rust/tests/ui/needless_late_init.rs

#![feature(let_chains)]
#![allow(unused, clippy::nonminimal_bool, clippy::let_unit_value)]

use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
use std::rc::Rc;

struct SignificantDrop;
impl std::ops::Drop for SignificantDrop {
    fn drop(&mut self) {
        println!("dropped");
    }
}

fn main() {
    let a;
    let n = 1;
    match n {
        1 => a = "one",
        _ => {
            a = "two";
        },
    }

    let b;
    if n == 3 {
        b = "four";
    } else {
        b = "five"
    }

    let d;
    if true {
        let temp = 5;
        d = temp;
    } else {
        d = 15;
    }

    let e;
    if true {
        e = format!("{} {}", a, b);
    } else {
        e = format!("{}", n);
    }

    let f;
    match 1 {
        1 => f = "three",
        _ => return,
    }; // has semi

    let g: usize;
    if true {
        g = 5;
    } else {
        panic!();
    }

    // Drop order only matters if both are significant
    let x;
    let y = SignificantDrop;
    x = 1;

    let x;
    let y = 1;
    x = SignificantDrop;

    let x;
    // types that should be considered insignificant
    let y = 1;
    let y = "2";
    let y = String::new();
    let y = vec![3.0];
    let y = HashMap::<usize, usize>::new();
    let y = BTreeMap::<usize, usize>::new();
    let y = HashSet::<usize>::new();
    let y = BTreeSet::<usize>::new();
    let y = Box::new(4);
    x = SignificantDrop;
}

async fn in_async() -> &'static str {
    async fn f() -> &'static str {
        "one"
    }

    let a;
    let n = 1;
    match n {
        1 => a = f().await,
        _ => {
            a = "two";
        },
    }

    a
}

const fn in_const() -> &'static str {
    const fn f() -> &'static str {
        "one"
    }

    let a;
    let n = 1;
    match n {
        1 => a = f(),
        _ => {
            a = "two";
        },
    }

    a
}

fn does_not_lint() {
    let z;
    if false {
        z = 1;
    }

    let x;
    let y;
    if true {
        x = 1;
    } else {
        y = 1;
    }

    let mut x;
    if true {
        x = 5;
        x = 10 / x;
    } else {
        x = 2;
    }

    let x;
    let _ = match 1 {
        1 => x = 10,
        _ => x = 20,
    };

    // using tuples would be possible, but not always preferable
    let x;
    let y;
    if true {
        x = 1;
        y = 2;
    } else {
        x = 3;
        y = 4;
    }

    // could match with a smarter heuristic to avoid multiple assignments
    let x;
    if true {
        let mut y = 5;
        y = 6;
        x = y;
    } else {
        x = 2;
    }

    let (x, y);
    if true {
        x = 1;
    } else {
        x = 2;
    }
    y = 3;

    macro_rules! assign {
        ($i:ident) => {
            $i = 1;
        };
    }
    let x;
    assign!(x);

    let x;
    if true {
        assign!(x);
    } else {
        x = 2;
    }

    macro_rules! in_macro {
        () => {
            let x;
            x = 1;

            let x;
            if true {
                x = 1;
            } else {
                x = 2;
            }
        };
    }
    in_macro!();

    // ignore if-lets - https://github.com/rust-lang/rust-clippy/issues/8613
    let x;
    if let Some(n) = Some("v") {
        x = 1;
    } else {
        x = 2;
    }

    let x;
    if true && let Some(n) = Some("let chains too") {
        x = 1;
    } else {
        x = 2;
    }

    // ignore mut bindings
    // https://github.com/shepmaster/twox-hash/blob/b169c16d86eb8ea4a296b0acb9d00ca7e3c3005f/src/sixty_four.rs#L88-L93
    // https://github.com/dtolnay/thiserror/blob/21c26903e29cb92ba1a7ff11e82ae2001646b60d/tests/test_generics.rs#L91-L100
    let mut x: usize;
    x = 1;
    x = 2;
    x = 3;

    // should not move the declaration if `x` has a significant drop, and there
    // is another binding with a significant drop between it and the first usage
    let x;
    let y = SignificantDrop;
    x = SignificantDrop;
}