Add the CustomTypeMarshallerAttribute type to make it easier to identify marshaller types (#65591)

13 files changed, 2082 insertions, 1634 deletions

diff --git a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/Ancillary.Interop.csproj b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/Ancillary.Interop.csproj
index 710d935b82f..a1c0dd27574 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/Ancillary.Interop.csproj
+++ b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/Ancillary.Interop.csproj
@@ -12,6 +12,9 @@
 
   <ItemGroup>
     <Compile Include="$(LibrariesProjectRoot)Common/src/System/Runtime/InteropServices/GeneratedMarshallingAttribute.cs" Link="GeneratedMarshallingAttribute.cs" />
+    <Compile Include="$(LibrariesProjectRoot)Common/src/System/Runtime/InteropServices/CustomTypeMarshallerKind.cs" Link="CustomTypeMarshallerKind.cs" />
+    <Compile Include="$(LibrariesProjectRoot)Common/src/System/Runtime/InteropServices/CustomTypeMarshallerDirection.cs" Link="CustomTypeMarshallerDirection.cs" />
+    <Compile Include="$(LibrariesProjectRoot)Common/src/System/Runtime/InteropServices/CustomTypeMarshallerFeatures.cs" Link="CustomTypeMarshallerFeatures.cs" />
     <Compile Include="$(LibrariesProjectRoot)Common/src/System/Runtime/InteropServices/ArrayMarshaller.cs" Link="ArrayMarshaller.cs" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/SpanMarshallers.cs b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/SpanMarshallers.cs
index 46cd7302fbf..358fc92cf6b 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/SpanMarshallers.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/SpanMarshallers.cs
@@ -6,7 +6,10 @@ using System.Runtime.CompilerServices;
 
 namespace System.Runtime.InteropServices.GeneratedMarshalling
 {
-    [GenericContiguousCollectionMarshaller]
+    // Stack-alloc threshold set to 256 bytes to enable small arrays to be passed on the stack.
+    // Number kept small to ensure that P/Invokes with a lot of array parameters doesn't
+    // blow the stack since this is a new optimization in the code-generated interop.
+    [CustomTypeMarshaller(typeof(ReadOnlySpan<>), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 0x200)]
     public unsafe ref struct ReadOnlySpanMarshaller<T>
     {
         private ReadOnlySpan<T> _managedSpan;
@@ -47,47 +50,15 @@ namespace System.Runtime.InteropServices.GeneratedMarshalling
             }
         }
 
-        /// <summary>
-        /// Stack-alloc threshold set to 256 bytes to enable small arrays to be passed on the stack.
-        /// Number kept small to ensure that P/Invokes with a lot of array parameters doesn't
-        /// blow the stack since this is a new optimization in the code-generated interop.
-        /// </summary>
-        public const int BufferSize = 0x200;
-        public const bool RequiresStackBuffer = true;
+        public ReadOnlySpan<T> GetManagedValuesSource() => _managedSpan;
 
-        public Span<T> ManagedValues => MemoryMarshal.CreateSpan(ref MemoryMarshal.GetReference(_managedSpan), _managedSpan.Length);
+        public Span<byte> GetNativeValuesDestination() => NativeValueStorage;
 
-        public Span<byte> NativeValueStorage { get; private set; }
+        private Span<byte> NativeValueStorage { get; }
 
         public ref byte GetPinnableReference() => ref MemoryMarshal.GetReference(NativeValueStorage);
 
-        public void SetUnmarshalledCollectionLength(int length)
-        {
-            _managedSpan = new T[length];
-        }
-
-        public byte* Value
-        {
-            get
-            {
-                return (byte*)Unsafe.AsPointer(ref GetPinnableReference());
-            }
-            set
-            {
-                if (value == null)
-                {
-                    _managedSpan = null;
-                    NativeValueStorage = default;
-                }
-                else
-                {
-                    _allocatedMemory = (IntPtr)value;
-                    NativeValueStorage = new Span<byte>(value, _managedSpan.Length * _sizeOfNativeElement);
-                }
-            }
-        }
-
-        public ReadOnlySpan<T> ToManaged() => _managedSpan;
+        public byte* ToNativeValue() => (byte*)Unsafe.AsPointer(ref GetPinnableReference());
 
         public void FreeNative()
         {
@@ -95,68 +66,69 @@ namespace System.Runtime.InteropServices.GeneratedMarshalling
         }
     }
 
-    [GenericContiguousCollectionMarshaller]
+    [CustomTypeMarshaller(typeof(Span<>), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 0x200)]
     public unsafe ref struct SpanMarshaller<T>
     {
-        private ReadOnlySpanMarshaller<T> _inner;
+        private Span<T> _managedSpan;
+        private readonly int _sizeOfNativeElement;
+        private IntPtr _allocatedMemory;
 
         public SpanMarshaller(int sizeOfNativeElement)
             : this()
         {
-            _inner = new ReadOnlySpanMarshaller<T>(sizeOfNativeElement);
+            _sizeOfNativeElement = sizeOfNativeElement;
         }
 
         public SpanMarshaller(Span<T> managed, int sizeOfNativeElement)
+            :this(managed, Span<byte>.Empty, sizeOfNativeElement)
         {
-            _inner = new ReadOnlySpanMarshaller<T>(managed, sizeOfNativeElement);
         }
 
         public SpanMarshaller(Span<T> managed, Span<byte> stackSpace, int sizeOfNativeElement)
         {
-            _inner = new ReadOnlySpanMarshaller<T>(managed, stackSpace, sizeOfNativeElement);
-        }
-
-        /// <summary>
-        /// Stack-alloc threshold set to 256 bytes to enable small arrays to be passed on the stack.
-        /// Number kept small to ensure that P/Invokes with a lot of array parameters doesn't
-        /// blow the stack since this is a new optimization in the code-generated interop.
-        /// </summary>
-        public const int BufferSize = ReadOnlySpanMarshaller<T>.BufferSize;
-        public const bool RequiresStackBuffer = ReadOnlySpanMarshaller<T>.RequiresStackBuffer;
-
-        public Span<T> ManagedValues => _inner.ManagedValues;
-
-        public Span<byte> NativeValueStorage
-        {
-            get => _inner.NativeValueStorage;
+            _allocatedMemory = default;
+            _sizeOfNativeElement = sizeOfNativeElement;
+            if (managed.Length == 0)
+            {
+                _managedSpan = default;
+                NativeValueStorage = default;
+                return;
+            }
+            _managedSpan = managed;
+            int spaceToAllocate = managed.Length * sizeOfNativeElement;
+            if (spaceToAllocate <= stackSpace.Length)
+            {
+                NativeValueStorage = stackSpace[0..spaceToAllocate];
+            }
+            else
+            {
+                _allocatedMemory = Marshal.AllocCoTaskMem(spaceToAllocate);
+                NativeValueStorage = new Span<byte>((void*)_allocatedMemory, spaceToAllocate);
+            }
         }
 
-        public ref byte GetPinnableReference() => ref _inner.GetPinnableReference();
-
-        public void SetUnmarshalledCollectionLength(int length)
-        {
-            _inner.SetUnmarshalledCollectionLength(length);
-        }
+        private Span<byte> NativeValueStorage { get; set; }
 
-        public byte* Value
-        {
-            get => _inner.Value;
-            set => _inner.Value = value;
-        }
+        public ReadOnlySpan<T> GetManagedValuesSource() => _managedSpan;
+        public Span<T> GetManagedValuesDestination(int length) => _managedSpan = new T[length];
+        public Span<byte> GetNativeValuesDestination() => NativeValueStorage;
+        public ReadOnlySpan<byte> GetNativeValuesSource(int length) => NativeValueStorage = new Span<byte>((void*)_allocatedMemory, length * _sizeOfNativeElement);
+        public ref byte GetPinnableReference() => ref NativeValueStorage.GetPinnableReference();
+        public byte* ToNativeValue() => (byte*)Unsafe.AsPointer(ref GetPinnableReference());
+        public void FromNativeValue(byte* value) => _allocatedMemory = (IntPtr)value;
 
         public Span<T> ToManaged()
         {
-            ReadOnlySpan<T> managedInner = _inner.ToManaged();
-            return MemoryMarshal.CreateSpan(ref MemoryMarshal.GetReference(managedInner), managedInner.Length);
+            return _managedSpan;
         }
 
         public void FreeNative()
         {
-            _inner.FreeNative();
+            Marshal.FreeCoTaskMem(_allocatedMemory);
         }
     }
 
-    [GenericContiguousCollectionMarshaller]
+    [CustomTypeMarshaller(typeof(Span<>), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 0x200)]
     public unsafe ref struct NeverNullSpanMarshaller<T>
     {
         private SpanMarshaller<T> _inner;
@@ -177,47 +149,14 @@ namespace System.Runtime.InteropServices.GeneratedMarshalling
             _inner = new SpanMarshaller<T>(managed, stackSpace, sizeOfNativeElement);
         }
 
-        /// <summary>
-        /// Stack-alloc threshold set to 256 bytes to enable small spans to be passed on the stack.
-        /// Number kept small to ensure that P/Invokes with a lot of span parameters doesn't
-        /// blow the stack.
-        /// </summary>
-        public const int BufferSize = SpanMarshaller<T>.BufferSize;
-
-        public Span<T> ManagedValues => _inner.ManagedValues;
-
-        public Span<byte> NativeValueStorage
-        {
-            get => _inner.NativeValueStorage;
-        }
-
-        public ref byte GetPinnableReference()
-        {
-            if (_inner.ManagedValues.Length == 0)
-            {
-                return ref *(byte*)0xa5a5a5a5;
-            }
-            return ref _inner.GetPinnableReference();
-        }
-
-        public void SetUnmarshalledCollectionLength(int length)
-        {
-            _inner.SetUnmarshalledCollectionLength(length);
-        }
 
-        public byte* Value
-        {
-            get
-            {
-                if (_inner.ManagedValues.Length == 0)
-                {
-                    return (byte*)0xa5a5a5a5;
-                }
-                return _inner.Value;
-            }
-
-            set => _inner.Value = value;
-        }
+        public ReadOnlySpan<T> GetManagedValuesSource() => _inner.GetManagedValuesSource();
+        public Span<T> GetManagedValuesDestination(int length) => _inner.GetManagedValuesDestination(length);
+        public Span<byte> GetNativeValuesDestination() => _inner.GetNativeValuesDestination();
+        public ReadOnlySpan<byte> GetNativeValuesSource(int length) => _inner.GetNativeValuesSource(length);
+        public ref byte GetPinnableReference() => ref _inner.GetPinnableReference();
+        public byte* ToNativeValue() => _inner.GetManagedValuesSource().Length == 0 ? (byte*)0xa5a5a5a5 : (byte*)Unsafe.AsPointer(ref GetPinnableReference());
+        public void FromNativeValue(byte* value) => _inner.FromNativeValue(value);
 
         public Span<T> ToManaged() => _inner.ToManaged();
 
@@ -227,7 +166,7 @@ namespace System.Runtime.InteropServices.GeneratedMarshalling
         }
     }
 
-    [GenericContiguousCollectionMarshaller]
+    [CustomTypeMarshaller(typeof(ReadOnlySpan<>), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 0x200)]
     public unsafe ref struct NeverNullReadOnlySpanMarshaller<T>
     {
         private ReadOnlySpanMarshaller<T> _inner;
@@ -248,50 +187,10 @@ namespace System.Runtime.InteropServices.GeneratedMarshalling
             _inner = new ReadOnlySpanMarshaller<T>(managed, stackSpace, sizeOfNativeElement);
         }
 
