Custom marshallers v2 usage (#71238)

* Enable using the new generator attributes before the new API shapes are approved

* Disable the diagnostic that verifies that a marshaller type has the v1 attribute.

* Convert some custom type marshallers to the v2 design.

Convert as many of the marshallers as possible to their correct representation with the currently implemented feature set.

This PR does not convert marshallers that can be represented with the new design but need more features to be accurately represented.

14 files changed, 383 insertions, 313 deletions

diff --git a/.editorconfig b/.editorconfig
index 15658bab8d0..598d07adf41 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -154,6 +154,9 @@ csharp_space_between_square_brackets = false
 # License header
 file_header_template = Licensed to the .NET Foundation under one or more agreements.\nThe .NET Foundation licenses this file to you under the MIT license.
 
+# Marshaller type must have CustomTypeMarshallerAttribute attribute
+dotnet_diagnostic.SYSLIB1056.severity = silent
+
 # C++ Files
 [*.{cpp,h,in}]
 curly_bracket_next_line = true
diff --git a/eng/generators.targets b/eng/generators.targets
index c123ad66387..92c76103b17 100644
--- a/eng/generators.targets
+++ b/eng/generators.targets
@@ -67,6 +67,11 @@
     <PropertyGroup>
         <LibraryImportGenerator_UseMarshalType>true</LibraryImportGenerator_UseMarshalType>
     </PropertyGroup>
+
+    <ItemGroup Condition="'$(NetCoreAppCurrentTargetFrameworkMoniker)' == '$(TargetFrameworkMoniker)' and '$(IncludeLibraryImportGeneratorSources)' != 'false'">
+      <Compile Include="$(LibrariesProjectRoot)System.Runtime.InteropServices/tests/Ancillary.Interop/CustomTypeMarshallersAttributeBase.cs" />
+      <Compile Include="$(LibrariesProjectRoot)System.Runtime.InteropServices/tests/Ancillary.Interop/ManagedToUnmanagedMarshallersAttribute.cs" />
+    </ItemGroup>
   </Target>
 
   <Import Project="$(LibrariesProjectRoot)System.Runtime.InteropServices\gen\LibraryImportGenerator\Microsoft.Interop.LibraryImportGenerator.props" />
diff --git a/src/libraries/Common/src/Interop/Interop.Ldap.cs b/src/libraries/Common/src/Interop/Interop.Ldap.cs
index 9486caeddfd..cce83e2111c 100644
--- a/src/libraries/Common/src/Interop/Interop.Ldap.cs
+++ b/src/libraries/Common/src/Interop/Interop.Ldap.cs
@@ -31,7 +31,7 @@ namespace System.DirectoryServices.Protocols
     }
 
 #if NET7_0_OR_GREATER
-    [NativeMarshalling(typeof(Native))]
+    [NativeMarshalling(typeof(Marshaller))]
 #endif
     [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
     internal struct SEC_WINNT_AUTH_IDENTITY_EX
@@ -49,8 +49,36 @@ namespace System.DirectoryServices.Protocols
         public int packageListLength;
 
 #if NET7_0_OR_GREATER
-        [CustomTypeMarshaller(typeof(SEC_WINNT_AUTH_IDENTITY_EX), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
+        [ManagedToUnmanagedMarshallers(typeof(SEC_WINNT_AUTH_IDENTITY_EX), InMarshaller = typeof(Marshaller))]
+        internal static class Marshaller
+        {
+            public static Native ConvertToUnmanaged(SEC_WINNT_AUTH_IDENTITY_EX managed)
+            {
+                Native n = default;
+                n.version = managed.version;
+                n.length = managed.length;
+                n.user = Marshal.StringToCoTaskMemUni(managed.user);
+                n.userLength = managed.userLength;
+                n.domain = Marshal.StringToCoTaskMemUni(managed.domain);
+                n.domainLength = managed.domainLength;
+                n.password = Marshal.StringToCoTaskMemUni(managed.password);
+                n.passwordLength = managed.passwordLength;
+                n.flags = managed.flags;
+                n.packageList = Marshal.StringToCoTaskMemUni(managed.packageList);
+                n.packageListLength = managed.packageListLength;
+                return n;
+            }
+
+            public static void Free(Native native)
+            {
+                Marshal.FreeCoTaskMem(native.user);
+                Marshal.FreeCoTaskMem(native.domain);
+                Marshal.FreeCoTaskMem(native.password);
+                Marshal.FreeCoTaskMem(native.packageList);
+            }
+        }
 #endif
+
         [StructLayout(LayoutKind.Sequential)]
         internal struct Native
         {
@@ -65,29 +93,6 @@ namespace System.DirectoryServices.Protocols
             public int flags;
             public IntPtr packageList;
             public int packageListLength;
-
-            public Native(SEC_WINNT_AUTH_IDENTITY_EX managed)
-            {
-                version = managed.version;
-                length = managed.length;
-                user = Marshal.StringToCoTaskMemUni(managed.user);
-                userLength = managed.userLength;
-                domain = Marshal.StringToCoTaskMemUni(managed.domain);
-                domainLength = managed.domainLength;
-                password = Marshal.StringToCoTaskMemUni(managed.password);
-                passwordLength = managed.passwordLength;
-                flags = managed.flags;
-                packageList = Marshal.StringToCoTaskMemUni(managed.packageList);
-                packageListLength = managed.packageListLength;
-            }
-
-            public void FreeNative()
-            {
-                Marshal.FreeCoTaskMem(user);
-                Marshal.FreeCoTaskMem(domain);
-                Marshal.FreeCoTaskMem(password);
-                Marshal.FreeCoTaskMem(packageList);
-            }
         }
     }
 
diff --git a/src/libraries/Common/src/Interop/Windows/CryptUI/Interop.CryptUIDlgCertificate.cs b/src/libraries/Common/src/Interop/Windows/CryptUI/Interop.CryptUIDlgCertificate.cs
index 216c3142045..23819aef230 100644
--- a/src/libraries/Common/src/Interop/Windows/CryptUI/Interop.CryptUIDlgCertificate.cs
+++ b/src/libraries/Common/src/Interop/Windows/CryptUI/Interop.CryptUIDlgCertificate.cs
@@ -14,7 +14,7 @@ internal static partial class Interop
     internal static partial class CryptUI
     {
 #if NET7_0_OR_GREATER
-        [NativeMarshalling(typeof(Native))]
+        [NativeMarshalling(typeof(Marshaller))]
 #else
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
 #endif
@@ -40,86 +40,95 @@ internal static partial class Interop
             internal uint nStartPage;
 
