Fix mocking hidden generic interface methods

src/TUnit.Mocks.SourceGenerator/Builders/MockImplBuilder.cs

@@ -588,7 +588,7 @@ private static void GenerateInterfaceMethod(CodeWriter writer, MockMemberModel m
         var signatureReturnType = (method.IsVoid && !method.IsAsync) ? "void" : method.ReturnType;
         var paramList = GetParameterList(method);
         var typeParams = GetTypeParameterList(method);
-        var constraints = GetConstraintClauses(method);
+        var constraints = GetConstraintClauses(method, forExplicitImplementation: method.ExplicitInterfaceName is not null);
 
         writer.AppendLineIfNotEmpty(method.ObsoleteAttribute);
 
@@ -599,7 +599,7 @@ private static void GenerateInterfaceMethod(CodeWriter writer, MockMemberModel m
                 // Return type is compatible (e.g. IEnumerable.GetEnumerator → IEnumerable<T>.GetEnumerator)
                 // — delegate to the public method.
                 var argPassList = GetArgPassList(method);
-                writer.AppendLine($"{signatureReturnType} {method.ExplicitInterfaceName}.{EscapeIdentifier(method.Name)}{typeParams}({paramList}){constraints} => {EscapeIdentifier(method.Name)}({argPassList});");
+                writer.AppendLine($"{signatureReturnType} {method.ExplicitInterfaceName}.{EscapeIdentifier(method.Name)}{typeParams}({paramList}){constraints} => {EscapeIdentifier(method.Name)}{typeParams}({argPassList});");
             }
             else
             {

tests/TUnit.Mocks.SourceGenerator.Tests/Issue6670Tests.cs

@@ -0,0 +1,50 @@
+namespace TUnit.Mocks.SourceGenerator.Tests;
+
+/// <summary>
+/// Regression: https://github.com/thomhurst/TUnit/issues/6670
+/// A derived interface can hide a generic base method with a different return type. The base
+/// slot then needs an explicit implementation, which cannot repeat inherited constraints such
+/// as <c>notnull</c> (CS0460).
+/// </summary>
+public class Issue6670Tests : SnapshotTestBase
+{
+    private const string Source = """
+        using System.Collections.Generic;
+        using TUnit.Mocks;
+
+        public interface ITest : ITestParent
+        {
+            new IList<T> Get<T>() where T : notnull;
+        }
+
+        public interface ITestParent
+        {
+            IEnumerable<T> Get<T>() where T : notnull;
+        }
+
+        public class TestUsage
+        {
+            void M()
+            {
+                var mock = ITest.Mock();
+            }
+        }
+        """;
+
+    [Test]
+    public async Task Hidden_Generic_Interface_Method_Does_Not_Repeat_Constraints_On_Explicit_Implementation()
+    {
+        var errors = GetGeneratedCompilationErrors(Source);
+        var genericImplementationErrors = errors
+            .Where(error => error.Id is "CS0411" or "CS0460")
+            .ToList();
+
+        await Assert.That(genericImplementationErrors).IsEmpty();
+    }
+
+    [Test]
+    public Task Hidden_Generic_Interface_Method_Generation_Snapshot()
+    {
+        return VerifyGeneratorOutput(Source);
+    }
+}

tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Hidden_Generic_Interface_Method_Generation_Snapshot.verified.txt

