CoreCLR NativeAOT - ByRef generics and ByRef implementing interfaces (#98070)

* ByRefLike generic/interface follow-up work

* Create negative tests

* Apply API review feedback.
Add FeatureFlag.

27 files changed, 528 insertions, 58 deletions

diff --git a/docs/design/features/byreflike-generics.md b/docs/design/features/byreflike-generics.md
index d644a25e7f3f..99aa905ebf0f 100644
--- a/docs/design/features/byreflike-generics.md
+++ b/docs/design/features/byreflike-generics.md
@@ -127,3 +127,129 @@ The following are IL sequences involving the `box` instruction. They are used fo
 `box` ; `isinst` ; `unbox.any` – The box, `isint`, and unbox target types are all equal.
 
 `box` ; `isinst` ; `br_true/false` &ndash; The box target type is equal to the unboxed target type or the box target type is `Nullable<T>` and target type equalities can be computed.
+
+## Examples
+
+Below are valid and invalid examples of ByRefLike as Generic parameters. All examples use the **not official** syntax, `allows ref struct`, for indicating the Generic permits ByRefLike types.
+
+**1) Valid**
+```csharp
+class A<T1> where T1: allows ref struct
+{
+    public void M();
+}
+
+// The derived class is okay to lack the 'allows'
+// because the base permits non-ByRefLike (default)
+// _and_ ByRefLike types.
+class B<T2> : A<T2>
+{
+    public void N()
+        => M(); // Any T2 satisfies the constraints from A<>
+}
+```
+
+**2) Invalid**
+```csharp
+class A<T1>
+{
+    public void M();
+}
+
+// The derived class cannot push up the allows
+// constraint for ByRefLike types.
+class B<T2> : A<T2> where T2: allows ref struct
+{
+    public void N()
+        => M(); // A<> may not permit a T2
+}
+```
+
+**3) Valid**
+```csharp
+interface IA
+{
+    void M();
+}
+
+ref struct A : IA
+{
+    public void M() { }
+}
+
+class B
+{
+    // This call is permitted because no boxing is needed
+    // to dispatch to the method - it is implemented on A.
+    public static void C<T>(T t) where T: IA, allows ref struct
+        => t.M();
+}
+```
+
+**4) Invalid**
+```csharp
+interface IA
+{
+    public void M() { }
+}
+
+ref struct A : IA
+{
+    // Relies on IA::M() implementation.
+}
+
+class B
+{
+    // Reliance on a DIM forces the generic parameter
+    // to be boxed, which is invalid for ByRefLike types.
+    public static void C<T>(T t) where T: IA, allows ref struct
+        => t.M();
+}
+```
+
+**5) Valid**
+```csharp
+class A<T1> where T1: allows ref struct
+{
+}
+
+class B<T2>
+{
+    // The type parameter is okay to lack the 'allows'
+    // because the field permits non-ByRefLike (default)
+    // _and_ ByRefLike types.
+    A<T2> Field;
+}
+```
+
+**6) Invalid**
+```csharp
+class A<T1>
+{
+}
+
+class B<T2> where T2: allows ref struct
+{
+    // The type parameter can be passed to
+    // the field type, but will fail if
+    // T2 is a ByRefLike type.
+    A<T2> Field;
+}
+```
+
+**7) Invalid**
+```csharp
+class A
+{
+    virtual void M<T1>() where T1: allows ref struct;
+}
+
+class B : A
+{
+    // Override methods need to match be at least
+    // as restrictive with respect to constraints.
+    // If a user has an instance of A, they are
+    // not aware they could be calling B.
+    override void M<T2>();
+}
+```
\ No newline at end of file
diff --git a/src/coreclr/ilasm/asmparse.y b/src/coreclr/ilasm/asmparse.y
index 73ef9a892b5e..c9861d58d797 100644
--- a/src/coreclr/ilasm/asmparse.y
+++ b/src/coreclr/ilasm/asmparse.y
@@ -486,7 +486,7 @@ typarAttrib             : '+'                               { $$ = gpCovariant;
                         | '-'                               { $$ = gpContravariant; }
                         | CLASS_                            { $$ = gpReferenceTypeConstraint; }
                         | VALUETYPE_                        { $$ = gpNotNullableValueTypeConstraint; }
-                        | BYREFLIKE_                        { $$ = gpAcceptByRefLike; }
+                        | BYREFLIKE_                        { $$ = gpAllowByRefLike; }
                         | _CTOR                             { $$ = gpDefaultConstructorConstraint; }
                         | FLAGS_ '(' int32 ')'              { $$ = (CorGenericParamAttr)$3; }
                         ;
diff --git a/src/coreclr/ilasm/prebuilt/asmparse.cpp b/src/coreclr/ilasm/prebuilt/asmparse.cpp
index 6bf91f56c57f..08f686f29018 100644
--- a/src/coreclr/ilasm/prebuilt/asmparse.cpp
+++ b/src/coreclr/ilasm/prebuilt/asmparse.cpp
@@ -2523,7 +2523,7 @@ case 152:
 { yyval.int32 = gpNotNullableValueTypeConstraint; } break;
 case 153:
 #line 489 "asmparse.y"
-{ yyval.int32 = gpAcceptByRefLike; } break;
+{ yyval.int32 = gpAllowByRefLike; } break;
 case 154:
 #line 490 "asmparse.y"
 { yyval.int32 = gpDefaultConstructorConstraint; } break;
diff --git a/src/coreclr/ildasm/dasm.cpp b/src/coreclr/ildasm/dasm.cpp
index be95e36fa5d5..21dff99a3812 100644
--- a/src/coreclr/ildasm/dasm.cpp
+++ b/src/coreclr/ildasm/dasm.cpp
@@ -3081,7 +3081,7 @@ char *DumpGenericPars(_Inout_updates_(SZSTRING_SIZE) char* szString, mdToken tok
         if ((attr & gpNotNullableValueTypeConstraint) != 0)
             szptr += sprintf_s(szptr,SZSTRING_REMAINING_SIZE(szptr), "valuetype ");
         CHECK_REMAINING_SIZE;
-        if ((attr & gpAcceptByRefLike) != 0)
+        if ((attr & gpAllowByRefLike) != 0)
             szptr += sprintf_s(szptr,SZSTRING_REMAINING_SIZE(szptr), "byreflike ");
         CHECK_REMAINING_SIZE;
         if ((attr & gpDefaultConstructorConstraint) != 0)
diff --git a/src/coreclr/inc/corhdr.h b/src/coreclr/inc/corhdr.h
index 3f67b33da916..c12c1cfdd4f7 100644
--- a/src/coreclr/inc/corhdr.h
+++ b/src/coreclr/inc/corhdr.h
@@ -847,7 +847,7 @@ typedef enum CorGenericParamAttr
     gpReferenceTypeConstraint = 0x0004,      // type argument must be a reference type
     gpNotNullableValueTypeConstraint   =   0x0008,      // type argument must be a value type but not Nullable
     gpDefaultConstructorConstraint = 0x0010, // type argument must have a public default constructor
-    gpAcceptByRefLike = 0x0020, // type argument can be ByRefLike
+    gpAllowByRefLike = 0x0020, // type argument can be ByRefLike
 } CorGenericParamAttr;
 
