Trait attribute that asserts no blanket impl will be added
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Description
We should have some sort of attribute we can put on a trait that says "this trait will NEVER have a blanket impl". The idea here is that we could put it on things like AsRef and this would change coherence to let me do something like
impl AsRef<LocalType> for StdType { ... }
AIUI this is not allowed today because if AsRef gains a blanket impl this would then cause coherence issues. But if we can assert that AsRef will never have a blanket impl then this should be safe to declare.
/cc @nikomatsakis
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Research direction
Start with the issue's proposal for a trait attribute, using AsRef, blanket implementations, and coherence as the key concepts to investigate. A complete contribution would need a settled design for the assertion and its coherence implications, but the payload names no implementation files or tests.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100