Fix UnixFileSystem.MoveFile on macOS when just changing file casing

src/Common/src/Interop/Unix/System.Native/Interop.Stat.cs

@@ -27,6 +27,8 @@ internal struct FileStatus
             internal long MTime;
             internal long CTime;
             internal long BirthTime;
+            internal long Dev;
+            internal long Ino;
         }
 
         internal static class FileTypes

src/Native/Unix/System.Native/pal_io.cpp

@@ -140,6 +140,8 @@ static_assert(PAL_IN_ISDIR == IN_ISDIR, "");
 
 static void ConvertFileStatus(const struct stat_& src, FileStatus* dst)
 {
+    dst->Dev = static_cast<int64_t>(src.st_dev);
+    dst->Ino = static_cast<int64_t>(src.st_ino);
     dst->Flags = FILESTATUS_FLAGS_NONE;
     dst->Mode = static_cast<int32_t>(src.st_mode);
     dst->Uid = src.st_uid;

src/Native/Unix/System.Native/pal_io.h

@@ -24,6 +24,8 @@ struct FileStatus
     int64_t MTime;     // time of last modification
     int64_t CTime;     // time of last status change
     int64_t BirthTime; // time the file was created
+    int64_t Dev;       // ID of the device containing the file
+    int64_t Ino;       // inode number of the file
 };
 
 /************

src/System.IO.FileSystem/src/System/IO/UnixFileSystem.cs

@@ -82,8 +82,24 @@ public override void MoveFile(string sourceFullPath, string destFullPath)
         {
             // The desired behavior for Move(source, dest) is to not overwrite the destination file
             // if it exists. Since rename(source, dest) will replace the file at 'dest' if it exists,
-            // link/unlink are used instead. Note that the Unix FileSystemWatcher will treat a Move 
-            // as a Creation and Deletion instead of a Rename and thus differ from Windows.
+            // link/unlink are used instead. However, if the source path and the dest path refer to
+            // the same file, then do a rename rather than a link and an unlink.  This is important
+            // for case-insensitive file systems (e.g. renaming a file in a way that just changes casing),
+            // so that we support changing the casing in the naming of the file. If this fails in any
+            // way (e.g. source file doesn't exist, dest file doesn't exist, rename fails, etc.), we
+            // just fall back to trying the link/unlink approach and generating any exceptional messages
+            // from there as necessary.
+            Interop.Sys.FileStatus sourceStat, destStat;
+            if (Interop.Sys.LStat(sourceFullPath, out sourceStat) == 0 && // source file exists
+                Interop.Sys.LStat(destFullPath, out destStat) == 0 && // dest file exists
+                sourceStat.Dev == destStat.Dev && // source and dest are on the same device
+                sourceStat.Ino == destStat.Ino && // and source and dest are the same file on that device
+                Interop.Sys.Rename(sourceFullPath, destFullPath) == 0) // try the rename
+            {
+                // Renamed successfully.
+                return;
+            }
+
             if (Interop.Sys.Link(sourceFullPath, destFullPath) < 0)
             {
                 // If link fails, we can fall back to doing a full copy, but we'll only do so for

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

@@ -120,6 +120,34 @@ public void MoveIntoParentDirectory()
             Assert.True(File.Exists(testFileDest.FullName));
         }
 
+        [Fact]
+        public void MoveToSameName()
+        {
+            string testDir = GetTestFilePath();
+            Directory.CreateDirectory(testDir);
+
+            FileInfo testFileSource = new FileInfo(Path.Combine(testDir, GetTestFileName()));
+            testFileSource.Create().Dispose();
+
+            Move(testFileSource.FullName, testFileSource.FullName);
+            Assert.True(File.Exists(testFileSource.FullName));
+        }
+
+        [Fact]
+        public void MoveToSameNameDifferentCasing()
+        {
+            string testDir = GetTestFilePath();
+            Directory.CreateDirectory(testDir);
+
+            FileInfo testFileSource = new FileInfo(Path.Combine(testDir, Path.GetRandomFileName().ToLowerInvariant()));
+            testFileSource.Create().Dispose();
+
+            FileInfo testFileDest = new FileInfo(Path.Combine(testFileSource.DirectoryName, testFileSource.Name.ToUpperInvariant()));
+
+            Move(testFileSource.FullName, testFileDest.FullName);
+            Assert.True(File.Exists(testFileDest.FullName));
+        }
+
         [Fact]
         public void MultipleMoves()
         {