 // structures and enums moved from COR.H
diff --git a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/TypeLoader/ConstraintValidator.cs b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/TypeLoader/ConstraintValidator.cs
index ccb1a9279f0a..d347b6d0f4af 100644
--- a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/TypeLoader/ConstraintValidator.cs
+++ b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/TypeLoader/ConstraintValidator.cs
@@ -13,9 +13,9 @@ namespace Internal.Reflection.Execution
     {
         private static bool SatisfiesConstraints(this Type genericVariable, SigTypeContext typeContextOfConstraintDeclarer, Type typeArg)
         {
-            GenericParameterAttributes specialConstraints = genericVariable.GenericParameterAttributes & GenericParameterAttributes.SpecialConstraintMask;
+            GenericParameterAttributes attributes = genericVariable.GenericParameterAttributes;
 
-            if ((specialConstraints & GenericParameterAttributes.NotNullableValueTypeConstraint) != 0)
+            if ((attributes & GenericParameterAttributes.NotNullableValueTypeConstraint) != 0)
             {
                 if (!typeArg.IsValueType)
                 {
@@ -30,19 +30,19 @@ namespace Internal.Reflection.Execution
                 }
             }
 
-            if ((specialConstraints & GenericParameterAttributes.ReferenceTypeConstraint) != 0)
+            if ((attributes & GenericParameterAttributes.ReferenceTypeConstraint) != 0)
             {
                 if (typeArg.IsValueType)
                     return false;
             }
 
-            if ((specialConstraints & GenericParameterAttributes.DefaultConstructorConstraint) != 0)
+            if ((attributes & GenericParameterAttributes.DefaultConstructorConstraint) != 0)
             {
                 if (!typeArg.HasExplicitOrImplicitPublicDefaultConstructor())
                     return false;
             }
 
-            if (typeArg.IsByRefLike && (specialConstraints & (GenericParameterAttributes)0x20 /* GenericParameterAttributes.AcceptByRefLike */) == 0)
+            if (typeArg.IsByRefLike && (attributes & (GenericParameterAttributes)0x20 /* GenericParameterAttributes.AllowByRefLike */) == 0)
                 return false;
 
             // Now check general subtype constraints
diff --git a/src/coreclr/tools/Common/TypeSystem/Common/GenericParameterDesc.cs b/src/coreclr/tools/Common/TypeSystem/Common/GenericParameterDesc.cs
index e1bf789b1123..c361733737d4 100644
--- a/src/coreclr/tools/Common/TypeSystem/Common/GenericParameterDesc.cs
+++ b/src/coreclr/tools/Common/TypeSystem/Common/GenericParameterDesc.cs
@@ -61,7 +61,7 @@ namespace Internal.TypeSystem
         /// <summary>
         /// A type is permitted to be ByRefLike.
         /// </summary>
-        AcceptByRefLike = 0x20,
+        AllowByRefLike = 0x20,
     }
 
     public abstract partial class GenericParameterDesc : TypeDesc
@@ -159,13 +159,13 @@ namespace Internal.TypeSystem
         }
 
