How can I delete all the files in a directory but not the directory itself in Rust?

If the directory isn't being used, watched, or anything else that prevents it being deleted. Then you could just delete the whole directory using fs::remove_dir_all() and create it immediately after using fs::create_dir(), i.e.:

use std::fs;

let path = "tmp/my_items";
fs::remove_dir_all(path).unwrap();
fs::create_dir(path).unwrap();

Otherwise, you seem to have confused what fs::read_dir() actually returns.

It returns a Result<ReadDir>, which need to be unwrapped. However, while ReadDir does implement Iterator, it doesn't actually produce paths. It actually produces Result<DirEntry>, which also need to be unwrapped and still isn't a path. To get the actual path you have to call path().

use std::fs;
use std::io;
use std::path::Path;

fn remove_dir_contents<P: AsRef<Path>>(path: P) -> io::Result<()> {
    for entry in fs::read_dir(path)? {
        fs::remove_file(entry?.path())?;
    }
    Ok(())
}

fn main() {
    remove_dir_contents("tmp/my_items").unwrap();
}

If the directory doesn't only strictly contain files, then you need to check the file type and remove directories and their contents as well.

use std::fs;
use std::io;
use std::path::Path;

fn remove_dir_contents<P: AsRef<Path>>(path: P) -> io::Result<()> {
    for entry in fs::read_dir(path)? {
        let entry = entry?;
        let path = entry.path();

        if entry.file_type()?.is_dir() {
            remove_dir_contents(&path)?;
            fs::remove_dir(path)?;
        } else {
            fs::remove_file(path)?;
        }
    }
    Ok(())
}

read_dir returns an iterator over io::Result<DirEntry> objects. DirEntry is not a path itself (it's got many separate features, and they didn't implement silent coercion to Path possibly to avoid confusion), but it has a .path() method. Something like this (based on the example given for .path()) should work:

for entry in std::fs::read_dir("tmp/my_items")? {
    let entry = entry?;
    std::fs::remove_file(entry.path())?;
}

As another answer has pointed out, std::fs::read_dir returns ReadDir (inside a Result), which is an iterator over DirEntrys (inside Results).

In a similar style to this answer, you could just remove the directory and all its contents and then recreate the directory in one go with Result::and_then.

use std::fs;

let path = "tmp/my_items";
fs::remove_dir_all(path).and_then(|_| fs::create_dir(path))?;