More nullability work, mostly Shell32

Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <Version>4.0.0</Version>
+    <Version>4.0.0-beta</Version>
     <TargetFrameworks>net45;net48;net6.0;net7.0;netstandard2.0;netcoreapp3.1</TargetFrameworks>
     <Configurations>Debug;Release</Configurations>
     <Platforms>AnyCPU;x64;x86</Platforms>
@@ -9,6 +9,7 @@
     <Authors>David Hall</Authors>
     <Company>GitHub Community</Company>
     <Copyright>Copyright © 2017-2023</Copyright>
+    <EnableUnsafeBinaryFormatterSerialization>true</EnableUnsafeBinaryFormatterSerialization>
     <GenerateAssemblyInfo>true</GenerateAssemblyInfo>
     <GenerateAssemblyConfigurationAttribute>false</GenerateAssemblyConfigurationAttribute>
     <GenerateAssemblyInformationalVersionAttribute>false</GenerateAssemblyInformationalVersionAttribute>

PInvoke/SearchApi/SearchApi.cs

@@ -895,7 +895,7 @@ public interface IFilter
 		// origPos, REFIID riid, void **ppunk );
 		[PInvokeData("filter.h")]
 		[PreserveSig]
-		HRESULT BindRegion([In] FILTERREGION origPos, [In] in Guid riid, [MarshalAs(UnmanagedType.IUnknown, IidParameterIndex = 1)] out object ppunk);
+		HRESULT BindRegion([In] FILTERREGION origPos, [In] in Guid riid, [MarshalAs(UnmanagedType.IUnknown, IidParameterIndex = 1)] out object? ppunk);
 	}
 
 	/// <summary>
@@ -944,7 +944,7 @@ public interface ILoadFilter
 		[PInvokeData("filtereg.h", MSDNShortId = "920c976e-4dde-4e53-85b7-7547291736a0")]
 		[PreserveSig]
 		HRESULT LoadIFilter([In, Optional, MarshalAs(UnmanagedType.LPWStr)] string? pwcsPath, in FILTERED_DATA_SOURCES pFilteredSources, [In, MarshalAs(UnmanagedType.IUnknown)] object? pUnkOuter,
-			[In, MarshalAs(UnmanagedType.Bool)] bool fUseDefault, out Guid pFilterClsid, [Optional] IntPtr SearchDecSize, [Optional] IntPtr pwcsSearchDesc, out IFilter ppIFilt);
+			[In, MarshalAs(UnmanagedType.Bool)] bool fUseDefault, out Guid pFilterClsid, [Optional] IntPtr SearchDecSize, [Optional] IntPtr pwcsSearchDesc, out IFilter? ppIFilt);
 
 		/// <summary>
 		/// <para>Not implemented.</para>
@@ -965,7 +965,7 @@ HRESULT LoadIFilter([In, Optional, MarshalAs(UnmanagedType.LPWStr)] string? pwcs
 		[PInvokeData("filtereg.h", MSDNShortId = "b4eff132-9022-4091-a2a3-1d8e11a35b39")]
 		[Obsolete, PreserveSig]
 		HRESULT LoadIFilterFromStorage([In] IStorage pStg, [In, MarshalAs(UnmanagedType.IUnknown)] object? pUnkOuter, [In, MarshalAs(UnmanagedType.LPWStr)] string pwcsOverride,
-			[In, MarshalAs(UnmanagedType.Bool)] bool fUseDefault, out Guid pFilterClsid, [Optional] IntPtr SearchDecSize, [Optional] IntPtr pwcsSearchDesc, out IFilter ppIFilt);
+			[In, MarshalAs(UnmanagedType.Bool)] bool fUseDefault, out Guid pFilterClsid, [Optional] IntPtr SearchDecSize, [Optional] IntPtr pwcsSearchDesc, out IFilter? ppIFilt);
 
 		/// <summary>
 		/// <para>Not implemented.</para>
@@ -986,7 +986,7 @@ HRESULT LoadIFilterFromStorage([In] IStorage pStg, [In, MarshalAs(UnmanagedType.
 		[PInvokeData("filtereg.h", MSDNShortId = "6a577306-d5ff-43c1-ab9f-3a7437661d2a")]
 		[Obsolete, PreserveSig]
 		HRESULT LoadIFilterFromStream([In] IStream pStm, in FILTERED_DATA_SOURCES pFilteredSources, [In, MarshalAs(UnmanagedType.IUnknown)] object? pUnkOuter,
-			[In, MarshalAs(UnmanagedType.Bool)] bool fUseDefault, out Guid pFilterClsid, [Optional] IntPtr SearchDecSize, [Optional] IntPtr pwcsSearchDesc, out IFilter ppIFilt);
+			[In, MarshalAs(UnmanagedType.Bool)] bool fUseDefault, out Guid pFilterClsid, [Optional] IntPtr SearchDecSize, [Optional] IntPtr pwcsSearchDesc, out IFilter? ppIFilt);
 	}
 