 #if NET7_0_OR_GREATER
-            [CustomTypeMarshaller(typeof(CRYPTUI_VIEWCERTIFICATE_STRUCTW), Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
-            internal unsafe struct Native
+            [ManagedToUnmanagedMarshallers(typeof(CRYPTUI_VIEWCERTIFICATE_STRUCTW), InMarshaller = typeof(Marshaller), RefMarshaller = typeof(Marshaller), OutMarshaller = typeof(Marshaller))]
+            public static class Marshaller
             {
-                private uint dwSize;
-                private IntPtr hwndParent;
-                private uint dwFlags;
-                private IntPtr szTitle;
-                private IntPtr pCertContext;
-                private IntPtr rgszPurposes;
-                private uint cPurposes;
-                private IntPtr pCryptProviderData;
-                private bool fpCryptProviderDataTrustedUsage;
-                private uint idxSigner;
-                private uint idxCert;
-                private bool fCounterSigner;
-                private uint idxCounterSigner;
-                private uint cStores;
-                private IntPtr rghStores;
-                private uint cPropSheetPages;
-                private IntPtr rgPropSheetPages;
-                private uint nStartPage;
-
-                public Native(CRYPTUI_VIEWCERTIFICATE_STRUCTW managed)
-                {
-                    dwSize = managed.dwSize;
-                    hwndParent = managed.hwndParent;
-                    dwFlags = managed.dwFlags;
-                    szTitle = Marshal.StringToCoTaskMemUni(managed.szTitle);
-                    pCertContext = managed.pCertContext;
-                    rgszPurposes = managed.rgszPurposes;
-                    cPurposes = managed.cPurposes;
-                    pCryptProviderData = managed.pCryptProviderData;
-                    fpCryptProviderDataTrustedUsage = managed.fpCryptProviderDataTrustedUsage;
-                    idxSigner = managed.idxSigner;
-                    idxCert = managed.idxCert;
-                    fCounterSigner = managed.fCounterSigner;
-                    idxCounterSigner = managed.idxCounterSigner;
-                    cStores = managed.cStores;
-                    rghStores = managed.rghStores;
-                    cPropSheetPages = managed.cPropSheetPages;
-                    rgPropSheetPages = managed.rgPropSheetPages;
-                    nStartPage = managed.nStartPage;
+                public static Native ConvertToUnmanaged(CRYPTUI_VIEWCERTIFICATE_STRUCTW managed) => new(managed);
 
-                }
+                public static CRYPTUI_VIEWCERTIFICATE_STRUCTW ConvertToManaged(Native n) => n.ToManaged();
 
-                public void FreeNative()
-                {
-                    Marshal.FreeCoTaskMem(szTitle);
-                }
+                public static void Free(Native native) => native.FreeNative();
 
-                public CRYPTUI_VIEWCERTIFICATE_STRUCTW ToManaged()
+                internal unsafe struct Native
                 {
-                    return new()
+                    private uint dwSize;
+                    private IntPtr hwndParent;
+                    private uint dwFlags;
+                    private IntPtr szTitle;
+                    private IntPtr pCertContext;
+                    private IntPtr rgszPurposes;
+                    private uint cPurposes;
+                    private IntPtr pCryptProviderData;
+                    private bool fpCryptProviderDataTrustedUsage;
+                    private uint idxSigner;
+                    private uint idxCert;
+                    private bool fCounterSigner;
+                    private uint idxCounterSigner;
+                    private uint cStores;
+                    private IntPtr rghStores;
+                    private uint cPropSheetPages;
+                    private IntPtr rgPropSheetPages;
+                    private uint nStartPage;
+
+                    public Native(CRYPTUI_VIEWCERTIFICATE_STRUCTW managed)
+                    {
+                        dwSize = managed.dwSize;
+                        hwndParent = managed.hwndParent;
+                        dwFlags = managed.dwFlags;
+                        szTitle = Marshal.StringToCoTaskMemUni(managed.szTitle);
+                        pCertContext = managed.pCertContext;
+                        rgszPurposes = managed.rgszPurposes;
+                        cPurposes = managed.cPurposes;
+                        pCryptProviderData = managed.pCryptProviderData;
+                        fpCryptProviderDataTrustedUsage = managed.fpCryptProviderDataTrustedUsage;
+                        idxSigner = managed.idxSigner;
+                        idxCert = managed.idxCert;
+                        fCounterSigner = managed.fCounterSigner;
+                        idxCounterSigner = managed.idxCounterSigner;
+                        cStores = managed.cStores;
+                        rghStores = managed.rghStores;
+                        cPropSheetPages = managed.cPropSheetPages;
+                        rgPropSheetPages = managed.rgPropSheetPages;
+                        nStartPage = managed.nStartPage;
+
+                    }
+
+                    public void FreeNative()
+                    {
+                        Marshal.FreeCoTaskMem(szTitle);
+                    }
+
+                    public CRYPTUI_VIEWCERTIFICATE_STRUCTW ToManaged()
                     {
-                        dwSize = dwSize,
-                        hwndParent = hwndParent,
-                        dwFlags = dwFlags,
-                        szTitle = Marshal.PtrToStringUni(szTitle),
-                        pCertContext = pCertContext,
-                        rgszPurposes = rgszPurposes,
-                        cPurposes = cPurposes,
-                        pCryptProviderData = pCryptProviderData,
-                        fpCryptProviderDataTrustedUsage = fpCryptProviderDataTrustedUsage,
-                        idxSigner = idxSigner,
-                        idxCert = idxCert,
-                        fCounterSigner = fCounterSigner,
-                        idxCounterSigner = idxCounterSigner,
-                        cStores = cStores,
-                        rghStores = rghStores,
-                        cPropSheetPages = cPropSheetPages,
-                        rgPropSheetPages = rgPropSheetPages,
-                        nStartPage = nStartPage
-                    };
+                        return new()
+                        {
+                            dwSize = dwSize,
+                            hwndParent = hwndParent,
+                            dwFlags = dwFlags,
+                            szTitle = Marshal.PtrToStringUni(szTitle),
+                            pCertContext = pCertContext,
+                            rgszPurposes = rgszPurposes,
+                            cPurposes = cPurposes,
+                            pCryptProviderData = pCryptProviderData,
+                            fpCryptProviderDataTrustedUsage = fpCryptProviderDataTrustedUsage,
+                            idxSigner = idxSigner,
+                            idxCert = idxCert,
+                            fCounterSigner = fCounterSigner,
+                            idxCounterSigner = idxCounterSigner,
+                            cStores = cStores,
+                            rghStores = rghStores,
+                            cPropSheetPages = cPropSheetPages,
+                            rgPropSheetPages = rgPropSheetPages,
+                            nStartPage = nStartPage
+                        };
+                    }
                 }
             }
 #endif
         }
 
