PowerShell
@@ -515,6 +515,11 @@ internal static bool NonWindowsIsDirectory(string path)
             return Unix.NativeMethods.IsDirectory(path);
         }
 
+        internal static bool NonWindowsIsSameFileSystemItem(string pathOne, string pathTwo)
+        {
+            return Unix.NativeMethods.IsSameFileSystemItem(pathOne, pathTwo);
+        }
+
         internal static bool NonWindowsIsExecutable(string path)
         {
             return Unix.NativeMethods.IsExecutable(path);
@@ -530,7 +535,7 @@ internal static int NonWindowsGetProcessParentPid(int pid)
             return IsOSX ? Unix.NativeMethods.GetPPid(pid) : Unix.GetProcFSParentPid(pid);
         }
 
-       
+
 
         // Unix specific implementations of required functionality
         //
@@ -722,6 +727,11 @@ internal static extern int CreateHardLink([MarshalAs(UnmanagedType.LPStr)]string
                 [DllImport(psLib, CharSet = CharSet.Ansi, SetLastError = true)]
                 [return: MarshalAs(UnmanagedType.I1)]
                 internal static extern bool IsDirectory([MarshalAs(UnmanagedType.LPStr)]string filePath);
+
+                [DllImport(psLib, CharSet = CharSet.Ansi, SetLastError = true)]
+                [return: MarshalAs(UnmanagedType.I1)]
+                internal static extern bool IsSameFileSystemItem([MarshalAs(UnmanagedType.LPStr)]string filePathOne,
+                                                                 [MarshalAs(UnmanagedType.LPStr)]string filePathTwo);
             }
         }
     }

@@ -62,6 +62,11 @@ public sealed partial class FileSystemProvider : NavigationCmdletProvider,
         // copy script will accomodate the new value.
         private const int FILETRANSFERSIZE = 4 * 1024 * 1024;
 
+        // The name of the key in an exception's Data dictionary when attempting
+        // to copy an item onto itself.
+        private const string SelfCopyDataKey = "SelfCopy";
+
+
         /// <summary>
         /// An instance of the PSTraceSource class used for trace output
         /// using "FileSystemProvider" as the category.
@@ -3460,14 +3465,14 @@ protected override void CopyItem(
             _excludeMatcher = SessionStateUtilities.CreateWildcardsFromStrings(Exclude, WildcardOptions.IgnoreCase);
 
             // if the source and destination path are same (for a local copy) then flag it as error.
-            if ((toSession == null) && (fromSession == null) && path.Equals(destinationPath, StringComparison.OrdinalIgnoreCase))
+            if ((toSession == null) && (fromSession == null) && InternalSymbolicLinkLinkCodeMethods.IsSameFileSystemItem(path, destinationPath))
             {
                 String error = StringUtil.Format(FileSystemProviderStrings.CopyError, path);
                 Exception e = new IOException(error);
+                e.Data[SelfCopyDataKey] = destinationPath;
                 WriteError(new ErrorRecord(e, "CopyError", ErrorCategory.WriteError, path));
                 return;
             }
-
             // Copy-Item from session
             if (fromSession != null)
             {
@@ -3777,14 +3782,14 @@ private void CopyFileInfoItem(FileInfo file, string destinationPath, bool force,
                 }
 
                 //if the source and destination path are same then flag it as error.
-                if (destinationPath.Equals(file.FullName, StringComparison.OrdinalIgnoreCase))
+                if (InternalSymbolicLinkLinkCodeMethods.IsSameFileSystemItem(destinationPath, file.FullName))
                 {
                     String error = StringUtil.Format(FileSystemProviderStrings.CopyError, destinationPath);
                     Exception e = new IOException(error);
+                    e.Data[SelfCopyDataKey] = file.FullName;
                     WriteError(new ErrorRecord(e, "CopyError", ErrorCategory.WriteError, destinationPath));
                     return;
                 }
-
                 // Verify that the target doesn't represent a device name
                 if (PathIsReservedDeviceName(destinationPath, "CopyError"))
                 {
@@ -8211,6 +8216,42 @@ internal static bool WinIsHardLink(FileSystemInfo fileInfo)
             return isHardLink;
         }
 