         /// <summary>
-        /// Does this generic parameter have the AcceptByRefLike flag
+        /// Does this generic parameter have the AllowByRefLike flag
         /// </summary>
-        public bool HasAcceptByRefLikeConstraint
+        public bool HasAllowByRefLikeConstraint
         {
             get
             {
-                return (Constraints & GenericConstraints.AcceptByRefLike) != 0;
+                return (Constraints & GenericConstraints.AllowByRefLike) != 0;
             }
         }
 
diff --git a/src/coreclr/tools/Common/TypeSystem/Common/TypeSystemConstraintsHelpers.cs b/src/coreclr/tools/Common/TypeSystem/Common/TypeSystemConstraintsHelpers.cs
index acd8e291cebd..97bceb5b1b83 100644
--- a/src/coreclr/tools/Common/TypeSystem/Common/TypeSystemConstraintsHelpers.cs
+++ b/src/coreclr/tools/Common/TypeSystem/Common/TypeSystemConstraintsHelpers.cs
@@ -50,7 +50,7 @@ namespace Internal.TypeSystem
             }
 
             // Check for ByRefLike support
-            if (instantiationParam.IsByRefLike && (constraints & GenericConstraints.AcceptByRefLike) == 0)
+            if (instantiationParam.IsByRefLike && (constraints & GenericConstraints.AllowByRefLike) == 0)
                 return false;
 
             var instantiatedConstraints = default(ArrayBuilder<TypeDesc>);
diff --git a/src/coreclr/tools/Common/TypeSystem/Ecma/EcmaGenericParameter.cs b/src/coreclr/tools/Common/TypeSystem/Ecma/EcmaGenericParameter.cs
index ac6cd4307ca7..8ffa09bc12eb 100644
--- a/src/coreclr/tools/Common/TypeSystem/Ecma/EcmaGenericParameter.cs
+++ b/src/coreclr/tools/Common/TypeSystem/Ecma/EcmaGenericParameter.cs
@@ -113,7 +113,7 @@ namespace Internal.TypeSystem.Ecma
             {
                 Debug.Assert((int)GenericConstraints.DefaultConstructorConstraint == (int)GenericParameterAttributes.DefaultConstructorConstraint);
                 GenericParameter parameter = _module.MetadataReader.GetGenericParameter(_handle);
-                const GenericParameterAttributes mask = GenericParameterAttributes.SpecialConstraintMask | (GenericParameterAttributes)GenericConstraints.AcceptByRefLike;
+                const GenericParameterAttributes mask = GenericParameterAttributes.SpecialConstraintMask | (GenericParameterAttributes)GenericConstraints.AllowByRefLike;
                 return (GenericConstraints)(parameter.Attributes & mask);
             }
         }
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeGenericInfoMapNode.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeGenericInfoMapNode.cs
index e6b4762433df..8905c2aa31d7 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeGenericInfoMapNode.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeGenericInfoMapNode.cs
@@ -59,7 +59,7 @@ namespace ILCompiler.DependencyAnalysis.ReadyToRun
                     if ((genericParameter.Attributes & GenericParameterAttributes.VarianceMask) != GenericParameterAttributes.None)
                         hasVariance = true;
 
-                    if ((genericParameter.Attributes & (GenericParameterAttributes.SpecialConstraintMask | (GenericParameterAttributes)GenericConstraints.AcceptByRefLike)) != default(GenericParameterAttributes) ||
+                    if ((genericParameter.Attributes & (GenericParameterAttributes.SpecialConstraintMask | (GenericParameterAttributes)GenericConstraints.AllowByRefLike)) != default(GenericParameterAttributes) ||
                         (genericParameter.GetConstraints().Count > 0))
                     {
                         hasConstraints = true;
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeValidationChecker.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeValidationChecker.cs
index 88882e12f1f5..a257dbbe967f 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeValidationChecker.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeValidationChecker.cs
@@ -107,7 +107,7 @@ namespace ILCompiler.DependencyAnalysis.ReadyToRun
             // The runtime has a number of checks in the type loader which it will skip running if the SkipValidation flag is set
             // This function attempts to document all of them, and implement *some* of them.
 
-            // This function performs a portion of the validation skipping that has been found to have some importance, or to serve as 
+            // This function performs a portion of the validation skipping that has been found to have some importance, or to serve as
             // In addition, there are comments about all validation skipping activities that the runtime will perform.
             try
             {
@@ -488,8 +488,9 @@ namespace ILCompiler.DependencyAnalysis.ReadyToRun
                     if (!parameterOfDecl.HasReferenceTypeConstraint)
                         return false;
 
-                if (parameterOfDecl.HasAcceptByRefLikeConstraint)
-                    if (!parameterOfImpl.HasAcceptByRefLikeConstraint)
+                // Constraints that 'allow' must check the impl first
+                if (parameterOfImpl.HasAllowByRefLikeConstraint)
+                    if (!parameterOfDecl.HasAllowByRefLikeConstraint)
                         return false;
 