 #if NET7_0_OR_GREATER
-        [NativeMarshalling(typeof(Native))]
+        [NativeMarshalling(typeof(Marshaller))]
 #else
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
 #endif
@@ -143,73 +152,82 @@ internal static partial class Interop
             internal IntPtr hSelectedCertStore;
 
 #if NET7_0_OR_GREATER
-            [CustomTypeMarshaller(typeof(CRYPTUI_SELECTCERTIFICATE_STRUCTW), Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
-            internal unsafe struct Native
+            [ManagedToUnmanagedMarshallers(typeof(CRYPTUI_SELECTCERTIFICATE_STRUCTW), InMarshaller = typeof(Marshaller), RefMarshaller = typeof(Marshaller), OutMarshaller = typeof(Marshaller))]
+            public static class Marshaller
             {
-                private uint dwSize;
-                private IntPtr hwndParent;
-                private uint dwFlags;
-                private IntPtr szTitle;
-                private uint dwDontUseColumn;
-                private IntPtr szDisplayString;
-                private IntPtr pFilterCallback;
-                private IntPtr pDisplayCallback;
-                private IntPtr pvCallbackData;
-                private uint cDisplayStores;
-                private IntPtr rghDisplayStores;
-                private uint cStores;
-                private IntPtr rghStores;
-                private uint cPropSheetPages;
-                private IntPtr rgPropSheetPages;
-                internal IntPtr hSelectedCertStore;
-
-                public Native(CRYPTUI_SELECTCERTIFICATE_STRUCTW managed)
-                {
-                    dwSize = managed.dwSize;
-                    hwndParent = managed.hwndParent;
-                    dwFlags = managed.dwFlags;
-                    szTitle = Marshal.StringToCoTaskMemUni(managed.szTitle);
-                    dwDontUseColumn = managed.dwDontUseColumn;
-                    szDisplayString = Marshal.StringToCoTaskMemUni(managed.szDisplayString);
-                    pFilterCallback = managed.pFilterCallback;
-                    pDisplayCallback = managed.pDisplayCallback;
-                    pvCallbackData = managed.pvCallbackData;
-                    cDisplayStores = managed.cDisplayStores;
-                    rghDisplayStores = managed.rghDisplayStores;
-                    cStores = managed.cStores;
-                    rghStores = managed.rghStores;
-                    cPropSheetPages = managed.cPropSheetPages;
-                    rgPropSheetPages = managed.rgPropSheetPages;
-                    hSelectedCertStore = managed.hSelectedCertStore;
-                }
+                public static Native ConvertToUnmanaged(CRYPTUI_SELECTCERTIFICATE_STRUCTW managed) => new(managed);
 
-                public void FreeNative()
-                {
-                    Marshal.FreeCoTaskMem(szTitle);
-                    Marshal.FreeCoTaskMem(szDisplayString);
-                }
+                public static CRYPTUI_SELECTCERTIFICATE_STRUCTW ConvertToManaged(Native n) => n.ToManaged();
+
+                public static void Free(Native native) => native.FreeNative();
 