-        /// <summary>
-        /// Stack-alloc threshold set to 256 bytes to enable small spans to be passed on the stack.
-        /// Number kept small to ensure that P/Invokes with a lot of span parameters doesn't
-        /// blow the stack.
-        /// </summary>
-        public const int BufferSize = SpanMarshaller<T>.BufferSize;
-        public const bool RequiresStackBuffer = SpanMarshaller<T>.RequiresStackBuffer;
-
-        public Span<T> ManagedValues => _inner.ManagedValues;
-
-        public Span<byte> NativeValueStorage
-        {
-            get => _inner.NativeValueStorage;
-        }
-
-        public ref byte GetPinnableReference()
-        {
-            if (_inner.ManagedValues.Length == 0)
-            {
-                return ref *(byte*)0xa5a5a5a5;
-            }
-            return ref _inner.GetPinnableReference();
-        }
-
-        public void SetUnmarshalledCollectionLength(int length)
-        {
-            _inner.SetUnmarshalledCollectionLength(length);
-        }
-
-        public byte* Value
-        {
-            get
-            {
-                if (_inner.ManagedValues.Length == 0)
-                {
-                    return (byte*)0xa5a5a5a5;
-                }
-                return _inner.Value;
-            }
-
-            set => _inner.Value = value;
-        }
-
-        public ReadOnlySpan<T> ToManaged() => _inner.ToManaged();
+        public ReadOnlySpan<T> GetManagedValuesSource() => _inner.GetManagedValuesSource();
+        public Span<byte> GetNativeValuesDestination() => _inner.GetNativeValuesDestination();
+        public ref byte GetPinnableReference() => ref _inner.GetPinnableReference();
+        public byte* ToNativeValue() => _inner.GetManagedValuesSource().Length == 0 ? (byte*)0xa5a5a5a5 : (byte*)Unsafe.AsPointer(ref GetPinnableReference());
 
         public void FreeNative()
         {
@@ -299,22 +198,18 @@ namespace System.Runtime.InteropServices.GeneratedMarshalling
         }
     }
 
-    [GenericContiguousCollectionMarshaller]
+    // Stack-alloc threshold set to 0 so that the generator can use the constructor that takes a stackSpace to let the marshaller know that the original data span can be used and safely pinned.
+    [CustomTypeMarshaller(typeof(Span<>), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 0)]
     public unsafe ref struct DirectSpanMarshaller<T>
         where T : unmanaged
     {
-        private int _unmarshalledLength;
         private T* _allocatedMemory;
+        private T* _nativeValue;
         private Span<T> _data;
 
         public DirectSpanMarshaller(int sizeOfNativeElement)
             :this()
         {
-            // This check is not exhaustive, but it will catch the majority of cases.
-            if (typeof(T) == typeof(bool) || typeof(T) == typeof(char) || Unsafe.SizeOf<T>() != sizeOfNativeElement)
-            {
-                throw new ArgumentException("This marshaller only supports blittable element types. The provided type parameter must be blittable", nameof(T));
-            }
         }
 
         public DirectSpanMarshaller(Span<T> managed, int sizeOfNativeElement)
@@ -337,42 +232,29 @@ namespace System.Runtime.InteropServices.GeneratedMarshalling
             _data = managed;
         }
 
-        /// <summary>
-        /// Stack-alloc threshold set to 0 so that the generator can use the constructor that takes a stackSpace to let the marshaller know that the original data span can be used and safely pinned.
-        /// </summary>
-        public const int BufferSize = 0;
-
-        public Span<T> ManagedValues => _data;
-
-        public Span<byte> NativeValueStorage => _allocatedMemory != null
+        public ReadOnlySpan<T> GetManagedValuesSource() => _data;
+        public Span<T> GetManagedValuesDestination(int length) => _data = new Span<T>(_nativeValue, length);
+        public Span<byte> GetNativeValuesDestination() => _allocatedMemory != null
             ? new Span<byte>(_allocatedMemory, _data.Length * Unsafe.SizeOf<T>())
             : MemoryMarshal.Cast<T, byte>(_data);
 
+        public ReadOnlySpan<byte> GetNativeValuesSource(int length) => new ReadOnlySpan<byte>(_nativeValue, length * sizeof(T));
+        
         public ref T GetPinnableReference() => ref _data.GetPinnableReference();
 
-        public void SetUnmarshalledCollectionLength(int length)
+        public T* ToNativeValue()
         {
-            _unmarshalledLength = length;
+            if (_allocatedMemory  != null)
+            {
+                return _allocatedMemory;
+            }
+            return (T*)Unsafe.AsPointer(ref GetPinnableReference());
         }
 
-        public T* Value
+        public void FromNativeValue(T* value)
         {
-            get
-            {
-                if (_allocatedMemory  != null)
-                {
-                    return _allocatedMemory;
-                }
-                return (T*)Unsafe.AsPointer(ref GetPinnableReference());
-            }
-            set
-            {
-                // We don't save the pointer assigned here to be freed
-                // since this marshaller passes back the actual memory span from native code
-                // back to managed code.
-                _allocatedMemory = null;
-                _data = new Span<T>(value, _unmarshalledLength);
-            }
+            _allocatedMemory = null;
+            _nativeValue = value;
         }
 
         public Span<T> ToManaged()
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/ArrayTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/ArrayTests.cs
index 8fd114021a4..6075ce224ee 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/ArrayTests.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/ArrayTests.cs
@@ -77,7 +77,7 @@ namespace LibraryImportGenerator.IntegrationTests
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = "transpose_matrix")]
             [return: MarshalUsing(CountElementName = "numColumns")]
-            [return: MarshalUsing(CountElementName = "numRows", ElementIndirectionLevel = 1)]
+            [return: MarshalUsing(CountElementName = "numRows", ElementIndirectionDepth = 1)]
             public static partial int[][] TransposeMatrix(int[][] matrix, int[] numRows, int numColumns);
         }
     }
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/CollectionTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/CollectionTests.cs
index f8676d68e26..f77258710ca 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/CollectionTests.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/CollectionTests.cs
@@ -36,20 +36,20 @@ namespace LibraryImportGenerator.IntegrationTests
             public static partial void CreateRange_Out(int start, int end, out int numValues, [MarshalUsing(typeof(ListMarshaller<int>), CountElementName = "numValues")] out List<int> res);
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = "sum_string_lengths")]
-            public static partial int SumStringLengths([MarshalUsing(typeof(ListMarshaller<string>)), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionLevel = 1)] List<string> strArray);
+            public static partial int SumStringLengths([MarshalUsing(typeof(ListMarshaller<string>)), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionDepth = 1)] List<string> strArray);
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = "reverse_strings_replace")]
-            public static partial void ReverseStrings_Ref([MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionLevel = 1)] ref List<string> strArray, out int numElements);
+            public static partial void ReverseStrings_Ref([MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionDepth = 1)] ref List<string> strArray, out int numElements);
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = "reverse_strings_return")]
-            [return: MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionLevel = 1)]
-            public static partial List<string> ReverseStrings_Return([MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionLevel = 1)] List<string> strArray, out int numElements);
+            [return: MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionDepth = 1)]
+            public static partial List<string> ReverseStrings_Return([MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionDepth = 1)] List<string> strArray, out int numElements);
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = "reverse_strings_out")]
             public static partial void ReverseStrings_Out(
-                [MarshalUsing(typeof(ListMarshaller<string>)), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionLevel = 1)] List<string> strArray,
+                [MarshalUsing(typeof(ListMarshaller<string>)), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionDepth = 1)] List<string> strArray,
                 out int numElements,
-                [MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionLevel = 1)] out List<string> res);
+                [MarshalUsing(typeof(ListMarshaller<string>), CountElementName = "numElements"), MarshalUsing(typeof(Utf16StringMarshaller), ElementIndirectionDepth = 1)] out List<string> res);
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = "get_long_bytes")]
             [return:MarshalUsing(typeof(ListMarshaller<byte>), ConstantElementCount = sizeof(long))]
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/SetLastErrorTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/SetLastErrorTests.cs
index 057bef953c7..18a3ac4fc1a 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/SetLastErrorTests.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/SetLastErrorTests.cs
@@ -8,6 +8,7 @@ using Xunit;
 
 namespace LibraryImportGenerator.IntegrationTests
 {
+    [CustomTypeMarshaller(typeof(int))]
     public struct SetLastErrorMarshaller
     {
         public int val;
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AdditionalAttributesOnStub.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AdditionalAttributesOnStub.cs
index e9a7f5c47b4..fa879e7d134 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AdditionalAttributesOnStub.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AdditionalAttributesOnStub.cs
@@ -31,6 +31,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
@@ -82,6 +83,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
@@ -172,6 +174,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
@@ -204,6 +207,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
@@ -236,6 +240,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AttributeForwarding.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AttributeForwarding.cs
index f876a914e0f..7edda25746c 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AttributeForwarding.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/AttributeForwarding.cs
@@ -38,6 +38,7 @@ struct S
 {{
 }}
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {{
     public Native(S s) {{ }}
@@ -79,6 +80,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
@@ -122,6 +124,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
@@ -169,6 +172,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
@@ -220,6 +224,7 @@ struct S
 {{
 }}
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {{
     public Native(S s) {{ }}
@@ -268,6 +273,7 @@ struct S
 {
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     public Native(S s) { }
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CodeSnippets.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CodeSnippets.cs
index 93b822d6f7b..3312098bfe5 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CodeSnippets.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CodeSnippets.cs
@@ -381,6 +381,7 @@ partial class Test
         {
             string typeName = typeof(T).ToString();
             return BasicParametersAndModifiersWithStringMarshallingCustomType(typeName, "Native", DisableRuntimeMarshalling) + @$"
+[CustomTypeMarshaller(typeof({typeName}))]
 struct Native
 {{
     public Native({typeName} s) {{ }}
@@ -636,6 +637,7 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     private int i;
@@ -655,6 +657,7 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S))]
 struct Native
 {
     private int i;
@@ -674,6 +677,7 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 1)]
 struct Native
 {
     private int i;
@@ -683,8 +687,6 @@ struct Native
     }
 
     public S ToManaged() => new S { b = i != 0 };
-
-    public const int BufferSize = 1;
 }
 ";
         public static string CustomStructMarshallingStackallocOnlyRefParameter = BasicParameterWithByRefModifier("ref", "S", DisableRuntimeMarshalling) + @"
@@ -694,6 +696,7 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.Out, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 1)]
 struct Native
 {
     private int i;
@@ -703,9 +706,6 @@ struct Native
     }
 
     public S ToManaged() => new S { b = i != 0 };
-
-    public const int BufferSize = 1;
-    public const bool RequiresStackBuffer = false;
 }
 ";
         public static string CustomStructMarshallingOptionalStackallocParametersAndModifiers = BasicParametersAndModifiers("S", DisableRuntimeMarshalling) + @"
@@ -715,6 +715,7 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 1)]
 struct Native
 {
     private int i;
@@ -728,9 +729,6 @@ struct Native
     }
 
     public S ToManaged() => new S { b = i != 0 };
-
-    public const int BufferSize = 1;
-    public const bool RequiresStackBuffer = true;
 }
 ";
 
@@ -741,18 +739,17 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 1)]
 struct Native
 {
     public Native(S s, System.Span<byte> b)
     {
-        Value = s.b ? 1 : 0;
     }
 
-    public S ToManaged() => new S { b = Value != 0 };
-
-    public int Value { get; set; }
+    public S ToManaged() => new S { b = true };
 