 	/// <summary>

PInvoke/Shell32/ShObjIdl.IExplorerBrowser.cs

@@ -244,7 +244,7 @@ public interface IExplorerBrowser
 		/// </param>
 		/// <param name="dwFlags">One of the EXPLORER_BROWSER_FILL_FLAGS values.</param>
 		[MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-		void FillFromObject([In, MarshalAs(UnmanagedType.IUnknown)] object punk, [In] EXPLORER_BROWSER_FILL_FLAGS dwFlags);
+		void FillFromObject([In, MarshalAs(UnmanagedType.IUnknown)] object? punk, [In] EXPLORER_BROWSER_FILL_FLAGS dwFlags);
 
 		/// <summary>Removes all items from the results folder.</summary>
 		[MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]

PInvoke/Shell32/ShObjIdl.IExplorerCommand.cs

@@ -167,7 +167,7 @@ public interface IExplorerCommand
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-iexplorercommand-gettitle HRESULT GetTitle(
 		// IShellItemArray *psiItemArray, LPWSTR *ppszName );
 		[PreserveSig]
-		HRESULT GetTitle(IShellItemArray psiItemArray, [MarshalAs(UnmanagedType.LPWStr)] out string ppszName);
+		HRESULT GetTitle(IShellItemArray psiItemArray, [MarshalAs(UnmanagedType.LPWStr)] out string? ppszName);
 
 		/// <summary>Gets an icon resource string of the icon associated with the specified Windows Explorer command item.</summary>
 		/// <param name="psiItemArray">
@@ -188,7 +188,7 @@ public interface IExplorerCommand
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-iexplorercommand-geticon HRESULT GetIcon(
 		// IShellItemArray *psiItemArray, LPWSTR *ppszIcon );
 		[PreserveSig]
-		HRESULT GetIcon(IShellItemArray psiItemArray, [MarshalAs(UnmanagedType.LPWStr)] out string ppszIcon);
+		HRESULT GetIcon(IShellItemArray psiItemArray, [MarshalAs(UnmanagedType.LPWStr)] out string? ppszIcon);
 
 		/// <summary>Gets the tooltip string associated with a specified Windows Explorer command item.</summary>
 		/// <param name="psiItemArray">
@@ -206,7 +206,7 @@ public interface IExplorerCommand
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-iexplorercommand-gettooltip HRESULT
 		// GetToolTip( IShellItemArray *psiItemArray, LPWSTR *ppszInfotip );
 		[PreserveSig]
-		HRESULT GetToolTip(IShellItemArray psiItemArray, [MarshalAs(UnmanagedType.LPWStr)] out string ppszInfotip);
+		HRESULT GetToolTip(IShellItemArray psiItemArray, [MarshalAs(UnmanagedType.LPWStr)] out string? ppszInfotip);
 
 		/// <summary>Gets the GUID of an Windows Explorer command.</summary>
 		/// <param name="pguidCommandName">
@@ -340,7 +340,7 @@ public interface IExplorerCommand
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-iexplorercommand-enumsubcommands HRESULT
 		// EnumSubCommands( IEnumExplorerCommand **ppEnum );
 		[PreserveSig]
-		HRESULT EnumSubCommands(out IEnumExplorerCommand ppEnum);
+		HRESULT EnumSubCommands(out IEnumExplorerCommand? ppEnum);
 	}
 
 	/// <summary>Exposes methods to create Explorer commands and command enumerators.</summary>
@@ -378,7 +378,7 @@ public interface IExplorerCommandProvider
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-iexplorercommandprovider-getcommands
 		// HRESULT GetCommands( IUnknown *punkSite, REFIID riid, void **ppv );
 		[PreserveSig]
-		HRESULT GetCommands([MarshalAs(UnmanagedType.IUnknown)] object punkSite, in Guid riid, [MarshalAs(UnmanagedType.IUnknown)] out object ppv);
+		HRESULT GetCommands([MarshalAs(UnmanagedType.IUnknown)] object punkSite, in Guid riid, [MarshalAs(UnmanagedType.IUnknown)] out object? ppv);
 
 		// IExplorerCommand
 		/// <summary>Gets a specified Explorer command instance.</summary>
@@ -401,7 +401,7 @@ public interface IExplorerCommandProvider
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-iexplorercommandprovider-getcommand HRESULT
 		// GetCommand( REFGUID rguidCommandId, REFIID riid, void **ppv );
 		[PreserveSig]
-		HRESULT GetCommand(in Guid rguidCommandId, in Guid riid, [MarshalAs(UnmanagedType.IUnknown)] out object ppv);
+		HRESULT GetCommand(in Guid rguidCommandId, in Guid riid, [MarshalAs(UnmanagedType.IUnknown)] out object? ppv);
 	}
 
