Fix UnsafeAccessor signature for byref struct this

src/coreclr/vm/genericdict.cpp

@@ -848,7 +848,8 @@ Dictionary::PopulateEntry(
                 th = th.GetMethodTable()->GetMethodTableMatchingParentClass(declaringType.AsMethodTable());
             }
 
-            th.GetMethodTable()->EnsureInstanceActive();
+            PTR_MethodTable pMT = th.IsByRef() ? th.GetTypeParam().GetMethodTable() : th.GetMethodTable();
+            pMT->EnsureInstanceActive();
 
             result = (CORINFO_GENERIC_HANDLE)th.AsPtr();
             break;
@@ -992,7 +993,7 @@ Dictionary::PopulateEntry(
                 if (nonExpansive)
                     return NULL;
 
-                pOwnerMT = ownerType.GetMethodTable();
+                pOwnerMT = ownerType.IsByRef() ? ownerType.GetTypeParam().GetMethodTable() : ownerType.GetMethodTable();
                 _ASSERTE(pOwnerMT != NULL);
 
                 IfFailThrow(ptr.GetData(&methodFlags));

src/tests/baseservices/compilerservices/UnsafeAccessors/UnsafeAccessorsTests.Generics.cs

@@ -9,7 +9,19 @@
 
 using Xunit;
 
-struct Struct { }
+struct Struct
+{
+    public Type Value;
+    private void SetType(Type type) => Value = type;
+    private void SetType<T>() => Value = typeof(T);
+}
+
+struct GenericStruct<T>
+{
+    public Type Value;
+    private void SetType(Type type) => Value = type;
+    private void SetType<U>() => Value = typeof(U);
+}
 
 interface I1 { }
 
@@ -112,6 +124,12 @@ static class Accessors<V>
         [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "CreateMessage")]
         public extern static string CreateMessage(GenericBase<V> b, V v);
 
+        [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "SetType")]
+        public extern static void SetType(ref GenericStruct<V> s, Type type);
+
+        [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "SetType")]
+        public extern static void SetType<U>(ref GenericStruct<V> s);
+
         [UnsafeAccessor(UnsafeAccessorKind.StaticMethod, Name = "ElementType")]
         public extern static Type ElementType(MyList<V> l);
 
@@ -128,6 +146,15 @@ static class Accessors<V>
         public extern static ref V GetPrivateStaticField(MyList<V> d);
     }
 
+    static class Accessors
+    {
+        [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "SetType")]
+        public extern static void SetType<U>(ref Struct s);
+
+        [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "SetType")]
+        public extern static void SetType(ref Struct s, Type type);
+    }
+
     [Fact]
     public static void Verify_Generic_AccessStaticFieldClass()
     {
@@ -459,6 +486,68 @@ public static void Verify_Generic_GenericTypeGenericStaticMethod()
         }
     }
 
+    [Fact]
+    public static void Verify_Generic_Structs()
+    {
+        Console.WriteLine($"Running {nameof(Verify_Generic_Structs)}");
+
+        {
+            Struct s = new();
+            Accessors.SetType(ref s, typeof(int));
+            Assert.Equal(typeof(int), s.Value);
+            Accessors.SetType(ref s, typeof(string));
+            Assert.Equal(typeof(string), s.Value);
+            Accessors.SetType(ref s, typeof(Struct));
+            Assert.Equal(typeof(Struct), s.Value);
+            Accessors.SetType(ref s, typeof(GenericStruct<int>));
+            Assert.Equal(typeof(GenericStruct<int>), s.Value);
+            Accessors.SetType(ref s, typeof(GenericStruct<string>));
+            Assert.Equal(typeof(GenericStruct<string>), s.Value);
+        }
+
+        {
+            Struct s = new();
+            Accessors.SetType<int>(ref s);
+            Assert.Equal(typeof(int), s.Value);
+            Accessors.SetType<string>(ref s);
+            Assert.Equal(typeof(string), s.Value);
+            Accessors.SetType<Struct>(ref s);
+            Assert.Equal(typeof(Struct), s.Value);
+            Accessors.SetType<GenericStruct<int>>(ref s);
+            Assert.Equal(typeof(GenericStruct<int>), s.Value);
+            Accessors.SetType<GenericStruct<string>>(ref s);
+            Assert.Equal(typeof(GenericStruct<string>), s.Value);
+        }
+
+        {
+            GenericStruct<int> s = new();
+            Accessors<int>.SetType(ref s, typeof(int));
+            Assert.Equal(typeof(int), s.Value);
+            Accessors<int>.SetType<string>(ref s);
+            Assert.Equal(typeof(string), s.Value);
+            Accessors<int>.SetType<Struct>(ref s);
+            Assert.Equal(typeof(Struct), s.Value);
+            Accessors<int>.SetType<GenericStruct<int>>(ref s);
+            Assert.Equal(typeof(GenericStruct<int>), s.Value);
+            Accessors<int>.SetType<GenericStruct<string>>(ref s);
+            Assert.Equal(typeof(GenericStruct<string>), s.Value);
+        }
+
+        {
+            GenericStruct<string> s = new();
+            Accessors<string>.SetType(ref s, typeof(int));
+            Assert.Equal(typeof(int), s.Value);
+            Accessors<string>.SetType<string>(ref s);
+            Assert.Equal(typeof(string), s.Value);
+            Accessors<string>.SetType<Struct>(ref s);
+            Assert.Equal(typeof(Struct), s.Value);
+            Accessors<string>.SetType<GenericStruct<int>>(ref s);
+            Assert.Equal(typeof(GenericStruct<int>), s.Value);
+            Accessors<string>.SetType<GenericStruct<string>>(ref s);
+            Assert.Equal(typeof(GenericStruct<string>), s.Value);
+        }
+    }
+
     class MethodWithConstraints
     {
         private string M<T, U>() where T : U, I2<T>