Open
Description
Using the following flags
--force-warn clippy::missing_transmute_annotations
this code:
async fn empty() {}
async fn meow(a: [u8; 100]) {
empty().await;
dbg!(a);
}
fn main() {
let v = meow([0; 100]);
let e = [0u8; 202];
let _ = || unsafe {
use std::{mem, ptr};
let mut copy = ptr::read(&v);
ptr::write(&mut copy, mem::transmute(ptr::read(&e)));
mem::forget(copy);
};
}caused the following diagnostics:
Checking _110151 v0.1.0 (/tmp/icemaker_global_tempdir.t8dYaH8PqaqW/icemaker_clippyfix_tempdir.QCq7tmv8PvKz/_110151)
warning: transmute used without annotations
--> src/main.rs:14:30
|
14 | ptr::write(&mut copy, mem::transmute(ptr::read(&e)));
| ^^^^^^^^^ help: consider adding missing annotations: `transmute::<[u8; 202], impl std::future::Future<Output = ()>>`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#missing_transmute_annotations
= note: requested on the command line with `--force-warn clippy::missing-transmute-annotations`
warning: `_110151` (bin "_110151") generated 1 warning
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.14s
However after applying these diagnostics, the resulting code:
async fn empty() {}
async fn meow(a: [u8; 100]) {
empty().await;
dbg!(a);
}
fn main() {
let v = meow([0; 100]);
let e = [0u8; 202];
let _ = || unsafe {
use std::{mem, ptr};
let mut copy = ptr::read(&v);
ptr::write(&mut copy, mem::transmute::<[u8; 202], impl std::future::Future<Output = ()>>(ptr::read(&e)));
mem::forget(copy);
};
}no longer compiled:
Checking _110151 v0.1.0 (/tmp/icemaker_global_tempdir.t8dYaH8PqaqW/icemaker_clippyfix_tempdir.QCq7tmv8PvKz/_110151)
error[E0562]: `impl Trait` is not allowed in paths
--> src/main.rs:14:53
|
14 | ptr::write(&mut copy, mem::transmute::<[u8; 202], impl std::future::Future<Output = ()>>(ptr::read(&e)));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
For more information about this error, try `rustc --explain E0562`.
error: could not compile `_110151` (bin "_110151") due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_110151` (bin "_110151" test) due to 1 previous error
Version:
rustc 1.89.0-nightly (076ec59ff 2025-06-05)
binary: rustc
commit-hash: 076ec59ff1dcf538b9d3a0b8e0d7f4edd0559959
commit-date: 2025-06-05
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5