Unblock paths > MAX_PATH without extended syntax.

Also allow directories up to max component length (255) as opening does not
require extended syntax.

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

@@ -14,7 +14,8 @@ internal partial class mincore
 
         internal static bool CreateDirectory(string path, ref SECURITY_ATTRIBUTES lpSecurityAttributes)
         {
-            path = PathInternal.AddExtendedPathPrefixForLongPaths(path);
+            // We always want to add for CreateDirectory to get around the legacy 248 character limitation
+            path = PathInternal.AddExtendedPathPrefix(path);
             return CreateDirectoryPrivate(path, ref lpSecurityAttributes);
         }
     }

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

@@ -2,17 +2,38 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using System.IO;
 using System.Runtime.InteropServices;
 using System.Text;
 
 partial class Interop
 {
     partial class mincore
     {
+        /// <summary>
+        /// WARNING: This overload does not implicitly handle long paths.
+        /// </summary>
         [DllImport(Libraries.CoreFile_L1, SetLastError = true, CharSet = CharSet.Unicode, BestFitMapping = false)]
         internal unsafe static extern int GetFullPathNameW(char* path, int numBufferChars, char* buffer, IntPtr mustBeZero);
 
-        [DllImport(Libraries.CoreFile_L1, SetLastError = true, CharSet = CharSet.Unicode, BestFitMapping = false)]
-        internal static extern int GetFullPathNameW(string path, int numBufferChars, [Out]StringBuilder buffer, IntPtr mustBeZero);
+        [DllImport(Libraries.CoreFile_L1, EntryPoint = "GetFullPathNameW", SetLastError = true, CharSet = CharSet.Unicode, BestFitMapping = false)]
+        private static extern int GetFullPathNameWPrivate(string path, int numBufferChars, [Out]StringBuilder buffer, IntPtr mustBeZero);
+
+        internal static int GetFullPathNameW(string path, int numBufferChars, [Out]StringBuilder buffer, IntPtr mustBeZero)
+        {
+            bool wasExtended = PathInternal.IsExtended(path);
+            if (!wasExtended)
+            {
+                path = PathInternal.AddExtendedPathPrefixForLongPaths(path);
+            }
+            int result = GetFullPathNameWPrivate(path, numBufferChars, buffer, mustBeZero);
+
+            if (!wasExtended)
+            {
+                // We don't want to give back \\?\ if we possibly added it ourselves
+                PathInternal.RemoveExtendedPathPrefix(buffer);
+            }
+            return result;
+        }
     }
 }

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

@@ -1,17 +1,38 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System.IO;
 using System.Text;
 using System.Runtime.InteropServices;
 
 partial class Interop
 {
     partial class mincore
     {
+        /// <summary>
+        /// WARNING: This overload does not implicitly handle long paths.
+        /// </summary>
         [DllImport(Libraries.CoreFile_L1, SetLastError = true, CharSet = CharSet.Unicode, BestFitMapping = false)]
         internal unsafe static extern int GetLongPathNameW(char* path, char* longPathBuffer, int bufferLength);
 
-        [DllImport(Libraries.CoreFile_L1, SetLastError = true, CharSet = CharSet.Unicode, BestFitMapping = false)]
-        internal static extern int GetLongPathNameW(string path, [Out]StringBuilder longPathBuffer, int bufferLength);
+        [DllImport(Libraries.CoreFile_L1, EntryPoint = "GetLongPathNameW", SetLastError = true, CharSet = CharSet.Unicode, BestFitMapping = false)]
+        private static extern int GetLongPathNameWPrivate(string path, [Out]StringBuilder longPathBuffer, int bufferLength);
+
+        internal static int GetLongPathNameW(string path, [Out]StringBuilder longPathBuffer, int bufferLength)
+        {
+            bool wasExtended = PathInternal.IsExtended(path);
+            if (!wasExtended)
+            {
+                path = PathInternal.AddExtendedPathPrefixForLongPaths(path);
+            }
+            int result = GetLongPathNameWPrivate(path, longPathBuffer, bufferLength);
+
+            if (!wasExtended)
+            {
+                // We don't want to give back \\?\ if we possibly added it ourselves
+                PathInternal.RemoveExtendedPathPrefix(longPathBuffer);
+            }
+            return result;
+        }
     }
 }

