private_bounds: false negative on trait impl
Open
Nobody has claimed this yet.
A-lints
C-bug
L-false-negative
L-private_bounds
T-compiler
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
Code
#![allow(unused)]
struct Type<T>(T);
trait PubTrait {}
mod a {
trait PrivTrait {}
impl<T: PrivTrait> super::PubTrait for super::Type<T> {}
}
Current output
None
Desired output
private_bounds warning
Rationale and extra context
The T: PrivTrait bound is more private than both PubTrait and Type, so that should give a warning.
Other cases
Rust Version
rustc 1.88.0-nightly (1799887bb 2025-03-29)
binary: rustc
commit-hash: 1799887bb281d1ab49287750f1950b8c738c6b77
commit-date: 2025-03-29
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.1
Anything else?
No response
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 provided Rust snippet with rustc 1.88.0-nightly and compare the current output with the requested private_bounds warning. Start by tracing how private bounds are evaluated for trait implementations; done means the T: PrivTrait bound produces a warning in this case without regressing the other visibility checks.
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
- 45/100