`[expr; 0]` ignores lifetimes
Open
Nobody has claimed this yet.
A-array
A-lifetimes
A-ZST
C-bug
T-compiler
T-types
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
I tried this code:
use std::marker::PhantomData;
pub struct Thing<'a> {
_phantom: PhantomData<fn(&'a ()) -> &'a ()>,
}
pub fn foo<'a, 'b>(x: Thing<'a>) -> [Thing<'b>; 0] {
[x; 0]
}
pub fn lol<'a, 'b>(x: &'a i32) -> [&'b i32; 0] {
[x; 0]
}
I expected the code not to compile, but instead it compiles without errors or warnings.
See also https://github.com/rust-lang/rust/issues/79580, which is about [expr; 0] being weird.
Meta
Reproducible on the playground with 1.90.0-nightly (2025-07-15 3014e79f9c8d5510ea7b)
@rustbot labels +A-zst +A-lifetimes
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 two examples in the Rust Playground using the nightly version reported in the issue, then read issue #79580 for related repeat-expression behavior. Trace how [expr; 0] handles the lifetimes in these cases; done means the examples' lifetime expectations are addressed and regression coverage is added.
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
- 42/100