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

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System.IO;
 using System.Text;
 using System.Runtime.InteropServices;
 

src/Common/src/System/IO/PathInternal.Windows.cs

@@ -41,33 +41,37 @@ internal static partial class PathInternal
         /// </summary>
         internal static bool IsPathTooLong(string fullPath)
         {
+            // We'll never know precisely what will fail as paths get changed internally in Windows and
+            // may grow to exceed MaxExtendedPath. We'll only try to catch ones we know will absolutely
+            // fail.
+
+            if (fullPath.Length < MaxExtendedPath - UncExtendedPathPrefix.Length)
+            {
+                // For sure is ok
+                return false;
+            }
+
+            // We need to check if we have a prefix to account for one being implicitly added.
             if (IsExtended(fullPath))
             {
+                // We won't prepend, just check
                 return fullPath.Length >= MaxExtendedPath;
             }
-            else
+
+            if (fullPath.StartsWith(UncPathPrefix, StringComparison.Ordinal))
             {
-                // Will need to be updated with #2581 to allow all paths to MaxExtendedPath
-                // minus legth of extended local or UNC prefix.
-                return fullPath.Length >= MaxShortPath;
+                return fullPath.Length + UncExtendedPrefixToInsert.Length >= MaxExtendedPath;
             }
+
+            return fullPath.Length + ExtendedPathPrefix.Length >= MaxExtendedPath;
         }
 
         /// <summary>
         /// Returns true if the directory is too long
         /// </summary>
         internal static bool IsDirectoryTooLong(string fullPath)
         {
-            if (IsExtended(fullPath))
-            {
-                return fullPath.Length >= MaxExtendedPath;
-            }
-            else
-            {
-                // Will need to be updated with #2581 to allow all paths to MaxExtendedPath
-                // minus legth of extended local or UNC prefix.
-                return fullPath.Length >= MaxShortDirectoryPath;
-            }
+            return IsPathTooLong(fullPath);
         }
 
         /// <summary>
@@ -272,17 +276,17 @@ internal static bool IsPathRelative(string path)
                 return true;
             }
 
-            if ((path[0] == '\\') || (path[0] == '/'))
+            if ((path[0] == Path.DirectorySeparatorChar) || (path[0] == Path.AltDirectorySeparatorChar))
             {
                 // There is no valid way to specify a relative path with two initial slashes
-                return !((path[1] == '\\') || (path[1] == '/'));
+                return !((path[1] == Path.DirectorySeparatorChar) || (path[1] == Path.AltDirectorySeparatorChar));
             }
 
             // The only way to specify a fixed path that doesn't begin with two slashes
             // is the drive, colon, slash format- i.e. C:\
             return !((path.Length >= 3)
-                && (path[1] == ':')
-                && ((path[2] == '\\') || (path[2] == '/')));
+                && (path[1] == Path.VolumeSeparatorChar)
+                && ((path[2] == Path.DirectorySeparatorChar) || (path[2] == Path.AltDirectorySeparatorChar)));
         }
 
         internal static bool IsDirectorySeparator(char c)

src/System.IO.FileSystem/tests/Directory/CreateDirectory.cs

@@ -210,20 +210,44 @@ public void DirectoryWithComponentLongerThanMaxComponentAsPath_ThrowsPathTooLong
 
         [Fact]
         [PlatformSpecific(PlatformID.Windows)]
-        public void DirectoryLongerThanMaxPathAsPath_ThrowsPathTooLongException()
+        public void DirectoryLongerThanMaxPath_Succeeds()
         {
             var paths = IOInputs.GetPathsLongerThanMaxPath();
             Assert.All(paths, (path) =>
+            {
+                DirectoryInfo result = Create(path);
+                Assert.True(Directory.Exists(result.FullName));
+            });
+        }
+
+        [Fact]
+        [PlatformSpecific(PlatformID.Windows)]
+        public void DirectoryLongerThanMaxLongPath_ThrowsPathTooLongException()
+        {
+            var paths = IOInputs.GetPathsLongerThanMaxLongPath();
+            Assert.All(paths, (path) =>
+            {
+                Assert.Throws<PathTooLongException>(() => Create(path));
+            });
+        }
+
+        [Fact]
+        [PlatformSpecific(PlatformID.Windows)]
+        public void DirectoryLongerThanMaxLongPathWithExtendedSyntax_ThrowsPathTooLongException()
+        {
+            var paths = IOInputs.GetPathsLongerThanMaxLongPath(useExtendedSyntax: true);
+            Assert.All(paths, (path) =>
             {
                 Assert.Throws<PathTooLongException>(() => Create(path));
             });
         }
 