 	/// <summary>Exposes a single method that allows retrieval of the command state.</summary>

PInvoke/Shell32/ShObjIdl.INamespaceWalk.cs

@@ -322,7 +322,7 @@ public interface INamespaceWalkCB
 		// https://docs.microsoft.com/en-us/windows/desktop/api/shobjidl_core/nf-shobjidl_core-inamespacewalkcb-initializeprogressdialog
 		// HRESULT InitializeProgressDialog( LPWSTR *ppszTitle, LPWSTR *ppszCancel );
 		[PreserveSig]
-		HRESULT InitializeProgressDialog([Out, MarshalAs(UnmanagedType.LPWStr)] out string ppszTitle, [Out, MarshalAs(UnmanagedType.LPWStr)] out string ppszCancel);
+		HRESULT InitializeProgressDialog([Out, MarshalAs(UnmanagedType.LPWStr)] out string? ppszTitle, [Out, MarshalAs(UnmanagedType.LPWStr)] out string? ppszCancel);
 	}
 
 	/// <summary>
@@ -421,7 +421,7 @@ public interface INamespaceWalkCB2 : INamespaceWalkCB
 		// https://docs.microsoft.com/en-us/windows/desktop/api/shobjidl_core/nf-shobjidl_core-inamespacewalkcb-initializeprogressdialog
 		// HRESULT InitializeProgressDialog( LPWSTR *ppszTitle, LPWSTR *ppszCancel );
 		[PreserveSig]
-		new HRESULT InitializeProgressDialog([Out, MarshalAs(UnmanagedType.LPWStr)] out string ppszTitle, [Out, MarshalAs(UnmanagedType.LPWStr)] out string ppszCancel);
+		new HRESULT InitializeProgressDialog([Out, MarshalAs(UnmanagedType.LPWStr)] out string? ppszTitle, [Out, MarshalAs(UnmanagedType.LPWStr)] out string? ppszCancel);
 
 		/// <summary>Removes data collected during a namespace walk.</summary>
 		/// <param name="hr">

PInvoke/Shell32/ShObjIdl.IShellFolder.cs

@@ -472,7 +472,7 @@ public interface ICategoryProvider
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-icategoryprovider-createcategory HRESULT
 		// CreateCategory( const GUID *pguid, REFIID riid, void **ppv );
 		[PreserveSig]
-		HRESULT CreateCategory(in Guid pguid, in Guid riid, [MarshalAs(UnmanagedType.IUnknown, IidParameterIndex = 1)] out object ppv);
+		HRESULT CreateCategory(in Guid pguid, in Guid riid, [MarshalAs(UnmanagedType.IUnknown, IidParameterIndex = 1)] out object? ppv);
 	}
 
 	/// <summary>Creates a category object.</summary>
@@ -1093,7 +1093,7 @@ public interface IShellFolder
 		// GetUIObjectOf( HWND hwndOwner, UINT cidl, PCUITEMID_CHILD_ARRAY apidl, REFIID riid, UINT *rgfReserved, void **ppv );
 		[PreserveSig]
 		HRESULT GetUIObjectOf(HWND hwndOwner, uint cidl, [In, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] IntPtr[] apidl, in Guid riid,
-			[In, Out, Optional] IntPtr rgfReserved, [MarshalAs(UnmanagedType.Interface, IidParameterIndex = 3)] out object ppv);
+			[In, Out, Optional] IntPtr rgfReserved, [MarshalAs(UnmanagedType.Interface, IidParameterIndex = 3)] out object? ppv);
 
 		/// <summary>Retrieves the display name for the specified file object or subfolder.</summary>
 		/// <param name="pidl">
@@ -1604,7 +1604,7 @@ public interface IShellFolder2 : IShellFolder
 		/// </remarks>
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-ishellfolder-createviewobject
 		[PreserveSig]
-		new HRESULT CreateViewObject(HWND hwndOwner, in Guid riid, [MarshalAs(UnmanagedType.Interface, IidParameterIndex = 1)] out object ppv);
+		new HRESULT CreateViewObject(HWND hwndOwner, in Guid riid, [MarshalAs(UnmanagedType.Interface, IidParameterIndex = 1)] out object? ppv);
 
