pattern matching ignores inaccessibility annotation

[cppio]

Prerequisites

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

example : (x : Bool × Bool) → x.fst = x.snd ⊕' Unit → Unit
  | (.(b), b), .inl rfl => ()
  | (_, false), _ => ()
  | (_, true), _ => ()

During elaboration, Lean.Elab.Term.ToDepElimPattern.normalize ignores the explicit inaccessible pattern in (.(b), b) and rewrites it to (b, .(b)), which causes an error since the second component is now neither a constructor nor a variable pattern.

Steps to Reproduce

Run the code above.

Expected behavior: The code succeeds with no errors.

Actual behavior: The code results in the following error:

dependent match elimination failed, inaccessible pattern found
  .(fst✝)
constructor expected

Versions

Lean 4.16.0-nightly-2025-01-06
This behavior has existed since Lean 4.0.0-m1

Impact

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