-    public const int BufferSize = 1;
+    public int ToNativeValue() => throw null;
+    public void FromNativeValue(int value) => throw null;
 }
 ";
         public static string CustomStructMarshallingValuePropertyParametersAndModifiers = BasicParametersAndModifiers("S", DisableRuntimeMarshalling) + @"
@@ -762,16 +759,17 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
 struct Native
 {
     public Native(S s)
     {
-        Value = s.b ? 1 : 0;
     }
 
-    public S ToManaged() => new S { b = Value != 0 };
+    public S ToManaged() => new S { b = true };
 
-    public int Value { get; set; }
+    public int ToNativeValue() => throw null;
+    public void FromNativeValue(int value) => throw null;
 }
 ";
         public static string CustomStructMarshallingPinnableParametersAndModifiers = BasicParametersAndModifiers("S", DisableRuntimeMarshalling) + @"
@@ -783,6 +781,7 @@ class S
     public ref int GetPinnableReference() => ref i;
 }
 
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
 unsafe struct Native
 {
     private int* ptr;
@@ -794,15 +793,14 @@ unsafe struct Native
 
     public S ToManaged() => new S { i = *ptr };
 
-    public nint Value
-    {
-        get => (nint)ptr;
-        set => ptr = (int*)value;
-    }
+    public nint ToNativeValue() => (nint)ptr;
+
+    public void FromNativeValue(nint value) => ptr = (int*)value;
 }
 ";
 
         public static string CustomStructMarshallingNativeTypePinnable = @"
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System;
 
@@ -814,6 +812,7 @@ class S
     public byte c;
 }
 
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 1)]
 unsafe ref struct Native
 {
     private byte* ptr;
@@ -823,6 +822,7 @@ unsafe ref struct Native
     {
         ptr = (byte*)Marshal.AllocCoTaskMem(sizeof(byte));
         *ptr = s.c;
+        stackBuffer = new Span<byte>(ptr, 1);
     }
 
     public Native(S s, Span<byte> buffer) : this()
@@ -831,18 +831,16 @@ unsafe ref struct Native
         stackBuffer[0] = s.c;
     }
 
-    public ref byte GetPinnableReference() => ref (ptr != null ? ref *ptr : ref stackBuffer.GetPinnableReference());
+    public ref byte GetPinnableReference() => ref stackBuffer.GetPinnableReference();
 
     public S ToManaged()
     {
         return new S { c = *ptr };
     }
 
-    public byte* Value
-    {
-        get => ptr != null ? ptr : throw new InvalidOperationException();
-        set => ptr = value;
-    }
+    public byte* ToNativeValue() => (byte*)Unsafe.AsPointer(ref GetPinnableReference());
+
+    public void FromNativeValue(byte* value) => ptr = value;
 
     public void FreeNative()
     {
@@ -851,8 +849,6 @@ unsafe ref struct Native
             Marshal.FreeCoTaskMem((IntPtr)ptr);
         }
     }
-
-    public const int BufferSize = 1;
 }
 
 partial class Test
@@ -871,6 +867,7 @@ class S
     public byte c = 0;
 }
 
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
 unsafe struct Native
 {
     private S value;
@@ -880,7 +877,7 @@ unsafe struct Native
         value = s;
     }
 
-    public ref byte Value { get => ref value.c; }
+    public ref byte ToNativeValue() => ref value.c;
 }
 ";
 
@@ -921,6 +918,7 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In)]
 struct Native
 {
     private int i;
@@ -939,6 +937,7 @@ struct S
     public bool b;
 }
 
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In)]
 struct Native
 {
     private int i;
@@ -957,6 +956,7 @@ struct S
 }
 
 [StructLayout(LayoutKind.Sequential)]
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.Out)]
 struct Native
 {
     private int i;
@@ -971,16 +971,17 @@ public struct IntStructWrapper
     public int Value;
 }
 
+[CustomTypeMarshaller(typeof(IntStructWrapper), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
 public struct IntStructWrapperNative
 {
     public IntStructWrapperNative(IntStructWrapper managed)
     {
-        Value = managed.Value;
     }
 
-    public int Value { get; set; }
+    public int ToNativeValue() => throw null;
+    public void FromNativeValue(int value) => throw null;
 
-    public IntStructWrapper ToManaged() => new IntStructWrapper { Value = Value };
+    public IntStructWrapper ToManaged() => new IntStructWrapper { Value = 1 };
 }
 ";
 
@@ -991,6 +992,7 @@ public struct IntStructWrapper
     public int Value;
 }
 
+[CustomTypeMarshaller(typeof(IntStructWrapper))]
 public struct IntStructWrapperNative
 {
     private int value;
@@ -1116,13 +1118,18 @@ struct RecursiveStruct2
 [NativeMarshalling(typeof(Marshaller<>))]
 class TestCollection<T> {}
 
-[GenericContiguousCollectionMarshaller]
+[CustomTypeMarshaller(typeof(TestCollection<>), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
 ref struct Marshaller<T>
 {
+    public Marshaller(int nativeElementSize) : this() {}
     public Marshaller(TestCollection<T> managed, int nativeElementSize) : this() {}
-    public System.Span<T> ManagedValues { get; }
-    public System.Span<byte> NativeValueStorage { get; }
-    public System.IntPtr Value { get; }
+    public System.ReadOnlySpan<T> GetManagedValuesSource() => throw null;
+    public System.Span<T> GetManagedValuesDestination(int length) => throw null;
+    public System.ReadOnlySpan<byte> GetNativeValuesSource(int length) => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(System.IntPtr value) => throw null;
+    public TestCollection<T> ToManaged() => throw null;
 }
 ";
 
@@ -1150,15 +1157,17 @@ partial class Test
             string nativeMarshallingAttribute = enableDefaultMarshalling ? "[NativeMarshalling(typeof(Marshaller<>))]" : string.Empty;
             return nativeMarshallingAttribute + @"class TestCollection<T> {}
 
-[GenericContiguousCollectionMarshaller]
+[CustomTypeMarshaller(typeof(TestCollection<>), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
 ref struct Marshaller<T>
 {
     public Marshaller(int nativeElementSize) : this() {}
     public Marshaller(TestCollection<T> managed, int nativeElementSize) : this() {}
-    public System.Span<T> ManagedValues { get; }
-    public System.Span<byte> NativeValueStorage { get; }
-    public System.IntPtr Value { get; set; }
-    public void SetUnmarshalledCollectionLength(int length) {}
+    public System.ReadOnlySpan<T> GetManagedValuesSource() => throw null;
+    public System.Span<T> GetManagedValuesDestination(int length) => throw null;
+    public System.ReadOnlySpan<byte> GetNativeValuesSource(int length) => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(System.IntPtr value) => throw null;
     public TestCollection<T> ToManaged() => throw null;
 }";
         }
@@ -1247,13 +1256,18 @@ partial class Test
 [NativeMarshalling(typeof(Marshaller<,>))]
 class TestCollection<T> {}
 
-[GenericContiguousCollectionMarshaller]
+[CustomTypeMarshaller(typeof(TestCollection<>), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
 ref struct Marshaller<T, U>
 {
     public Marshaller(TestCollection<T> managed, int nativeElementSize) : this() {}
-    public System.Span<T> ManagedValues { get; }
-    public System.Span<byte> NativeValueStorage { get; }
-    public System.IntPtr Value { get; }
+
+    public System.ReadOnlySpan<T> GetManagedValuesSource() => throw null;
+    public System.Span<T> GetManagedValuesDestination(int length) => throw null;
+    public System.ReadOnlySpan<byte> GetNativeValuesSource(int length) => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(System.IntPtr value) => throw null;
+
     public TestCollection<T> ToManaged() => throw null;
 }";
 
@@ -1264,13 +1278,13 @@ partial class Test
 {
     [LibraryImport(""DoesNotExist"")]
     [return:MarshalUsing(ConstantElementCount=10)]
-    [return:MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 1)]
+    [return:MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 1)]
     public static partial TestCollection<int> Method(
-        [MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 1)] TestCollection<int> p,
-        [MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 1)] in TestCollection<int> pIn,
+        [MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 1)] TestCollection<int> p,
+        [MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 1)] in TestCollection<int> pIn,
         int pRefSize,
-        [MarshalUsing(CountElementName = ""pRefSize""), MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 1)] ref TestCollection<int> pRef,
-        [MarshalUsing(CountElementName = ""pOutSize"")][MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 1)] out TestCollection<int> pOut,
+        [MarshalUsing(CountElementName = ""pRefSize""), MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 1)] ref TestCollection<int> pRef,
+        [MarshalUsing(CountElementName = ""pOutSize"")][MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 1)] out TestCollection<int> pOut,
         out int pOutSize
         );
 }
@@ -1283,14 +1297,14 @@ struct IntWrapper
 
 " + CustomCollectionWithMarshaller(enableDefaultMarshalling: true);
 
-        public static string GenericCollectionWithCustomElementMarshallingDuplicateElementIndirectionLevel => @"
+        public static string GenericCollectionWithCustomElementMarshallingDuplicateElementIndirectionDepth => @"
 using System.Runtime.InteropServices;
 [assembly:System.Runtime.CompilerServices.DisableRuntimeMarshalling]
 partial class Test
 {
     [LibraryImport(""DoesNotExist"")]
     public static partial void Method(
-        [MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 1)] [MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 1)] TestCollection<int> p);
+        [MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 1)] [MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 1)] TestCollection<int> p);
 }
 
 struct IntWrapper
@@ -1301,14 +1315,14 @@ struct IntWrapper
 
 " + CustomCollectionWithMarshaller(enableDefaultMarshalling: true);
 
-        public static string GenericCollectionWithCustomElementMarshallingUnusedElementIndirectionLevel => @"
+        public static string GenericCollectionWithCustomElementMarshallingUnusedElementIndirectionDepth => @"
 using System.Runtime.InteropServices;
 [assembly:System.Runtime.CompilerServices.DisableRuntimeMarshalling]
 partial class Test
 {
     [LibraryImport(""DoesNotExist"")]
     public static partial void Method(
-        [MarshalUsing(typeof(IntWrapper), ElementIndirectionLevel = 2)] TestCollection<int> p);
+        [MarshalUsing(typeof(IntWrapper), ElementIndirectionDepth = 2)] TestCollection<int> p);
 }
 
