leanprover / leanprover/lean4

`unsafe opaque` does not allow unsafe body

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bug P-low
Dominant language
Lean
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Merged PRs (30d)
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Description

unsafe opaque verySafeCast : α → β := unsafeCast
-- (kernel) invalid declaration, it uses unsafe declaration 'unsafeCast'

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the Lean reproducer from the issue and tracing the compiler or kernel handling of unsafe opaque declarations. No source files or tests are named, so locate the relevant declaration-safety checks first. Done means the shown declaration is accepted without the reported invalid-declaration error, with regression coverage for the reproducer.

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
Mostly clear
Newbie friendliness
32/100

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