+
         [Fact]
         [PlatformSpecific(PlatformID.Windows)]
-        public void ExtendedDirectoryLongerThanLegacyMaxPathSucceeds()
+        public void ExtendedDirectoryLongerThanLegacyMaxPath_Succeeds()
         {
-            var paths = IOInputs.GetPathsLongerThanMaxPath(useExtendedSyntax: true, includeExtendedMaxPath: false);
+            var paths = IOInputs.GetPathsLongerThanMaxPath(useExtendedSyntax: true);
             Assert.All(paths, (path) =>
             {
                 Assert.True(Create(path).Exists);
@@ -232,12 +256,13 @@ public void ExtendedDirectoryLongerThanLegacyMaxPathSucceeds()
 
         [Fact]
         [PlatformSpecific(PlatformID.Windows)]
-        public void DirectoryLongerThanMaxDirectoryAsPath_ThrowsPathTooLongException()
+        public void DirectoryLongerThanMaxDirectoryAsPath_Succeeds()
         {
             var paths = IOInputs.GetPathsLongerThanMaxDirectory();
             Assert.All(paths, (path) =>
             {
-                Assert.Throws<PathTooLongException>(() => Create(path));
+                var result = Create(path);
+                Assert.True(Directory.Exists(result.FullName));
             });
         }
 

src/System.IO.FileSystem/tests/Directory/Exists.cs

@@ -105,9 +105,9 @@ public void DotDotAsPath_ReturnsTrue()
         }
 
         [Fact]
-        public void DirectoryLongerThanMaxPathAsPath_DoesntThrow()
+        public void DirectoryLongerThanMaxLongPath_DoesntThrow()
         {
-            Assert.All((IOInputs.GetPathsLongerThanMaxPath()), (path) =>
+            Assert.All((IOInputs.GetPathsLongerThanMaxLongPath()), (path) =>
             {
                 Assert.False(Exists(path), path);
             });

src/System.IO.FileSystem/tests/Directory/Move.cs

@@ -127,11 +127,11 @@ public void IncludeSubdirectories()
         }
 
         [Fact]
-        public void Path_Longer_Than_MaxPath_Throws_Exception()
+        public void Path_Longer_Than_MaxLongPath_Throws_Exception()
         {
             string testDir = GetTestFilePath();
             Directory.CreateDirectory(testDir);
-            Assert.All((IOInputs.GetPathsLongerThanMaxPath()), (path) =>
+            Assert.All((IOInputs.GetPathsLongerThanMaxLongPath()), (path) =>
             {
                 Assert.Throws<PathTooLongException>(() => Move(testDir, path));
                 Assert.Throws<PathTooLongException>(() => Move(path, testDir));
@@ -144,14 +144,26 @@ public void Path_Longer_Than_MaxPath_Throws_Exception()
 
         [Fact]
         [PlatformSpecific(PlatformID.Windows)]
-        public void Path_With_Longer_Than_MaxDirectory_Throws_Exception()
+        public void Path_With_Longer_Than_MaxDirectory_Succeeds()
         {
             string testDir = GetTestFilePath();
             Directory.CreateDirectory(testDir);
+            Assert.True(Directory.Exists(testDir), "test directory should exist");
             Assert.All((IOInputs.GetPathsLongerThanMaxDirectory()), (path) =>
             {
-                Assert.Throws<PathTooLongException>(() => Move(testDir, path));
-                Assert.Throws<PathTooLongException>(() => Move(path, testDir));
+                string baseDestinationPath = Path.GetDirectoryName(path);
+                if (!Directory.Exists(baseDestinationPath))
+                {
+                    Directory.CreateDirectory(baseDestinationPath);
+                }
+                Assert.True(Directory.Exists(baseDestinationPath), "base destination path should exist");
+
+                Move(testDir, path);
+                Assert.False(Directory.Exists(testDir), "source directory should exist");
+                Assert.True(Directory.Exists(path), "destination directory should exist");
+                Move(path, testDir);
+                Assert.False(Directory.Exists(path), "source directory should exist");
+                Assert.True(Directory.Exists(testDir), "destination directory should exist");
             });
         }
 

src/System.IO.FileSystem/tests/File/Move.cs

@@ -149,8 +149,26 @@ public void LongPath()
             //Create a destination path longer than the traditional Windows limit of 256 characters
             string testFileSource = Path.Combine(TestDirectory, GetTestFileName());
             File.Create(testFileSource).Dispose();
+            Assert.True(File.Exists(testFileSource), "test file should exist");
 
