ignored-unit-patterns suggestion is missing a reference #15187
Description
Using the following flags
--force-warn clippy::ignored-unit-patterns
this code:
type LifetimeBound<'r> = &'r dyn Fn(&'r ());
fn main() {
let capture = String::new();
let func = move |_| drop(&capture);
let func_ref_bound: LifetimeBound = &func;
drop(func_ref_bound);
}caused the following diagnostics:
Checking _snippet_1 v0.1.0 (/tmp/icemaker_global_tempdir.IbV1PR0WiGNQ/icemaker_clippyfix_tempdir.hkoPnYXFL2QE/_snippet_1)
warning: matching over `()` is more explicit
--> src/main.rs:5:19
|
5 | let func = move |_| drop(&capture);
| ^ help: use `()` instead of `_`: `()`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ignored_unit_patterns
= note: requested on the command line with `--force-warn clippy::ignored-unit-patterns`
warning: `_snippet_1` (bin "_snippet_1") generated 1 warning (run `cargo clippy --fix --bin "_snippet_1"` to apply 1 suggestion)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s
However after applying these diagnostics, the resulting code:
type LifetimeBound<'r> = &'r dyn Fn(&'r ());
fn main() {
let capture = String::new();
let func = move |()| drop(&capture);
let func_ref_bound: LifetimeBound = &func;
drop(func_ref_bound);
}no longer compiled:
Checking _snippet_1 v0.1.0 (/tmp/icemaker_global_tempdir.IbV1PR0WiGNQ/icemaker_clippyfix_tempdir.hkoPnYXFL2QE/_snippet_1)
error[E0631]: type mismatch in closure arguments
--> src/main.rs:6:38
|
5 | let func = move |()| drop(&capture);
| --------- found signature defined here
6 | let func_ref_bound: LifetimeBound = &func;
| ^^^^^ expected due to this
|
= note: expected closure signature `fn(&()) -> _`
found closure signature `fn(()) -> _`
= note: required for the cast from `&{closure@src/main.rs:5:13: 5:22}` to `&dyn std::ops::Fn(&())`
help: consider adjusting the signature so it borrows its argument
|
5 | let func = move |&()| drop(&capture);
| +
For more information about this error, try `rustc --explain E0631`.
error: could not compile `_snippet_1` (bin "_snippet_1" test) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_snippet_1` (bin "_snippet_1") due to 1 previous error
Version:
rustc 1.90.0-nightly (ed2d75978 2025-06-29)
binary: rustc
commit-hash: ed2d759783dc9de134bbb3f01085b1e6dbf539f3
commit-date: 2025-06-29
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.7