rust-clippy/tests/ui/drop_ref.rs

#![warn(clippy::drop_ref)]
#![allow(clippy::toplevel_ref_arg)]
#![allow(clippy::map_err_ignore)]
#![allow(clippy::unnecessary_wraps, clippy::drop_non_drop)]

use std::mem::drop;

struct SomeStruct;

fn main() {
    drop(&SomeStruct);

    let mut owned1 = SomeStruct;
    drop(&owned1);
    drop(&&owned1);
    drop(&mut owned1);
    drop(owned1); //OK

    let reference1 = &SomeStruct;
    drop(reference1);

    let reference2 = &mut SomeStruct;
    drop(reference2);

    let ref reference3 = SomeStruct;
    drop(reference3);
}

#[allow(dead_code)]
fn test_generic_fn_drop<T>(val: T) {
    drop(&val);
    drop(val); //OK
}

#[allow(dead_code)]
fn test_similarly_named_function() {
    fn drop<T>(_val: T) {}
    drop(&SomeStruct); //OK; call to unrelated function which happens to have the same name
    std::mem::drop(&SomeStruct);
}

#[derive(Copy, Clone)]
pub struct Error;
fn produce_half_owl_error() -> Result<(), Error> {
    Ok(())
}

fn produce_half_owl_ok() -> Result<bool, ()> {
    Ok(true)
}

#[allow(dead_code)]
fn test_owl_result() -> Result<(), ()> {
    produce_half_owl_error().map_err(|_| ())?;
    produce_half_owl_ok().map(|_| ())?;
    // the following should not be linted,
    // we should not force users to use toilet closures
    // to produce owl results when drop is more convenient
    produce_half_owl_error().map_err(drop)?;
    produce_half_owl_ok().map_err(drop)?;
    Ok(())
}

#[allow(dead_code)]
fn test_owl_result_2() -> Result<u8, ()> {
    produce_half_owl_error().map_err(|_| ())?;
    produce_half_owl_ok().map(|_| ())?;
    // the following should not be linted,
    // we should not force users to use toilet closures
    // to produce owl results when drop is more convenient
    produce_half_owl_error().map_err(drop)?;
    produce_half_owl_ok().map(drop)?;
    Ok(1)
}

#[allow(unused)]
#[allow(clippy::unit_cmp)]
fn issue10122(x: u8) {
    // This is a function which returns a reference and has a side-effect, which means
    // that calling drop() on the function is considered an idiomatic way of achieving the side-effect
    // in a match arm.
    fn println_and<T>(t: &T) -> &T {
        println!("foo");
        t
    }

    match x {
        0 => drop(println_and(&12)), // Don't lint (copy type), we only care about side-effects
        1 => drop(println_and(&String::new())), // Don't lint (no copy type), we only care about side-effects
        2 => {
            drop(println_and(&13)); // Lint, even if we only care about the side-effect, it's already in a block
        },
        3 if drop(println_and(&14)) == () => (), // Lint, idiomatic use is only in body of `Arm`
        4 => drop(&2),                           // Lint, not a fn/method call
        _ => (),
    }
}