Hi Nico,

Thanks for the observation. A new stable snapshot with the bug fix is online [1,2]. BaseX 12.3 is scheduled for February or March.

Cheers,

Christian

[1] https://github.com/BaseXdb/basex/issues/2594

[2] https://files.basex.org/releases/latest/

Von: Nico Kutscherauer via BaseX-Talk
Gesendet: Mittwoch, 11. Februar 2026 14:08
Bis: basex-talk@mailman.uni-konstanz.de
Betreff: [basex-talk] Bug where sorting arrays causes a type error?

Hi BaseX team,

I have the following simple query:

let $strings := ('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j')
let $arrays as array(*)* := (array{1 to 2}, array{3 to 6}, array{7 to 9})
let $arrays := sort($arrays, (), fn($seq){array:size($seq) * -1})
let $largest := $arrays => head()
return
  for $idx in $largest?* return $strings[$idx]

When I execute it with BaseX 12.2 I get the following suprising error:

[XPTY0004] One item expected, 4 found: (3 to 6).

Much more suprising is that if I wrap the $arrays?* into a trace call it works:

let $strings := ('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j')
let $arrays as array(*)* := (array{1 to 2}, array{3 to 6}, array{7 to 9})
let $arrays := sort($arrays, (), fn($seq){array:size($seq) * -1})
let $largest := $arrays => head()
return
  for $idx in trace($largest?*) return $strings[$idx]

Result:

c
d
e
f

The root cause seems to be the sort function. Because if I remove that line it works without the trace.

Best Regards,
Nico

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