@@ -0,0 +1,172 @@
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+public sealed class ITestMock : global::TUnit.Mocks.Mock<global::ITest>, global::ITest
+{
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    internal ITestMock(global::ITest mockObject, global::TUnit.Mocks.MockEngine<global::ITest> engine)
+        : base(mockObject, engine) { }
+
+    global::System.Collections.Generic.IList<T> global::ITest.Get<T>() => Object.Get<T>();
+
+    global::System.Collections.Generic.IEnumerable<T> global::ITestParent.Get<T>() => ((global::ITestParent)Object).Get<T>();
+}
+
+
+// ===== FILE SEPARATOR =====
+
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+file sealed class ITestMockImpl : global::ITest, global::TUnit.Mocks.IRaisable, global::TUnit.Mocks.IMockObject
+{
+    private readonly global::TUnit.Mocks.MockEngine<global::ITest> _engine;
+
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
+
+    internal ITestMockImpl(global::TUnit.Mocks.MockEngine<global::ITest> engine)
+    {
+        _engine = engine;
+    }
+
+    public global::System.Collections.Generic.IList<T> Get<T>() where T : notnull
+    {
+        return _engine.HandleCallWithReturn<global::System.Collections.Generic.IList<T>>(0, "Get", global::System.Array.Empty<object?>(), global::System.Array.Empty<T>(), global::TUnit.Mocks.TypeArguments.Of<T>.Value);
+    }
+
+    global::System.Collections.Generic.IEnumerable<T> global::ITestParent.Get<T>() => Get<T>();
+
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    public void RaiseEvent(string eventName, object? args)
+    {
+        throw new global::System.InvalidOperationException($"No event named '{eventName}' exists on this mock.");
+    }
+}
+
+internal static class ITestMockFactory
+{
+    [global::System.Runtime.CompilerServices.ModuleInitializer]
+    internal static void Register()
+    {
+        global::TUnit.Mocks.MockRegistry.RegisterFactory<global::ITest>(Create);
+    }
+
+    internal static global::TUnit.Mocks.Mock<global::ITest> CreateAutoMock(global::TUnit.Mocks.MockBehavior behavior)
+    {
+        var engine = new global::TUnit.Mocks.MockEngine<global::ITest>(behavior);
+        var impl = new ITestMockImpl(engine);
+        engine.Raisable = impl;
+        var mock = new ITestMock(impl, engine);
+        return mock;
+    }
+
+    internal static global::TUnit.Mocks.Mock<global::ITest> Create(global::TUnit.Mocks.MockBehavior behavior, object[] constructorArgs)
+    {
+        if (constructorArgs.Length > 0) throw new global::System.ArgumentException($"Interface mock 'global::ITest' does not support constructor arguments, but {constructorArgs.Length} were provided.");
+        var engine = new global::TUnit.Mocks.MockEngine<global::ITest>(behavior);
+        var impl = new ITestMockImpl(engine);
+        engine.Raisable = impl;
+        var mock = new ITestMock(impl, engine);
+        return mock;
+    }
+}
+
+
+// ===== FILE SEPARATOR =====
+
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+namespace TUnit.Mocks.Generated
+{
+    public static class ITest_MockMemberExtensions
+    {
+        public static global::TUnit.Mocks.MockMethodCall<global::System.Collections.Generic.IList<T>> Get<T>(this global::TUnit.Mocks.Mock<global::ITest> mock) where T : notnull
+        {
+            var matchers = global::System.Array.Empty<global::TUnit.Mocks.Arguments.IArgumentMatcher>();
+            return new global::TUnit.Mocks.MockMethodCall<global::System.Collections.Generic.IList<T>>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Get", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
+        }
+
+        #if NET9_0_OR_GREATER
+        [global::System.Runtime.CompilerServices.OverloadResolutionPriority(-1)]
+        public static void Reset(this global::TUnit.Mocks.Mock<global::ITest> mock)
+            => global::TUnit.Mocks.Mock.Reset(mock);
+