 		/// <summary>Gets the attributes of one or more file or folder objects contained in the object represented by IShellFolder.</summary>
 		/// <param name="cidl">
@@ -1744,7 +1744,7 @@ public interface IShellFolder2 : IShellFolder
 		// GetUIObjectOf( HWND hwndOwner, UINT cidl, PCUITEMID_CHILD_ARRAY apidl, REFIID riid, UINT *rgfReserved, void **ppv );
 		[PreserveSig]
 		new HRESULT GetUIObjectOf(HWND hwndOwner, uint cidl, [In, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] IntPtr[] apidl, in Guid riid,
-			[In, Out, Optional] IntPtr rgfReserved, [MarshalAs(UnmanagedType.Interface, IidParameterIndex = 3)] out object ppv);
+			[In, Out, Optional] IntPtr rgfReserved, [MarshalAs(UnmanagedType.Interface, IidParameterIndex = 3)] out object? ppv);
 
 		/// <summary>Retrieves the display name for the specified file object or subfolder.</summary>
 		/// <param name="pidl">
@@ -1889,7 +1889,7 @@ public interface IShellFolder2 : IShellFolder
 		/// </returns>
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-ishellfolder2-enumsearches
 		[PreserveSig]
-		HRESULT EnumSearches(out IEnumExtraSearch ppenum);
+		HRESULT EnumSearches(out IEnumExtraSearch? ppenum);
 
 		/// <summary>Gets the default sorting and display columns.</summary>
 		/// <param name="dwRes">
@@ -2012,7 +2012,7 @@ public interface IShellFolder2 : IShellFolder
 		/// </remarks>
 		// https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-ishellfolder2-getdetailsex
 		[PreserveSig]
-		HRESULT GetDetailsEx([In] PIDL pidl, in PROPERTYKEY pscid, [MarshalAs(UnmanagedType.Struct)] out object pv);
+		HRESULT GetDetailsEx([In] PIDL pidl, in PROPERTYKEY pscid, [MarshalAs(UnmanagedType.Struct)] out object? pv);
 
 		/// <summary>Gets detailed information, identified by a column index, on an item in a Shell folder.</summary>
 		/// <param name="pidl">

PInvoke/Shell32/ShObjIdl.cs

@@ -1221,7 +1221,7 @@ public interface IFileIsInUse
 		// https://docs.microsoft.com/en-us/windows/desktop/api/shobjidl_core/nf-shobjidl_core-ifileisinuse-getappname HRESULT
 		// GetAppName( LPWSTR *ppszName );
 		[PreserveSig]
-		HRESULT GetAppName([MarshalAs(UnmanagedType.LPWStr)] out string ppszName);
+		HRESULT GetAppName([MarshalAs(UnmanagedType.LPWStr)] out string? ppszName);
 
 		/// <summary>Gets a value that indicates how the file in use is being used.</summary>
 		/// <param name="pfut">

PInvoke/Shell32/ShlObj.cs

@@ -1,6 +1,7 @@
 #pragma warning disable IL2050 // Correctness of COM interop cannot be guaranteed after trimming. Interfaces and interface members might be removed.
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Runtime.InteropServices.ComTypes;
 using System.Security;
 using static Vanara.Extensions.BitHelper;
@@ -5268,7 +5269,7 @@ public static extern HRESULT SHCreateFileExtractIconW([MarshalAs(UnmanagedType.L
 	// PCIDLIST_ABSOLUTE pidlParent, IShellFolder *psfParent, PCUITEMID_CHILD pidl, IShellItem **ppsi );
 	[DllImport(Lib.Shell32, SetLastError = false, ExactSpelling = true)]
 	[PInvokeData("shlobj_core.h", MSDNShortId = "d4371cdf-a8f4-4a39-ba66-97fd40ed46ae")]
-	public static extern HRESULT SHCreateShellItem(PIDL pidlParent, IShellFolder? psfParent, PIDL pidl, out IShellItem ppsi);
+	public static extern HRESULT SHCreateShellItem([Optional] PIDL pidlParent, [Optional] IShellFolder? psfParent, PIDL pidl, out IShellItem? ppsi);
 
 	/// <summary>
 	/// <para>

PInvoke/Ws2_32/WinSock2.cs

@@ -2511,6 +2511,11 @@ private SafeSOCKET() : base() { }
 		/// <returns>The result of the conversion.</returns>
 		public static implicit operator SOCKET(SafeSOCKET h) => h.handle;
 
+		/// <summary>Performs an implicit conversion from <see cref="SafeSOCKET"/> to <see cref="SOCKET"/>.</summary>
+		/// <param name="h">The safe handle instance.</param>
+		/// <returns>The result of the conversion.</returns>
+		public static implicit operator SOCKET?(SafeSOCKET? h) => h?.handle;
+
 		/// <inheritdoc/>
 		protected override bool InternalReleaseHandle() => closesocket(this) == 0;
 	}