+        internal static bool IsSameFileSystemItem(string pathOne, string pathTwo)
+        {
+#if UNIX
+            return Platform.NonWindowsIsSameFileSystemItem(pathOne, pathTwo);
+#else
+            return WinIsSameFileSystemItem(pathOne, pathTwo);
+#endif
+        }
+
+        internal static bool WinIsSameFileSystemItem(string pathOne, string pathTwo)
+        {
+            var access = FileAccess.Read;
+            var share = FileShare.Read;
+            var creation = FileMode.Open;
+            var attributes = FileAttributes.BackupSemantics | FileAttributes.PosixSemantics;
+
+            using (var sfOne = AlternateDataStreamUtilities.NativeMethods.CreateFile(pathOne, access, share, IntPtr.Zero, creation, (int)attributes, IntPtr.Zero))
+            using (var sfTwo = AlternateDataStreamUtilities.NativeMethods.CreateFile(pathTwo, access, share, IntPtr.Zero, creation, (int)attributes, IntPtr.Zero))
+            {
+                if (!sfOne.IsInvalid && !sfTwo.IsInvalid)
+                {
+                    BY_HANDLE_FILE_INFORMATION  infoOne;
+                    BY_HANDLE_FILE_INFORMATION  infoTwo;
+                    if (   GetFileInformationByHandle(sfOne.DangerousGetHandle(), out infoOne)
+                        && GetFileInformationByHandle(sfTwo.DangerousGetHandle(), out infoTwo))
+                    {
+                        return    infoOne.VolumeSerialNumber == infoTwo.VolumeSerialNumber
+                               && infoOne.FileIndexHigh == infoTwo.FileIndexHigh
+                               && infoOne.FileIndexLow == infoTwo.FileIndexLow;
+                    }
+                }
+            }
+
+            return false;
+        }
+
         internal static bool IsHardLink(ref IntPtr handle)
         {
 #if UNIX
@@ -8664,7 +8705,7 @@ internal static void SetZoneOfOrigin(string path, SecurityZone securityZone)
             // the code above seems cleaner and more robust than the IAttachmentExecute approach
         }
 
-        private static class NativeMethods
+        internal static class NativeMethods
         {
             internal const int ERROR_HANDLE_EOF = 38;
             internal enum StreamInfoLevels { FindStreamInfoStandard = 0 }

@@ -13,6 +13,7 @@ add_library(psl-native SHARED
   geterrorcategory.cpp
   isfile.cpp
   isdirectory.cpp
+  issamefilesystemitem.cpp
   issymlink.cpp
   isexecutable.cpp
   setdate.cpp

@@ -0,0 +1,48 @@
+//! @file issamefilesystemitem.cpp
+//! @author Jeff Bienstadt <v-jebien@microsoft.com>
+//! @brief Determines whether two paths ultimately point to the same filesystem object
+
+#include "getstat.h"
+#include "issamefilesystemitem.h"
+
+#include <assert.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+//! @brief Returns a boolean value indicating whether two paths ultimately refer to the same file or directory.
+//!
+//! IsSameFileSystemItem
+//!
+//! @param[in] path_one
+//! @parblock
+//! A pointer to the buffer that contains the first path.
+//!
+//! char* is marshaled as an LPStr, which on Linux is UTF-8.
+//! @endparblock
+//!
+//! @param[in] path_two
+//! @parblock
+//! A pointer to the buffer that contains the second path.
+//!
+//! char* is marshaled as an LPStr, which on Linux is UTF-8.
+//! @endparblock
+//!
+//! @retval true if both paths point to the same filesystem object,
+//! false otherwise
+//!
+bool IsSameFileSystemItem(const char* path_one, const char* path_two)
+{
+    assert(path_one);
+    assert(path_two);
+
+    struct stat buf_1;
+    struct stat buf_2;
+
+    if (GetStat(path_one, &buf_1) == 0 && GetStat(path_two, &buf_2) == 0)
+    {
+        return buf_1.st_dev == buf_2.st_dev && buf_1.st_ino == buf_2.st_ino;
+    }
+
+    return false;
+}
@@ -0,0 +1,11 @@
+#pragma once
+
+#include "pal.h"
+
+#include <stdbool.h>
+
+PAL_BEGIN_EXTERNC
+
+bool IsSameFileSystemItem(const char* path_one, const char* path_two);
+
+PAL_END_EXTERNC
@@ -246,6 +246,157 @@ Describe "Basic FileSystem Provider Tests" -Tags "CI" {
     }
 }
 
