Eliminate extra IFileSystemObject allocation on Win32 and Unix

FileSystemInfo/FileInfo/DirectoryInfo all carry a IFileSystemObject
which is used internally for the actual implementation. While this
enables FileSystemInfo/FileInfo/DirectoryInfo to be used with WinRT,
it comes with the cost of an extra unnecessary allocation for plain
Win32 and Unix. This change eliminates the allocation on Win32 and
Unix. After this change, the extra object allocation only happens
when the WinRT APIs need to be used.

Author: justinvp

src/Common/src/Interop/Windows/mincore/Interop.GetFileAttributesEx.cs

@@ -30,7 +30,7 @@ internal struct WIN32_FILE_ATTRIBUTE_DATA
             internal uint fileSizeHigh;
             internal uint fileSizeLow;
 
-            internal void PopulateFrom(WIN32_FIND_DATA findData)
+            internal void PopulateFrom(ref WIN32_FIND_DATA findData)
             {
                 // Copy the information to data
                 fileAttributes = (int)findData.dwFileAttributes;

src/System.IO.FileSystem/src/System.IO.FileSystem.csproj

@@ -57,6 +57,8 @@
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
     <Compile Include="Microsoft\Win32\SafeHandles\SafeFileHandle.Windows.cs" />
     <Compile Include="Microsoft\Win32\SafeHandles\SafeFindHandle.Windows.cs" />
+    <Compile Include="System\IO\DirectoryInfo.Windows.cs" />
+    <Compile Include="System\IO\FileInfo.Windows.cs" />
     <Compile Include="System\IO\FileStream.Win32.cs" />
     <Compile Include="System\IO\FileSystemInfo.Windows.cs" />
     <Compile Include="System\IO\PathHelpers.Windows.cs" />
@@ -191,6 +193,7 @@
       <Link>Common\Interop\Windows\Interop.CopyFile.cs</Link>
     </Compile>
     <Compile Include="System\IO\FileSystem.Current.Win32.cs" />
+    <Compile Include="System\IO\FileSystemInfo.Win32.cs" />
     <Compile Include="$(CommonPath)\Interop\Windows\mincore\Interop.CreateFile.cs">
       <Link>Common\Interop\Windows\Interop.CreateFile.cs</Link>
     </Compile>
@@ -219,6 +222,7 @@
       <Link>Common\Interop\Windows\WinRT\Interop.SetErrorMode.cs</Link>
     </Compile>
     <Compile Include="System\IO\FileSystem.Current.MuxWin32WinRT.cs" />
+    <Compile Include="System\IO\FileSystemInfo.WinRT.cs" />
     <Compile Include="System\IO\MultiplexingWin32WinRTFileSystem.cs" />
     <Compile Include="System\IO\WinRTIOExtensions.cs" />
     <Compile Include="System\IO\WinRTFileStream.cs" />

src/System.IO.FileSystem/src/System/IO/DirectoryInfo.Windows.cs

@@ -0,0 +1,19 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Diagnostics;
+using System.Security;
+
+namespace System.IO
+{
+    partial class DirectoryInfo
+    {
+        [SecurityCritical]
+        internal DirectoryInfo(string fullPath, ref Interop.mincore.WIN32_FIND_DATA findData)
+            : this(fullPath, findData.cFileName)
+        {
+            Debug.Assert(string.Equals(findData.cFileName, Path.GetFileName(fullPath), StringComparison.Ordinal));
+            Init(ref findData);
+        }
+    }
+}

src/System.IO.FileSystem/src/System/IO/DirectoryInfo.cs

@@ -8,7 +8,7 @@
 
 namespace System.IO
 {
-    public sealed class DirectoryInfo : FileSystemInfo
+    public sealed partial class DirectoryInfo : FileSystemInfo
     {
         [System.Security.SecuritySafeCritical]
         public DirectoryInfo(String path)
@@ -23,12 +23,12 @@ public DirectoryInfo(String path)
         }
 
         [System.Security.SecuritySafeCritical]
-        internal DirectoryInfo(String fullPath, IFileSystemObject fileSystemObject) : base(fileSystemObject)
+        internal DirectoryInfo(String fullPath, String originalPath)
         {
-            Debug.Assert(PathInternal.GetRootLength(fullPath) > 0, "fullPath must be fully qualified!");
-            
+            Debug.Assert(Path.IsPathRooted(fullPath), "fullPath must be fully qualified!");
+
             // Fast path when we know a DirectoryInfo exists.
-            OriginalPath = Path.GetFileName(fullPath);
+            OriginalPath = originalPath ?? Path.GetFileName(fullPath);
             FullPath = fullPath;
             DisplayPath = GetDisplayName(OriginalPath, FullPath);
         }

src/System.IO.FileSystem/src/System/IO/FileInfo.Windows.cs

@@ -0,0 +1,19 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Diagnostics;
+using System.Security;
+
+namespace System.IO
+{
+    partial class FileInfo
+    {
+        [SecurityCritical]
+        internal FileInfo(string fullPath, ref Interop.mincore.WIN32_FIND_DATA findData)
+            : this(fullPath, findData.cFileName)
+        {
+            Debug.Assert(string.Equals(findData.cFileName, Path.GetFileName(fullPath), StringComparison.Ordinal));
+            Init(ref findData);
+        }
+    }
+}

src/System.IO.FileSystem/src/System/IO/FileInfo.cs

@@ -13,7 +13,7 @@ namespace System.IO
 {
     // Class for creating FileStream objects, and some basic file management
     // routines such as Delete, etc.
-    public sealed class FileInfo : FileSystemInfo
+    public sealed partial class FileInfo : FileSystemInfo
     {
         private String _name;
 
@@ -48,10 +48,10 @@ private String GetDisplayPath(String originalPath)
         }
 
         [System.Security.SecuritySafeCritical]
-        internal FileInfo(String fullPath, IFileSystemObject fileSystemObject) : base(fileSystemObject)
+        internal FileInfo(String fullPath, String originalPath)
         {
             Debug.Assert(Path.IsPathRooted(fullPath), "fullPath must be fully qualified!");
-            _name = Path.GetFileName(fullPath);
+            _name = originalPath ?? Path.GetFileName(fullPath);
             OriginalPath = _name;
             FullPath = fullPath;
             DisplayPath = _name;