+        [global::System.Runtime.CompilerServices.OverloadResolutionPriority(-1)]
+        public static void VerifyAll(this global::TUnit.Mocks.Mock<global::ITest> mock)
+            => global::TUnit.Mocks.Mock.VerifyAll(mock);
+
+        [global::System.Runtime.CompilerServices.OverloadResolutionPriority(-1)]
+        public static void VerifyNoOtherCalls(this global::TUnit.Mocks.Mock<global::ITest> mock)
+            => global::TUnit.Mocks.Mock.VerifyNoOtherCalls(mock);
+
+        [global::System.Runtime.CompilerServices.OverloadResolutionPriority(-1)]
+        public static void SetupAllProperties(this global::TUnit.Mocks.Mock<global::ITest> mock)
+            => global::TUnit.Mocks.Mock.SetupAllProperties(mock);
+
+        [global::System.Runtime.CompilerServices.OverloadResolutionPriority(-1)]
+        public static global::TUnit.Mocks.Diagnostics.MockDiagnostics GetDiagnostics(this global::TUnit.Mocks.Mock<global::ITest> mock)
+            => global::TUnit.Mocks.Mock.GetDiagnostics(mock);
+
+        [global::System.Runtime.CompilerServices.OverloadResolutionPriority(-1)]
+        public static void SetState(this global::TUnit.Mocks.Mock<global::ITest> mock, string? stateName)
+            => global::TUnit.Mocks.Mock.SetState(mock, stateName);
+
+        [global::System.Runtime.CompilerServices.OverloadResolutionPriority(-1)]
+        public static void InState(this global::TUnit.Mocks.Mock<global::ITest> mock, string stateName, global::System.Action<global::TUnit.Mocks.Mock<global::ITest>> configure)
+            => global::TUnit.Mocks.Mock.InState(mock, stateName, configure);
+
+        extension(global::TUnit.Mocks.Mock<global::ITest> mock)
+        {
+            public global::System.Collections.Generic.IReadOnlyList<global::TUnit.Mocks.Verification.CallRecord> Invocations => global::TUnit.Mocks.Mock.Invocations(mock);
+
+            public global::TUnit.Mocks.MockBehavior Behavior => global::TUnit.Mocks.Mock.Behavior(mock);
+
+            public global::TUnit.Mocks.IDefaultValueProvider? DefaultValueProvider
+            {
+                get => global::TUnit.Mocks.Mock.GetDefaultValueProvider(mock);
+                set => global::TUnit.Mocks.Mock.SetDefaultValueProvider(mock, value);
+            }
+        }
+        #endif
+    }
+}
+
+
+// ===== FILE SEPARATOR =====
+
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+namespace TUnit.Mocks
+{
+    public static class ITest_MockStaticExtension
+    {
+        extension(global::ITest _)
+        {
+            public static global::ITestMock Mock()
+            {
+                return (global::ITestMock)global::ITestMockFactory.CreateAutoMock(global::TUnit.Mocks.Mock.DefaultBehavior);
+            }
+
+            public static global::ITestMock Mock(global::TUnit.Mocks.MockBehavior behavior)
+            {
+                return (global::ITestMock)global::ITestMockFactory.CreateAutoMock(behavior);
+            }
+        }
+    }
+}
+
+
+// ===== FILE SEPARATOR =====
+
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+namespace TUnit.Mocks.Generated;

tests/TUnit.Mocks.Tests/Issue6670Tests.cs

@@ -0,0 +1,30 @@
+using TUnit.Mocks;
+
+namespace TUnit.Mocks.Tests;
+
+public interface IIssue6670Test : IIssue6670TestParent
+{
+    new IList<T> Get<T>() where T : notnull;
+}
+
+public interface IIssue6670TestParent
+{
+    IEnumerable<T> Get<T>() where T : notnull;
+}
+
+public class Issue6670Tests
+{
+    [Test]
+    public async Task Hidden_Generic_Interface_Method_Mock_Works()
+    {
+        var mock = IIssue6670Test.Mock();
+        var configured = new List<string> { "configured" };
+        mock.Get<string>().Returns(configured);
+
+        IIssue6670Test derived = mock;
+        IIssue6670TestParent parent = mock;
+
+        await Assert.That(derived.Get<string>()).IsSameReferenceAs(configured);
+        await Assert.That(parent.Get<string>()).IsSameReferenceAs(configured);
+    }
+}