unnecessary_lazy_evaluations suggests a fix that panics

[tuxbzh]

Summary

In the example below, unnecessary_lazy_evaluations suggests a fix that is not functionally equivalent to the original code and that panics (the original code works normally).

Lint Name

unnecessary_lazy_evaluations

Reproducer

I tried this code:

fn try_sub(a: u32, b: u32) -> Option<u32> {
    (a >= b).then(|| a - b)
    //(a >= b).then_some(a - b) // Suggested by clippy but panic...
}

fn main() {
    assert_eq!(try_sub(10, 4), Some(6));
    assert_eq!(try_sub(4, 10), None);
}

I saw this happen:

warning: unnecessary closure used with `bool::then`
 --> src/main.rs:2:5
  |
2 |     (a >= b).then(|| a - b)
  |     ^^^^^^^^^--------------
  |              |
  |              help: use `then_some(..)` instead: `then_some(a - b)`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_lazy_evaluations
  = note: `#[warn(clippy::unnecessary_lazy_evaluations)]` on by default

I expected to see this happen: No suggestion.

Version

rustc 1.74.0 (79e9716c9 2023-11-13)
binary: rustc
commit-hash: 79e9716c980570bfd1f666e3b16ac583f0168962
commit-date: 2023-11-13
host: x86_64-unknown-linux-gnu
release: 1.74.0
LLVM version: 17.0.4

Additional Labels

No response

[y21]

This was fixed in #11002 and should no longer fire here in more recent nightly versions (tested 2023-12-04 and this build seems to have the fix)

[y21]

Closing as fixed. The fix for it also made it into today's stable, so this should no longer emit a warning on any channel. Thanks for the report!