Ability to suppress unused universe parameter error
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Description
Prerequisites
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Description
In Lean 4 unused universe parameters are now a hard error.
There are situations where it is desirable to suppress this error, e.g. the existing implementation of lifting universes for categories in Mathlib (see link below).
Currently, we have a hacky fix to sidestep this error. This is not a good permanent state.
Steps to Reproduce
def ULiftHom.{w,u} (C : Type u) : Type u := C
Expected behavior: A linter warning which can be turned off.
Actual behavior: There is no way to toggle the error off.
Reproduces how often: 100%
Thanks.
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 unused-universe-parameter error with the ULiftHom example, then inspect the referenced Mathlib/CategoryTheory/Category/ULift.lean workaround and the linked Lean change. Done means unused universe parameters can be treated as a configurable warning rather than an unavoidable error.
Written by the indexing model from the issue text.
Assessment
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100