fix: custom namespaces and types work

Tuxedo.SourceGenerators/RefinementSourceGenerator.cs

@@ -65,7 +65,12 @@ ImmutableArray<MethodDeclarationSyntax> methodDeclarations
                 .Expression.ToString();
 
             // get the first parameter type
-            var parameterType = methodDeclaration.ParameterList.Parameters.First().Type!.ToString();
+            var parameterTypeSemanticModel = compilation.GetSemanticModel(
+                methodDeclaration.ParameterList.Parameters.First().Type!.SyntaxTree
+            );
+            var parameterType = parameterTypeSemanticModel
+                .GetTypeInfo(methodDeclaration.ParameterList.Parameters.First().Type!)
+                .Type!.ToDisplayString();
 
             // get the generic type arguments
             var genericTypeArguments = methodSymbol.TypeArguments;

Tuxedo.Tests/CustomTypeRefinement.cs

@@ -0,0 +1,42 @@
+using FluentAssertions;
+using Tuxedo.Tests.Custom;
+using Xunit;
+
+namespace Tuxedo.Tests
+{
+    namespace Custom
+    {
+        public sealed record Widget(int Id, string Name);
+    }
+
+    public static class CustomTypeRefinement
+    {
+        [Refinement("The widget must have a valid Id and Name")]
+        public static bool ValidWidget(Widget widget) =>
+            widget.Id > 0 && !string.IsNullOrWhiteSpace(widget.Name);
+    }
+
+    public sealed class CustomTypeRefinementTests
+    {
+        [Fact(DisplayName = "A widget can be refined to a valid widget")]
+        public void Case1()
+        {
+            var widget = new Widget(1, "Widget");
+            Refined<Widget, ValidWidget> refined = widget;
+            refined.Value.Should().Be(widget);
+            refined.Value.Id.Should().Be(1);
+            refined.Value.Name.Should().Be("Widget");
+        }
+
+        [Fact(DisplayName = "An invalid widget should fail the refinement")]
+        public void Case2()
+        {
+            var widget = new Widget(0, "Widget");
+            Assert
+                .Throws<RefinementFailureException>(() => (Refined<Widget, ValidWidget>)widget)
+                .Message.Should()
+                .Be("The widget must have a valid Id and Name");
+            Refined.TryRefine(widget, out Refined<Widget, ValidWidget> _).Should().BeFalse();
+        }
+    }
+}