                 HashSet<TypeDesc> constraintsOnDecl = new HashSet<TypeDesc>();
diff --git a/src/coreclr/tools/aot/ILCompiler.TypeSystem.Tests/CoreTestAssembly/Platform.cs b/src/coreclr/tools/aot/ILCompiler.TypeSystem.Tests/CoreTestAssembly/Platform.cs
index fda0f02f5630..a2c1a1e06ad6 100644
--- a/src/coreclr/tools/aot/ILCompiler.TypeSystem.Tests/CoreTestAssembly/Platform.cs
+++ b/src/coreclr/tools/aot/ILCompiler.TypeSystem.Tests/CoreTestAssembly/Platform.cs
@@ -244,6 +244,7 @@ namespace System.Runtime.CompilerServices
     public static class RuntimeFeature
     {
         public const string ByRefFields = nameof(ByRefFields);
+        public const string ByRefLikeGenerics = nameof(ByRefLikeGenerics);
         public const string UnmanagedSignatureCallingConvention = nameof(UnmanagedSignatureCallingConvention);
         public const string VirtualStaticsInInterfaces = nameof(VirtualStaticsInInterfaces);
     }
diff --git a/src/coreclr/vm/siginfo.cpp b/src/coreclr/vm/siginfo.cpp
index 115b5454bf59..531f6d95f686 100644
--- a/src/coreclr/vm/siginfo.cpp
+++ b/src/coreclr/vm/siginfo.cpp
@@ -4813,9 +4813,11 @@ BOOL MetaSig::CompareVariableConstraints(const Substitution *pSubst1,
             if ((specialConstraints2 & (gpDefaultConstructorConstraint | gpNotNullableValueTypeConstraint)) == 0)
                 return FALSE;
         }
-        if ((specialConstraints1 & gpAcceptByRefLike) != 0)
+
+        // Constraints that 'allow' must check the overridden first
+        if ((specialConstraints2 & gpAllowByRefLike) != 0)
         {
-            if ((specialConstraints2 & gpAcceptByRefLike) == 0)
+            if ((specialConstraints1 & gpAllowByRefLike) == 0)
                 return FALSE;
         }
     }
diff --git a/src/coreclr/vm/typedesc.cpp b/src/coreclr/vm/typedesc.cpp
index ccb342ca0358..72bc9e50c29b 100644
--- a/src/coreclr/vm/typedesc.cpp
+++ b/src/coreclr/vm/typedesc.cpp
@@ -1497,7 +1497,7 @@ BOOL TypeVarTypeDesc::SatisfiesConstraints(SigTypeContext *pTypeContextOfConstra
                 return FALSE;
         }
 
-        if (thArg.IsByRefLike() && (specialConstraints & gpAcceptByRefLike) == 0)
+        if (thArg.IsByRefLike() && (specialConstraints & gpAllowByRefLike) == 0)
             return FALSE;
     }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Reflection/GenericParameterAttributes.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/GenericParameterAttributes.cs
index c05d0ec6f200..26bb5d929a4f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Reflection/GenericParameterAttributes.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/GenericParameterAttributes.cs
@@ -14,5 +14,6 @@ namespace System.Reflection
         ReferenceTypeConstraint = 0x0004,
         NotNullableValueTypeConstraint = 0x0008,
         DefaultConstructorConstraint = 0x0010,
+        AllowByRefLike = 0x0020,
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs
index e69436494251..392a4902337a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs
@@ -33,6 +33,11 @@ namespace System.Runtime.CompilerServices
         public const string ByRefFields = nameof(ByRefFields);
 
         /// <summary>
+        /// Represents a runtime feature where byref-like types can be used in Generic parameters.
+        /// </summary>
+        public const string ByRefLikeGenerics = nameof(ByRefLikeGenerics);
+
+        /// <summary>
         /// Indicates that this version of runtime supports virtual static members of interfaces.
         /// </summary>
         public const string VirtualStaticsInInterfaces = nameof(VirtualStaticsInInterfaces);
@@ -52,6 +57,7 @@ namespace System.Runtime.CompilerServices
                 case PortablePdb:
                 case CovariantReturnsOfClasses:
                 case ByRefFields:
+                case ByRefLikeGenerics:
                 case UnmanagedSignatureCallingConvention:
                 case DefaultImplementationsOfInterfaces:
                 case VirtualStaticsInInterfaces:
diff --git a/src/libraries/System.Private.CoreLib/src/System/RuntimeType.cs b/src/libraries/System.Private.CoreLib/src/System/RuntimeType.cs
index bd6a6f89bb13..17fbb2950c6c 100644
--- a/src/libraries/System.Private.CoreLib/src/System/RuntimeType.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/RuntimeType.cs
@@ -692,7 +692,7 @@ namespace System
 
                     if (constraint.IsGenericParameter)
                     {
-                        GenericParameterAttributes special = constraint.GenericParameterAttributes & GenericParameterAttributes.SpecialConstraintMask;
+                        GenericParameterAttributes special = constraint.GenericParameterAttributes;
 
                         if ((special & GenericParameterAttributes.ReferenceTypeConstraint) == 0 &&
                             (special & GenericParameterAttributes.NotNullableValueTypeConstraint) == 0)
@@ -704,7 +704,7 @@ namespace System
 