 struct IntWrapper
@@ -1385,72 +1399,72 @@ partial class Test
 {
     [LibraryImport(""DoesNotExist"")]
     public static partial void Method(
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]
-        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionLevel = 4)]
-        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionLevel = 5)]
-        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionLevel = 6)]
-        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionLevel = 7)]
-        [MarshalUsing(CountElementName=""arr8"", ElementIndirectionLevel = 8)]
-        [MarshalUsing(CountElementName=""arr9"", ElementIndirectionLevel = 9)]
-        [MarshalUsing(CountElementName=""arr10"", ElementIndirectionLevel = 10)] ref int[][][][][][][][][][][] arr11,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]
-        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionLevel = 4)]
-        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionLevel = 5)]
-        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionLevel = 6)]
-        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionLevel = 7)]
-        [MarshalUsing(CountElementName=""arr8"", ElementIndirectionLevel = 8)]
-        [MarshalUsing(CountElementName=""arr9"", ElementIndirectionLevel = 9)]ref int[][][][][][][][][][] arr10,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]
-        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionLevel = 4)]
-        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionLevel = 5)]
-        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionLevel = 6)]
-        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionLevel = 7)]
-        [MarshalUsing(CountElementName=""arr8"", ElementIndirectionLevel = 8)]ref int[][][][][][][][][] arr9,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]
-        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionLevel = 4)]
-        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionLevel = 5)]
-        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionLevel = 6)]
-        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionLevel = 7)]ref int[][][][][][][][][] arr8,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]
-        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionLevel = 4)]
-        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionLevel = 5)]
-        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionLevel = 6)]ref int[][][][][][][] arr7,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]
-        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionLevel = 4)]
-        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionLevel = 5)]ref int[][][][][][] arr6,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]
-        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionLevel = 4)]ref int[][][][][] arr5,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]
-        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionLevel = 3)]ref int[][][][] arr4,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]
-        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionLevel = 2)]ref int[][][] arr3,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]
-        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionLevel = 1)]ref int[][] arr2,
-        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionLevel = 0)]ref int[] arr1,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]
+        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionDepth = 4)]
+        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionDepth = 5)]
+        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionDepth = 6)]
+        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionDepth = 7)]
+        [MarshalUsing(CountElementName=""arr8"", ElementIndirectionDepth = 8)]
+        [MarshalUsing(CountElementName=""arr9"", ElementIndirectionDepth = 9)]
+        [MarshalUsing(CountElementName=""arr10"", ElementIndirectionDepth = 10)] ref int[][][][][][][][][][][] arr11,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]
+        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionDepth = 4)]
+        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionDepth = 5)]
+        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionDepth = 6)]
+        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionDepth = 7)]
+        [MarshalUsing(CountElementName=""arr8"", ElementIndirectionDepth = 8)]
+        [MarshalUsing(CountElementName=""arr9"", ElementIndirectionDepth = 9)]ref int[][][][][][][][][][][] arr10,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]
+        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionDepth = 4)]
+        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionDepth = 5)]
+        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionDepth = 6)]
+        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionDepth = 7)]
+        [MarshalUsing(CountElementName=""arr8"", ElementIndirectionDepth = 8)]ref int[][][][][][][][][][] arr9,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]
+        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionDepth = 4)]
+        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionDepth = 5)]
+        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionDepth = 6)]
+        [MarshalUsing(CountElementName=""arr7"", ElementIndirectionDepth = 7)]ref int[][][][][][][][][] arr8,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]
+        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionDepth = 4)]
+        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionDepth = 5)]
+        [MarshalUsing(CountElementName=""arr6"", ElementIndirectionDepth = 6)]ref int[][][][][][][] arr7,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]
+        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionDepth = 4)]
+        [MarshalUsing(CountElementName=""arr5"", ElementIndirectionDepth = 5)]ref int[][][][][][] arr6,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]
+        [MarshalUsing(CountElementName=""arr4"", ElementIndirectionDepth = 4)]ref int[][][][][] arr5,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]
+        [MarshalUsing(CountElementName=""arr3"", ElementIndirectionDepth = 3)]ref int[][][][] arr4,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]
+        [MarshalUsing(CountElementName=""arr2"", ElementIndirectionDepth = 2)]ref int[][][] arr3,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]
+        [MarshalUsing(CountElementName=""arr1"", ElementIndirectionDepth = 1)]ref int[][] arr2,
+        [MarshalUsing(CountElementName=""arr0"", ElementIndirectionDepth = 0)]ref int[] arr1,
         ref int arr0
     );
 }
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CompileFails.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CompileFails.cs
index 262072e940c..3a5403e70c3 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CompileFails.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CompileFails.cs
@@ -110,8 +110,8 @@ namespace LibraryImportGenerator.UnitTests
             yield return new object[] { CodeSnippets.GenericCollectionMarshallingArityMismatch, 2, 0 };
 
