => _inner.Overlaps(other);
+    public bool Remove(TElement item) => _inner.Remove(item);
+    public bool SetEquals(IEnumerable<TElement> other) => _inner.SetEquals(other);
+    public void SymmetricExceptWith(IEnumerable<TElement> other) => _inner.SymmetricExceptWith(other);
+    public void UnionWith(IEnumerable<TElement> other) => _inner.UnionWith(other);
+    void ICollection<TElement>.Add(TElement item) => _inner.Add(item);
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
 }

src/FastCloner.Tests/FastCloner.Tests.csproj

@@ -23,7 +23,7 @@
     <PackageReference Include="System.Drawing.Common" Version="10.0.1" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Analyzer.Testing" Version="1.1.3" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing" Version="1.1.3" />
-    <PackageReference Include="TUnit" Version="1.19.16" />
+    <PackageReference Include="TUnit" Version="1.22.6" />
   </ItemGroup>
 
   <PropertyGroup>

src/FastCloner.Tests/TypeNameConflictTests.cs

@@ -0,0 +1,65 @@
+using FastCloner.SourceGenerator.Shared;
+using System.Threading.Tasks;
+
+namespace FastCloner.Tests.TypeNameConflict;
+
+/// <summary>
+/// Regression test for https://github.com/AnyMindGroup/FastCloner/issues/37
+/// A user-defined "Type" in the same namespace as a FastClonerContext must not
+/// shadow System.Type in generated code. The source generator must emit
+/// global::System.Type instead of unqualified Type.
+/// If the generator emits unqualified "Type", this file will fail to compile.
+/// </summary>
+public enum Type
+{
+    A,
+    B,
+    C
+}
+
+public class Widget
+{
+    public string Name { get; set; } = "";
+    public Type Kind { get; set; }
+}
+
+[FastClonerRegister(typeof(Widget))]
+public partial class WidgetCloningContext : FastClonerContext { }
+
+public class TypeNameConflictTests
+{
+    [Test]
+    public async Task Context_IsHandled_Should_Work_When_Type_Name_Is_Shadowed()
+    {
+        FastClonerContext ctx = new WidgetCloningContext();
+
+        await Assert.That(ctx.IsHandled(typeof(Widget))).IsTrue();
+        await Assert.That(ctx.IsHandled(typeof(string))).IsFalse();
+    }
+
+    [Test]
+    public async Task Context_TryClone_Should_Work_When_Type_Name_Is_Shadowed()
+    {
+        FastClonerContext ctx = new WidgetCloningContext();
+        Widget original = new Widget { Name = "gear", Kind = Type.B };
+
+        await Assert.That(ctx.TryClone(original, out object? clone)).IsTrue();
+        Widget cloned = (Widget)clone!;
+        await Assert.That(cloned).IsNotSameReferenceAs(original);
+        await Assert.That(cloned.Name).IsEqualTo("gear");
+        await Assert.That(cloned.Kind).IsEqualTo(Type.B);
+    }
+
+    [Test]
+    public async Task Context_Clone_Should_Work_When_Type_Name_Is_Shadowed()
+    {
+        WidgetCloningContext ctx = new WidgetCloningContext();
+        Widget original = new Widget { Name = "spring", Kind = Type.C };
+
+        Widget? cloned = ctx.Clone(original);
+        await Assert.That(cloned).IsNotNull();
+        await Assert.That(cloned).IsNotSameReferenceAs(original);
+        await Assert.That(cloned!.Name).IsEqualTo("spring");
+        await Assert.That(cloned.Kind).IsEqualTo(Type.C);
+    }
+}

src/FastCloner/Code/FastClonerExprGenerator.cs

@@ -347,7 +347,10 @@ private static bool ShouldDeepCloneStructReadonlyFields(Type type)
 
     internal static object? GenerateProcessMethod(Type realType, bool asObject) => GenerateProcessMethod(realType, asObject && realType.IsValueType(), new ExpressionPosition(0, 0));
     public static bool IsListType(Type type) => type.IsGenericType && type.GetGenericTypeDefinition() == typeof(List<>);
-    public static bool IsSetType(Type type) => type.GetInterfaces().Any(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(ISet<>));
+    public static bool IsSetType(Type type) => GetSetInterface(type) is not null;
+
+    private static Type? GetSetInterface(Type type) =>
+        type.GetInterfaces().FirstOrDefault(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(ISet<>));
 
     public static bool IsConcurrentBagOrQueue(Type type)
     {
@@ -921,9 +924,10 @@ private static FastClonerCache.TypeShape BuildTypeShape(Type type)
             return GenerateProcessConcurrentBagOrQueueMethod(type, position);
         }
 
-        if (IsSetType(type))
+        Type? setInterface = GetSetInterface(type);
+        if (setInterface is not null)
         {
-            return GenerateProcessSetMethod(type, position);
+            return GenerateProcessSetMethod(type, setInterface, position);
         }
 
         if (type.IsArray)
@@ -1853,7 +1857,7 @@ private static object GenerateProcessConcurrentBagOrQueueMethod(Type type, Expre
         ).Compile();
     }
 
-    private static object GenerateProcessSetMethod(Type type, ExpressionPosition position)
+    private static object GenerateProcessSetMethod(Type type, Type setInterface, ExpressionPosition position)
     {
         if (FastClonerCache.IsTypeIgnored(type))
         {
@@ -1862,7 +1866,7 @@ private static object GenerateProcessSetMethod(Type type, ExpressionPosition pos
             return Expression.Lambda<Func<object, FastCloneState, object>>(pFrom, pFrom, pState).Compile();
         }
 
-        Type elementType = type.GenericArguments()[0];
+        Type elementType = setInterface.GetGenericArguments()[0];
 
         // Fast path check first - avoid creating expressions if we don't need them
         bool isImmutable = IsImmutableCollection(type);