Compiler allows marker trait bounds to be omitted in implementations when using RPITIT
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A-auto-traits
A-impl-trait
C-bug
T-compiler
T-types
- Dominant language
- Rust
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- 119k
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Description
I tried this code:
pub trait Example {
fn test() -> impl Eq + Ord + Send;
}
impl Example for u8 {
fn test() -> impl Eq + Ord {
"example"
}
}
I expected an error or at least a warning, but the code compiled with no diagnostics. Omitting Eq orOrd from the implementing function does produce an error.
Meta
Tested with both stable (1.92) and nightly (2026-01-19) in the Playground.
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 Rust Playground reproducer showing an RPITIT implementation omitting the Send bound, and compare its behavior on stable 1.92 and nightly 2026-01-19. Trace the compiler's handling of marker trait bounds in this case, then add coverage so the omission produces the intended diagnostic while valid implementations remain accepted.
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
- Active
- Clarity
- Clearly specified
- Newbie friendliness
- 52/100