-                public CRYPTUI_SELECTCERTIFICATE_STRUCTW ToManaged()
+                internal unsafe struct Native
                 {
-                    return new()
+                    private uint dwSize;
+                    private IntPtr hwndParent;
+                    private uint dwFlags;
+                    private IntPtr szTitle;
+                    private uint dwDontUseColumn;
+                    private IntPtr szDisplayString;
+                    private IntPtr pFilterCallback;
+                    private IntPtr pDisplayCallback;
+                    private IntPtr pvCallbackData;
+                    private uint cDisplayStores;
+                    private IntPtr rghDisplayStores;
+                    private uint cStores;
+                    private IntPtr rghStores;
+                    private uint cPropSheetPages;
+                    private IntPtr rgPropSheetPages;
+                    internal IntPtr hSelectedCertStore;
+
+                    public Native(CRYPTUI_SELECTCERTIFICATE_STRUCTW managed)
+                    {
+                        dwSize = managed.dwSize;
+                        hwndParent = managed.hwndParent;
+                        dwFlags = managed.dwFlags;
+                        szTitle = Marshal.StringToCoTaskMemUni(managed.szTitle);
+                        dwDontUseColumn = managed.dwDontUseColumn;
+                        szDisplayString = Marshal.StringToCoTaskMemUni(managed.szDisplayString);
+                        pFilterCallback = managed.pFilterCallback;
+                        pDisplayCallback = managed.pDisplayCallback;
+                        pvCallbackData = managed.pvCallbackData;
+                        cDisplayStores = managed.cDisplayStores;
+                        rghDisplayStores = managed.rghDisplayStores;
+                        cStores = managed.cStores;
+                        rghStores = managed.rghStores;
+                        cPropSheetPages = managed.cPropSheetPages;
+                        rgPropSheetPages = managed.rgPropSheetPages;
+                        hSelectedCertStore = managed.hSelectedCertStore;
+                    }
+
+                    public void FreeNative()
+                    {
+                        Marshal.FreeCoTaskMem(szTitle);
+                        Marshal.FreeCoTaskMem(szDisplayString);
+                    }
+
+                    public CRYPTUI_SELECTCERTIFICATE_STRUCTW ToManaged()
                     {
-                        dwSize = dwSize,
-                        hwndParent = hwndParent,
-                        dwFlags = dwFlags,
-                        szTitle = Marshal.PtrToStringUni(szTitle),
-                        dwDontUseColumn = dwDontUseColumn,
-                        szDisplayString = Marshal.PtrToStringUni(szDisplayString),
-                        pFilterCallback = pFilterCallback,
-                        pDisplayCallback = pDisplayCallback,
-                        pvCallbackData = pvCallbackData,
-                        cDisplayStores = cDisplayStores,
-                        rghDisplayStores = rghDisplayStores,
-                        cStores = cStores,
-                        rghStores = rghStores,
-                        cPropSheetPages = cPropSheetPages,
-                        rgPropSheetPages = rgPropSheetPages,
-                        hSelectedCertStore = hSelectedCertStore
-                    };
+                        return new()
+                        {
+                            dwSize = dwSize,
+                            hwndParent = hwndParent,
+                            dwFlags = dwFlags,
+                            szTitle = Marshal.PtrToStringUni(szTitle),
+                            dwDontUseColumn = dwDontUseColumn,
+                            szDisplayString = Marshal.PtrToStringUni(szDisplayString),
+                            pFilterCallback = pFilterCallback,
+                            pDisplayCallback = pDisplayCallback,
+                            pvCallbackData = pvCallbackData,
+                            cDisplayStores = cDisplayStores,
+                            rghDisplayStores = rghDisplayStores,
+                            cStores = cStores,
+                            rghStores = rghStores,
+                            cPropSheetPages = cPropSheetPages,
+                            rgPropSheetPages = rgPropSheetPages,
+                            hSelectedCertStore = hSelectedCertStore
+                        };
+                    }
                 }
             }
 #endif
diff --git a/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp.cs b/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp.cs
index e968ca3a1b3..a40773a564d 100644
--- a/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp.cs
+++ b/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp.cs
@@ -56,26 +56,20 @@ internal static partial class Interop
             uint modifiers);
 
 #if NET7_0_OR_GREATER
-        [CustomTypeMarshaller(typeof(StringBuilder), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling)]
-        private unsafe struct SimpleStringBufferMarshaller
+        [ManagedToUnmanagedMarshallers(typeof(StringBuilder), InMarshaller = typeof(SimpleStringBufferMarshaller))]
+        private static unsafe class SimpleStringBufferMarshaller
         {
-            public SimpleStringBufferMarshaller(StringBuilder builder)
+            public static void* ConvertToUnmanaged(StringBuilder builder)
             {
                 int length = builder.Length + 1;
-                Value = NativeMemory.Alloc(sizeof(char) * (nuint)length);
-                Span<char> buffer = new(Value, length);
+                void* value = NativeMemory.Alloc(sizeof(char) * (nuint)length);
+                Span<char> buffer = new(value, length);
                 buffer.Clear();
                 builder.CopyTo(0, buffer, length - 1);
+                return value;
             }
 
-            private void* Value { get; }
-
-            public void* ToNativeValue() => Value;
-
-            public void FreeNative()
-            {
-                NativeMemory.Free(Value);
-            }
+            public static void Free(void* value) => NativeMemory.Free(value);
         }
 #endif
 
diff --git a/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs b/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs
index 7833cacc76c..f83448e81b1 100644
--- a/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs
+++ b/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs
@@ -248,7 +248,7 @@ internal static partial class Interop
             uint statusInformationLength);
 
 #if NET7_0_OR_GREATER
-        [NativeMarshalling(typeof(Native))]
+        [NativeMarshalling(typeof(Marshaller))]
 #endif
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
         public struct WINHTTP_AUTOPROXY_OPTIONS
@@ -262,42 +262,51 @@ internal static partial class Interop
             [MarshalAs(UnmanagedType.Bool)]
             public bool AutoLoginIfChallenged;
 #if NET7_0_OR_GREATER
-            [CustomTypeMarshaller(typeof(WINHTTP_AUTOPROXY_OPTIONS), Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
-            public struct Native
+            [ManagedToUnmanagedMarshallers(typeof(WINHTTP_AUTOPROXY_OPTIONS), InMarshaller = typeof(Marshaller), RefMarshaller = typeof(Marshaller), OutMarshaller = typeof(Marshaller))]
+            public static class Marshaller
             {
-                private uint Flags;
-                private uint AutoDetectFlags;
-                private IntPtr AutoConfigUrl;
-                private IntPtr Reserved1;
-                private uint Reserved2;
-                private int AutoLoginIfChallenged;
-
-                public Native(WINHTTP_AUTOPROXY_OPTIONS managed)
-                {
-                    Flags = managed.Flags;
-                    AutoDetectFlags = managed.AutoDetectFlags;
-                    AutoConfigUrl = managed.AutoConfigUrl is not null ? Marshal.StringToCoTaskMemUni(managed.AutoConfigUrl) : IntPtr.Zero;
-                    Reserved1 = managed.Reserved1;
-                    Reserved2 = managed.Reserved2;
-                    AutoLoginIfChallenged = managed.AutoLoginIfChallenged ? 1 : 0;
-                }
+                public static Native ConvertToUnmanaged(WINHTTP_AUTOPROXY_OPTIONS managed) => new(managed);
 