                 if (baseType == ObjectType)
                 {
-                    GenericParameterAttributes special = GenericParameterAttributes & GenericParameterAttributes.SpecialConstraintMask;
+                    GenericParameterAttributes special = GenericParameterAttributes;
                     if ((special & GenericParameterAttributes.NotNullableValueTypeConstraint) != 0)
                         baseType = ValueType;
                 }
diff --git a/src/libraries/System.Runtime/ref/System.Runtime.cs b/src/libraries/System.Runtime/ref/System.Runtime.cs
index b787a2af8c68..68b91e6794c9 100644
--- a/src/libraries/System.Runtime/ref/System.Runtime.cs
+++ b/src/libraries/System.Runtime/ref/System.Runtime.cs
@@ -11599,6 +11599,7 @@ namespace System.Reflection
         NotNullableValueTypeConstraint = 8,
         DefaultConstructorConstraint = 16,
         SpecialConstraintMask = 28,
+        AllowByRefLike = 32,
     }
     public partial interface ICustomAttributeProvider
     {
@@ -13113,6 +13114,7 @@ namespace System.Runtime.CompilerServices
     public static partial class RuntimeFeature
     {
         public const string ByRefFields = "ByRefFields";
+        public const string ByRefLikeGenerics = "ByRefLikeGenerics";
         public const string CovariantReturnsOfClasses = "CovariantReturnsOfClasses";
         public const string DefaultImplementationsOfInterfaces = "DefaultImplementationsOfInterfaces";
         public const string NumericIntPtr = "NumericIntPtr";
diff --git a/src/tests/Common/XUnitWrapperGenerator/XUnitWrapperGenerator.cs b/src/tests/Common/XUnitWrapperGenerator/XUnitWrapperGenerator.cs
index 50a7b0943e59..765ebd4ad5be 100644
--- a/src/tests/Common/XUnitWrapperGenerator/XUnitWrapperGenerator.cs
+++ b/src/tests/Common/XUnitWrapperGenerator/XUnitWrapperGenerator.cs
@@ -806,6 +806,10 @@ public sealed class XUnitWrapperGenerator : IIncrementalGenerator
                         // If we're building tests not for Mono, we can skip handling the specifics of the SkipOnMonoAttribute.
                         continue;
                     }
+                    if (filterAttribute.ConstructorArguments.Length <= 1)
+                    {
+                        return ImmutableArray<ITestInfo>.Empty;
+                    }
                     testInfos = DecorateWithSkipOnPlatform(testInfos, (int)filterAttribute.ConstructorArguments[1].Value!, options);
                     break;
                 case "Xunit.SkipOnPlatformAttribute":
diff --git a/src/tests/Loader/classloader/DefaultInterfaceMethods/constrainedcall/constrained2_brl.il b/src/tests/Loader/classloader/DefaultInterfaceMethods/constrainedcall/constrained2_brl.il
new file mode 100644
index 000000000000..9382ff66730c
--- /dev/null
+++ b/src/tests/Loader/classloader/DefaultInterfaceMethods/constrainedcall/constrained2_brl.il
@@ -0,0 +1,153 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+.assembly extern System.Console { .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A ) }
+.assembly extern System.Runtime { .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A ) }
+.assembly extern Microsoft.DotNet.XUnitExtensions {}
+.assembly extern xunit.core {}
+.assembly constrained2_brl { }
+
+.class interface private auto ansi abstract
+  IAdder
+{
+  .method public hidebysig newslot virtual
+    instance int32 Add(int32) cil managed
+  {
+    ldstr "Calling DIM from ByRefLike type is invalid"
+    newobj instance void [System.Runtime]System.Exception::.ctor(string)
+    throw
+  }
+}
+
+.class private sequential ansi sealed beforefieldinit Adder
+  extends [System.Runtime]System.ValueType
+  implements IAdder
+{
+  .custom instance void [System.Runtime]System.Runtime.CompilerServices.IsByRefLikeAttribute::.ctor() = (
+      01 00 00 00
+  )
+
+  .field private int32 _field
+
+  .method public hidebysig specialname rtspecialname
+    instance void .ctor (int32) cil managed
+  {
+    ldarg.0
+    ldarg.1
+    stfld int32 Adder::_field
+    ret
+  }
+
+  .method public hidebysig newslot virtual
+    instance int32 Add(int32) cil managed
+  {
+    // Load field and add with argument
+    ldarg.0
+    dup
+    ldfld int32 valuetype Adder::_field
+    ldarg.1
+    add
+
+    // Update the field
+    stfld int32 valuetype Adder::_field
+
+    // Return the field value
+    ldarg.0
+    ldfld int32 valuetype Adder::_field
+    ret
+  }
+}
+
