Fix ilasm/ildasm roundtrip constraint duplication issue

src/tests/Regressions/coreclr/GitHub_122933/Test122933.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="test122933.cs" />
+  </ItemGroup>
+</Project>

src/tests/Regressions/coreclr/GitHub_122933/test122933.cs

@@ -0,0 +1,84 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Reflection;
+using Xunit;
+
+// Small repro for ilasm/ildasm roundtrip issue with duplicated constraints
+// This demonstrates the issue where constraints get duplicated during ilasm roundtrip
+public interface IComp<TSelf>
+    : IEq<TSelf>
+        where TSelf : IComp<TSelf>?
+{
+}
+
+public interface IEq<TSelf>
+        where TSelf : IEq<TSelf>?
+{
+}
+
+public class Test122933
+{
+    [Fact]
+    public static int TestEntryPoint()
+    {
+        // Get the types
+        Type ieqType = typeof(IEq<>);
+        Type icompType = typeof(IComp<>);
+
+        // Get the generic type parameter for IEq<TSelf>
+        Type[] ieqTypeParams = ieqType.GetGenericArguments();
+        if (ieqTypeParams.Length != 1)
+        {
+            Console.WriteLine($"FAIL: IEq should have 1 generic parameter, but has {ieqTypeParams.Length}");
+            return -1;
+        }
+        Type ieqTSelf = ieqTypeParams[0];
+
+        // Get the constraints on IEq's TSelf parameter
+        Type[] ieqConstraints = ieqTSelf.GetGenericParameterConstraints();
+
+        // There should be exactly one constraint: IEq<TSelf>
+        if (ieqConstraints.Length != 1)
+        {
+            Console.WriteLine($"FAIL: IEq<TSelf> should have 1 constraint, but has {ieqConstraints.Length}");
+            return -1;
+        }
+
+        if (ieqConstraints[0].GetGenericTypeDefinition() != ieqType)
+        {
+            Console.WriteLine($"FAIL: IEq<TSelf> constraint should be IEq<>, but is {ieqConstraints[0].GetGenericTypeDefinition()}");
+            return -1;
+        }
+
+        // Get the generic type parameter for IComp<TSelf>
+        Type[] icompTypeParams = icompType.GetGenericArguments();
+        if (icompTypeParams.Length != 1)
+        {
+            Console.WriteLine($"FAIL: IComp should have 1 generic parameter, but has {icompTypeParams.Length}");
+            return -1;
+        }
+        Type icompTSelf = icompTypeParams[0];
+
+        // Get the constraints on IComp's TSelf parameter
+        Type[] icompConstraints = icompTSelf.GetGenericParameterConstraints();
+
+        // There should be exactly one constraint: IComp<TSelf>
+        // After ilasm roundtrip, this becomes duplicated - that's the bug
+        if (icompConstraints.Length != 1)
+        {
+            Console.WriteLine($"FAIL: IComp<TSelf> should have 1 constraint, but has {icompConstraints.Length}");
+            return -1;
+        }
+
+        if (icompConstraints[0].GetGenericTypeDefinition() != icompType)
+        {
+            Console.WriteLine($"FAIL: IComp<TSelf> constraint should be IComp<>, but is {icompConstraints[0].GetGenericTypeDefinition()}");
+            return -1;
+        }
+
+        return 100;
+    }
+}