fix(mv): prevent hang when moving directories containing FIFO files

Fixes #9656

When moving a directory containing FIFO files, copy_dir_contents_recursive()
would call fs::copy() on the FIFO, causing an indefinite hang. This fix adds
FIFO detection before the copy operation and uses make_fifo() instead, matching
the behavior of rename_fifo_fallback().

- Add FIFO detection in copy_dir_contents_recursive()
- Create new FIFO at destination using make_fifo()
- Add test with timeout protection to prevent future regressions

Author: naoNao89

src/uu/mv/src/mv.rs

@@ -1082,15 +1082,28 @@ fn copy_dir_contents_recursive(
                 display_manager,
             )?;
         } else {
-            // Copy file with or without hardlink support based on platform
+            // Check if this is a FIFO to avoid blocking on fs::copy (issue #9656)
             #[cfg(unix)]
             {
-                copy_file_with_hardlinks_helper(
-                    &from_path,
-                    &to_path,
-                    hardlink_tracker,
-                    hardlink_scanner,
-                )?;
+                let metadata = from_path.symlink_metadata()?;
+                let file_type = metadata.file_type();
+
+                if is_fifo(file_type) {
+                    // Handle FIFO specially to avoid blocking on fs::copy
+                    if to_path.try_exists()? {
+                        fs::remove_file(&to_path)?;
+                    }
+                    make_fifo(&to_path)?;
+                    fs::remove_file(&from_path)?;
+                } else {
+                    // Copy file with hardlink support
+                    copy_file_with_hardlinks_helper(
+                        &from_path,
+                        &to_path,
+                        hardlink_tracker,
+                        hardlink_scanner,
+                    )?;
+                }
             }
             #[cfg(not(unix))]
             {

tests/by-util/test_mv.rs

@@ -2537,6 +2537,56 @@ fn test_special_file_different_filesystem() {
     std::fs::remove_dir_all("/dev/shm/tmp").unwrap();
 }
 
+/// Test moving a directory containing a FIFO file across different filesystems (issue #9656)
+/// Without proper FIFO handling, this test will hang indefinitely when
+/// copy_dir_contents_recursive tries to fs::copy() the FIFO
+#[cfg(unix)]
+#[test]
+fn test_mv_dir_containing_fifo_cross_filesystem() {
+    use std::time::Duration;
+
+    // Skip if /dev/shm not available
+    if !Path::new("/dev/shm").exists() {
+        return;
+    }
+
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.mkdir("a");
+    at.mkfifo("a/f");
+
+    // This will hang without the fix, so use timeout
+    // Move to /dev/shm which is typically a different filesystem (tmpfs)
+    ucmd.args(&["a", "/dev/shm/test_mv_fifo_dir"])
+        .timeout(Duration::from_secs(2))
+        .succeeds();
+
+    assert!(!at.dir_exists("a"));
+    assert!(Path::new("/dev/shm/test_mv_fifo_dir").exists());
+    assert!(Path::new("/dev/shm/test_mv_fifo_dir/f").exists());
+    std::fs::remove_dir_all("/dev/shm/test_mv_fifo_dir").ok();
+}
+
+/// Test moving a directory containing a FIFO file (same filesystem - issue #9656)
+/// This tests FIFO handling doesn't fail even on same filesystem
+#[cfg(unix)]
+#[test]
+fn test_mv_dir_containing_fifo_same_filesystem() {
+    use std::time::Duration;
+
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.mkdir("a");
+    at.mkfifo("a/f");
+
+    // This will hang without the fix, so use timeout
+    ucmd.args(&["a", "b"])
+        .timeout(Duration::from_secs(2))
+        .succeeds();
+
+    assert!(!at.dir_exists("a"));
+    assert!(at.dir_exists("b"));
+    assert!(at.is_fifo("b/f"));
+}
+
 /// Test cross-device move with permission denied error
 /// This test mimics the scenario from the GNU part-fail test where
 /// a cross-device move fails due to permission errors when removing the target file