alloc-instead-of-core there is no core::Layout #15579
Description
Using the following flags
--force-warn clippy::alloc-instead-of-core
this code:
use core::sync::atomic::AtomicBool;
use core::sync::atomic::Ordering;
use std::alloc;
static FLAG: AtomicBool = AtomicBool::new(false);
fn protector_data_race(v: &u8) {
println!("{v}");
FLAG.store(true, Ordering::Release);
// Implicit read from protector not detected as a data race(?), but uncommenting this will be
// detected:
//println!("{v}");
}
fn main() {
let layout = alloc::Layout::new::<u8>();
let ptr = unsafe { alloc::alloc(layout) };
assert!(!ptr.is_null());
unsafe { *ptr = 8 };
struct SendPtr(*mut u8);
unsafe impl Send for SendPtr {}
let send_ptr = SendPtr(ptr);
std::thread::spawn(|| {
let send_ptr = send_ptr;
let r = unsafe { &*send_ptr.0 };
protector_data_race(r);
});
loop {
if FLAG.load(Ordering::Acquire) {
// There is an actual race since we need to delay here to prevent the dealloc from
// running while the protector still exists (generating a different kind of error).
//
// But we want to preserve the race to test the race detector... so this just loops,
// perhaps there is a better and less fragile way to do this.
for _ in 0..100 {}
unsafe { alloc::dealloc(ptr.cast(), layout) };
break;
}
}
}caused the following diagnostics:
Checking _snippet_0 v0.1.0 (/tmp/icemaker_global_tempdir.W9mV5T7suTWy/icemaker_clippyfix_tempdir.0KPPgB6AQPhi/_snippet_0)
warning: used import from `alloc` instead of `core`
--> src/main.rs:16:18
|
16 | let layout = alloc::Layout::new::<u8>();
| ^^^^^ help: consider importing the item from `core`: `core`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#alloc_instead_of_core
= note: requested on the command line with `--force-warn clippy::alloc-instead-of-core`
warning: `_snippet_0` (bin "_snippet_0") generated 1 warning (run `cargo clippy --fix --bin "_snippet_0"` to apply 1 suggestion)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s
However after applying these diagnostics, the resulting code:
use core::sync::atomic::AtomicBool;
use core::sync::atomic::Ordering;
use std::alloc;
static FLAG: AtomicBool = AtomicBool::new(false);
fn protector_data_race(v: &u8) {
println!("{v}");
FLAG.store(true, Ordering::Release);
// Implicit read from protector not detected as a data race(?), but uncommenting this will be
// detected:
//println!("{v}");
}
fn main() {
let layout = core::Layout::new::<u8>();
let ptr = unsafe { alloc::alloc(layout) };
assert!(!ptr.is_null());
unsafe { *ptr = 8 };
struct SendPtr(*mut u8);
unsafe impl Send for SendPtr {}
let send_ptr = SendPtr(ptr);
std::thread::spawn(|| {
let send_ptr = send_ptr;
let r = unsafe { &*send_ptr.0 };
protector_data_race(r);
});
loop {
if FLAG.load(Ordering::Acquire) {
// There is an actual race since we need to delay here to prevent the dealloc from
// running while the protector still exists (generating a different kind of error).
//
// But we want to preserve the race to test the race detector... so this just loops,
// perhaps there is a better and less fragile way to do this.
for _ in 0..100 {}
unsafe { alloc::dealloc(ptr.cast(), layout) };
break;
}
}
}no longer compiled:
Checking _snippet_0 v0.1.0 (/tmp/icemaker_global_tempdir.W9mV5T7suTWy/icemaker_clippyfix_tempdir.0KPPgB6AQPhi/_snippet_0)
warning: error applying suggestions to `src/main.rs`
The full error message was:
> cannot replace slice of data that was already replaced
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
warning: failed to automatically apply fixes suggested by rustc to crate `_snippet_0`
after fixes were automatically applied the compiler reported errors within these files:
* src/main.rs
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
The following errors were reported:
error[E0433]: failed to resolve: could not find `Layout` in `core`
--> src/main.rs:16:24
|
16 | let layout = core::Layout::new::<u8>();
| ^^^^^^ could not find `Layout` in `core`
|
help: consider importing one of these structs
|
1 + use crate::alloc::Layout;
|
1 + use std::alloc::Layout;
|
help: if you import `Layout`, refer to it directly
|
16 - let layout = core::Layout::new::<u8>();
16 + let layout = Layout::new::<u8>();
|
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0433`.
Original diagnostics will follow.
error[E0433]: failed to resolve: could not find `Layout` in `core`
--> src/main.rs:16:24
|
16 | let layout = core::Layout::new::<u8>();
| ^^^^^^ could not find `Layout` in `core`
|
help: consider importing one of these structs
|
1 + use crate::alloc::Layout;
|
1 + use std::alloc::Layout;
|
help: if you import `Layout`, refer to it directly
|
16 - let layout = core::Layout::new::<u8>();
16 + let layout = Layout::new::<u8>();
|
For more information about this error, try `rustc --explain E0433`.
error: could not compile `_snippet_0` (bin "_snippet_0" test) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
warning: error applying suggestions to `src/main.rs`
The full error message was:
> cannot replace slice of data that was already replaced
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
warning: failed to automatically apply fixes suggested by rustc to crate `_snippet_0`
after fixes were automatically applied the compiler reported errors within these files:
* src/main.rs
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
The following errors were reported:
error[E0433]: failed to resolve: could not find `Layout` in `core`
--> src/main.rs:16:24
|
16 | let layout = core::Layout::new::<u8>();
| ^^^^^^ could not find `Layout` in `core`
|
help: consider importing one of these structs
|
1 + use crate::alloc::Layout;
|
1 + use std::alloc::Layout;
|
help: if you import `Layout`, refer to it directly
|
16 - let layout = core::Layout::new::<u8>();
16 + let layout = Layout::new::<u8>();
|
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0433`.
Original diagnostics will follow.
error: could not compile `_snippet_0` (bin "_snippet_0") due to 1 previous error
Version:
rustc 1.91.0-nightly (91ee6a405 2025-08-26)
binary: rustc
commit-hash: 91ee6a4057ce4bf1ab6d2f932cae497488d67c81
commit-date: 2025-08-26
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.0