             yield return new object[] { CodeSnippets.MarshalAsAndMarshalUsingOnReturnValue, 2, 0 };
-            yield return new object[] { CodeSnippets.GenericCollectionWithCustomElementMarshallingDuplicateElementIndirectionLevel, 2, 0 };
-            yield return new object[] { CodeSnippets.GenericCollectionWithCustomElementMarshallingUnusedElementIndirectionLevel, 1, 0 };
+            yield return new object[] { CodeSnippets.GenericCollectionWithCustomElementMarshallingDuplicateElementIndirectionDepth, 2, 0 };
+            yield return new object[] { CodeSnippets.GenericCollectionWithCustomElementMarshallingUnusedElementIndirectionDepth, 1, 0 };
             yield return new object[] { CodeSnippets.RecursiveCountElementNameOnReturnValue, 2, 0 };
             yield return new object[] { CodeSnippets.RecursiveCountElementNameOnParameter, 2, 0 };
             yield return new object[] { CodeSnippets.MutuallyRecursiveCountElementNameOnParameter, 4, 0 };
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomTypeMarshallerFixerTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomTypeMarshallerFixerTests.cs
new file mode 100644
index 00000000000..9707345179c
--- /dev/null
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomTypeMarshallerFixerTests.cs
@@ -0,0 +1,1769 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Testing;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Xunit;
+using static Microsoft.Interop.Analyzers.CustomTypeMarshallerAnalyzer;
+
+using VerifyCS = LibraryImportGenerator.UnitTests.Verifiers.CSharpCodeFixVerifier<
+    Microsoft.Interop.Analyzers.CustomTypeMarshallerAnalyzer,
+    Microsoft.Interop.Analyzers.CustomTypeMarshallerFixer>;
+
+namespace LibraryImportGenerator.UnitTests
+{
+    [ActiveIssue("https://github.com/dotnet/runtime/issues/60650", TestRuntimes.Mono)]
+    public class CustomTypeMarshallerFixerTests
+    {
+        [Fact]
+        public async Task NullNativeType_ReportsDiagnostic()
+        {
+            string source = @"
+using System.Runtime.InteropServices;
+
+[{|#0:NativeMarshalling(null)|}]
+struct S
+{
+    public string s;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustHaveCustomTypeMarshallerAttributeRule).WithLocation(0).WithArguments("S"),
+                source);
+        }
+
+        [Fact]
+        public async Task NonNamedNativeType_ReportsDiagnostic()
+        {
+            string source = @"
+using System.Runtime.InteropServices;
+
+[{|#0:NativeMarshalling(typeof(int*))|}]
+struct S
+{
+    public string s;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustHaveCustomTypeMarshallerAttributeRule).WithLocation(0).WithArguments("S"),
+                source);
+        }
+
+        [Fact]
+        public async Task NonBlittableNativeType_ReportsDiagnostic()
+        {
+            string source = @"
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S))]
+struct {|#0:Native|}
+{
+    private string value;
+
+    public Native(S s)
+    {
+        value = s.s;
+    }
+
+    public S ToManaged() => new S { s = value };
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task ClassNativeType_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+struct S
+{
+    public string s;
+}
+
+[{|CS0592:CustomTypeMarshaller|}(typeof(S))]
+class {|#0:Native|}
+{
+    private IntPtr value;
+
+    public Native(S s)
+    {
+    }
+
+    public S ToManaged() => new S();
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task BlittableNativeType_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S))]
+struct Native
+{
+    private IntPtr value;
+
+    public Native(S s)
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task BlittableNativeWithNonBlittableToNativeValue_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native
+{
+    private IntPtr value;
+
+    public Native(S s)
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+
+    public string {|#0:ToNativeValue|}() => throw null;
+    public void FromNativeValue(string value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("string", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task NonBlittableNativeTypeWithBlittableToNativeValue_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native
+{
+    private string value;
+
+    public Native(S s)
+    {
+        value = s.s;
+    }
+
+    public S ToManaged() => new S() { s = value };
+
+    public IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(IntPtr value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task NonBlittableGetPinnableReferenceReturnType_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public string s;
+
+    public ref string {|#0:GetPinnableReference|}() => ref s;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private IntPtr value;
+
+    public Native(S s)
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+
+    public IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(IntPtr value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(GetPinnableReferenceReturnTypeBlittableRule).WithLocation(0),
+                source);
+        }
+
+        [Fact]
+        public async Task BlittableGetPinnableReferenceReturnType_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+
+    public ref byte GetPinnableReference() => ref c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private IntPtr value;
+
+    public Native(S s) : this()
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+
+    public IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(IntPtr value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task NonBlittableMarshallerGetPinnableReferenceReturnType_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public char c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private IntPtr value;
+
+    public Native(S s)
+    {
+        value = IntPtr.Zero;
+    }
+
+    public ref char GetPinnableReference() => ref System.Runtime.CompilerServices.Unsafe.NullRef<char>();
+
+    public S ToManaged() => new S();
+
+    public IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(IntPtr value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task BlittableMarshallerGetPinnableReferenceReturnType_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private IntPtr value;
+
+    public Native(S s) : this()
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+
+    public ref byte GetPinnableReference() => ref System.Runtime.CompilerServices.Unsafe.NullRef<byte>();
+
+    public IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(IntPtr value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task TypeWithGetPinnableReferenceNonPointerReturnType_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+
+    public ref byte GetPinnableReference() => ref c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private IntPtr value;
+
+    public Native(S s) : this()
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+
+    public int {|#0:ToNativeValue|}() => throw null;
+    public void FromNativeValue(int value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustBePointerSizedRule).WithLocation(0).WithArguments("int", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task TypeWithGetPinnableReferencePointerReturnType_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+
+    public ref byte GetPinnableReference() => ref c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private IntPtr value;
+
+    public Native(S s) : this()
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+
+    public int* ToNativeValue() => throw null;
+    public void FromNativeValue(int* value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task TypeWithGetPinnableReferenceByRefValuePropertyType_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+
+    public ref byte GetPinnableReference() => ref c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private S value;
+
+    public Native(S s) : this()
+    {
+        value = s;
+    }
+    public ref byte {|#0:ToNativeValue|}() => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(RefNativeValueUnsupportedRule).WithLocation(0).WithArguments("Native"),
+                source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithGetPinnableReferenceByRefValuePropertyType_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private S value;
+
+    public Native(S s) : this()
+    {
+        value = s;
+    }
+
+    public ref byte GetPinnableReference() => ref value.c;
+
+    public ref byte {|#0:ToNativeValue|}() => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(RefNativeValueUnsupportedRule).WithLocation(0).WithArguments("Native"),
+                source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithGetPinnableReferenceNoValueProperty_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In)]
+unsafe struct Native
+{
+    private byte value;
+
+    public Native(S s) : this()
+    {
+        value = s.c;
+    }
+
+    public ref byte {|#0:GetPinnableReference|}() => ref System.Runtime.CompilerServices.Unsafe.NullRef<byte>();
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(MarshallerGetPinnableReferenceRequiresTwoStageMarshallingRule).WithLocation(0).WithArguments("Native"),
+                source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithGetPinnableReferenceWithNonPointerValueProperty_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    private byte value;
+
+    public Native(S s) : this()
+    {
+        value = s.c;
+    }
+
+    public ref byte GetPinnableReference() => ref System.Runtime.CompilerServices.Unsafe.NullRef<byte>();
+
+    public int ToNativeValue() => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithNoMarshallingMethods_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.None)]
+struct {|#0:Native|}
+{
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(CustomMarshallerTypeMustSupportDirectionRule).WithLocation(0).WithArguments("Native", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithNoMarshallingMethods_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.None)]
+struct {|#0:Native|}
+{
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(CustomMarshallerTypeMustSupportDirectionRule).WithLocation(0).WithArguments("Native", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithWrongConstructor_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct {|#0:Native|}
+{
+    public Native(S s) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct Native
+{
+    public Native(S s) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+
+    public Native(S managed, int nativeElementSize)
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(LinearCollectionInRequiresTwoParameterConstructorRule).WithLocation(0).WithArguments("Native", "S"),
+                fixedSource);
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithCorrectConstructor_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct Native
+{
+    public Native(S s, int nativeElementSize) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithIncorrectStackallocConstructor_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 1)]
+ref struct {|#0:Native|}
+{
+    public Native(S s, Span<byte> stackSpace) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 1)]
+ref struct Native
+{
+    public Native(S s, Span<byte> stackSpace) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+
+    public Native(S managed, int nativeElementSize)
+    {
+        throw new NotImplementedException();
+    }
+
+    public Native(S managed, Span<byte> buffer, int nativeElementSize)
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                fixedSource,
+                    VerifyCS.Diagnostic(LinearCollectionInRequiresTwoParameterConstructorRule).WithLocation(0).WithArguments("Native", "S"),
+                    VerifyCS.Diagnostic(LinearCollectionInCallerAllocatedBufferRequiresSpanConstructorRule).WithLocation(0).WithArguments("Native", "S"));
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithOnlyStackallocConstructor_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 1)]
+ref struct {|#0:Native|}
+{
+    public Native(S s, Span<byte> stackSpace, int nativeElementSize) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer | CustomTypeMarshallerFeatures.TwoStageMarshalling, BufferSize = 1)]
+ref struct Native
+{
+    public Native(S s, Span<byte> stackSpace, int nativeElementSize) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+
+    public Native(S managed, int nativeElementSize)
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                fixedSource,
+                VerifyCS.Diagnostic(CallerAllocMarshallingShouldSupportAllocatingMarshallingFallbackRule).WithLocation(0).WithArguments("Native", "S"),
+                VerifyCS.Diagnostic(LinearCollectionInRequiresTwoParameterConstructorRule).WithLocation(0).WithArguments("Native", "S"));
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithMissingManagedValuesSource_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct {|#0:Native|}
+{
+    public Native(S s, int nativeElementSize) : this() {}
+
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct Native
+{
+    public Native(S s, int nativeElementSize) : this() {}
+
+    public System.Span<byte> GetNativeValuesDestination() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+
+    public ReadOnlySpan<object> GetManagedValuesSource()
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(LinearCollectionInRequiresCollectionMethodsRule).WithLocation(0).WithArguments("Native", "S"),
+                fixedSource);
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithMissingNativeValuesDestination_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct {|#0:Native|}
+{
+    public Native(S s, int nativeElementSize) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct Native
+{
+    public Native(S s, int nativeElementSize) : this() {}
+
+    public System.ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public System.IntPtr ToNativeValue() => throw null;
+
+    public Span<byte> GetNativeValuesDestination()
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(LinearCollectionInRequiresCollectionMethodsRule).WithLocation(0).WithArguments("Native", "S"),
+                fixedSource);
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithCorrectRefShape_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct Native
+{
+    public Native(int nativeElementSize) : this() {}
+    public Native(S s, int nativeElementSize) : this() {}
+
+    public ReadOnlySpan<int> GetManagedValuesSource() => throw null;
+    public Span<byte> GetNativeValuesDestination() => throw null;
+    public ReadOnlySpan<byte> GetNativeValuesSource(int length) => throw null;
+    public Span<int> GetManagedValuesDestination(int length) => throw null;
+    public IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(IntPtr value) => throw null;
+    public S ToManaged() => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task CollectionNativeTypeWithMismatched_Element_Type_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+ref struct Native
+{
+    public Native(int nativeElementSize) : this() {}
+    public Native(S s, int nativeElementSize) : this() {}
+
+    public ReadOnlySpan<int> {|#0:GetManagedValuesSource|}() => throw null;
+    public Span<byte> GetNativeValuesDestination() => throw null;
+    public ReadOnlySpan<byte> GetNativeValuesSource(int length) => throw null;
+    public Span<long> GetManagedValuesDestination(int length) => throw null;
+    public IntPtr ToNativeValue() => throw null;
+    public void FromNativeValue(IntPtr value) => throw null;
+    public S ToManaged() => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                source,
+                VerifyCS.Diagnostic(LinearCollectionElementTypesMustMatchRule)
+                    .WithLocation(0));
+        }
+
+        [Fact]
+        public async Task NativeTypeWithOnlyConstructor_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In)]
+struct Native
+{
+    public Native(S s) {}
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithOnlyToManagedMethod_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.Out)]
+struct Native
+{
+    public S ToManaged() => new S();
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithOnlyStackallocConstructor_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x100)]
+struct {|#0:Native|}
+{
+    public Native(S s, Span<byte> buffer) {}
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x100)]
+struct Native
+{
+    public Native(S s, Span<byte> buffer) {}
+
+    public Native(S managed)
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                fixedSource,
+                VerifyCS.Diagnostic(CallerAllocMarshallingShouldSupportAllocatingMarshallingFallbackRule).WithLocation(0).WithArguments("Native", "S"),
+                VerifyCS.Diagnostic(ValueInRequiresOneParameterConstructorRule).WithLocation(0).WithArguments("Native", "S"));
+        }
+
+        [Fact]
+        public async Task TypeWithOnlyGetPinnableReference_AndInSupport_ReportsDiagnostics()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class {|#0:S|}
+{
+    public byte c;
+    public ref byte GetPinnableReference() => ref c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.Out)]
+struct {|#1:Native|}
+{
+    public S ToManaged() => default;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(GetPinnableReferenceShouldSupportAllocatingMarshallingFallbackRule).WithLocation(0).WithArguments("S", "Native"),
+                source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithConstructorAndFromNativeValueMethod_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct {|#0:Native|}
+{
+    public Native(S s) {}
+
+    public void FromNativeValue(IntPtr value) => throw null;
+
+    public S ToManaged() => new S();
+}";
+
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native
+{
+    public Native(S s) {}
+
+    public void FromNativeValue(IntPtr value) => throw null;
+
+    public S ToManaged() => new S();
+
+    public IntPtr ToNativeValue()
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(InTwoStageMarshallingRequiresToNativeValueRule).WithLocation(0).WithArguments("Native"),
