A simple implementation to rename files when on the same device or move them by copy and delete if not.

move_files.rs

use std::{fs, io, path::Path};

pub fn move_recursively(from: impl AsRef<Path>, to: impl AsRef<Path>) -> Result<(), io::Error> {
    if !to.as_ref().exists() {
        fs::create_dir_all(to.as_ref())?;
    }

    let from_meta = from.as_ref().metadata()?;
    let to_meta = to.as_ref().metadata()?;

    // On non-unix systems, we can not check if from and to are on the same device, so we
    // just perform a full recursive move by copy.
    #[cfg(not(unix))]
    return move_by_copy_recursively(from, to);

    // On unix-system, we can simply use rename to move files if both from and to are on
    // the same storage device. Otherwise, we need to perform a full recursive move by copy.
    #[cfg(unix)]
    {
        use std::os::unix::fs::MetadataExt;
        if from_meta.dev() == to_meta.dev() {
            fs::rename(from, to)?;
        } else {
            move_by_copy_recursively(from.as_ref(), to.as_ref())?;
        }
        Ok(())
    }
}

pub fn move_by_copy_recursively(from: &Path, to: &Path) -> Result<(), io::Error> {
    if !to.exists() {
        fs::create_dir(to)?;
    }

    for entry in fs::read_dir(from)? {
        let entry = entry?;
        let path = entry.path();
        let to_path = to.join(path.file_name().expect("file name"));

        if entry.metadata()?.is_dir() {
            move_by_copy_recursively(&path, &to_path)?;
            fs::remove_dir(&path)?;
        } else {
            fs::copy(&path, &to_path)?;
            fs::remove_file(&path)?;
        }
    }

    Ok(())
}