rust-lang / rust-lang/rust-clippy
`let-and-return` suggests invalid cast
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I-suggestion-causes-error
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Description
Using the following flags
--force-warn clippy::let-and-return
this code:
fn bindings() -> *const u8 {
let x = 0;
let x = &x;
x
}
pub fn main() {}
caused the following diagnostics:
Checking _a v0.1.0 (/tmp/icemaker_global_tempdir.LTN5gk3lY4Yf/icemaker_clippyfix_tempdir.VkBZzezo6BF0/_a)
warning: returning the result of a `let` binding from a block
--> src/main.rs:4:5
|
3 | let x = &x;
| ----------- unnecessary `let` binding
4 | x
| ^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_and_return
= note: requested on the command line with `--force-warn clippy::let-and-return`
help: return the expression directly
|
3 ~
4 ~ (&x) as _
|
warning: `_a` (bin "_a") generated 1 warning (run `cargo clippy --fix --bin "_a" -p _a` to apply 1 suggestion)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s
However after applying these diagnostics, the resulting code:
fn bindings() -> *const u8 {
let x = 0;
(&x) as _
}
pub fn main() {}
no longer compiled:
Checking _a v0.1.0 (/tmp/icemaker_global_tempdir.LTN5gk3lY4Yf/icemaker_clippyfix_tempdir.VkBZzezo6BF0/_a)
error[E0606]: casting `&i32` as `*const u8` is invalid
--> src/main.rs:4:5
|
4 | (&x) as _
| ^^^^^^^^^
For more information about this error, try `rustc --explain E0606`.
error: could not compile `_a` (bin "_a") due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_a` (bin "_a" test) due to 1 previous error
Version:
rustc 1.93.0-nightly (94b49fd99 2025-11-22)
binary: rustc
commit-hash: 94b49fd998d6723e0a9240a7cff5f9df37b84dd8
commit-date: 2025-11-22
host: x86_64-unknown-linux-gnu
release: 1.93.0-nightly
LLVM version: 21.1.5
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the provided let-and-return example with cargo clippy --fix and confirm that the suggested cast fails to compile. Trace the lint's suggestion generation and add a regression case showing that the fix must preserve compilation for this pointer-returning function.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 52/100