JSON_ARRAY_INTERSECT returns NULL when the nonconstant array is the first operand

JSON_ARRAY_INTERSECT(j, '[2]') returns NULL for rows whose stored JSON arrays overlap [2], while exchanging the operands returns [2]. This was observed with MariaDB 12.3.3 on Linux/amd64.

Reproducer

CREATE DATABASE IF NOT EXISTS test;

USE test;

SET NAMES utf8mb4;

DROP TABLE IF EXISTS array_inputs;

CREATE TABLE array_inputs (

  id INT PRIMARY KEY,

  j LONGTEXT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin

    CHECK (JSON_VALID(j))

) ENGINE=InnoDB;

INSERT INTO array_inputs VALUES

  (1, '[1,2]'),

  (2, '[2,3]'),

  (3, '[4]');

CREATE TEMPORARY TABLE intersections AS

SELECT id,

       JSON_ARRAY_INTERSECT(j, '[2]') AS candidate,

       JSON_ARRAY_INTERSECT('[2]', j) AS commuted_control

FROM array_inputs;

SELECT id, candidate, commuted_control

FROM intersections

ORDER BY id;

SELECT 'disagreement_count',

       SUM(NOT (candidate <=> commuted_control))

FROM intersections;

DROP TEMPORARY TABLE intersections;

DROP TABLE array_inputs;

The query produces:

id	candidate	commuted_control

1	NULL	[2]

2	NULL	[2]

3	NULL	NULL

disagreement_count	SUM(NOT (candidate <=> commuted_control))

disagreement_count	2

Rows 1 and 2 return NULL with the column first but [2] with the constant first. JSON array intersection is independent of operand order, so the two expressions should be NULL-safe equal for every row and the disagreement count should be 0. Rows 1 and 2 should return [2] from both expressions; row 3 may return NULL from both because it has no overlap.

The available source analysis indicates that the first operand is evaluated before argument normalization can exchange the operands, after which a hash is initialized from the stale pre-swap value. Per-row parsing does not repair that state.

This occurs when JSON_ARRAY_INTERSECT compares a JSON value stored in a column with a constant JSON array and the column is supplied as the first operand.