PANIC at Lean.MVarId.falseOrByContra Lean.Elab.Tactic.FalseOrByContra:58:44: expected one sugoal [sic]

[eric-wieser]

Prerequisites

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Description

The false_or_by_contra tactic panics on some inputs

Steps to Reproduce

1. example : id (False → Nat) := by false_or_by_contra

Expected behavior: Either the tactic succeeds or it fails

Actual behavior: PANIC at Lean.MVarId.falseOrByContra Lean.Elab.Tactic.FalseOrByContra:58:44: expected one sugoal. Additionally, the infoview shows [error when printing message: unknown goal [anonymous]].

Versions

4.11.0-rc1

Additional Information

Note the web editor does not show panics.

The typo in the PR description is in the error message itself; and so this is not quite the same bug as #4984

Impact

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