Missing inlay hint on inst-implicit auto-implicit
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bug
P-medium
- Dominant language
- Lean
- Stars
- 9.2k
- Forks
- 990
- Avg merge
- 1d 17h
- Merged PRs (30d)
- 175
Description
example (a : α) : α := a -- inlay hint for `α`
example (a : α α) : α := a -- inlay hint for `α`
example [Typo α] : α := a -- no inlay hints
Expected behavior: Typo (and, less importantly, α) should be shown as an inlay hint to signal that the name is unbound
Actual behavior: Only the confusing error message
invalid binder annotation, type is not a class instance
?m.160
appears
Impact
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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 three examples in Lean and compare the inlay-hint behavior with the confusing invalid-binder-annotation error. Trace the elaboration and inlay-hint handling for auto-implicit binders; done means Typo and α are shown as unbound-name hints in the affected example without regressing the existing cases.
Written by the indexing model from the issue text.
Assessment
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 35/100