Allow use of long paths

src/System.Management.Automation/engine/Utils.cs

@@ -1153,8 +1153,22 @@ internal static bool PathIsUnc(string path)
 
         internal class NativeMethods
         {
-            [DllImport(PinvokeDllNames.GetFileAttributesDllName, CharSet = CharSet.Unicode, SetLastError = true)]
-            internal static extern int GetFileAttributes(string lpFileName);
+            private static string EnsureLongPathPrefixIfNeeded(string path)
+            {
+                if (path.Length >= MAX_PATH && !path.StartsWith(@"\\?\", StringComparison.Ordinal))
+                    return @"\\?\" + path;
+
+                return path;
+            }
+
+            [DllImport(PinvokeDllNames.GetFileAttributesDllName, EntryPoint = "GetFileAttributesW", CharSet = CharSet.Unicode, SetLastError = true)]
+            private static extern int GetFileAttributesPrivate(string lpFileName);
+
+            internal static int GetFileAttributes(string fileName)
+            {
+                fileName = EnsureLongPathPrefixIfNeeded(fileName);
+                return GetFileAttributesPrivate(fileName);
+            }
 
             [Flags]
             internal enum FileAttributes

test/powershell/Modules/Microsoft.PowerShell.Management/FileSystem.Tests.ps1

@@ -663,6 +663,47 @@ Describe "Copy-Item can avoid copying an item onto itself" -Tags "CI", "RequireA
     }
 }
 
+Describe "Handling long paths" -Tags "CI" {
+    BeforeAll {
+        $longDir = 'a' * 250
+        $longSubDir = 'b' * 250
+        $fileName = "file1.txt"
+        $topPath = Join-Path $TestDrive $longDir
+        $longDirPath = Join-Path $topPath $longSubDir
+        $longFilePath = Join-Path $longDirPath $fileName
+        $cwd = Get-Location
+    }
+    BeforeEach {
+        New-Item -ItemType File -Path $longFilePath -Force | Out-Null
+    }
+    AfterEach {
+        Remove-Item -Path $topPath -Force -Recurse -ErrorAction SilentlyContinue
+        Set-Location $cwd
+    }
+
+    It "Can remove a file via a long path" {
+        Remove-Item -Path $longFilePath -ErrorVariable e -ErrorAction SilentlyContinue
+        $e | Should BeNullOrEmpty
+        $longFilePath | Should Not Exist
+    }
+    It "Can rename a file via a long path" {
+        $newFileName = "new-file.txt"
+        $newPath = Join-Path $longDirPath $newFileName
+        Rename-Item -Path $longFilePath -NewName $newFileName
+        $longFilePath | Should Not Exist
+        $newPath | Should Exist
+    }
+    It "Can change into a directory via a long path" {
+        Set-Location -Path $longDirPath -ErrorVariable e -ErrorAction SilentlyContinue
+        $e | Should BeNullOrEmpty
+        $c = Get-Location
+        $fileName | Should Exist
+    }
+    It "Can use Test-Path to check for a file via a long path" {
+        Test-Path $longFilePath | Should Be $true
+    }
+}
+
 Describe "Extended FileSystem Item/Content Cmdlet Provider Tests" -Tags "Feature" {
     BeforeAll {
         $testDir = "testDir"