-                public WINHTTP_AUTOPROXY_OPTIONS ToManaged()
-                {
-                    return new WINHTTP_AUTOPROXY_OPTIONS
-                    {
-                        Flags = Flags,
-                        AutoDetectFlags = AutoDetectFlags,
-                        AutoConfigUrl = AutoConfigUrl != IntPtr.Zero ? Marshal.PtrToStringUni(AutoConfigUrl) : null,
-                        Reserved1 = Reserved1,
-                        Reserved2 = Reserved2,
-                        AutoLoginIfChallenged = AutoLoginIfChallenged != 0
-                    };
-                }
+                public static WINHTTP_AUTOPROXY_OPTIONS ConvertToManaged(Native native) => native.ToManaged();
 
-                public void FreeNative()
+                public static void Free(Native native) => native.FreeNative();
+
+                public struct Native
                 {
-                    Marshal.FreeCoTaskMem(AutoConfigUrl);
+                    private uint Flags;
+                    private uint AutoDetectFlags;
+                    private IntPtr AutoConfigUrl;
+                    private IntPtr Reserved1;
+                    private uint Reserved2;
+                    private int AutoLoginIfChallenged;
+
+                    public Native(WINHTTP_AUTOPROXY_OPTIONS managed)
+                    {
+                        Flags = managed.Flags;
+                        AutoDetectFlags = managed.AutoDetectFlags;
+                        AutoConfigUrl = managed.AutoConfigUrl is not null ? Marshal.StringToCoTaskMemUni(managed.AutoConfigUrl) : IntPtr.Zero;
+                        Reserved1 = managed.Reserved1;
+                        Reserved2 = managed.Reserved2;
+                        AutoLoginIfChallenged = managed.AutoLoginIfChallenged ? 1 : 0;
+                    }
+
+                    public WINHTTP_AUTOPROXY_OPTIONS ToManaged()
+                    {
+                        return new WINHTTP_AUTOPROXY_OPTIONS
+                        {
+                            Flags = Flags,
+                            AutoDetectFlags = AutoDetectFlags,
+                            AutoConfigUrl = AutoConfigUrl != IntPtr.Zero ? Marshal.PtrToStringUni(AutoConfigUrl) : null,
+                            Reserved1 = Reserved1,
+                            Reserved2 = Reserved2,
+                            AutoLoginIfChallenged = AutoLoginIfChallenged != 0
+                        };
+                    }
+
+                    public void FreeNative()
+                    {
+                        Marshal.FreeCoTaskMem(AutoConfigUrl);
+                    }
                 }
             }
 #endif
diff --git a/src/libraries/Common/src/Interop/Windows/WinMm/Interop.waveOutGetDevCaps.cs b/src/libraries/Common/src/Interop/Windows/WinMm/Interop.waveOutGetDevCaps.cs
index c8cdab71522..587146bd942 100644
--- a/src/libraries/Common/src/Interop/Windows/WinMm/Interop.waveOutGetDevCaps.cs
+++ b/src/libraries/Common/src/Interop/Windows/WinMm/Interop.waveOutGetDevCaps.cs
@@ -13,7 +13,7 @@ internal static partial class Interop
     {
 #pragma warning disable CA1823 // unused fields
 #if NET7_0_OR_GREATER
-        [NativeMarshalling(typeof(Native))]
+        [NativeMarshalling(typeof(Marshaller))]
 #endif
         internal struct WAVEOUTCAPS
         {
@@ -28,48 +28,54 @@ internal static partial class Interop
             private ushort wReserved1;
             private ushort dwSupport;
 #if NET7_0_OR_GREATER
-            [CustomTypeMarshaller(typeof(WAVEOUTCAPS))]
-            internal unsafe struct Native
+            [ManagedToUnmanagedMarshallers(typeof(WAVEOUTCAPS), InMarshaller = typeof(Marshaller), RefMarshaller = typeof(Marshaller), OutMarshaller = typeof(Marshaller))]
+            public static class Marshaller
             {
-                private ushort wMid;
-                private ushort wPid;
-                private uint vDriverVersion;
-                internal fixed char szPname[szPnameLength];
-                private uint dwFormats;
-                private ushort wChannels;
-                private ushort wReserved1;
-                private ushort dwSupport;
+                public static Native ConvertToUnmanaged(WAVEOUTCAPS managed) => new(managed);
+                public static WAVEOUTCAPS ConvertToManaged(Native native) => native.ToManaged();
 
-                public Native(WAVEOUTCAPS managed)
+                internal unsafe struct Native
                 {
-                    wMid = managed.wMid;
-                    wPid = managed.wPid;
-                    vDriverVersion = managed.vDriverVersion;
-                    fixed (char* pszPname = szPname)
+                    private ushort wMid;
+                    private ushort wPid;
+                    private uint vDriverVersion;
+                    internal fixed char szPname[szPnameLength];
+                    private uint dwFormats;
+                    private ushort wChannels;
+                    private ushort wReserved1;
+                    private ushort dwSupport;
+
+                    public Native(WAVEOUTCAPS managed)
                     {
-                        managed.szPname.AsSpan().CopyTo(new Span<char>(pszPname, szPnameLength));
+                        wMid = managed.wMid;
+                        wPid = managed.wPid;
+                        vDriverVersion = managed.vDriverVersion;
+                        fixed (char* pszPname = szPname)
+                        {
+                            managed.szPname.AsSpan().CopyTo(new Span<char>(pszPname, szPnameLength));
+                        }
+                        dwFormats = managed.dwFormats;
+                        wChannels = managed.wChannels;
+                        wReserved1 = managed.wReserved1;
+                        dwSupport = managed.dwSupport;
                     }
-                    dwFormats = managed.dwFormats;
-                    wChannels = managed.wChannels;
-                    wReserved1 = managed.wReserved1;
-                    dwSupport = managed.dwSupport;
-                }
 
