Rollup merge of #140062 - xizheyin:issue-139958, r=workingjubilee

std: mention `remove_dir_all` can emit `DirectoryNotEmpty` when concurrently written into

Closes #139958

The current documentation for `std::fs::remove_dir_all` function does not explicitly mention the error types that may be returned in concurrent scenarios. Specifically, when one thread attempts to remove a directory tree while another thread simultaneously writes files to that directory, the function may return an `io::ErrorKind::DirectoryNotEmpty` error, but this behavior is not clearly mentioned in the current documentation.

r? libs

library/std/src/fs.rs

@@ -2874,6 +2874,8 @@ pub fn remove_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
 ///
 /// Consider ignoring the error if validating the removal is not required for your use case.
 ///
+/// This function may return [`io::ErrorKind::DirectoryNotEmpty`] if the directory is concurrently
+/// written into, which typically indicates some contents were removed but not all.
 /// [`io::ErrorKind::NotFound`] is only returned if no removal occurs.
 ///
 /// [`fs::remove_file`]: remove_file