Instance creates defs regardless of whether the typeclass is Prop- or Type-valued

[jjdishere]

Prerequisites

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• [x] Check that your issue is not already filed: https://github.com/leanprover/lean4/issues
• [x] Reduce the issue to a minimal, self-contained, reproducible test case. Avoid dependencies to Mathlib or Batteries.
• [x] 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

Instance always creates defs instead of theorems regardless of whether the typeclass is Prop- or Type-valued.

Context

Given a type class class A : Prop, the instances of this typeclass should be theorems. However, currently, all instances are defs.

MWE from the zulip discussion:

import Lean.Elab.Command

open Lean

class A : Prop

instance a : A where

/-- info: it's a definition -/
#guard_msgs in
run_meta do
  if let .defnInfo _ ← getConstInfo `a then
    logInfo "it's a definition"

Versions

4.12.0-nightly-2024-10-10 (using live.lean-lang.org)

Impact

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