-                public WAVEOUTCAPS ToManaged()
-                {
-                    fixed (char* pszPname = szPname)
+                    public WAVEOUTCAPS ToManaged()
                     {
-                        return new WAVEOUTCAPS
+                        fixed (char* pszPname = szPname)
                         {
-                            wMid = wMid,
-                            wPid = wPid,
-                            vDriverVersion = vDriverVersion,
-                            szPname = new Span<char>(pszPname, szPnameLength).ToString(),
-                            dwFormats = dwFormats,
-                            wChannels = wChannels,
-                            wReserved1 = wReserved1,
-                            dwSupport = dwSupport,
-                        };
+                            return new WAVEOUTCAPS
+                            {
+                                wMid = wMid,
+                                wPid = wPid,
+                                vDriverVersion = vDriverVersion,
+                                szPname = new Span<char>(pszPname, szPnameLength).ToString(),
+                                dwFormats = dwFormats,
+                                wChannels = wChannels,
+                                wReserved1 = wReserved1,
+                                dwSupport = dwSupport,
+                            };
+                        }
                     }
                 }
             }
diff --git a/src/libraries/Common/src/Interop/Windows/WinSock/Interop.WinsockBSD.cs b/src/libraries/Common/src/Interop/Windows/WinSock/Interop.WinsockBSD.cs
index 7ab26fa8a09..3612939ff6e 100644
--- a/src/libraries/Common/src/Interop/Windows/WinSock/Interop.WinsockBSD.cs
+++ b/src/libraries/Common/src/Interop/Windows/WinSock/Interop.WinsockBSD.cs
@@ -69,45 +69,50 @@ internal static partial class Interop
         }
 
         // Argument structure for IPV6_ADD_MEMBERSHIP and IPV6_DROP_MEMBERSHIP.
-        [NativeMarshalling(typeof(Native))]
+        [NativeMarshalling(typeof(Marshaller))]
         internal struct IPv6MulticastRequest
         {
             internal byte[] MulticastAddress; // IP address of group.
             internal int InterfaceIndex; // Local interface index.
-
-            [CustomTypeMarshaller(typeof(IPv6MulticastRequest))]
-            public unsafe struct Native
+            [ManagedToUnmanagedMarshallers(typeof(IPv6MulticastRequest), InMarshaller = typeof(Marshaller), RefMarshaller = typeof(Marshaller), OutMarshaller = typeof(Marshaller))]
+            public static class Marshaller
             {
-                private const int MulticastAddressLength = 16;
-                private fixed byte _multicastAddress[MulticastAddressLength];
-                private int _interfaceIndex;
+                public static Native ConvertToUnmanaged(IPv6MulticastRequest managed) => new(managed);
+                public static IPv6MulticastRequest ConvertToManaged(Native native) => native.ToManaged();
 
-                public Native(IPv6MulticastRequest managed)
+                public unsafe struct Native
                 {
-                    Debug.Assert(managed.MulticastAddress.Length == MulticastAddressLength);
-                    fixed (void* dest = _multicastAddress)
+                    private const int MulticastAddressLength = 16;
+                    private fixed byte _multicastAddress[MulticastAddressLength];
+                    private int _interfaceIndex;
+
+                    public Native(IPv6MulticastRequest managed)
                     {
-                        managed.MulticastAddress.CopyTo(new Span<byte>(dest, MulticastAddressLength));
+                        Debug.Assert(managed.MulticastAddress.Length == MulticastAddressLength);
+                        fixed (void* dest = _multicastAddress)
+                        {
+                            managed.MulticastAddress.CopyTo(new Span<byte>(dest, MulticastAddressLength));
+                        }
+                        _interfaceIndex = managed.InterfaceIndex;
                     }
-                    _interfaceIndex = managed.InterfaceIndex;
-                }
 
-                public IPv6MulticastRequest ToManaged()
-                {
-                    IPv6MulticastRequest managed = new()
-                    {
-                        MulticastAddress = new byte[MulticastAddressLength],
-                        InterfaceIndex = _interfaceIndex
-                    };
-                    fixed (void* src = _multicastAddress)
+                    public IPv6MulticastRequest ToManaged()
                     {
-                        new Span<byte>(src, 16).CopyTo(managed.MulticastAddress);
+                        IPv6MulticastRequest managed = new()
+                        {
+                            MulticastAddress = new byte[MulticastAddressLength],
+                            InterfaceIndex = _interfaceIndex
+                        };
+                        fixed (void* src = _multicastAddress)
+                        {
+                            new Span<byte>(src, 16).CopyTo(managed.MulticastAddress);
+                        }
+                        return managed;
                     }
-                    return managed;
                 }
             }
 
-            internal static readonly unsafe int Size = sizeof(Native);
+            internal static readonly unsafe int Size = sizeof(Marshaller.Native);
         }
 
