Better error messages when reflinking directories.

On macos, `clonefile` can handle directories (https://www.manpagez.com/man/2/clonefile/, https://opensource.apple.com/source/xnu/xnu-3789.21.4/bsd/man/man2/clonefile.2.auto.html - sorry, i couldn't find any better source online), which is a lot faster than manually walking the directory tree. This currently leads to a confusing error messages when the target directory exists, saying just `the source path is not an existing regular file` and not reporting the real cause, `File exists (os error 17)`.

This PR makes two changes: We return the original error for both files and directories, and for the error for irregular src paths, we still display the original error so the information isn't lost.

src/lib.rs

@@ -44,6 +44,7 @@ use std::path::Path;
 ///
 /// Uses `clonefile` library function. This is supported on OS X Version >=10.12 and iOS version >= 10.0
 /// This will work on APFS partitions (which means most desktop systems are capable).
+/// If src names a directory, the directory hierarchy is cloned as if each item was cloned individually.
 ///
 /// ## Windows
 ///
@@ -101,12 +102,12 @@ pub fn reflink_or_copy(from: impl AsRef<Path>, to: impl AsRef<Path>) -> io::Resu
 }
 
 fn check_is_file_and_error(from: &Path, err: io::Error) -> io::Error {
-    if from.is_file() {
+    if fs::symlink_metadata(from).map_or(false, |m| m.is_file() || m.is_dir()) {
         err
     } else {
         io::Error::new(
             io::ErrorKind::InvalidInput,
-            "the source path is not an existing regular file",
+            format!("the source path is not an existing regular file: {}", err),
         )
     }
 }

tests/reflink.rs

@@ -48,6 +48,25 @@ fn reflink_dest_is_dir() {
     }
 }
 
+#[cfg(unix)] // No reliable symlinking on windows
+#[test]
+fn reflink_src_is_symlink() {
+    let dir = tempdir().unwrap();
+    let target = dir.path().join("target.txt");
+    let symlink = dir.path().join("symlink.txt");
+    File::create(&target).unwrap();
+    std::os::unix::fs::symlink(&target, &symlink).unwrap();
+    let dest_file_path = dir.path().join("dest.txt");
+
+    match reflink(symlink, dest_file_path) {
+        Ok(()) => panic!(),
+        Err(e) => {
+            println!("{:?}", e);
+            assert_eq!(e.kind(), io::ErrorKind::InvalidInput)
+        }
+    }
+}
+
 #[test]
 fn reflink_src_is_dir() {
     let dir = tempdir().unwrap();
@@ -57,11 +76,31 @@ fn reflink_src_is_dir() {
         Ok(()) => panic!(),
         Err(e) => {
             println!("{:?}", e);
-            assert_eq!(e.kind(), io::ErrorKind::InvalidInput)
+            // `io::ErrorKind::IsADirectory` is unstable
+            assert_eq!(e.kind().to_string(), "is a directory")
         }
     }
 }
 
+#[test]
+fn reflink_existing_dest_dir_results_in_error() {
+    let dir = tempdir().unwrap();
+    let src_file_path = dir.path().join("src");
+    let dest_file_path = dir.path().join("dest");
+
+    let _src_file = fs::create_dir(&src_file_path).unwrap();
+    let _dest_file = fs::create_dir(&dest_file_path).unwrap();
+
+    match reflink(&src_file_path, &dest_file_path) {
+        Ok(()) => panic!(),
+        Err(e) => {
+            println!("{:?}", e);
+            assert_eq!(e.kind(), io::ErrorKind::AlreadyExists)
+        }
+    }
+}
+
+
 #[test]
 fn reflink_existing_dest_results_in_error() {
     let dir = tempdir().unwrap();