proper error message when inter-partition copying fails with test

src/uu/mv/src/mv.rs

@@ -662,7 +662,17 @@ fn rename_with_fallback(
             }
         } else {
             if to.is_symlink() {
-                fs::remove_file(to)?;
+                fs::remove_file(to).map_err(|err| {
+                    let to = to.to_string_lossy();
+                    let from = from.to_string_lossy();
+                    io::Error::new(
+                        err.kind(),
+                        format!(
+                            "inter-device move failed: '{from}' to '{to}'\
+                            ; unable to remove target: {err}"
+                        ),
+                    )
+                })?;
             }
             #[cfg(all(unix, not(any(target_os = "macos", target_os = "redox"))))]
             fs::copy(from, to)

tests/by-util/test_mv.rs

@@ -1629,21 +1629,25 @@ fn test_acl() {
 fn test_mv_unlinks_dest_symlink() {
     let scene = TestScenario::new(util_name!());
     let at = &scene.fixtures;
+
     // create a file in the current partition.
     at.write("src", "src contents");
 
     // create a folder in another partition.
-    let other_fs_tempdir = tempfile::TempDir::new_in("/dev/shm/").unwrap();
+    let other_fs_tempdir =
+        tempfile::TempDir::new_in("/dev/shm/").expect("Unable to create temp directory");
 
     // create a file inside that folder.
-    let file_path = other_fs_tempdir.path().join("other_fs_file.txt");
-    let mut file = std::fs::File::create(&file_path).expect("Unable to create file");
+    let other_fs_file_path = other_fs_tempdir.path().join("other_fs_file");
+    let mut file =
+        std::fs::File::create(&other_fs_file_path).expect("Unable to create other_fs_file");
     std::io::Write::write_all(&mut file, b"other fs file contents")
-        .expect("Unable to write to file");
+        .expect("Unable to write to other_fs_file");
 
     // create a symlink to the file inside the same directory.
-    let symlink_path = other_fs_tempdir.path().join("symlink_to_file.txt");
-    std::os::unix::fs::symlink(&file_path, &symlink_path).unwrap();
+    let symlink_path = other_fs_tempdir.path().join("symlink_to_file");
+    std::os::unix::fs::symlink(&other_fs_file_path, &symlink_path)
+        .expect("Unable to create symlink_to_file");
 
     // mv src to symlink in another partition
     scene
@@ -1651,8 +1655,73 @@ fn test_mv_unlinks_dest_symlink() {
         .arg("src")
         .arg(symlink_path.to_str().unwrap())
         .succeeds();
+
     // make sure that src got removed.
     assert!(!at.file_exists("src"));
+
     // make sure symlink got unlinked
     assert!(!symlink_path.is_symlink());
+
+    // make sure that file contents in other_fs_file didn't change.
+    let mut new_contents = String::new();
+    std::io::Read::read_to_string(
+        &mut std::fs::File::open(&other_fs_file_path).expect("Unable to open other_fs_file"),
+        &mut new_contents,
+    )
+    .expect("Unable to read other_fs_file");
+    assert_eq!(new_contents, "other fs file contents");
+
+    // make sure that src file contents got copied into new file created in symlink_path .
+    let mut new_contents = String::new();
+    std::io::Read::read_to_string(
+        &mut std::fs::File::open(&symlink_path).expect("Unable to open file"),
+        &mut new_contents,
+    )
+    .expect("Unable to read file");
+    assert_eq!(new_contents, "src contents");
+}
+
+// In an inter-partition move if unlinking the destination symlink fails, ensure
+// that it would output the proper error message.
+#[cfg(target_os = "linux")]
+#[test]
+fn test_mv_unlinks_dest_symlink_error_message() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    // create a file in the current partition.
+    at.write("src", "src contents");
+
+    // create a folder in another partition.
+    let other_fs_tempdir =
+        tempfile::TempDir::new_in("/dev/shm/").expect("Unable to create temp directory");
+
+    // create a file inside that folder.
+    let other_fs_file_path = other_fs_tempdir.path().join("other_fs_file");
+    let mut file =
+        std::fs::File::create(&other_fs_file_path).expect("Unable to create other_fs_file");
+    std::io::Write::write_all(&mut file, b"other fs file contents")
+        .expect("Unable to write to other_fs_file");
+
+    // create a symlink to the file inside the same directory.
+    let symlink_path = other_fs_tempdir.path().join("symlink_to_file");
+    std::os::unix::fs::symlink(&other_fs_file_path, &symlink_path)
+        .expect("Unable to create symlink_to_file");
+
+    // disable write for the target folder so that when mv tries to remove the
+    // the destination symlink inside the target directory it would fail.
+    std::fs::set_permissions(
+        other_fs_tempdir.path(),
+        std::os::unix::fs::PermissionsExt::from_mode(0o555),
+    )
+    .expect("Unable to set permissions for temp directory");
+
+    // mv src to symlink in another partition
+    scene
+        .ucmd()
+        .arg("src")
+        .arg(symlink_path.to_str().unwrap())
+        .fails()
+        .stderr_contains("inter-device move failed:")
+        .stderr_contains("Permission denied");
 }