         [StructLayout(LayoutKind.Sequential)]
diff --git a/src/libraries/System.Diagnostics.EventLog/src/System/Diagnostics/Reader/UnsafeNativeMethods.cs b/src/libraries/System.Diagnostics.EventLog/src/System/Diagnostics/Reader/UnsafeNativeMethods.cs
index c41416115e4..3c6a4f5e61b 100644
--- a/src/libraries/System.Diagnostics.EventLog/src/System/Diagnostics/Reader/UnsafeNativeMethods.cs
+++ b/src/libraries/System.Diagnostics.EventLog/src/System/Diagnostics/Reader/UnsafeNativeMethods.cs
@@ -690,7 +690,7 @@ namespace Microsoft.Win32
                             out int propCount);
 
 #if NET7_0_OR_GREATER
-        [NativeMarshalling(typeof(Native))]
+        [NativeMarshalling(typeof(Marshaller))]
 #endif
         [StructLayout(LayoutKind.Explicit, CharSet = CharSet.Unicode)]
         internal struct EvtStringVariant
@@ -703,37 +703,44 @@ namespace Microsoft.Win32
             public uint Type;
 
 #if NET7_0_OR_GREATER
-            [CustomTypeMarshaller(typeof(EvtStringVariant), Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
-            [StructLayout(LayoutKind.Explicit)]
-            public struct Native
+            [ManagedToUnmanagedMarshallers(typeof(EvtStringVariant), InMarshaller = typeof(Marshaller), RefMarshaller = typeof(Marshaller), OutMarshaller = typeof(Marshaller))]
+            public static class Marshaller
             {
-                [FieldOffset(0)]
-                private IntPtr StringVal;
-                [FieldOffset(8)]
-                private uint Count;
-                [FieldOffset(12)]
-                private uint Type;
-
-                public Native(EvtStringVariant managed)
-                {
-                    StringVal = Marshal.StringToCoTaskMemUni(managed.StringVal);
-                    Count = managed.Count;
-                    Type = managed.Type;
-                }
+                public static Native ConvertToUnmanaged(EvtStringVariant managed) => new(managed);
+                public static EvtStringVariant ConvertToManaged(Native native) => native.ToManaged();
+                public static void Free(Native native) => native.FreeNative();
 
-                public EvtStringVariant ToManaged()
+                [StructLayout(LayoutKind.Explicit)]
+                public struct Native
                 {
-                    return new EvtStringVariant
+                    [FieldOffset(0)]
+                    private IntPtr StringVal;
+                    [FieldOffset(8)]
+                    private uint Count;
+                    [FieldOffset(12)]
+                    private uint Type;
+
+                    public Native(EvtStringVariant managed)
                     {
-                        StringVal = Marshal.PtrToStringUni(StringVal),
-                        Count = Count,
-                        Type = Type
-                    };
-                }
+                        StringVal = Marshal.StringToCoTaskMemUni(managed.StringVal);
+                        Count = managed.Count;
+                        Type = managed.Type;
+                    }
 
-                public void FreeNative()
-                {
-                    Marshal.FreeCoTaskMem(StringVal);
+                    public EvtStringVariant ToManaged()
+                    {
+                        return new EvtStringVariant
+                        {
+                            StringVal = Marshal.PtrToStringUni(StringVal),
+                            Count = Count,
+                            Type = Type
+                        };
+                    }
+
+                    public void FreeNative()
+                    {
+                        Marshal.FreeCoTaskMem(StringVal);
+                    }
                 }
             }
 #endif
diff --git a/src/libraries/System.Drawing.Common/src/Interop/Windows/Interop.Gdi32.cs b/src/libraries/System.Drawing.Common/src/Interop/Windows/Interop.Gdi32.cs
index e57ca965a90..08bd1c39710 100644
--- a/src/libraries/System.Drawing.Common/src/Interop/Windows/Interop.Gdi32.cs
+++ b/src/libraries/System.Drawing.Common/src/Interop/Windows/Interop.Gdi32.cs
@@ -176,7 +176,7 @@ internal static partial class Interop
         }
 
 #if NET7_0_OR_GREATER
-        [NativeMarshalling(typeof(Native))]
+        [NativeMarshalling(typeof(Marshaller))]
 #endif
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
         internal sealed class DOCINFO
@@ -188,29 +188,35 @@ internal static partial class Interop
             internal int fwType;
 
 #if NET7_0_OR_GREATER
-            [CustomTypeMarshaller(typeof(DOCINFO), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.UnmanagedResources)]
-            internal struct Native
+            [ManagedToUnmanagedMarshallers(typeof(DOCINFO), InMarshaller = typeof(Marshaller))]
+            public static class Marshaller
             {
-                internal int cbSize;
-                internal IntPtr lpszDocName;
-                internal IntPtr lpszOutput;
-                internal IntPtr lpszDatatype;
-                internal int fwType;
+                public static Native ConvertToUnmanaged(DOCINFO managed) => new(managed);
+                public static void Free(Native native) => native.FreeNative();
 
-                public Native(DOCINFO docInfo)
+                internal struct Native
                 {
-                    cbSize = docInfo.cbSize;
-                    lpszDocName = Marshal.StringToCoTaskMemAuto(docInfo.lpszDocName);
-                    lpszOutput = Marshal.StringToCoTaskMemAuto(docInfo.lpszOutput);
-                    lpszDatatype = Marshal.StringToCoTaskMemAuto(docInfo.lpszDatatype);
-                    fwType = docInfo.fwType;
-                }
+                    internal int cbSize;
+                    internal IntPtr lpszDocName;
+                    internal IntPtr lpszOutput;
+                    internal IntPtr lpszDatatype;
+                    internal int fwType;
 
