rust-clippy/tests/ui/unnecessary_lazy_eval.rs

// run-rustfix
#![warn(clippy::unnecessary_lazy_evaluations)]
#![allow(clippy::redundant_closure)]
#![allow(clippy::bind_instead_of_map)]
#![allow(clippy::map_identity)]

struct Deep(Option<usize>);

#[derive(Copy, Clone)]
struct SomeStruct {
    some_field: usize,
}

impl SomeStruct {
    fn return_some_field(&self) -> usize {
        self.some_field
    }
}

fn some_call<T: Default>() -> T {
    T::default()
}

fn main() {
    let astronomers_pi = 10;
    let ext_arr: [usize; 1] = [2];
    let ext_str = SomeStruct { some_field: 10 };

    let mut opt = Some(42);
    let ext_opt = Some(42);
    let nested_opt = Some(Some(42));
    let nested_tuple_opt = Some(Some((42, 43)));

    // Should lint - Option
    let _ = opt.unwrap_or_else(|| 2);
    let _ = opt.unwrap_or_else(|| astronomers_pi);
    let _ = opt.unwrap_or_else(|| ext_str.some_field);
    let _ = opt.unwrap_or_else(|| ext_arr[0]);
    let _ = opt.and_then(|_| ext_opt);
    let _ = opt.or_else(|| ext_opt);
    let _ = opt.or_else(|| None);
    let _ = opt.get_or_insert_with(|| 2);
    let _ = opt.ok_or_else(|| 2);
    let _ = nested_tuple_opt.unwrap_or_else(|| Some((1, 2)));

    // Cases when unwrap is not called on a simple variable
    let _ = Some(10).unwrap_or_else(|| 2);
    let _ = Some(10).and_then(|_| ext_opt);
    let _: Option<usize> = None.or_else(|| ext_opt);
    let _ = None.get_or_insert_with(|| 2);
    let _: Result<usize, usize> = None.ok_or_else(|| 2);
    let _: Option<usize> = None.or_else(|| None);

    let mut deep = Deep(Some(42));
    let _ = deep.0.unwrap_or_else(|| 2);
    let _ = deep.0.and_then(|_| ext_opt);
    let _ = deep.0.or_else(|| None);
    let _ = deep.0.get_or_insert_with(|| 2);
    let _ = deep.0.ok_or_else(|| 2);

    // Should not lint - Option
    let _ = opt.unwrap_or_else(|| ext_str.return_some_field());
    let _ = nested_opt.unwrap_or_else(|| Some(some_call()));
    let _ = nested_tuple_opt.unwrap_or_else(|| Some((some_call(), some_call())));
    let _ = opt.or_else(some_call);
    let _ = opt.or_else(|| some_call());
    let _: Result<usize, usize> = opt.ok_or_else(|| some_call());
    let _: Result<usize, usize> = opt.ok_or_else(some_call);
    let _ = deep.0.get_or_insert_with(|| some_call());
    let _ = deep.0.or_else(some_call);
    let _ = deep.0.or_else(|| some_call());
    let _ = opt.ok_or_else(|| ext_arr[0]);

    // should not lint, bind_instead_of_map takes priority
    let _ = Some(10).and_then(|idx| Some(ext_arr[idx]));
    let _ = Some(10).and_then(|idx| Some(idx));

    // should lint, bind_instead_of_map doesn't apply
    let _: Option<usize> = None.or_else(|| Some(3));
    let _ = deep.0.or_else(|| Some(3));
    let _ = opt.or_else(|| Some(3));

    // Should lint - Result
    let res: Result<usize, usize> = Err(5);
    let res2: Result<usize, SomeStruct> = Err(SomeStruct { some_field: 5 });

    let _ = res2.unwrap_or_else(|_| 2);
    let _ = res2.unwrap_or_else(|_| astronomers_pi);
    let _ = res2.unwrap_or_else(|_| ext_str.some_field);

    // Should not lint - Result
    let _ = res.unwrap_or_else(|err| err);
    let _ = res.unwrap_or_else(|err| ext_arr[err]);
    let _ = res2.unwrap_or_else(|err| err.some_field);
    let _ = res2.unwrap_or_else(|err| err.return_some_field());
    let _ = res2.unwrap_or_else(|_| ext_str.return_some_field());

    // should not lint, bind_instead_of_map takes priority
    let _: Result<usize, usize> = res.and_then(|x| Ok(x));
    let _: Result<usize, usize> = res.or_else(|err| Err(err));

    let _: Result<usize, usize> = res.and_then(|_| Ok(2));
    let _: Result<usize, usize> = res.and_then(|_| Ok(astronomers_pi));
    let _: Result<usize, usize> = res.and_then(|_| Ok(ext_str.some_field));

    let _: Result<usize, usize> = res.or_else(|_| Err(2));
    let _: Result<usize, usize> = res.or_else(|_| Err(astronomers_pi));
    let _: Result<usize, usize> = res.or_else(|_| Err(ext_str.some_field));

    // should lint, bind_instead_of_map doesn't apply
    let _: Result<usize, usize> = res.and_then(|_| Err(2));
    let _: Result<usize, usize> = res.and_then(|_| Err(astronomers_pi));
    let _: Result<usize, usize> = res.and_then(|_| Err(ext_str.some_field));

    let _: Result<usize, usize> = res.or_else(|_| Ok(2));
    let _: Result<usize, usize> = res.or_else(|_| Ok(astronomers_pi));
    let _: Result<usize, usize> = res.or_else(|_| Ok(ext_str.some_field));

    // neither bind_instead_of_map nor unnecessary_lazy_eval applies here
    let _: Result<usize, usize> = res.and_then(|x| Err(x));
    let _: Result<usize, usize> = res.or_else(|err| Ok(err));
}