+.class private sequential ansi sealed beforefieldinit Adder_Invalid
+  extends [System.Runtime]System.ValueType
+  implements IAdder
+{
+  .custom instance void [System.Runtime]System.Runtime.CompilerServices.IsByRefLikeAttribute::.ctor() = (
+      01 00 00 00
+  )
+
+  .method public hidebysig specialname rtspecialname
+    instance void .ctor (int32) cil managed
+  {
+    ret
+  }
+
+  //
+  // Deferring to the DIM on IAdder
+  //
+}
+
+.method public hidebysig static int32 Check<byreflike (IAdder) T>(!!0, int32)
+{
+  ldarga.s 0
+  ldarg.1
+  constrained. !!0
+  callvirt instance int32 IAdder::Add(int32)
+  ret
+}
+
+.class public auto ansi abstract sealed beforefieldinit constrained2_brl
+    extends [System.Runtime]System.Object
+{
+  .method public hidebysig static int32 Main()
+  {
+      .custom instance void [xunit.core]Xunit.FactAttribute::.ctor() = (
+          01 00 00 00
+      )
+      .custom instance void [Microsoft.DotNet.XUnitExtensions]Xunit.SkipOnMonoAttribute::.ctor(string, valuetype [Microsoft.DotNet.XUnitExtensions]Xunit.TestPlatforms) = (
+        01 00 2c 4d 6f 6e 6f 20 64 6f 65 73 20 6e 6f 74
+        20 73 75 70 70 6f 72 74 20 42 79 52 65 66 4c 69
+        6b 65 20 67 65 6e 65 72 69 63 73 20 79 65 74 ff
+        ff ff ff 00 00
+      )
+      .entrypoint
+
+      .locals init (
+        valuetype Adder,
+        valuetype Adder_Invalid
+      )
+
+      // Initialize Adder instance
+      ldloca.s 0
+      ldc.i4 10
+      call instance void Adder::.ctor(int32)
+
+      ldstr "Validate constrained call of ByRefLike interface method passes"
+      call void [System.Console]System.Console::WriteLine(string)
+      ldloc.0
+      ldc.i4 20
+      call int32 Check<valuetype Adder>(!!0, int32)
+      ldc.i4 30
+      ceq
+      brfalse FAIL
+
+      // Initialize Adder_Invalid instance
+      ldloca.s 1
+      ldc.i4 10
+      call instance void Adder_Invalid::.ctor(int32)
+
+      .try
+      {
+        ldstr "Validate constrained call of ByRefLike interface DIM fails"
+        call void [System.Console]System.Console::WriteLine(string)
+
+        ldloc.1
+        ldc.i4 20
+        call int32 Check<valuetype Adder_Invalid>(!!0, int32)
+        leave FAIL
+      }
+      catch [System.Runtime]System.Exception
+      {
+        pop
+        leave ExpectedFailure
+      }
+
+  ExpectedFailure:
+      ldc.i4 100
+      ret
+
+  FAIL:
+      ldc.i4 101
+      ret
+  }
+}
diff --git a/src/tests/Loader/classloader/DefaultInterfaceMethods/constrainedcall/constrained2_brl.ilproj b/src/tests/Loader/classloader/DefaultInterfaceMethods/constrainedcall/constrained2_brl.ilproj
new file mode 100644
index 000000000000..8aceddffe8f5
--- /dev/null
+++ b/src/tests/Loader/classloader/DefaultInterfaceMethods/constrainedcall/constrained2_brl.ilproj
@@ -0,0 +1,5 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <ItemGroup>
+    <Compile Include="constrained2_brl.il" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/Loader/classloader/generics/ByRefLike/GenericTypeSubstitution.cs b/src/tests/Loader/classloader/generics/ByRefLike/GenericTypeSubstitution.cs
index 3453b2a1d3e5..b35e59576abb 100644
--- a/src/tests/Loader/classloader/generics/ByRefLike/GenericTypeSubstitution.cs
+++ b/src/tests/Loader/classloader/generics/ByRefLike/GenericTypeSubstitution.cs
@@ -16,7 +16,7 @@ public class GenericTypeSubstitution
     public static void AllowByRefLike_Substituted_For_AllowByRefLike()
     {
         Console.WriteLine($"{nameof(AllowByRefLike_Substituted_For_AllowByRefLike)}...");
-        
+
         Console.WriteLine($" -- Instantiate: {Exec.TypeSubstitutionInterfaceImplementationAllowByRefLike()}");
         Console.WriteLine($" -- Instantiate: {Exec.TypeSubstitutionInheritanceAllowByRefLike()}");
         Console.WriteLine($" -- Instantiate: {Exec.TypeSubstitutionFieldAllowByRefLike()}");
@@ -26,18 +26,18 @@ public class GenericTypeSubstitution
     [SkipOnMono("Mono does not support ByRefLike generics yet")]
     public static void NonByRefLike_Substituted_For_AllowByRefLike()
     {
+        Console.WriteLine($"{nameof(NonByRefLike_Substituted_For_AllowByRefLike)}...");
+
         Console.WriteLine($" -- Instantiate: {Exec.TypeSubstitutionInterfaceImplementationNonByRefLike()}");
         Console.WriteLine($" -- Instantiate: {Exec.TypeSubstitutionInheritanceNonByRefLike()}");
         Console.WriteLine($" -- Instantiate: {Exec.TypeSubstitutionFieldNonByRefLike()}");
     }
 
