======================
Empty bracket argument
======================

message([[]])

---
(source_file
  (command_invocation
    (identifier)
    (arguments
      (argument
        (bracket_argument
          (bracket_open)
          (bracket_close)
        )
      )
    )
  )
)

======================
One bracket argument
======================

message([[An argument]])

---
(source_file
  (command_invocation
    (identifier)
    (arguments
      (argument
        (bracket_argument
          (bracket_open)
          (bracket_content)
          (bracket_close)
        )
      )
    )
  )
)