+                fixedSource);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithToManagedAndToNativeValueMethod_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct {|#0:Native|}
+{
+    public Native(S managed) {}
+
+    public S ToManaged() => new S();
+
+    public IntPtr ToNativeValue() => IntPtr.Zero;
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native
+{
+    public Native(S managed) {}
+
+    public S ToManaged() => new S();
+
+    public IntPtr ToNativeValue() => IntPtr.Zero;
+
+    public void FromNativeValue(IntPtr value)
+    {
+        throw new NotImplementedException();
+    }
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(OutTwoStageMarshallingRequiresFromNativeValueRule).WithLocation(0).WithArguments("Native"),
+                fixedSource);
+        }
+
+        [Fact]
+        public async Task BlittableNativeTypeOnMarshalUsingParameter_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S))]
+struct Native
+{
+    private IntPtr value;
+
+    public Native(S s)
+    {
+        value = IntPtr.Zero;
+    }
+
+    public S ToManaged() => new S();
+}
+
+
+static class Test
+{
+    static void Foo([MarshalUsing(typeof(Native))] S s)
+    {}
+}
+";
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task NonBlittableNativeTypeOnMarshalUsingParameter_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S))]
+struct {|#0:Native|}
+{
+    private string value;
+
+    public Native(S s) : this()
+    {
+    }
+
+    public S ToManaged() => new S();
+}
+
+
+static class Test
+{
+    static void Foo([MarshalUsing(typeof(Native))] S s)
+    {}
+}
+";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task NonBlittableNativeTypeOnMarshalUsingReturn_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S))]
+struct {|#0:Native|}
+{
+    private string value;
+
+    public Native(S s) : this()
+    {
+    }
+
+    public S ToManaged() => new S();
+}
+
+
+static class Test
+{
+    [return: MarshalUsing(typeof(Native))]
+    static S Foo() => new S();
+}
+";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task GenericNativeTypeWithGenericMemberInstantiatedWithBlittable_DoesNotReportDiagnostic()
+        {
+
+            string source = @"
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native<int>))]
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native<T>
+    where T : unmanaged
+{
+    public Native(S s)
+    {
+    }
+
+    public S ToManaged() => new S();
+
+    public T ToNativeValue() => throw null;
+    public void FromNativeValue(T value) => throw null;
+}";
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task UninstantiatedGenericNativeTypeOnNonGeneric_ReportsDiagnostic()
+        {
+
+            string source = @"
+using System.Runtime.InteropServices;
+
+[{|#0:NativeMarshalling(typeof(Native<>))|}]
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native<T>
+    where T : unmanaged
+{
+    public Native(S s)
+    {
+    }
+
+    public S ToManaged() => new S();
+
+    public T ToNativeValue() => throw null;
+    public void FromNativeValue(T value) => throw null;
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeGenericTypeMustBeClosedOrMatchArityRule).WithLocation(0).WithArguments("Native<>", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task MarshalUsingUninstantiatedGenericNativeType_ReportsDiagnostic()
+        {
+
+            string source = @"
+using System.Runtime.InteropServices;
+
+struct S
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native<T>
+    where T : unmanaged
+{
+    public Native(S s)
+    {
+    }
+
+    public S ToManaged() => new S();
+
+    public T ToNativeValue() => throw null;
+    public void FromNativeValue(T value) => throw null;
+}
+
+static class Test
+{
+    static void Foo([{|#0:MarshalUsing(typeof(Native<>))|}] S s)
+    {}
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(NativeGenericTypeMustBeClosedOrMatchArityRule).WithLocation(0).WithArguments("Native<>", "S"),
+                source);
+        }
+
+        [Fact]
+        public async Task UninstantiatedGenericNativeTypeOnGenericWithArityMismatch_ReportsDiagnostic()
+        {
+            string source = @"
+using System.Runtime.InteropServices;
+
+[{|#0:NativeMarshalling(typeof(Native<,>))|}]
+struct S<T>
+{
+    public string s;
+}
+
+[CustomTypeMarshaller(typeof(S<>), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct {|#1:Native|}<T, U>
+    where T : new()
+{
+    public Native(S<T> s)
+    {
+    }
+
+    public S<T> ToManaged() => new S<T>();
+
+    public T ToNativeValue() => throw null;
+    public void FromNativeValue(T value) => throw null;
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                source,
+                VerifyCS.Diagnostic(NativeTypeMustHaveCustomTypeMarshallerAttributeRule).WithLocation(0).WithArguments("S<T>"),
+                VerifyCS.Diagnostic(NativeGenericTypeMustBeClosedOrMatchArityRule).WithLocation(1).WithArguments("Native<T, U>", "S<>"));
+        }
+
+        [Fact]
+        public async Task UninstantiatedGenericNativeTypeOnGenericWithArityMatch_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native<>))]
+struct S<T>
+{
+    public T t;
+}
+
+[CustomTypeMarshaller(typeof(S<>), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+struct Native<T>
+    where T : new()
+{
+    public Native(S<T> s)
+    {
+    }
+
+    public S<T> ToManaged() => new S<T>();
+
+    public T ToNativeValue() => throw null;
+    public void FromNativeValue(T value) => throw null;
+}";
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task NativeTypeWithStackallocConstructorWithoutBufferSize_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer)]
+struct Native
+{
+    public Native(S s) {}
+    public {|#0:Native|}(S s, Span<byte> buffer) {}
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                VerifyCS.Diagnostic(CallerAllocConstructorMustHaveBufferSizeRule).WithLocation(0).WithArguments("Native"),
+                source);
+        }
+
+        [Fact]
+        public async Task CustomTypeMarshallerForTypeWithPlaceholder_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[CustomTypeMarshaller(typeof(CustomTypeMarshallerAttribute.GenericPlaceholder), Direction = CustomTypeMarshallerDirection.In)]
+struct Native<T>
+{
+    public Native(T a) {}
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task CustomTypeMarshallerForArrayTypeWithPlaceholder_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[CustomTypeMarshaller(typeof(CustomTypeMarshallerAttribute.GenericPlaceholder[]), Direction = CustomTypeMarshallerDirection.In)]
+struct Native<T>
+{
+    public Native(T[] a) {}
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task CustomTypeMarshallerForPointerTypeWithPlaceholder_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[CustomTypeMarshaller(typeof(CustomTypeMarshallerAttribute.GenericPlaceholder*), Direction = CustomTypeMarshallerDirection.In)]
+unsafe struct Native<T> where T : unmanaged
+{
+    public Native(T* a) {}
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task CustomTypeMarshallerForArrayOfPointerTypeWithPlaceholder_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[CustomTypeMarshaller(typeof(CustomTypeMarshallerAttribute.GenericPlaceholder*[]), Direction = CustomTypeMarshallerDirection.In)]
+unsafe struct Native<T> where T : unmanaged
+{
+    public Native(T*[] a) {}
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source, source);
+        }
+
+        [Fact]
+        public async Task CustomTypeMarshallerWithFreeNativeMethod_NoUnmanagedResourcesFeatures_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In)]
+unsafe struct {|#0:Native|}
+{
+    public Native(S s){}
+
+    public void FreeNative() { }
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.Value, Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
+unsafe struct Native
+{
+    public Native(S s){}
+
+    public void FreeNative() { }
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                fixedSource,
+                VerifyCS.Diagnostic(FreeNativeMethodProvidedShouldSpecifyUnmanagedResourcesFeatureRule)
+                    .WithArguments("Native")
+                    .WithLocation(0));
+        }
+        [Fact]
+        public async Task CustomTypeMarshallerWithCallerAllocatedBufferConstructor_NoFeature_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, BufferSize = 0x100)]
+unsafe struct {|#0:Native|}
+{
+    public Native(S s){}
+
+    public Native(S s, Span<byte> buffer) { }
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.Value, Direction = CustomTypeMarshallerDirection.In, BufferSize = 256, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer)]
+unsafe struct Native
+{
+    public Native(S s){}
+
+    public Native(S s, Span<byte> buffer) { }
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                fixedSource,
+                VerifyCS.Diagnostic(CallerAllocatedBufferConstructorProvidedShouldSpecifyFeatureRule)
+                    .WithArguments("Native")
+                    .WithLocation(0));
+        }
+
+        [Fact]
+        public async Task Add_Feature_Declaration_Preserves_Attribute_Argument_Location()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.None, Direction = CustomTypeMarshallerDirection.In)]
+unsafe struct {|#0:Native|}
+{
+    public Native(S s){}
+
+    public void FreeNative() { }
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.Value, Features = CustomTypeMarshallerFeatures.UnmanagedResources, Direction = CustomTypeMarshallerDirection.In)]
+unsafe struct Native
+{
+    public Native(S s){}
+
+    public void FreeNative() { }
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                fixedSource,
+                VerifyCS.Diagnostic(FreeNativeMethodProvidedShouldSpecifyUnmanagedResourcesFeatureRule)
+                    .WithArguments("Native")
+                    .WithLocation(0));
+        }
+
+        [Fact]
+        public async Task CustomTypeMarshallerWithTwoStageMarshallingMethod_NoFeature_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S))]
+unsafe struct {|#0:Native|}
+{
+    public Native(S s){}
+
+    public int ToNativeValue() => throw null;
+
+    public S ToManaged() => throw null;
+}
+
+[CustomTypeMarshaller(typeof(S))]
+unsafe struct {|#1:Native2|}
+{
+    public Native2(S s){}
+
+    public void FromNativeValue(int value) { }
+
+    public S ToManaged() => throw null;
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+struct S { }
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.Value, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    public Native(S s){}
+
+    public int ToNativeValue() => throw null;
+
+    public S ToManaged() => throw null;
+
+    public void FromNativeValue(int value)
+    {
+        throw new NotImplementedException();
+    }
+}
+
+[CustomTypeMarshaller(typeof(S), CustomTypeMarshallerKind.Value, Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native2
+{
+    public Native2(S s){}
+
+    public void FromNativeValue(int value) { }
+
+    public S ToManaged() => throw null;
+
+    public int ToNativeValue()
+    {
+        throw new NotImplementedException();
+    }
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                new[]
+                {
+                    VerifyCS.Diagnostic(ToNativeValueMethodProvidedShouldSpecifyTwoStageMarshallingFeatureRule)
+                        .WithArguments("Native")
+                        .WithLocation(0),
+                    VerifyCS.Diagnostic(FromNativeValueMethodProvidedShouldSpecifyTwoStageMarshallingFeatureRule)
+                        .WithArguments("Native2")
+                        .WithLocation(1)
+                },
+                fixedSource,
+                // One code-fix run is expected for each of the two diagnostics.
+                // Each fix of the "specifiy the feature" diagnostic will result in code that reports another diagnostic
+                // for the missing other member.
+                // The second two code-fix runs are the fixes for those diagnostics.
+                numIncrementalIterations: 4,
+                // The first run adds the feature flag and the second adds the missing members for the feature.
+                numFixAllIterations: 2);
+        }
+
+        [Fact]
+        public async Task Mismatched_NativeValue_Type_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    public Native(S s) { }
+
+    public S ToManaged() => new S();
+
+    public int {|#0:ToNativeValue|}() => throw null;
+    public void FromNativeValue(long value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                source,
+                VerifyCS.Diagnostic(TwoStageMarshallingNativeTypesMustMatchRule)
+                    .WithLocation(0));
+        }
+
+        [Fact]
+        public async Task Same_NativeValue_Type_DifferentName_DoesNotReportDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+using Value2 = N.Value;
+
+namespace N
+{
+    struct Value
+    {
+        private int i;
+    }
+}
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
+unsafe struct Native
+{
+    public Native(S s) { }
+
+    public S ToManaged() => new S();
+
+    public N.Value ToNativeValue() => throw null;
+    public void FromNativeValue(Value2 value) => throw null;
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(source,
+                source);
+        }
+    }
+}
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/ManualTypeMarshallingAnalyzerTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/ManualTypeMarshallingAnalyzerTests.cs
deleted file mode 100644
index bdc1eaf3625..00000000000
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/ManualTypeMarshallingAnalyzerTests.cs
+++ /dev/null
@@ -1,1240 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.CodeAnalysis;
-using Microsoft.CodeAnalysis.Testing;
-using System.Collections.Generic;
-using System.Threading.Tasks;
-using Xunit;
-using static Microsoft.Interop.Analyzers.ManualTypeMarshallingAnalyzer;
-
-using VerifyCS = LibraryImportGenerator.UnitTests.Verifiers.CSharpAnalyzerVerifier<Microsoft.Interop.Analyzers.ManualTypeMarshallingAnalyzer>;
-
-namespace LibraryImportGenerator.UnitTests
-{
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/60650", TestRuntimes.Mono)]
-    public class ManualTypeMarshallingAnalyzerTests
-    {
-        [Fact]
-        public async Task NullNativeType_ReportsDiagnostic()
-        {
-            string source = @"
-using System.Runtime.InteropServices;
-
-[{|#0:NativeMarshalling(null)|}]
-struct S
-{
-    public string s;
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBeNonNullRule).WithLocation(0).WithArguments("S"));
-        }
-
-        [Fact]
-        public async Task NonNamedNativeType_ReportsDiagnostic()
-        {
-            string source = @"
-using System.Runtime.InteropServices;
-
-[{|#0:NativeMarshalling(typeof(int*))|}]
-struct S
-{
-    public string s;
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("int*", "S"));
-        }
-
-        [Fact]
-        public async Task NonBlittableNativeType_ReportsDiagnostic()
-        {
-            string source = @"
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-struct S
-{
-    public string s;
-}
-
-struct {|#0:Native|}
-{
-    private string value;
-
-    public Native(S s)
-    {
-        value = s.s;
-    }
-
-    public S ToManaged() => new S { s = value };
-}";
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task ClassNativeType_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-struct S
-{
-    public string s;
-}
-
-class {|#0:Native|}
-{
-    private IntPtr value;
-
-    public Native(S s)
-    {
-    }
-
-    public S ToManaged() => new S();
-}";
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task BlittableNativeType_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-struct S
-{
-    public string s;
-}
-
-struct Native
-{
-    private IntPtr value;
-
-    public Native(S s)
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task BlittableNativeWithNonBlittableValueProperty_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-struct S
-{
-    public string s;
-}
-
-struct Native
-{
-    private IntPtr value;
-
-    public Native(S s)
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-
-    public string {|#0:Value|} { get => null; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("string", "S"));
-        }
-
-        [Fact]
-        public async Task NonBlittableNativeTypeWithBlittableValueProperty_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-struct S
-{
-    public string s;
-}
-
-struct Native
-{
-    private string value;
-
-    public Native(S s)
-    {
-        value = s.s;
-    }
-
-    public S ToManaged() => new S() { s = value };
-
-    public IntPtr Value { get => IntPtr.Zero; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task ClassNativeTypeWithValueProperty_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-struct S
-{
-    public string s;
-}
-
-class {|#0:Native|}
-{
-    private string value;
-
-    public Native(S s)
-    {
-        value = s.s;
-    }
-
-    public S ToManaged() => new S() { s = value };
-
-    public IntPtr Value { get => IntPtr.Zero; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task NonBlittableGetPinnableReferenceReturnType_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public string s;
-
-    public ref string {|#0:GetPinnableReference|}() => ref s;
-}
-
-unsafe struct Native
-{
-    private IntPtr value;
-
-    public Native(S s)
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-
-    public IntPtr Value { get => IntPtr.Zero; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(GetPinnableReferenceReturnTypeBlittableRule).WithLocation(0));
-        }
-
-        [Fact]
-        public async Task BlittableGetPinnableReferenceReturnType_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-
-    public ref byte GetPinnableReference() => ref c;
-}
-
-unsafe struct Native
-{
-    private IntPtr value;
-
-    public Native(S s) : this()
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-
-    public IntPtr Value { get => IntPtr.Zero; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task NonBlittableMarshallerGetPinnableReferenceReturnType_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public char c;
-}
-
-unsafe struct Native