     [Fact]
-    [ActiveIssue("To be created", TestRuntimes.CoreCLR)]
     [SkipOnMono("Mono does not support ByRefLike generics yet")]
-    public static void AllowByRefLike_Substituted_For_NonByRefLike_Invalid()
+    public static void AllowByRefLike_Substituted_For_NonByRefLike()
     {
-        Assert.Throws<TypeLoadException>(() => { Exec.TypeSubstitutionInterfaceImplementationAllowByRefLikeIntoNonByRefLike(); });
-        Assert.Throws<TypeLoadException>(() => { Exec.TypeSubstitutionInheritanceAllowByRefLikeIntoNonByRefLike(); });
-        Assert.Throws<TypeLoadException>(() => { Exec.TypeSubstitutionFieldAllowByRefLikeIntoNonByRefLike(); });
+        Console.WriteLine($"{nameof(AllowByRefLike_Substituted_For_NonByRefLike)}...");
+        Exec.TypeSubstitutionFieldAllowNonByRefLikeIntoNonByRefLike();
     }
 }
\ No newline at end of file
diff --git a/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharp.il b/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharp.il
index d81452d398af..8deff773fb24 100644
--- a/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharp.il
+++ b/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharp.il
@@ -439,15 +439,6 @@
 }
 
 // Invalid generic substitution of non-allow-byreflike with allow-byreflike
-.class interface public auto ansi abstract InvalidCSharp.GenericDerivedInterface_Invalid`1<byreflike T>
-    implements class InvalidCSharp.GenericInterface_Invalid`1<!T>
-{
-}
-
-.class public sequential ansi sealed beforefieldinit InvalidCSharp.GenericDerivedClass_Invalid`1<byreflike T>
-    extends class InvalidCSharp.GenericClass_Invalid`1<!T>
-{
-}
 
 .class public sequential ansi sealed beforefieldinit InvalidCSharp.GenericValueTypeWrapper_Invalid`1<byreflike T>
     extends [System.Runtime]System.ValueType
@@ -798,27 +789,9 @@
         callvirt instance string [System.Runtime]System.Object::ToString()
         ret
     }
-    
-    .method public hidebysig static
-        string TypeSubstitutionInterfaceImplementationAllowByRefLikeIntoNonByRefLike() cil managed
-    {
-        ldtoken class InvalidCSharp.GenericDerivedInterface_Invalid`1<valuetype RegularValueType>
-        call class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
-        callvirt instance string [System.Runtime]System.Object::ToString()
-        ret
-    }
-
-    .method public hidebysig static
-        string TypeSubstitutionInheritanceAllowByRefLikeIntoNonByRefLike() cil managed
-    {
-        ldtoken class InvalidCSharp.GenericDerivedClass_Invalid`1<valuetype RegularValueType>
-        call class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
-        callvirt instance string [System.Runtime]System.Object::ToString()
-        ret
-    }
 
