map_entry false positive when returning before inserting

[0x6273]

I want to check if a hashmap contains a key, and if it does not, I want to either return from the function early, or insert a value for that key, based on some logic.

fn main() {
	let mut map = std::collections::HashMap::<u32, u32>::new();
	let key = 9;

	// works, but triggers the `map_entry` lint
	if !map.contains_key(&key) {
		let value = match get_value() {
			Ok(value) => value,
			Err(_) => {
				println!("error");
				return;
			}
		};

		map.insert(key, value);
	}

	// does not work, since you can't return from the outside function in a closure
	map.entry(key).or_insert_with(|| {
		match get_value() {
			Ok(value) => value,
			Err(_) => {
				println!("error");
				return;
			}
		}
	});
}

fn get_value() -> Result<u32, ()> {
	// in my actual code this function is more expensive, so moving it to before checking if the key exists is undesired
	Ok(5)
}

Clippy complains that that using map.entry(key) will be more efficient, but I suspect this is a false positive in this case, since moving the return to inside the closure of .or_insert_with() will just return from the closure rather than the function.

[flip1995]

We should check if the if body contains a return statement.

I think you should still use the entry API but match on on entry.

use std::collections::hash_map::Entry;
use std::collections::HashMap;

fn main() {
    let mut map = HashMap::new();
    let key = 9;

    if let Entry::Vacant(o) = map.entry(&key) {
        let value = match get_value() {
            Ok(value) => value,
            Err(_) => {
                println!("error");
                return;
            }
        };
        o.insert(value);
    }
}

fn get_value() -> Result<u32, ()> {
    // in my actual code this function is more expensive, so moving it to before checking if the key exists is undesired
    Ok(5)
}