[significant_drop_tightening] value inside tuple may or may not be recognised as a valid drop.

[VictorGamerLOL]

Summary

If values are dropped using a tuple in a drop statement, some of the values may not be recognized as being dropped there and the lint will trigger.

Lint Name

significant_drop_tightening

Reproducer

I tried this code:

#![warn(clippy::nursery)]

use lazy_static::lazy_static;
use std::sync::{ Arc, Mutex };

struct Number {
    pub value: u32,
}

lazy_static! {
    static ref NUMBER: Arc<Mutex<Number>> = Arc::new(Mutex::new(Number { value: 1 }));
    static ref NUMBER2: Arc<Mutex<Number>> = Arc::new(Mutex::new(Number { value: 2 }));
    static ref NUMBER3: Arc<Mutex<Number>> = Arc::new(Mutex::new(Number { value: 3 }));
}

fn main() {
    do_something().unwrap();
}

fn do_something() -> Result<(), ()> {
    let mut lock = NUMBER.lock().unwrap();
    let mut lock2 = NUMBER2.lock().unwrap();
    let mut lock3 = NUMBER3.lock().unwrap();
    lock.value += 1;
    lock2.value += 1;
    lock3.value += 1;
    drop((lock, lock2, lock3));
    Ok(())
}

I saw this happen:

warning: temporary with significant `Drop` can be early dropped
  --> src/main.rs:21:13
   |
20 |   fn do_something() -> Result<(), ()> {
   |  _____________________________________-
21 | |     let mut lock = NUMBER.lock().unwrap();
   | |             ^^^^
22 | |     let mut lock2 = NUMBER2.lock().unwrap();
23 | |     let mut lock3 = NUMBER3.lock().unwrap();
...  |
28 | |     Ok(())
29 | | }
   | |_- temporary `lock` is currently being dropped at the end of its contained scope
   |
   = note: this might lead to unnecessary resource contention
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#significant_drop_tightening
note: the lint level is defined here
  --> src/main.rs:1:9
   |
1  | #![warn(clippy::nursery)]
   |         ^^^^^^^^^^^^^^^
   = note: `#[warn(clippy::significant_drop_tightening)]` implied by `#[warn(clippy::nursery)]`
help: drop the temporary after the end of its last usage
   |
27 ~     drop((lock, lock2, lock3));
28 +     drop(lock);
   |

I expected to see this happen:

Version

rustc 1.71.0 (8ede3aae2 2023-07-12)
binary: rustc
commit-hash: 8ede3aae28fe6e4d52b38157d7bfe0d3bceef225
commit-date: 2023-07-12
host: x86_64-unknown-linux-gnu
release: 1.71.0
LLVM version: 16.0.5

Additional Labels

No response

[c410-f3r]

@rustbot claim