rust-lang / rust-lang/rust-clippy
[lint request] unspecified_result_transmute
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Description
Some people transmute Results into other stuff, but Result is repr(Rust) and its layout is, AFAICT, currently, always unspecified, so we should warn on this.
I know, because I'm one of them. For example, I use Result in C FFI, to represent C error codes, by using a Result<(), NonZeroCInt> and relying on the fact that a niche optimizations currently always happens on nightly, and therefore the layout of that type will be that of libc::c_int.
Note that transmuting Option in similar cases is ok, because we guarantee their layout.
cc @eddyb - we currently do not guarantee any niche optimizations for Result-like enums. This might be something worth RFCing.
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 reviewing Clippy's existing transmute-related lints and the Rust layout guarantees described in the issue. Determine the cases involving Result that should produce a warning, then add coverage showing the warning for an unspecified Result layout and no warning for the guaranteed Option case.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- tooling
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100