2 failures:
  @7 (⟨1, 7⟩): expected ')'
    ""
  @7 (⟨1, 7⟩): unterminated string literal
    ""

Final stack:
  (Lean.Doc.Syntax.named
   "("
   `x
   ":="
   (Lean.Doc.Syntax.arg_str <missing>)
   <missing>)