rust-lang / rust-lang/rust-clippy
`unnecessary-operation` suggestion on `[();1][<expr>]` is werid
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Description
Summary
Because of my minimal rust version (1.56), I have to use the hack [(); 1][<expr>] in const block for const assertions.
Lint Name
unnecessary-operation
Reproducer
I tried this code:
const _: () = {
use std::os::windows::io::RawHandle;
let std_layout = Layout::new::<RawHandle>();
let win_sys_layout = Layout::new::<usize>();
// MSRV(Rust v1.57): use assert! instead
[(); 1][std_layout.size() - win_sys_layout.size()];
};
I saw this happen:
error: unnecessary operation
--> src/internals/c.rs:42:5
|
42 | [(); 1][std_layout.size() - win_sys_layout.size()];
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([(); 1].len() > std_layout.size() - win_sys_layout.size());`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_operation
= note: `-D clippy::unnecessary-operation` implied by `-D warnings`
I expected to see this happen: It's my fault for using nightly clippy for msrv, however I expect that clippy should suggest
assert!(std_layout.size() == win_sys_layout.size());
Version
rustc 1.80.0-nightly (1a7397988 2024-05-17)
binary: rustc
commit-hash: 1a7397988684934ae01a71f524bdfff24895d8cc
commit-date: 2024-05-17
host: x86_64-unknown-linux-gnu
release: 1.80.0-nightly
LLVM version: 18.1.4
Additional Labels
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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 with the reproducer in the issue and inspect the unnecessary-operation lint behavior around src/internals/c.rs:42. Compare the current suggestion with the expected assertion shown in the report. Done means the lint handles this [(); 1][] const-assertion pattern without suggesting the misleading replacement, with coverage for the reported case.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100