`symm` tactic produces term with mvars
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bug
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Description
Description
The symm tactic produces a term containing metavariables when the symmetry lemma has a typeclass assumption.
axiom Foo : Prop
attribute [class] Foo
axiom R : Nat → Nat → Prop
@[symm]
axiom R.symm [Foo] {n m} : R n m → R m n
/- (kernel) declaration has metavariables '_example' -/
example [Foo] {n m} : R n m → R m n := by
intro; symm; assumption
Versions
Lean 4.24.0-nightly-2025-08-19
Target: x86_64-unknown-linux-gnu
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Contributor guide
First steps
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Research direction
Reproduce the example using Lean 4.24.0-nightly-2025-08-19 and start by tracing the symm tactic's handling of the [Foo] typeclass assumption. Confirm that the generated declaration no longer contains metavariables, and add a regression test covering this example.
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
- 42/100