Creating an inductive type with a constructor called `rec` crashes Lean

Prerequisites

Please put an X between the brackets as you perform the following steps:

• 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

This code crashes the server:

inductive X where
  | rec

Expected behavior: Probably it should be forbidden to have a constructor called rec.

Actual behavior: Server crashes

Versions

4.20.0-nightly-2025-05-07 on live.lean-lang.org

Impact

Add 👍 to issues you consider important. If others are impacted by this issue, please ask them to add 👍 to it.

Start by running the minimal inductive X where | rec example against the current Lean nightly or in live.lean-lang.org and trace where server handling fails. Done means the example no longer crashes the server and its handling matches the intended restriction or diagnostic for a constructor named rec.