-{
-    private IntPtr value;
-
-    public Native(S s)
-    {
-        value = IntPtr.Zero;
-    }
-
-    public ref char GetPinnableReference() => ref System.Runtime.CompilerServices.Unsafe.NullRef<char>();
-
-    public S ToManaged() => new S();
-
-    public IntPtr Value { get => IntPtr.Zero; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task BlittableMarshallerGetPinnableReferenceReturnType_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-unsafe struct Native
-{
-    private IntPtr value;
-
-    public Native(S s) : this()
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-
-    public ref byte GetPinnableReference() => ref System.Runtime.CompilerServices.Unsafe.NullRef<byte>();
-
-    public IntPtr Value { get => IntPtr.Zero; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task TypeWithGetPinnableReferenceNonPointerReturnType_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-
-    public ref byte GetPinnableReference() => ref c;
-}
-
-unsafe struct Native
-{
-    private IntPtr value;
-
-    public Native(S s) : this()
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-
-    public int {|#0:Value|} { get => 0; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBePointerSizedRule).WithLocation(0).WithArguments("int", "S"));
-        }
-
-        [Fact]
-        public async Task TypeWithGetPinnableReferencePointerReturnType_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-
-    public ref byte GetPinnableReference() => ref c;
-}
-
-unsafe struct Native
-{
-    private IntPtr value;
-
-    public Native(S s) : this()
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-
-    public int* Value { get => null; set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task TypeWithGetPinnableReferenceByRefValuePropertyType_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-
-    public ref byte GetPinnableReference() => ref c;
-}
-
-unsafe struct Native
-{
-    private S value;
-
-    public Native(S s) : this()
-    {
-        value = s;
-    }
-
-    public ref byte {|#0:Value|} { get => ref value.GetPinnableReference(); }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(RefValuePropertyUnsupportedRule).WithLocation(0).WithArguments("Native"));
-        }
-
-        [Fact]
-        public async Task NativeTypeWithGetPinnableReferenceByRefValuePropertyType_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-unsafe struct Native
-{
-    private S value;
-
-    public Native(S s) : this()
-    {
-        value = s;
-    }
-
-    public ref byte GetPinnableReference() => ref value.c;
-
-    public ref byte {|#0:Value|} { get => ref GetPinnableReference(); }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(RefValuePropertyUnsupportedRule).WithLocation(0).WithArguments("Native"));
-        }
-
-        [Fact]
-        public async Task NativeTypeWithGetPinnableReferenceNoValueProperty_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-unsafe struct Native
-{
-    private byte value;
-
-    public Native(S s) : this()
-    {
-        value = s.c;
-    }
-
-    public ref byte {|#0:GetPinnableReference|}() => ref System.Runtime.CompilerServices.Unsafe.NullRef<byte>();
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(MarshallerGetPinnableReferenceRequiresValuePropertyRule).WithLocation(0).WithArguments("Native"));
-        }
-
-        [Fact]
-        public async Task NativeTypeWithGetPinnableReferenceWithNonPointerValueProperty_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-unsafe struct Native
-{
-    private byte value;
-
-    public Native(S s) : this()
-    {
-        value = s.c;
-    }
-
-    public ref byte GetPinnableReference() => ref System.Runtime.CompilerServices.Unsafe.NullRef<byte>();
-
-    public int Value { get; set; }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task NativeTypeWithNoMarshallingMethods_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-struct {|#0:Native|}
-{
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task CollectionNativeTypeWithNoMarshallingMethods_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-[GenericContiguousCollectionMarshaller]
-struct {|#0:Native|}
-{
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CollectionNativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task CollectionNativeTypeWithWrongConstructor_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-[GenericContiguousCollectionMarshaller]
-ref struct {|#0:Native|}
-{
-    public Native(S s) : this() {}
-
-    public Span<int> ManagedValues { get; set; }
-    public Span<byte> NativeValueStorage { get; set; }
-
-    public IntPtr Value { get; }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CollectionNativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task CollectionNativeTypeWithCorrectConstructor_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-[GenericContiguousCollectionMarshaller]
-ref struct Native
-{
-    public Native(S s, int nativeElementSize) : this() {}
-
-    public Span<int> ManagedValues { get; set; }
-    public Span<byte> NativeValueStorage { get; set; }
-
-    public IntPtr Value { get; }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task CollectionNativeTypeWithIncorrectStackallocConstructor_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-[GenericContiguousCollectionMarshaller]
-ref struct {|#0:Native|}
-{
-    public Native(S s, Span<byte> stackSpace) : this() {}
-
-    public const int BufferSize = 1;
-
-    public Span<int> ManagedValues { get; set; }
-    public Span<byte> NativeValueStorage { get; set; }
-
-    public IntPtr Value { get; }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CollectionNativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task CollectionNativeTypeWithOnlyStackallocConstructor_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-[GenericContiguousCollectionMarshaller]
-ref struct {|#0:Native|}
-{
-    public Native(S s, Span<byte> stackSpace, int nativeElementSize) : this() {}
-
-    public const int BufferSize = 1;
-
-    public Span<int> ManagedValues { get; set; }
-    public Span<byte> NativeValueStorage { get; set; }
-
-    public IntPtr Value { get; }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CallerAllocMarshallingShouldSupportAllocatingMarshallingFallbackRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task CollectionNativeTypeWithMissingManagedValuesProperty_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-[GenericContiguousCollectionMarshaller]
-ref struct {|#0:Native|}
-{
-    public Native(S s, int nativeElementSize) : this() {}
-
-    public Span<byte> NativeValueStorage { get; set; }
-
-    public IntPtr Value { get; }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CollectionNativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task CollectionNativeTypeWithMissingNativeValueStorageProperty_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-[GenericContiguousCollectionMarshaller]
-ref struct {|#0:Native|}
-{
-    public Native(S s, int nativeElementSize) : this() {}
-
-    public Span<int> ManagedValues { get; set; }
-
-    public IntPtr Value { get; }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CollectionNativeTypeMustHaveRequiredShapeRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task NativeTypeWithOnlyConstructor_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-struct Native
-{
-    public Native(S s) {}
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task NativeTypeWithOnlyToManagedMethod_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-struct Native
-{
-    public S ToManaged() => new S();
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task NativeTypeWithOnlyStackallocConstructor_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-struct {|#0:Native|}
-{
-    public Native(S s, Span<byte> buffer) {}
-
-    public const int BufferSize = 0x100;
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CallerAllocMarshallingShouldSupportAllocatingMarshallingFallbackRule).WithLocation(0).WithArguments("Native"));
-        }
-
-        [Fact]
-        public async Task TypeWithOnlyNativeStackallocConstructorAndGetPinnableReference_ReportsDiagnostics()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[{|#0:NativeMarshalling(typeof(Native))|}]
-class S
-{
-    public byte c;
-    public ref byte GetPinnableReference() => ref c;
-}
-
-struct {|#1:Native|}
-{
-    public Native(S s, Span<byte> buffer) {}
-
-    public IntPtr Value => IntPtr.Zero;
-
-    public const int BufferSize = 0x100;
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CallerAllocMarshallingShouldSupportAllocatingMarshallingFallbackRule).WithLocation(1).WithArguments("Native"),
-                VerifyCS.Diagnostic(GetPinnableReferenceShouldSupportAllocatingMarshallingFallbackRule).WithLocation(0).WithArguments("S", "Native"));
-        }
-
-        [Fact]
-        public async Task NativeTypeWithConstructorAndSetOnlyValueProperty_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-struct Native
-{
-    public Native(S s) {}
-
-    public IntPtr {|#0:Value|} { set {} }
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(ValuePropertyMustHaveGetterRule).WithLocation(0).WithArguments("Native"));
-        }
-
-        [Fact]
-        public async Task NativeTypeWithToManagedAndGetOnlyValueProperty_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-struct Native
-{
-    public S ToManaged() => new S();
-
-    public IntPtr {|#0:Value|} => IntPtr.Zero;
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(ValuePropertyMustHaveSetterRule).WithLocation(0).WithArguments("Native"));
-        }
-
-        [Fact]
-        public async Task BlittableNativeTypeOnMarshalUsingParameter_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-struct S
-{
-    public string s;
-}
-
-struct Native
-{
-    private IntPtr value;
-
-    public Native(S s)
-    {
-        value = IntPtr.Zero;
-    }
-
-    public S ToManaged() => new S();
-}
-
-
-static class Test
-{
-    static void Foo([MarshalUsing(typeof(Native))] S s)
-    {}
-}
-";
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task NonBlittableNativeTypeOnMarshalUsingParameter_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-struct S
-{
-    public string s;
-}
-
-struct {|#0:Native|}
-{
-    private string value;
-
-    public Native(S s) : this()
-    {
-    }
-
-    public S ToManaged() => new S();
-}
-
-
-static class Test
-{
-    static void Foo([MarshalUsing(typeof(Native))] S s)
-    {}
-}
-";
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task NonBlittableNativeTypeOnMarshalUsingParameter_MultipleCompilations_ReportsDiagnostic_WithLocation()
-        {
-            string source1 = @"
-using System;
-using System.Runtime.InteropServices;
-
-public struct S
-{
-    public string s;
-}
-
-public struct Native
-{
-    private string value;
-
-    public Native(S s) : this()
-    {
-    }
-
-    public S ToManaged() => new S();
-}
-";
-            Compilation compilation1 = await TestUtils.CreateCompilation(source1);
-
-            string source2 = @"
-using System;
-using System.Runtime.InteropServices;
-
-static class Test
-{
-    static void Foo([{|#0:MarshalUsing(typeof(Native))|}] S s)
-    {}
-}
-";
-            var test = new Verifiers.CSharpCodeFixVerifier<Microsoft.Interop.Analyzers.ManualTypeMarshallingAnalyzer, EmptyCodeFixProvider>.Test
-            {
-                ExpectedDiagnostics =
-                {
-                    VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S")
-                },
-                SolutionTransforms =
-                {
-                    (solution, projectId) => solution.AddMetadataReference(projectId, compilation1.ToMetadataReference())
-                },
-                TestCode = source2
-            };
-
-            await test.RunAsync();
-        }
-
-        [Fact]
-        public async Task NonBlittableNativeTypeOnMarshalUsingReturn_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-struct S
-{
-    public string s;
-}
-
-struct {|#0:Native|}
-{
-    private string value;
-
-    public Native(S s) : this()
-    {
-    }
-
-    public S ToManaged() => new S();
-}
-
-
-static class Test
-{
-    [return: MarshalUsing(typeof(Native))]
-    static S Foo() => new S();
-}
-";
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task NonBlittableNativeTypeOnMarshalUsingField_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-struct S
-{
-    public string s;
-}
-
-struct {|#0:Native|}
-{
-    private string value;
-
-    public Native(S s) : this()
-    {
-    }
-
-    public S ToManaged() => new S();
-}
-
-
-struct Test
-{
-    [MarshalUsing(typeof(Native))]
-    S s;
-}
-";
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithLocation(0).WithArguments("Native", "S"));
-        }
-
-        [Fact]
-        public async Task GenericNativeTypeWithValueTypeValueProperty_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native<S>))]
-struct S
-{
-    public string s;
-}
-
-struct Native<T>
-    where T : new()
-{
-    public Native(T s)
-    {
-        Value = 0;
-    }
-
-    public T ToManaged() => new T();
-
-    public int Value { get; set; }
-}";
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task GenericNativeTypeWithGenericMemberInstantiatedWithBlittable_DoesNotReportDiagnostic()
-        {
-
-            string source = @"
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native<int>))]
-struct S
-{
-    public string s;
-}
-
-struct Native<T>
-    where T : new()
-{
-    public Native(S s)
-    {
-        Value = new T();
-    }
-
-    public S ToManaged() => new S();
-
-    public T Value { get; set; }
-}";
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task UninstantiatedGenericNativeTypeOnNonGeneric_ReportsDiagnostic()
-        {
-
-            string source = @"
-using System.Runtime.InteropServices;
-
-[{|#0:NativeMarshalling(typeof(Native<>))|}]
-struct S
-{
-    public string s;
-}
-
-struct Native<T>
-    where T : new()
-{
-    public Native(S s)
-    {
-        Value = new T();
-    }
-
-    public S ToManaged() => new S();
-
-    public T Value { get; set; }
-}";
-            await VerifyCS.VerifyAnalyzerAsync(source, VerifyCS.Diagnostic(NativeGenericTypeMustBeClosedOrMatchArityRule).WithLocation(0).WithArguments("Native<>", "S"));
-        }
-
-        [Fact]
-        public async Task UninstantiatedGenericNativeTypeOnGenericWithArityMismatch_ReportsDiagnostic()
-        {
-            string source = @"
-using System.Runtime.InteropServices;
-
-[{|#0:NativeMarshalling(typeof(Native<,>))|}]
-struct S<T>
-{
-    public string s;
-}
-
-struct Native<T, U>
-    where T : new()
-{
-    public Native(S<T> s)
-    {
-        Value = 0;
-    }
-
-    public S<T> ToManaged() => new S<T>();
-
-    public int Value { get; set; }
-}";
-            await VerifyCS.VerifyAnalyzerAsync(source, VerifyCS.Diagnostic(NativeGenericTypeMustBeClosedOrMatchArityRule).WithLocation(0).WithArguments("Native<,>", "S<T>"));
-        }
-
-        [Fact]
-        public async Task UninstantiatedGenericNativeTypeOnGenericWithArityMatch_DoesNotReportDiagnostic()
-        {
-            string source = @"
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native<>))]
-struct S<T>
-{
-    public T t;
-}
-
-struct Native<T>
-    where T : new()
-{
-    public Native(S<T> s)
-    {
-        Value = 0;
-    }
-
-    public S<T> ToManaged() => new S<T>();
-
-    public int Value { get; set; }
-}";
-            await VerifyCS.VerifyAnalyzerAsync(source);
-        }
-
-        [Fact]
-        public async Task NativeTypeWithStackallocConstructorWithoutBufferSize_ReportsDiagnostic()
-        {
-            string source = @"
-using System;
-using System.Runtime.InteropServices;
-
-[NativeMarshalling(typeof(Native))]
-class S
-{
-    public byte c;
-}
-
-struct Native
-{
-    public Native(S s) {}
-    public {|#0:Native|}(S s, Span<byte> buffer) {}
-}";
-
-            await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(CallerAllocConstructorMustHaveBufferSizeConstantRule).WithLocation(0).WithArguments("Native"));
-        }
-    }
-}
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Verifiers/CSharpCodeFixVerifier.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Verifiers/CSharpCodeFixVerifier.cs
index f56377d272e..dd30ab7a8c8 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Verifiers/CSharpCodeFixVerifier.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Verifiers/CSharpCodeFixVerifier.cs
@@ -66,6 +66,34 @@ namespace LibraryImportGenerator.UnitTests.Verifiers
             await test.RunAsync(CancellationToken.None);
         }
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyCodeFixAsync(string, DiagnosticResult[], string)"/>
+        public static async Task VerifyCodeFixAsync(string source, string fixedSource, params DiagnosticResult[] expected)
+        {
+            var test = new Test
+            {
+                TestCode = source,
+                FixedCode = fixedSource,
+            };
+
+            test.ExpectedDiagnostics.AddRange(expected);
+            await test.RunAsync(CancellationToken.None);
+        }
+
+        public static async Task VerifyCodeFixAsync(string source, DiagnosticResult[] expected, string fixedSource,
+            int numIncrementalIterations, int numFixAllIterations)
+        {
+            var test = new Test
+            {
+                TestCode = source,
+                FixedCode = fixedSource,
+                NumberOfIncrementalIterations = numIncrementalIterations,
+                NumberOfFixAllIterations = numFixAllIterations
+            };
+
+            test.ExpectedDiagnostics.AddRange(expected);
+            await test.RunAsync(CancellationToken.None);
+        }
+
         internal class Test : CSharpCodeFixTest<TAnalyzer, TCodeFix, XUnitVerifier>
         {
             public Test()
diff --git a/src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/NonBlittable.cs b/src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/NonBlittable.cs
index e1211664390..155edea1bc9 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/NonBlittable.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/NonBlittable.cs
@@ -17,6 +17,7 @@ namespace SharedTypes
         public string str2;
     }
 
