Pattern-matching on `repeat` tactic fails with infinite loop

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

MWE:

import Lean

run_cmd do
  let t ← `(tactic| repeat fail) -- works
  match t with
  | `(tactic| repeat fail) => return -- max recursion depth has been reached
  | _ => return

I suspect this issue affects any recursive macro. E.g. this fails in the same way:

syntax "silly" : tactic
macro_rules
  | `(tactic| silly) => `(tactic| first | skip | silly)

run_cmd do
  let t ← `(tactic| silly) -- works
  match t with
  | `(tactic| silly) => return -- max recursion depth has been reached
  | _ => return

Versions

Lean 4.24.0-nightly-2025-08-26
Target: x86_64-unknown-linux-gnu

Impact

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Start by running the minimal repeat fail and silly examples from the issue against the specified Lean nightly. Trace the tactic quotation pattern matching that reaches the recursion-depth error; done means both matches terminate without the infinite loop or recursion-depth failure.