while_let_loop fails to see that temporary value needs to be dropped #9206
Description
Summary
There may be important temporary values in the if/while expression, like a mutex lock guard. In case of an if-statement-with-break, these are dropped after the statement. In case of a while-let loop, these are retained for the whole loop body.
I would expect that the lint might recognise this kind of thing and not warn. Seems hard though. But blindly "fixing" can lead to bad errors.
Lint Name
while_let_loop
Reproducer
I tried this code:
use std::sync::{Arc, Mutex}; fn handle_items(q: Arc<Mutex<Vec<i32>>>) { loop { let item = match q.lock().unwrap().pop() { Some(item) => item, None => break, }; // lock guard dropped here println!("process: {}", item); if item > 10 { // deadlocks here if while-let q.lock().unwrap().insert(0, item - 1); } } } fn main() { let q = Arc::new(Mutex::new(vec![1, 2, 3, 12, 7])); handle_items(q); }I saw this happen:
warning: this loop could be written as a `while let` loop --> src/main.rs:4:2 | 4 | / loop { 5 | | let item = match q.lock().unwrap().pop() { 6 | | Some(item) => item, 7 | | None => break, ... | 14 | | } 15 | | } | |_____^ help: try: `while let Some(item) = q.lock().unwrap().pop() { .. }` | = note: `#[warn(clippy::while_let_loop)]` on by default = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#while_let_loop I expected to see this happen:
Nothing. The suggested code will deadlock.
Version
rustc 1.62.0 (a8314ef7d 2022-06-27) binary: rustc commit-hash: a8314ef7d0ec7b75c336af2c9857bfaf43002bfc commit-date: 2022-06-27 host: x86_64-unknown-linux-gnu release: 1.62.0 LLVM version: 14.0.5 Additional Labels
No response