#eval Lean.versionString -- "4.19.0-nightly-2025-03-19"

theorem extracted_1 (x y : BitVec 9) :
    (y - y.srem x).sdiv x = y.sdiv x := by
  ac_nf

Prerequisites

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• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

The following call to ac_nf triggers:

(deterministic) timeout at `whnf`, maximum number of heartbeats (200000) has been reached
Use `set_option maxHeartbeats <num>` to set the limit.

Additional diagnostic information may be available using the `set_option diagnostics true` command.

Context

I tested this with https://github.com/leanprover/lean4-nightly/releases/tag/nightly-2025-03-18, where the very same code works flawlessly. Looking at the changelog of https://github.com/leanprover/lean4-nightly/releases/tag/nightly-2025-03-19, leanprover/lean4-nightly@3857603 may have triggered a regression. @nomeata may be able to confirm.

Steps to Reproduce

1. Copy test case into latest lean
2. Wait for error

Expected behavior: Tactic finishes instantly with an unmodified goal state.

Actual behavior: Error triggered and proof fails.

Versions

nightly-2025-03-19 and nightly-2025-03-20 fail
nightly-2025-03-18 works

Impact

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