Lean panics on malformed syntax match

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

open Lean

def foo (stx : Syntax) : Unit := 
  match stx with
  | _, `(bar) => sorry

Result:

Test.lean:6:2: error: unknown goal                                                                                                                                                                                                    
PANIC at _private.Lean.Elab.Quotation.0.Lean.Elab.Term.Quotation.compileStxMatch Lean.Elab.Quotation:601:12: unreachable code has been reached
backtrace: ...

Versions

Lean 4.24.0-nightly-2025-08-27
Target: x86_64-unknown-linux-gnu

Impact

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Reproduce the minimal example in Test.lean with Lean 4.24.0-nightly-2025-08-27 and confirm the unknown-goal error and panic. Start at Lean.Elab.Quotation.compileStxMatch, identified in the backtrace, and use the malformed syntax match as the regression case; done means it reports the malformed input without panicking.