     .method public hidebysig static
-        string TypeSubstitutionFieldAllowByRefLikeIntoNonByRefLike() cil managed
+        string TypeSubstitutionFieldAllowNonByRefLikeIntoNonByRefLike() cil managed
     {
         ldtoken valuetype InvalidCSharp.GenericValueTypeWrapper_Invalid`1<valuetype RegularValueType>
         call class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
diff --git a/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharpNegative.il b/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharpNegative.il
new file mode 100644
index 000000000000..08767e372ea4
--- /dev/null
+++ b/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharpNegative.il
@@ -0,0 +1,143 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+.assembly extern System.Console { .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A ) }
+.assembly extern System.Runtime { .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A ) }
+
+.assembly InvalidCSharpNegative { }
+
+.class public sequential ansi sealed beforefieldinit ByRefLikeType
+    extends [System.Runtime]System.ValueType
+{
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.IsByRefLikeAttribute::.ctor() = (
+        01 00 00 00
+    )
+}
+
+//
+// Begin invalid
+//
+
+.class public sequential ansi sealed beforefieldinit InvalidCSharpNegative.GenericClass_Invalid`1<T>
+    extends [System.Runtime]System.Object
+{
+    .method public hidebysig specialname rtspecialname
+        instance void .ctor () cil managed
+    {
+        ldarg.0
+        call instance void [System.Runtime]System.Object::.ctor()
+        ret
+    }
+}
+
+.class interface public auto ansi abstract InvalidCSharpNegative.GenericInterface_Invalid`1<T>
+{
+}
+
+.class public sequential ansi sealed beforefieldinit InvalidCSharpNegative.GenericValueType_Invalid`1<T>
+    extends [System.Runtime]System.ValueType
+{
+}
+
+// Invalid generic substitution of non-allow-byreflike with allow-byreflike
+.class interface public auto ansi abstract InvalidCSharpNegative.GenericDerivedInterface_Invalid`1<byreflike T>
+    implements class InvalidCSharpNegative.GenericInterface_Invalid`1<!T>
+{
+}
+
+.class public sequential ansi sealed beforefieldinit InvalidCSharpNegative.GenericDerivedClass_Invalid`1<byreflike T>
+    extends class InvalidCSharpNegative.GenericClass_Invalid`1<!T>
+{
+}
+
+.class public sequential ansi sealed beforefieldinit InvalidCSharpNegative.GenericValueTypeWrapper_Invalid`1<byreflike T>
+    extends [System.Runtime]System.ValueType
+{
+    .field public valuetype InvalidCSharpNegative.GenericValueType_Invalid`1<!T> fld;
+}
+
+.class public auto ansi beforefieldinit InvalidCSharpNegative.BaseClassWithGenericMethod
+    extends [System.Runtime]System.Object
+{
+    .method public hidebysig newslot virtual
+        instance void AcceptsByRefLike<byreflike T> () cil managed
+    {
+        ret
+    }
+    .method public hidebysig specialname rtspecialname
+        instance void .ctor () cil managed
+    {
+        ldarg.0
+        call instance void [System.Runtime]System.Object::.ctor()
+        ret
+    }
+}
+
+.class public auto ansi beforefieldinit InvalidCSharpNegative.DerivedClassWithGenericMethod_Invalid
+    extends InvalidCSharpNegative.BaseClassWithGenericMethod
+{
+    .method public hidebysig static
+        class InvalidCSharpNegative.BaseClassWithGenericMethod Create () cil managed noinlining
+    {
+        newobj instance void InvalidCSharpNegative.DerivedClassWithGenericMethod_Invalid::.ctor()
+        ret
+    }
+    .method public hidebysig virtual
+        instance void AcceptsByRefLike<T> () cil managed // Missing constraint
+    {
+        ret
+    }
+    .method private hidebysig specialname rtspecialname
+        instance void .ctor () cil managed
+    {
+        ldarg.0
+        call instance void InvalidCSharpNegative.BaseClassWithGenericMethod::.ctor()
+        ret
+    }
+}
+
+// Entry points
+
+.class public auto ansi abstract sealed beforefieldinit Exec
+    extends [System.Runtime]System.Object
+{
+    .method public hidebysig static
+        string TypeSubstitutionInterfaceImplementationAllowByRefLikeIntoNonByRefLike() cil managed
+    {
+        ldtoken class InvalidCSharpNegative.GenericDerivedInterface_Invalid`1<valuetype ByRefLikeType>
+        call class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
+        callvirt instance string [System.Runtime]System.Object::ToString()
+        ret
+    }
+
+    .method public hidebysig static
+        string TypeSubstitutionInheritanceAllowByRefLikeIntoNonByRefLike() cil managed
+    {
+        ldtoken class InvalidCSharpNegative.GenericDerivedClass_Invalid`1<valuetype ByRefLikeType>
+        call class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
+        callvirt instance string [System.Runtime]System.Object::ToString()
+        ret
+    }
+
+    .method public hidebysig static
+        string TypeSubstitutionFieldAllowByRefLikeIntoNonByRefLike() cil managed
+    {
+        ldtoken valuetype InvalidCSharpNegative.GenericValueTypeWrapper_Invalid`1<valuetype ByRefLikeType>
+        call class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
+        callvirt instance string [System.Runtime]System.Object::ToString()
+        ret
+    }
+
+    .method public hidebysig static
+        void OverrideMethodNotByRefLike() cil managed
+    {
+        .locals init (
+            [0] class InvalidCSharpNegative.BaseClassWithGenericMethod
+        )
+        call class InvalidCSharpNegative.BaseClassWithGenericMethod InvalidCSharpNegative.DerivedClassWithGenericMethod_Invalid::Create()
+        stloc.0
+        ldloc.0
+        callvirt instance void InvalidCSharpNegative.BaseClassWithGenericMethod::AcceptsByRefLike<valuetype ByRefLikeType>()
+        ret
+    }
+}
\ No newline at end of file
diff --git a/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharpNegative.ilproj b/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharpNegative.ilproj
new file mode 100644
index 000000000000..6b8ac61f3da1
--- /dev/null
+++ b/src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharpNegative.ilproj
@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <OutputType>library</OutputType>
+    <MonoAotIncompatible>true</MonoAotIncompatible>
+    <DisableProjectBuild Condition="'$(RuntimeFlavor)' == 'Mono'">true</DisableProjectBuild>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="InvalidCSharpNegative.il" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/tests/Loader/classloader/generics/ByRefLike/ValidateNegative.cs b/src/tests/Loader/classloader/generics/ByRefLike/ValidateNegative.cs
new file mode 100644
index 000000000000..7660130f253d
--- /dev/null
+++ b/src/tests/Loader/classloader/generics/ByRefLike/ValidateNegative.cs
@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.IO;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using InvalidCSharpNegative;
+
+using Xunit;
+
+public class ValidateNegative
+{
+    [Fact]
+    [SkipOnMono("Mono does not support ByRefLike generics yet")]
+    public static void AllowByRefLike_Substituted_For_NonByRefLike_Invalid()
+    {
+        Console.WriteLine($"{nameof(AllowByRefLike_Substituted_For_NonByRefLike_Invalid)}...");
+
+        Assert.Throws<TypeLoadException>(() => { Exec.TypeSubstitutionInterfaceImplementationAllowByRefLikeIntoNonByRefLike(); });
+        Assert.Throws<TypeLoadException>(() => { Exec.TypeSubstitutionInheritanceAllowByRefLikeIntoNonByRefLike(); });
+        Assert.Throws<TypeLoadException>(() => { Exec.TypeSubstitutionFieldAllowByRefLikeIntoNonByRefLike(); });
+        Assert.Throws<TypeLoadException>(() => { Exec.OverrideMethodNotByRefLike(); });
+    }
+}
\ No newline at end of file
diff --git a/src/tests/Loader/classloader/generics/ByRefLike/ValidateNegative.csproj b/src/tests/Loader/classloader/generics/ByRefLike/ValidateNegative.csproj
new file mode 100644
index 000000000000..433b007bbca0
--- /dev/null
+++ b/src/tests/Loader/classloader/generics/ByRefLike/ValidateNegative.csproj
@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <!-- Needed for mechanical merging of all remaining tests, this particular project may not actually need process isolation -->
+    <RequiresProcessIsolation>true</RequiresProcessIsolation>
+    <DisableProjectBuild Condition="'$(RuntimeFlavor)' == 'Mono'">true</DisableProjectBuild>
+
+    <!-- Crossgen is not intended to serve as an IL verifier, and is not designed to provide error semantics on bad input. -->
+    <CrossGenTest>false</CrossGenTest>
+    <NativeAotIncompatible>true</NativeAotIncompatible>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="ValidateNegative.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(TestLibraryProjectPath)" />
+    <ProjectReference Include="InvalidCSharpNegative.ilproj" />
+  </ItemGroup>
+</Project>