Fix case-sensitive rename.

Author: tmds

src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Unix.cs

@@ -387,7 +387,7 @@ private static void CreateParentsAndDirectory(string fullPath)
             }
         }
 
-        internal static void MoveDirectory(string sourceFullPath, string destFullPath)
+        private static void MoveDirectoryCore(string sourceFullPath, string destFullPath)
         {
             ReadOnlySpan<char> destNoDirectorySeparator = Path.TrimEndingDirectorySeparator(destFullPath.AsSpan());
             ReadOnlySpan<char> srcNoDirectorySeparator = Path.TrimEndingDirectorySeparator(sourceFullPath.AsSpan());
@@ -399,7 +399,7 @@ internal static void MoveDirectory(string sourceFullPath, string destFullPath)
                 throw new IOException(SR.Format(SR.IO_PathNotFound_Path, sourceFullPath));
             }
 
-            // The destination must not exist.
+            // The destination must not exist (unless it is a case-sensitive rename).
             // On Unix 'rename' will overwrite the destination file if it already exists, we need to manually check.
             if (Interop.Sys.LStat(destNoDirectorySeparator, out Interop.Sys.FileStatus destFileStatus) >= 0)
             {
@@ -410,30 +410,32 @@ internal static void MoveDirectory(string sourceFullPath, string destFullPath)
                 {
                     throw new DirectoryNotFoundException(SR.Format(SR.IO_PathNotFound_Path, sourceFullPath));
                 }
-                // Source and destination must not be the same file.
+                // Source and destination must not be the same file unless it is a case-sensitive rename.
                 else if (sourceFileStatus.Dev == destFileStatus.Dev &&
                          sourceFileStatus.Ino == destFileStatus.Ino)
                 {
-                    throw new IOException(SR.IO_SourceDestMustBeDifferent);
+                    // Assume the file system is case-insensitive, and allow a Rename when the FileName casing changes.
+                    if (!srcNoDirectorySeparator.Equals(destNoDirectorySeparator, StringComparison.OrdinalIgnoreCase) ||
+                        Path.GetFileName(srcNoDirectorySeparator).SequenceEqual(Path.GetFileName(destNoDirectorySeparator)))
+                    {
+                        throw new IOException(SR.IO_SourceDestMustBeDifferent);
+                    }
+                    // Fall through to Rename.
                 }
                 // When the path ends with a directory separator, it must be a directory.
                 else if ((sourceFileStatus.Mode & Interop.Sys.FileTypes.S_IFMT) != Interop.Sys.FileTypes.S_IFDIR
                     && Path.EndsInDirectorySeparator(sourceFullPath))
                 {
                     throw new IOException(SR.Format(SR.IO_PathNotFound_Path, sourceFullPath));
                 }
-
-                throw new IOException(SR.Format(SR.IO_AlreadyExists_Name, destFullPath));
+                else
+                {
+                    throw new IOException(SR.Format(SR.IO_AlreadyExists_Name, destFullPath));
+                }
             }
 
             if (Interop.Sys.Rename(sourceFullPath, destNoDirectorySeparator) < 0)
             {
-                // Source and destination must not be the same file.
-                if (srcNoDirectorySeparator.Equals(destNoDirectorySeparator, PathInternal.StringComparison))
-                {
-                    throw new IOException(SR.IO_SourceDestMustBeDifferent);
-                }
-
                 Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
                 switch (errorInfo.Error)
                 {

src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Windows.cs

@@ -154,7 +154,7 @@ public static DateTimeOffset GetLastWriteTime(string fullPath)
             return data.ftLastWriteTime.ToDateTimeOffset();
         }
 
-        internal static void MoveDirectory(string sourceFullPath, string destFullPath)
+        private static void MoveDirectoryCore(string sourceFullPath, string destFullPath)
         {
             // Source and destination must have the same root.
             ReadOnlySpan<char> sourceRoot = Path.GetPathRoot(sourceFullPath);
@@ -166,17 +166,6 @@ internal static void MoveDirectory(string sourceFullPath, string destFullPath)
 
             if (!Interop.Kernel32.MoveFile(sourceFullPath, destFullPath, overwrite: false))
             {
-                // Source and destination must not be the same file.
-                // We don't check upfront, but handle this as a MoveFile failure.
-                // MoveFile will fail because it requires the source to exist and the destination to not exist.
-                // That is not possible if they are the same file.
-                ReadOnlySpan<char> srcNoDirectorySeparator = Path.TrimEndingDirectorySeparator(sourceFullPath.AsSpan());
-                ReadOnlySpan<char> destNoDirectorySeparator = Path.TrimEndingDirectorySeparator(destFullPath.AsSpan());
-                if (srcNoDirectorySeparator.Equals(destNoDirectorySeparator, PathInternal.StringComparison))
-                {
-                    throw new IOException(SR.IO_SourceDestMustBeDifferent);
-                }
-
                 int errorCode = Marshal.GetLastWin32Error();
 
                 if (errorCode == Interop.Errors.ERROR_FILE_NOT_FOUND)

src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.cs

@@ -13,5 +13,24 @@ internal static void VerifyValidPath(string path, string argName)
                 throw new ArgumentException(SR.Argument_InvalidPathChars, argName);
             }
         }
+
+        internal static void MoveDirectory(string sourceFullPath, string destFullPath)
+        {
+            ReadOnlySpan<char> srcNoDirectorySeparator = Path.TrimEndingDirectorySeparator(sourceFullPath.AsSpan());
+            ReadOnlySpan<char> destNoDirectorySeparator = Path.TrimEndingDirectorySeparator(destFullPath.AsSpan());
+
+            // Don't allow the same path, except for changing the casing of the filename.
+            if (srcNoDirectorySeparator.Equals(destNoDirectorySeparator, PathInternal.StringComparison))
+            {
+                ReadOnlySpan<char> srcFileName = Path.GetFileName(srcNoDirectorySeparator);
+                ReadOnlySpan<char> destFileName = Path.GetFileName(destNoDirectorySeparator);
+                if (srcFileName.SequenceEqual(destFileName))
+                {
+                    throw new IOException(SR.IO_SourceDestMustBeDifferent);
+                }
+            }
+
+            MoveDirectoryCore(sourceFullPath, destFullPath);
+        }
     }
 }