fix(fs): avoid directory fsync on Windows publication

src/support/fs.rs

@@ -252,25 +252,29 @@ fn lock_holder_is_live(_pid: u32) -> bool {
 }
 
 pub fn best_effort_fsync_dir(path: &Path) -> std::io::Result<()> {
-    let dir = File::open(path)?;
-
     #[cfg(unix)]
-    unsafe {
-        let rc = libc::fsync(std::os::fd::AsRawFd::as_raw_fd(&dir));
-        if rc == 0 {
-            return Ok(());
-        }
+    {
+        let dir = File::open(path)?;
+
+        // SAFETY: `dir` owns a valid file descriptor for the duration of the call,
+        // and `fsync` does not retain it. The return code is checked below.
+        unsafe {
+            let rc = libc::fsync(std::os::fd::AsRawFd::as_raw_fd(&dir));
+            if rc == 0 {
+                return Ok(());
+            }
 
-        let error = std::io::Error::last_os_error();
-        if error.raw_os_error() == Some(libc::EINVAL) {
-            return Ok(());
+            let error = std::io::Error::last_os_error();
+            if error.raw_os_error() == Some(libc::EINVAL) {
+                return Ok(());
+            }
+            Err(error)
         }
-        return Err(error);
     }
 
     #[cfg(not(unix))]
     {
-        let _ = dir;
+        let _ = path;
         Ok(())
     }
 }
@@ -610,6 +614,8 @@ fn with_rollback_context(
 
 #[cfg(test)]
 mod tests {
+    #[cfg(windows)]
+    use super::replace_dir_atomically;
     use super::{
         acquire_advisory_lock, advisory_lock_owner_id, publish_file_atomically,
         publish_file_atomically_impl, read_advisory_lock_metadata, remove_path_if_exists,
@@ -824,6 +830,33 @@ mod tests {
         assert_eq!(fs::read_to_string(&destination).expect("dest"), "new");
     }
 
+    #[cfg(windows)]
+    #[test]
+    fn windows_publishes_staged_directory_to_new_target() {
+        let dir = tempdir().expect("tempdir");
+        let staging_dir = dir.path().join(".stage");
+        let target_dir = dir.path().join("target");
+        fs::create_dir(&staging_dir).expect("staging dir");
+        fs::write(staging_dir.join("payload.txt"), "payload").expect("payload");
+        assert!(!target_dir.exists());
+
+        let outcome = replace_dir_atomically(
+            &staging_dir,
+            &target_dir,
+            "test-run",
+            "test-target",
+            ".backup",
+        )
+        .expect("publish staged directory");
+
+        assert_eq!(outcome.cleanup_warning, None);
+        assert!(!staging_dir.exists());
+        assert_eq!(
+            fs::read_to_string(target_dir.join("payload.txt")).expect("target payload"),
+            "payload"
+        );
+    }
+
     #[cfg(windows)]
     #[test]
     fn windows_reports_missing_process_as_not_live() {