simp unfolds a local let with zetaDelta disabled

[b-mehta]

Prerequisites

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Description

variable {α : Type}

theorem test {n : Nat} {f : Fin n → α} : False := by
  let c (i : Fin n) : Nat := i
  let d : Fin n → Nat × Nat := fun i => (c i, c i + 1)
  have : ∀ i, (d i).2 ≠ c i * 2 := by
    simp only

The simp only call here unfolds d, even though the zetaDelta option is disabled.

Context

https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/simp.20and.20local.20lets

[Broader context that the issue occurred in. If there was any prior discussion on the Lean Zulip, link it here as well.]

Steps to Reproduce

1. Code as above

Expected behavior: simp only does not unfold c or d

Actual behavior: simp only unfolds d.

Versions

Tested on live.lean-lang.org nightly.

Additional Information

@fpvandoorn suggests:

I think it's a good idea to have the "projection-reduction" be aware of the zetaDelta (and zeta) options, and be more conservative if they are off.

Impact

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