rust-clippy/tests/ui/option_map_unit_fn.rs

// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![warn(clippy::option_map_unit_fn)]
#![allow(unused)]

fn do_nothing<T>(_: T) {}

fn diverge<T>(_: T) -> ! {
    panic!()
}

fn plus_one(value: usize) -> usize {
    value + 1
}

struct HasOption {
    field: Option<usize>,
}

impl HasOption {
    fn do_option_nothing(self: &Self, value: usize) {}

    fn do_option_plus_one(self: &Self, value: usize) -> usize {
        value + 1
    }
}

fn option_map_unit_fn() {
    let x = HasOption { field: Some(10) };

    x.field.map(plus_one);
    let _: Option<()> = x.field.map(do_nothing);

    x.field.map(do_nothing);

    x.field.map(do_nothing);

    x.field.map(diverge);

    let captured = 10;
    if let Some(value) = x.field {
        do_nothing(value + captured)
    };
    let _: Option<()> = x.field.map(|value| do_nothing(value + captured));

    x.field.map(|value| x.do_option_nothing(value + captured));

    x.field.map(|value| {
        x.do_option_plus_one(value + captured);
    });

    x.field.map(|value| do_nothing(value + captured));

    x.field.map(|value| do_nothing(value + captured));

    x.field.map(|value| {
        do_nothing(value + captured);
    });

    x.field.map(|value| {
        do_nothing(value + captured);
    });

    x.field.map(|value| diverge(value + captured));

    x.field.map(|value| diverge(value + captured));

    x.field.map(|value| {
        diverge(value + captured);
    });

    x.field.map(|value| {
        diverge(value + captured);
    });

    x.field.map(|value| plus_one(value + captured));
    x.field.map(|value| plus_one(value + captured));
    x.field.map(|value| {
        let y = plus_one(value + captured);
    });

    x.field.map(|value| {
        plus_one(value + captured);
    });

    x.field.map(|value| {
        plus_one(value + captured);
    });

    x.field.map(|ref value| do_nothing(value + captured));

    x.field.map(|value| {
        do_nothing(value);
        do_nothing(value)
    });

    x.field.map(|value| {
        if value > 0 {
            do_nothing(value);
            do_nothing(value)
        }
    });

    // Suggestion for the let block should be `{ ... }` as it's too difficult to build a
    // proper suggestion for these cases
    x.field.map(|value| {
        do_nothing(value);
        do_nothing(value)
    });
    x.field.map(|value| {
        do_nothing(value);
        do_nothing(value);
    });

    // The following should suggest `if let Some(_X) ...` as it's difficult to generate a proper let
    // variable name for them
    Some(42).map(diverge);
    "12".parse::<i32>().ok().map(diverge);
    Some(plus_one(1)).map(do_nothing);

    // Should suggest `if let Some(_y) ...` to not override the existing foo variable
    let y = Some(42);
    y.map(do_nothing);
}

fn main() {}