+    [CustomTypeMarshaller(typeof(StringContainer), Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
     public struct StringContainerNative
     {
         public IntPtr str1;
@@ -44,6 +45,7 @@ namespace SharedTypes
         }
     }
 
+    [CustomTypeMarshaller(typeof(double), Features = CustomTypeMarshallerFeatures.TwoStageMarshalling)]
     public struct DoubleToLongMarshaler
     {
         public long l;
@@ -55,11 +57,9 @@ namespace SharedTypes
 
         public double ToManaged() => MemoryMarshal.Cast<long, double>(MemoryMarshal.CreateSpan(ref l, 1))[0];
 
-        public long Value
-        {
-            get => l;
-            set => l = value;
-        }
+        public long ToNativeValue() => l;
+
+        public void FromNativeValue(long value) => l = value;
     }
 
     [NativeMarshalling(typeof(BoolStructNative))]
@@ -70,6 +70,7 @@ namespace SharedTypes
         public bool b3;
     }
 
+    [CustomTypeMarshaller(typeof(BoolStruct))]
     public struct BoolStructNative
     {
         public byte b1;
@@ -101,6 +102,7 @@ namespace SharedTypes
         public ref int GetPinnableReference() => ref i;
     }
 
+    [CustomTypeMarshaller(typeof(IntWrapper), Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling)]
     public unsafe struct IntWrapperMarshaler
     {
         public IntWrapperMarshaler(IntWrapper managed)
@@ -109,7 +111,10 @@ namespace SharedTypes
             *Value = managed.i;
         }
 
-        public int* Value { get; set; }
+        private int* Value { get; set; }
+
+        public int* ToNativeValue() => Value;
+        public void FromNativeValue(int* value) => Value = value;
 
         public IntWrapper ToManaged() => new IntWrapper { i = *Value };
 
@@ -119,6 +124,7 @@ namespace SharedTypes
         }
     }
 
+    [CustomTypeMarshaller(typeof(string), Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x100)]
     public unsafe ref struct Utf16StringMarshaller
     {
         private ushort* allocated;
@@ -160,24 +166,19 @@ namespace SharedTypes
             return ref span.GetPinnableReference();
         }
 
-        public ushort* Value
+        public ushort* ToNativeValue() => (ushort*)Unsafe.AsPointer(ref GetPinnableReference());
+
+        public void FromNativeValue(ushort* value)
         {
-            get
-            {
-                return (ushort*)Unsafe.AsPointer(ref GetPinnableReference());
-            }
-            set
+            allocated = value;
+            span = new Span<ushort>(value, value == null ? 0 : FindStringLength(value));
+            isNullString = value == null;
+
+            static int FindStringLength(ushort* ptr)
             {
-                allocated = value;
-                span = new Span<ushort>(value, value == null ? 0 : FindStringLength(value));
-                isNullString = value == null;
-
-                static int FindStringLength(ushort* ptr)
-                {
-                    // Implemented similarly to string.wcslen as we can't access that outside of CoreLib
-                    var searchSpace = new Span<ushort>(ptr, int.MaxValue);
-                    return searchSpace.IndexOf((ushort)0);
-                }
+                // Implemented similarly to string.wcslen as we can't access that outside of CoreLib
+                var searchSpace = new Span<ushort>(ptr, int.MaxValue);
+                return searchSpace.IndexOf((ushort)0);
             }
         }
 
@@ -190,11 +191,9 @@ namespace SharedTypes
         {
             Marshal.FreeCoTaskMem((IntPtr)allocated);
         }
-
-        public const int BufferSize = 0x100;
-        public const bool RequiresStackBuffer = true;
     }
     
+    [CustomTypeMarshaller(typeof(string), Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x100)]
     public unsafe ref struct Utf8StringMarshaller
     {
         private byte* allocated;
@@ -223,24 +222,13 @@ namespace SharedTypes
             }
         }
 
-        public byte* Value
-        {
-            get
-            {
-                return allocated != null ? allocated : (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(span));
-            }
-            set
-            {
-                allocated = value;
-            }
-        }
+        public byte* ToNativeValue() => allocated != null ? allocated : (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(span));
 
-        public string? ToManaged() => Marshal.PtrToStringUTF8((IntPtr)Value);
+        public void FromNativeValue(byte* value) => allocated = value;
 
-        public void FreeNative() => Marshal.FreeCoTaskMem((IntPtr)allocated);
+        public string? ToManaged() => Marshal.PtrToStringUTF8((IntPtr)allocated);
 
-        public const int BufferSize = 0x100;
-        public const bool RequiresStackBuffer = true;
+        public void FreeNative() => Marshal.FreeCoTaskMem((IntPtr)allocated);
     }
 
     [NativeMarshalling(typeof(IntStructWrapperNative))]
@@ -249,6 +237,7 @@ namespace SharedTypes
         public int Value;
     }
 
+    [CustomTypeMarshaller(typeof(IntStructWrapper))]
     public struct IntStructWrapperNative
     {
         public int value;
@@ -260,7 +249,7 @@ namespace SharedTypes
         public IntStructWrapper ToManaged() => new IntStructWrapper { Value = value };
     }
 
-    [GenericContiguousCollectionMarshaller]
+    [CustomTypeMarshaller(typeof(List<>), CustomTypeMarshallerKind.LinearCollection, Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x200)]
     public unsafe ref struct ListMarshaller<T>
     {
         private List<T> managedList;
@@ -302,48 +291,39 @@ namespace SharedTypes
             }
         }
 
-        /// <summary>
-        /// Stack-alloc threshold set to 256 bytes to enable small arrays to be passed on the stack.
-        /// Number kept small to ensure that P/Invokes with a lot of array parameters doesn't
-        /// blow the stack since this is a new optimization in the code-generated interop.
-        /// </summary>
-        public const int BufferSize = 0x200;
-        public const bool RequiresStackBuffer = true;
-
-        public Span<T> ManagedValues => CollectionsMarshal.AsSpan(managedList);
+        public ReadOnlySpan<T> GetManagedValuesSource() => CollectionsMarshal.AsSpan(managedList);
 
-        public Span<byte> NativeValueStorage { get; private set; }
-
-        public ref byte GetPinnableReference() => ref NativeValueStorage.GetPinnableReference();
-
-        public void SetUnmarshalledCollectionLength(int length)
+        public Span<T> GetManagedValuesDestination(int length)
         {
+            if (allocatedMemory == IntPtr.Zero)
+            {
+                managedList = null;
+                return default;
+            }
             managedList = new List<T>(length);
             for (int i = 0; i < length; i++)
             {
                 managedList.Add(default);
             }
+            return CollectionsMarshal.AsSpan(managedList);
         }
 
-        public byte* Value
+        private Span<byte> NativeValueStorage { get; set; }
+
+        public Span<byte> GetNativeValuesDestination() => NativeValueStorage;
+
+        public ReadOnlySpan<byte> GetNativeValuesSource(int length)
         {
-            get
-            {
-                return (byte*)Unsafe.AsPointer(ref GetPinnableReference());
-            }
-            set
-            {
-                if (value == null)
-                {
-                    managedList = null;
-                    NativeValueStorage = default;
-                }
-                else
-                {
-                    allocatedMemory = (IntPtr)value;
-                    NativeValueStorage = new Span<byte>(value, (managedList?.Count ?? 0) * sizeOfNativeElement);
-                }
-            }
+            return allocatedMemory == IntPtr.Zero ? default : NativeValueStorage = new Span<byte>((void*)allocatedMemory, length * sizeOfNativeElement);
+        }
+
+        public ref byte GetPinnableReference() => ref NativeValueStorage.GetPinnableReference();
+
+        public byte* ToNativeValue() => (byte*)Unsafe.AsPointer(ref GetPinnableReference());
+
+        public void FromNativeValue(byte* value)
+        {
+            allocatedMemory = (IntPtr)value;
         }
 
         public List<T> ToManaged() => managedList;