You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: flags.rs
    path of file: ./repos/catfs/src
    
    the code of the file until where you have to start completion: extern crate clap;
extern crate libc;

use std::any::Any;
use std::env;
use std::ffi::OsString;

use catfs::flags::DiskSpace;

pub struct Flag<'a, 'b> {
    pub arg: clap::Arg<'a, 'a>,
    pub value: &'b mut dyn Any,
}

pub fn parse_options<'a, 'b>(mut app: clap::App<'a, 'a>, flags: &'b mut [Flag<'a, 'b>]) {
    for f in flags.iter() {
        app = app.arg(f.arg.clone());
    }
    let mut argv = env::args_os().collect::<Vec<OsString>>();
    if argv.len() == 5 && argv[3] == OsString::from("-o") {
	// looks like it's coming from fstab!
        // [0]: catfs, [1] = src_dir#cache_dir, [2] = mnt
        // [3]: -o, [4] = opt1,opt2
        // XXX str has split but OsString doesn't

        // XXX2 this is more convoluted than necessary because paths
        // immutably borrows from argv and we can't modify elements of
        // argv again because that requires another mutable borrow

        // XXX3 need to initialize src/cache because the compiler is
        // not smart enough
        let mut src: OsString = Default::default();
        let mut cache: OsString = Default::default
    
pub fn parse_options<'a, 'b>(mut app: clap::App<'a, 'a>, flags: &'b mut [Flag<'a, 'b>]) {
    for f in flags.iter() {
        app = app.arg(f.arg.clone());
    }
    let mut argv = env::args_os().collect::<Vec<OsString>>();
    if argv.len() == 5 && argv[3] == OsString::from("-o") {
	// looks like it's coming from fstab!
        // [0]: catfs, [1] = src_dir#cache_dir, [2] = mnt
        // [3]: -o, [4] = opt1,opt2
        // XXX str has split but OsString doesn't

        // XXX2 this is more convoluted than necessary because paths
        // immutably borrows from argv and we can't modify elements of
        // argv again because that requires another mutable borrow

        // XXX3 need to initialize src/cache because the compiler is
        // not smart enough
        let mut src: OsString = Default::default();
        let mut cache: OsString = Default::default();
        let mut is_fstab = false;

        {
            let paths = argv[1].to_str().unwrap().splitn(2, '#').collect::<Vec<&str>>();
            if paths.len() == 2 {
                src = OsString::from(paths[0]);
                cache = OsString::from(paths[1]);
                is_fstab = true;
            }
        }

        if is_fstab {
            argv[1] = src;
            argv.insert(2, cache);
            let mut options = String::new();
            let mut arguments: Vec<OsString> = Default::default();

            // options are now pushed down
            for opt in argv[5].to_str().unwrap().split(',') {
                if opt.starts_with("-") {
                    arguments.push(OsString::from(opt));
                } else {
                    options += opt;
                    options += ",";
                }
            }

            if options.len() != 0 {
                options.pop();
                argv[5] = OsString::from(options);
            } else {
                // no options, pop -o and empty string
                argv.pop();
                argv.pop();
            }
            for arg in arguments {
                argv.insert(3, arg);
            }
        }
    }

    let matches = app.get_matches_from(argv);

    for f in flags.iter_mut() {
        let name = f.arg.b.name;

        if matches.is_present(name) {
            // cannot use else if here or rust would claim double
            // mutable borrow because apparently a borrow sends with
            // the last else if
            if let Some(v) = f.value.downcast_mut::<String>() {
                let s = matches.value_of(name).unwrap();
                *v = String::from(s);
                continue;
            }
            if let Some(v) = f.value.downcast_mut::<OsString>() {
                let s = matches.value_of_os(name).unwrap();
                *v = s.to_os_string();
                continue;
            }
            if let Some(v) = f.value.downcast_mut::<bool>() {
                *v = true;
                continue;
            }
            if let Some(v) = f.value.downcast_mut::<Vec<OsString>>() {
                let options = matches.values_of(name).unwrap();
                for s in options {
                    for s in s.split(',') {
                        v.push(OsString::from("-o"));
                        v.push(OsString::from(s));
                    }
                }
                continue;
            }
            if let Some(v) = f.value.downcast_mut::<DiskSpace>() {
                let s = matches.value_of(name).unwrap();
                *v = s.parse().unwrap();
                continue;
            }
            if let Some(v) = f.value.downcast_mut::<libc::uid_t>() {
                let s = matches.value_of(name).unwrap();
                *v = s.parse().unwrap();
                continue;
            }
            if let Some(v) = f.value.downcast_mut::<libc::gid_t>() {
                let s = matches.value_of(name).unwrap();
                *v = s.parse().unwrap();
                continue;
            }

            panic!("unknown type for {}", name);
        }
    }
}