rust-clippy/tests/ui/option_option.rs

fn input(_: Option<Option<u8>>) {}

fn output() -> Option<Option<u8>> {
    None
}

fn output_nested() -> Vec<Option<Option<u8>>> {
    vec![None]
}

// The lint only generates one warning for this
fn output_nested_nested() -> Option<Option<Option<u8>>> {
    None
}

struct Struct {
    x: Option<Option<u8>>,
}

impl Struct {
    fn struct_fn() -> Option<Option<u8>> {
        None
    }
}

trait Trait {
    fn trait_fn() -> Option<Option<u8>>;
}

enum Enum {
    Tuple(Option<Option<u8>>),
    Struct { x: Option<Option<u8>> },
}

// The lint allows this
type OptionOption = Option<Option<u32>>;

// The lint allows this
fn output_type_alias() -> OptionOption {
    None
}

// The line allows this
impl Trait for Struct {
    fn trait_fn() -> Option<Option<u8>> {
        None
    }
}

fn main() {
    input(None);
    output();
    output_nested();

    // The lint allows this
    let local: Option<Option<u8>> = None;

    // The lint allows this
    let expr = Some(Some(true));
}