Application type mismatch in omega

Prerequisites

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• Reduce the issue to a minimal, self-contained, reproducible test case.
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Description

The following input causes a failure in 4.21.0-rc3. It used to work in previous versions.

import Aesop

add_aesop_rules safe (by omega)

inductive Formula (α: Type): Type where
  | Not: Formula α → Formula α
  | Atom: α → Formula α

structure Struct (α: Type) where
  var_to_formula: Array (Formula α)
  formula_to_var: List (Formula α)

theorem test (c: Struct α) (f: Formula α)
  (i₃: ∀ i, i ≥ 1 → (h: i < c.var_to_formula.size) → c.var_to_formula[i] ∈ c.formula_to_var):
  (∀ i, i ≥ 1 → (h: i < c.var_to_formula.size + 1) →
    f = (c.var_to_formula.push f)[i]'(by simp [h]) ∨
    (c.var_to_formula.push f)[i]'(by simp [h]) ∈ c.formula_to_var) := by
        aesop (add norm Array.getElem_push)

Here are the error messages

error: Bugs/Panic2.lean:3:25: (kernel) application type mismatch
  @getElem (Array (Formula α)) Nat (Formula α) (fun xs i => i < xs.size) Array.instGetElemNatLtSize
    (Struct.var_to_formula α c) i a✝
argument has type
  ¬((∀ (h : i < Array.size (Struct.var_to_formula α c)),
        f =
          @getElem (Array (Formula α)) Nat (Formula α) (fun xs i => i < xs.size) Array.instGetElemNatLtSize
            (Struct.var_to_formula α c) i h) ∨
      f ∈ Struct.formula_to_var α c)
but function has type
  (fun xs i => i < xs.size) (Struct.var_to_formula α c) i → Formula α
error: Bugs/Panic2.lean:15:8: (kernel) unknown constant 'push_cases._proof_1_1'

Versions

Lean 4.21.0-rc3
Lean 4.21.0
Lean 4.22.0

Impact

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Start by running the minimal reproducer in Bugs/Panic2.lean against the listed Lean versions. Investigate the interaction between omega, Aesop, Array.getElem_push, and kernel elaboration that produces the application type mismatch and unknown push_cases constant. Done means the reproducer no longer emits either error, with a regression test covering the failure.