+
+Describe "Copy-Item can avoid copying an item onto itself" -Tags "CI", "RequireAdminOnWindows" {
+    BeforeAll {
+        # For now, we'll assume the tests are running the platform's
+        # native filesystem, in its default mode
+        $isCaseSensitive = $IsLinux
+
+        # The name of the key in an exception's Data dictionary when an
+        # attempt is made to copy an item onto itself.
+        $selfCopyKey = "SelfCopy"
+
+        $TestDrive = "TestDrive:"
+        $subDir = "$TestDrive/sub"
+        $otherSubDir = "$TestDrive/other-sub"
+        $fileName = "file.txt"
+        $filePath = "$TestDrive/$fileName"
+        $otherFileName = "other-file"
+        $otherFile = "$otherSubDir/$otherFileName"
+        $symToOther = "$subDir/sym-to-other"
+        $secondSymToOther = "$subDir/another-sym-to-other"
+        $symToSym = "$subDir/sym-to-sym-to-other"
+        $symToOtherFile = "$subDir/sym-to-other-file"
+        $hardToOtherFile = "$subDir/hard-to-other-file"
+        $symdToOther = "$subDir/symd-to-other"
+        $junctionToOther = "$subDir/junction-to-other"
+
+        New-Item -ItemType File $filePath -Value "stuff" >$null
+        New-Item -ItemType Directory $subDir >$null
+        New-Item -ItemType Directory $otherSubDir >$null
+        New-Item -ItemType File $otherFile -Value "some text" >$null
+        New-Item -ItemType SymbolicLink $symToOther -Value $otherSubDir >$null
+        New-Item -ItemType SymbolicLink $secondSymToOther -Value $otherSubDir >$null
+        New-Item -ItemType SymbolicLink $symToSym -Value $symToOther >$null
+        New-Item -ItemType SymbolicLink $symToOtherFile -Value $otherFile >$null
+        New-Item -ItemType HardLink $hardToOtherFile -Value $otherFile >$null
+
+        if ($IsWindows)
+        {
+            New-Item -ItemType Junction $junctionToOther -Value $otherSubDir >$null
+            New-Item -ItemType SymbolicLink $symdToOther -Value $otherSubDir >$null
+        }
+    }
+
+    Context "Copy-Item using different case (on case-sensitive file systems)" {
+        BeforeEach {
+            $sourcePath = $filePath
+            $destinationPath = "$TestDrive/" + $fileName.Toupper()
+        }
+        AfterEach {
+            Remove-Item -Path $destinationPath -ErrorAction SilentlyContinue
+        }
+
+        It "Copy-Item can copy to file name differing only by case" {
+            if ($isCaseSensitive)
+            {
+                Copy-Item -Path $sourcePath -Destination $destinationPath -ErrorAction SilentlyContinue | Should Be $null
+                Test-Path -Path $destinationPath | Should Be $true
+            }
+            else
+            {
+                { Copy-Item -Path $sourcePath -Destination $destinationPath -ErrorAction Stop } | ShouldBeErrorId "CopyError,Microsoft.PowerShell.Commands.CopyItemCommand"
+                $Error[0].Exception | Should BeOfType System.IO.IOException
+                $Error[0].Exception.Data[$selfCopyKey] | Should Not Be $null
+            }
+        }
+    }
+
+    Context "Copy-Item avoids copying an item onto itself" {
+        BeforeAll {
+            $testCases = @(
+                @{
+                    Name = "Copy to same path"
+                    Source = $otherFile
+                    Destination = $otherFile
+                }
+                @{
+                    Name = "Copy hard link"
+                    Source = $hardToOtherFile
+                    Destination = $otherFile
+                }
+                @{
+                    Name = "Copy hard link, reversed"
+                    Source = $otherFile
+                    Destination = $hardToOtherFile
+                }
+                @{
+                    Name = "Copy symbolic link to target"
+                    Source = $symToOtherFile
+                    Destination = $otherFile
+                }
+                @{
+                    Name = "Copy symbolic link to symbolic link with same target"
+                    Source = $secondSymToOther
+                    Destination = $symToOther
+                }
+                @{
+                    Name = "Copy through chain of symbolic links"
+                    Source = $symToSym
+                    Destination = $otherSubDir
+                }
+            )
+
+            # Junctions and directory symbolic links are Windows and NTFS only
+            $windowsTestCases = @(
+                @{
+                    Name = "Copy junction to target"
+                    Source = $junctionToOther
+                    Destination = $otherSubDir
+                }
+                @{
+                    Name = "Copy directory symbolic link to target"
+                    Source = $symdToOther
+                    Destination = $otherSubDir
+                }
+            )
+
+            function TestSelfCopy
+            {
+                Param (
+                    [string]$Source,
+                    [string]$Destination
+                )
+
+                { Copy-Item -Path $Source -Destination $Destination -ErrorAction Stop } | ShouldBeErrorId "CopyError,Microsoft.PowerShell.Commands.CopyItemCommand"
+                $Error[0].Exception | Should BeOfType System.IO.IOException
+                $Error[0].Exception.Data[$selfCopyKey] | Should Not Be $null
+            }
+        }
+
+        It "<Name>" -TestCases $testCases {
+            Param (
+                [string]$Name,
+                [string]$Source,
+                [string]$Destination
+            )
+
+            TestSelfCopy $Source $Destination
+        }
+
+        It "<Name>" -TestCases $windowsTestCases -Skip:(-not $IsWindows) {
+            Param (
+                [string]$Name,
+                [string]$Source,
+                [string]$Destination
+            )
+
+            TestSelfCopy $Source $Destination
+        }
+    }
+}
+
 Describe "Extended FileSystem Item/Content Cmdlet Provider Tests" -Tags "Feature" {
     BeforeAll {
         $testDir = "testDir"
@@ -629,14 +780,13 @@ Describe "Extended FileSystem Path/Location Cmdlet Provider Tests" -Tags "Featur
             $result = Split-Path -Path $level1_0Full -Leaf
             $result | Should Be $level1_0
         }
-        
+
         It 'Validate LeafBase' {
             $result = Split-Path -Path "$level2_1Full$fileExt" -LeafBase
             $result | Should Be $level2_1
         }
-
         It 'Validate LeafBase is not over-zealous' {
-            
+
             $result = Split-Path -Path "$level2_1Full$fileExt$fileExt" -LeafBase
             $result | Should Be "$level2_1$fileExt"
         }