rust-clippy/tests/ui/needless_borrow.rs

// run-rustfix

#![feature(lint_reasons)]

#[warn(clippy::all, clippy::needless_borrow)]
#[allow(unused_variables, clippy::unnecessary_mut_passed)]
fn main() {
    let a = 5;
    let ref_a = &a;
    let _ = x(&a); // no warning
    let _ = x(&&a); // warn

    let mut b = 5;
    mut_ref(&mut b); // no warning
    mut_ref(&mut &mut b); // warn

    let s = &String::from("hi");
    let s_ident = f(&s); // should not error, because `&String` implements Copy, but `String` does not
    let g_val = g(&Vec::new()); // should not error, because `&Vec<T>` derefs to `&[T]`
    let vec = Vec::new();
    let vec_val = g(&vec); // should not error, because `&Vec<T>` derefs to `&[T]`
    h(&"foo"); // should not error, because the `&&str` is required, due to `&Trait`
    let garbl = match 42 {
        44 => &a,
        45 => {
            println!("foo");
            &&a
        },
        46 => &&a,
        47 => {
            println!("foo");
            loop {
                println!("{}", a);
                if a == 25 {
                    break &ref_a;
                }
            }
        },
        _ => panic!(),
    };

    let _ = x(&&&a);
    let _ = x(&mut &&a);
    let _ = x(&&&mut b);
    let _ = x(&&ref_a);
    {
        let b = &mut b;
        x(&b);
    }

    // Issue #8191
    let mut x = 5;
    let mut x = &mut x;

    mut_ref(&mut x);
    mut_ref(&mut &mut x);
    let y: &mut i32 = &mut x;
    let y: &mut i32 = &mut &mut x;

    let y = match 0 {
        // Don't lint. Removing the borrow would move 'x'
        0 => &mut x,
        _ => &mut *x,
    };
    let y: &mut i32 = match 0 {
        // Lint here. The type given above triggers auto-borrow.
        0 => &mut x,
        _ => &mut *x,
    };
    fn ref_mut_i32(_: &mut i32) {}
    ref_mut_i32(match 0 {
        // Lint here. The type given above triggers auto-borrow.
        0 => &mut x,
        _ => &mut *x,
    });
    // use 'x' after to make sure it's still usable in the fixed code.
    *x = 5;

    let s = String::new();
    // let _ = (&s).len();
    // let _ = (&s).capacity();
    // let _ = (&&s).capacity();

    let x = (1, 2);
    let _ = (&x).0;
    let x = &x as *const (i32, i32);
    let _ = unsafe { (&*x).0 };

    // Issue #8367
    trait Foo {
        fn foo(self);
    }
    impl Foo for &'_ () {
        fn foo(self) {}
    }
    (&()).foo(); // Don't lint. `()` doesn't implement `Foo`
    (&&()).foo();

    impl Foo for i32 {
        fn foo(self) {}
    }
    impl Foo for &'_ i32 {
        fn foo(self) {}
    }
    (&5).foo(); // Don't lint. `5` will call `<i32 as Foo>::foo`
    (&&5).foo();

    trait FooRef {
        fn foo_ref(&self);
    }
    impl FooRef for () {
        fn foo_ref(&self) {}
    }
    impl FooRef for &'_ () {
        fn foo_ref(&self) {}
    }
    (&&()).foo_ref(); // Don't lint. `&()` will call `<() as FooRef>::foo_ref`
}

#[allow(clippy::needless_borrowed_reference)]
fn x(y: &i32) -> i32 {
    *y
}

fn mut_ref(y: &mut i32) {
    *y = 5;
}

fn f<T: Copy>(y: &T) -> T {
    *y
}

fn g(y: &[u8]) -> u8 {
    y[0]
}

trait Trait {}

impl<'a> Trait for &'a str {}

fn h(_: &dyn Trait) {}

#[allow(dead_code)]
fn check_expect_suppression() {
    let a = 5;
    #[expect(clippy::needless_borrow)]
    let _ = x(&&a);
}