`unreachable_patterns` emitted on `_` that matches a local of uninhabited type (that is uninitialized)
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A-lints
C-bug
L-unreachable_patterns
T-compiler
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
I tried this code:
enum Void {}
fn main() {
let void: Void;
match void {
_ => (),
}
}
I expected to see this happen: the code compiler without warnings and successfully runs doing nothing.
Instead, this happened: a warning is emitted (the code compiles and runs as expected):
warning: unreachable pattern
--> src/main.rs:6:9
|
6 | _ => (),
| ^-------
| |
| matches no values because `Void` is uninhabited
| help: remove the match arm
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
= note: `#[warn(unreachable_patterns)]` on by default
Meta
rustc version: 1.85.0-nightly (2024-12-23 bdc6b3de48646345549f)
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
Reproduce the warning from src/main.rs using the linked Rust Playground example and the reported nightly version. Compare the compiler's unreachable-pattern result for the uninitialized local with the expected behavior. Done means the example still compiles and runs without emitting the unreachable_patterns warning.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100