             Assert.All(IOInputs.GetPathsLongerThanMaxPath(), (path) =>
+            {
+                string baseDestinationPath = Path.GetDirectoryName(path);
+                if (!Directory.Exists(baseDestinationPath))
+                {
+                    Directory.CreateDirectory(baseDestinationPath);
+                }
+                Assert.True(Directory.Exists(baseDestinationPath), "base destination path should exist");
+
+                Move(testFileSource, path);
+                Assert.True(File.Exists(path), "moved test file should exist");
+                File.Delete(testFileSource);
+                Assert.False(File.Exists(testFileSource), "source test file should not exist");
+                Move(path, testFileSource);
+                Assert.True(File.Exists(testFileSource), "restored test file should exist");
+            });
+
+            Assert.All(IOInputs.GetPathsLongerThanMaxLongPath(), (path) =>
             {
                 Assert.Throws<PathTooLongException>(() => Move(testFileSource, path));
                 File.Delete(testFileSource);

src/System.IO.FileSystem/tests/PortedCommon/IOInputs.cs

@@ -21,13 +21,17 @@ internal static class IOInputs
     // Max path length (minus trailing \0). Unix values vary system to system; just using really long values here likely to be more than on the average system.
     public static readonly int MaxPath = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? 259 : 10000;
 
+    // Same as MaxPath on Unix
+    public static readonly int MaxLongPath = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? MaxExtendedPath : 10000;
+
     // Windows specific, this is the maximum length that can be passed to APIs taking directory names, such as Directory.CreateDirectory & Directory.Move.
     // Does not include the trailing \0.
-    public static readonly int MaxDirectory = 247;
+    public static readonly int MaxDirectory = MaxComponent - 1;
 
     // Windows specific, this is the maximum length that can be passed using extended syntax. Does not include the trailing \0.
     public static readonly int MaxExtendedPath = short.MaxValue - 1;
 
+
     public const int MaxComponent = 255;
 
     public const string ExtendedPrefix = @"\\?\";
@@ -218,16 +222,17 @@ public static IEnumerable<string> GetPathsLongerThanMaxDirectory()
         yield return GetLongPath(MaxDirectory + 3);
     }
 
-    public static IEnumerable<string> GetPathsLongerThanMaxPath(bool useExtendedSyntax = false, bool includeExtendedMaxPath = true)
+    public static IEnumerable<string> GetPathsLongerThanMaxPath(bool useExtendedSyntax = false)
     {
         yield return GetLongPath(MaxPath + 1, useExtendedSyntax);
         yield return GetLongPath(MaxPath + 2, useExtendedSyntax);
         yield return GetLongPath(MaxPath + 3, useExtendedSyntax);
-        if (includeExtendedMaxPath)
-        {
-            yield return GetLongPath(MaxExtendedPath + 1, useExtendedSyntax);
-            yield return GetLongPath(MaxExtendedPath + 2, useExtendedSyntax);
-        }
+    }
+
+    public static IEnumerable<string> GetPathsLongerThanMaxLongPath(bool useExtendedSyntax = false)
+    {
+        yield return GetLongPath(MaxExtendedPath + 1 - (useExtendedSyntax ? 0 : ExtendedPrefix.Length), useExtendedSyntax);
+        yield return GetLongPath(MaxExtendedPath + 2 - (useExtendedSyntax ? 0 : ExtendedPrefix.Length), useExtendedSyntax);
     }
 
     private static string GetLongPath(int characterCount, bool extended = false)

src/System.Runtime.Extensions/src/System/IO/Path.Unix.cs

@@ -18,6 +18,7 @@ public static partial class Path
         private static readonly char[] InvalidFileNameChars = { '\0', '/' };
 
         private static readonly int MaxPath = Interop.libc.MaxPath;
+        private static readonly int MaxLongPath = MaxPath;
         private static readonly int MaxComponentLength = Interop.libc.MaxName;
 
         private static bool IsDirectoryOrVolumeSeparator(char c)

src/System.Runtime.Extensions/src/System/IO/Path.Windows.cs

@@ -33,7 +33,7 @@ public static partial class Path
         // For example, D:\<256 char file name> isn't legal, even though it's under 260 chars.
         internal static readonly int MaxPath = 260;
         private static readonly int MaxComponentLength = 255;
-        private const int MaxLongPath = 32000;
+        internal static readonly int MaxLongPath = short.MaxValue;
 
         private static bool IsDirectoryOrVolumeSeparator(char c)
         {