-                public void FreeNative()
-                {
-                    Marshal.FreeCoTaskMem(lpszDocName);
-                    Marshal.FreeCoTaskMem(lpszOutput);
-                    Marshal.FreeCoTaskMem(lpszDatatype);
+                    public Native(DOCINFO docInfo)
+                    {
+                        cbSize = docInfo.cbSize;
+                        lpszDocName = Marshal.StringToCoTaskMemAuto(docInfo.lpszDocName);
+                        lpszOutput = Marshal.StringToCoTaskMemAuto(docInfo.lpszOutput);
+                        lpszDatatype = Marshal.StringToCoTaskMemAuto(docInfo.lpszDatatype);
+                        fwType = docInfo.fwType;
+                    }
+
+                    public void FreeNative()
+                    {
+                        Marshal.FreeCoTaskMem(lpszDocName);
+                        Marshal.FreeCoTaskMem(lpszOutput);
+                        Marshal.FreeCoTaskMem(lpszDatatype);
+                    }
                 }
             }
 #endif
diff --git a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/CustomTypeMarshallersAttributeBase.cs b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/CustomTypeMarshallersAttributeBase.cs
index e20f63a7146..be020d0f716 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/CustomTypeMarshallersAttributeBase.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/CustomTypeMarshallersAttributeBase.cs
@@ -11,7 +11,12 @@ namespace System.Runtime.InteropServices.Marshalling
     /// For the following attribute types, any marshaller types that are provided will be validated by an analyzer to have the correct members to prevent
     /// developers from accidentally typoing a member like Free() and causing memory leaks.
     /// </remarks>
-    public abstract class CustomUnmanagedTypeMarshallersAttributeBase : Attribute
+#if LIBRARYIMPORT_GENERATOR_TEST
+    public
+#else
+    internal
+#endif
+    abstract class CustomUnmanagedTypeMarshallersAttributeBase : Attribute
     {
         /// <summary>
         /// Placeholder type for generic parameter
diff --git a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/ManagedToUnmanagedMarshallersAttribute.cs b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/ManagedToUnmanagedMarshallersAttribute.cs
index c0221d15307..d950e222992 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/ManagedToUnmanagedMarshallersAttribute.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/Ancillary.Interop/ManagedToUnmanagedMarshallersAttribute.cs
@@ -1,12 +1,18 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
+#nullable enable
 
 namespace System.Runtime.InteropServices.Marshalling
 {
     /// <summary>
     /// Specify marshallers used in the managed to unmanaged direction (that is, P/Invoke)
     /// </summary>
-    public sealed class ManagedToUnmanagedMarshallersAttribute : CustomUnmanagedTypeMarshallersAttributeBase
+#if LIBRARYIMPORT_GENERATOR_TEST
+    public
+#else
+    internal
+#endif
+    sealed class ManagedToUnmanagedMarshallersAttribute : CustomUnmanagedTypeMarshallersAttributeBase
     {
         /// <summary>
         /// Create instance of <see cref="ManagedToUnmanagedMarshallersAttribute"/>.
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/LibraryImportGenerator.Tests.csproj b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/LibraryImportGenerator.Tests.csproj
index 6657d65092a..ad8f6d61e84 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/LibraryImportGenerator.Tests.csproj
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/LibraryImportGenerator.Tests.csproj
@@ -3,6 +3,7 @@
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <EnableLibraryImportGenerator>true</EnableLibraryImportGenerator>
+    <IncludeLibraryImportGeneratorSources>false</IncludeLibraryImportGeneratorSources>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/libraries/System.Windows.Extensions/src/System/Security/Cryptography/X509Certificates/X509Certificate2UI.cs b/src/libraries/System.Windows.Extensions/src/System/Security/Cryptography/X509Certificates/X509Certificate2UI.cs
index 7a3cb22e6eb..702182c401e 100644
--- a/src/libraries/System.Windows.Extensions/src/System/Security/Cryptography/X509Certificates/X509Certificate2UI.cs
+++ b/src/libraries/System.Windows.Extensions/src/System/Security/Cryptography/X509Certificates/X509Certificate2UI.cs
@@ -54,7 +54,7 @@ namespace System.Security.Cryptography.X509Certificates
                 // Initialize view structure.
                 Interop.CryptUI.CRYPTUI_VIEWCERTIFICATE_STRUCTW ViewInfo = default;
 #if NET7_0_OR_GREATER
-                ViewInfo.dwSize = (uint)sizeof(Interop.CryptUI.CRYPTUI_VIEWCERTIFICATE_STRUCTW.Native);
+                ViewInfo.dwSize = (uint)sizeof(Interop.CryptUI.CRYPTUI_VIEWCERTIFICATE_STRUCTW.Marshaller.Native);
 #else
                 ViewInfo.dwSize = (uint)Marshal.SizeOf<Interop.CryptUI.CRYPTUI_VIEWCERTIFICATE_STRUCTW>();
 #endif
@@ -121,9 +121,9 @@ namespace System.Security.Cryptography.X509Certificates
 #if NET7_0_OR_GREATER
             // Declare a local for Native to enable us to get the managed byte offset
             // without having a null check cause a failure.
-            Interop.CryptUI.CRYPTUI_SELECTCERTIFICATE_STRUCTW.Native native;
+            Interop.CryptUI.CRYPTUI_SELECTCERTIFICATE_STRUCTW.Marshaller.Native native;
             Unsafe.SkipInit(out native);
-            csc.dwSize = (uint)Unsafe.ByteOffset(ref Unsafe.As<Interop.CryptUI.CRYPTUI_SELECTCERTIFICATE_STRUCTW.Native, byte>(ref native), ref Unsafe.As<IntPtr, byte>(ref native.hSelectedCertStore));
+            csc.dwSize = (uint)Unsafe.ByteOffset(ref Unsafe.As<Interop.CryptUI.CRYPTUI_SELECTCERTIFICATE_STRUCTW.Marshaller.Native, byte>(ref native), ref Unsafe.As<IntPtr, byte>(ref native.hSelectedCertStore));
 #else
             csc.dwSize = (uint)Marshal.OffsetOf(typeof(Interop.CryptUI.CRYPTUI_SELECTCERTIFICATE_STRUCTW), "hSelectedCertStore");
 #endif