fix: support generic methods with allows ref struct constraint

Source/Mockolate.SourceGenerators/Entities/Method.cs

@@ -87,6 +87,81 @@ internal string GetUniqueNameString()
 		return $"\"{ContainingType}.{Name}\"";
 	}
 
+	/// <summary>
+	///     A method has an unsupported <c>allows ref struct</c> type parameter when one of its
+	///     own generic parameters declares the anti-constraint <i>and</i> is referenced in the
+	///     return type or any parameter type. The standard setup pipeline parameterizes
+	///     <c>ReturnMethodSetup&lt;T&gt;</c> / <c>IReturnMethodSetup&lt;T&gt;</c> on <c>T</c>, but
+	///     those runtime types do not carry <c>allows ref struct</c>, so the generated source
+	///     would fail with CS9244. Methods that match this predicate get a NotSupportedException
+	///     stub instead — see the carve-out for unsupported ref-struct shapes for the same shape.
+	/// </summary>
+	public bool HasUnsupportedAllowsRefStructTypeParameter
+	{
+		get
+		{
+			if (GenericParameters is null || GenericParameters.Value.Count == 0)
+			{
+				return false;
+			}
+
+			GenericParameter[] refStructParameters = GenericParameters.Value
+				.Where(g => g.AllowsRefStruct).ToArray();
+			if (refStructParameters.Length == 0)
+			{
+				return false;
+			}
+
+			if (ReturnType != Type.Void && ContainsAnyTypeParameter(ReturnType.Fullname, refStructParameters))
+			{
+				return true;
+			}
+
+			foreach (MethodParameter parameter in Parameters)
+			{
+				if (ContainsAnyTypeParameter(parameter.Type.Fullname, refStructParameters))
+				{
+					return true;
+				}
+			}
+
+			return false;
+		}
+	}
+
+	private static bool ContainsAnyTypeParameter(string text, GenericParameter[] genericParameters)
+	{
+		foreach (GenericParameter gp in genericParameters)
+		{
+			if (ContainsAsToken(text, gp.Name))
+			{
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	private static bool ContainsAsToken(string text, string name)
+	{
+		int idx = 0;
+		while ((idx = text.IndexOf(name, idx, StringComparison.Ordinal)) >= 0)
+		{
+			bool startBoundary = idx == 0 || !IsIdentifierChar(text[idx - 1]);
+			bool endBoundary = idx + name.Length == text.Length || !IsIdentifierChar(text[idx + name.Length]);
+			if (startBoundary && endBoundary)
+			{
+				return true;
+			}
+
+			idx++;
+		}
+
+		return false;
+	}
+
+	private static bool IsIdentifierChar(char c) => char.IsLetterOrDigit(c) || c == '_';
+
 	public bool IsToString()
 		=> Name == "ToString" && Parameters.Count == 0;
 

Source/Mockolate.SourceGenerators/Sources/Sources.MockClass.cs

@@ -3002,6 +3002,20 @@ private static void AppendMockSubject_ImplementClass_AddMethod(StringBuilder sb,
 		sb.AppendLine();
 		sb.AppendLine("\t\t{");
 
+		// Methods that use a generic type parameter declaring `allows ref struct` in their
+		// signature cannot route through the regular setup pipeline: ReturnMethodSetup<T> /
+		// IReturnMethodSetup<T> do not declare the same anti-constraint, so referencing them
+		// with such a T fails with CS9244. Mirroring the carve-out for unsupported ref-struct
+		// shapes, the body throws NotSupportedException so the rest of the type still compiles.
+		if (method.HasUnsupportedAllowsRefStructTypeParameter)
+		{
+			sb.Append(
+					"\t\t\tthrow new global::System.NotSupportedException(\"Mockolate: methods with a generic type parameter declaring 'allows ref struct' are not supported. Method '")
+				.Append(method.ContainingType).Append('.').Append(method.Name).Append("'.\");").AppendLine();
+			sb.AppendLine("\t\t}");
+			return;
+		}
+
 		// Methods with at least one ref-struct parameter (outside the Span/ReadOnlySpan wrapper
 		// carve-out) route through the ref-struct setup pipeline. The ref-struct value cannot
 		// be captured in a closure, so we emit a synchronous, stack-bound match/invoke loop.
@@ -3902,6 +3916,14 @@ private static void AppendMethodSetupDefinition(StringBuilder sb, Class @class,
 		bool useParameters, string? methodNameOverride = null, bool[]? valueFlags = null,
 		bool hasOverloadResolutionPriority = false)
 	{
+		// Methods using a generic type parameter that declares `allows ref struct` cannot expose
+		// a setup surface: IReturnMethodSetup<T> / IVoidMethodSetup<T> do not carry the same
+		// anti-constraint. The override body throws NotSupportedException, so no setup is needed.
+		if (method.HasUnsupportedAllowsRefStructTypeParameter)
+		{
+			return;
+		}
+
 		// Ref-struct pipeline: emit only the narrow IRefStruct*Setup declaration. We skip the
 		// value-flag overloads entirely because an explicit ref-struct value cannot be captured
 		// via `It.Is<T>(value)` (the static value would need to live in a class field). We also
@@ -4236,6 +4258,14 @@ private static void AppendMethodSetupImplementation(StringBuilder sb, Method met
 		string? methodNameOverride = null, bool[]? valueFlags = null,
 		string? scopeExpression = null)
 	{
+		// Setup-side carve-out: methods using a generic type parameter that declares
+		// `allows ref struct` have no setup interface declaration (see
+		// AppendMethodSetupDefinition), so no explicit implementation is emitted either.
+		if (method.HasUnsupportedAllowsRefStructTypeParameter)
+		{
+			return;
+		}
+
 		if (method.Parameters.Any(p => p.NeedsRefStructPipeline()))
 		{
 			// Emit exactly once: skip the useParameters=true variant (IParameters collection

Tests/Mockolate.SourceGenerators.Tests/MockTests.ClassTests.MethodTests.cs

@@ -179,6 +179,35 @@ public bool MyMethod1<T, U>(int index)
 					          """).IgnoringNewlineStyle();
 			}
 
+			[Fact]
+			public async Task GenericMethodWithAllowsRefStruct_ShouldCompile()
+			{
+				GeneratorResult result = Generator
+					.Run("""
+					     using Mockolate;
+
+					     namespace MyCode;
+
+					     public class Program
+					     {
+					         public static void Main(string[] args)
+					         {
+					              _ = IMyService.CreateMock();
+					         }
+					     }
+
+					     public interface IMyService
+					     {
+					         T G8<T>() where T : allows ref struct;
+					     }
+					     """);
+
+				await That(result.Diagnostics).IsEmpty();
+				await That(result.Sources).ContainsKey("Mock.IMyService.g.cs");
+				await That(result.Sources["Mock.IMyService.g.cs"])
+					.Contains("throw new global::System.NotSupportedException(\"Mockolate: methods with a generic type parameter declaring 'allows ref struct' are not supported. Method 'global::MyCode.IMyService.G8<T>'.\");");
+			}
+
 			[Fact]
 			public async Task InterfaceMethodWithParameterNamedMethodExecution_ShouldGenerateUniqueLocalVariableName()
 			{