Stateful elaboration of mutual block causes 'unknown free variable'
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Description
Description
Consider the following block of code:
mutual
def foo : Nat -> Nat := fun n =>
bar n
def bar : Nat -> Nat
| 0 => 0
| n+1 => foo n
def baz : Nat :=
1
end
It elaborates correctly. However, if we then comment out baz, unknown free variable '_fvar.9' is reported on foo. This error is not 'real' in that upon restarting the file worker (or just making a change above the entire block), it goes away.
Expected behavior: Mutual block is re-elaborated correctly without refreshing.
Actual behavior: An error is reported.
Versions
Lean 4.20.0-nightly-2025-05-04
Target: x86_64-unknown-linux-gnu
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
Run the provided mutual-block reproducer with Lean 4.20.0-nightly-2025-05-04, then reproduce the failure by commenting out baz without restarting the file worker. Trace stateful elaboration of the mutual block; done means the block re-elaborates without an unknown free variable error after that edit.
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
- 38/100