JSON_CONTAINS with a path answers 1 from a document that never formed a value, with no diagnostic

JSON_CONTAINS is documented to raise an error when the document is not
valid. Given a path, it stops the moment the path is found and never
reads the rest, so a document that breaks after the match is answered
from as though it were whole.

SELECT JSON_CONTAINS('{"a":1 "b":2}', '1', '$.a') AS v;

v

1

No warning is raised.

has no comma between its members
and is not a JSON document.

How to repeat

SELECT JSON_CONTAINS('{"a":1 "b":2}', '1', '$.a') AS v;   -- 1, silent

SELECT JSON_CONTAINS('[1 2]', '1', '$[0]')        AS v;   -- 1, silent

SELECT JSON_CONTAINS('{"a":1, "b"}', '1', '$.a')  AS v;   -- 1, silent

Every other reader refuses the same bytes:

SELECT JSON_EXTRACT('{"a":1 "b":2}', '$.a') AS v;

v

NULL

Warnings:

Warning  4038  Syntax error in JSON text in argument 1

              to function 'json_extract' at position 8

SELECT JSON_VALID('{"a":1 "b":2}') AS v;

v

0

And so does the same function, on the same bytes, with the path left
off:

SELECT JSON_CONTAINS('{"a":1, "b":2 "c":3}', '{"a":1}') AS v;

v

NULL

Warnings:

Warning  4038  Syntax error in JSON text in argument 1

              to function 'json_contains' at position 15

Root cause

The search stops at the first success and the remainder of the document
is never scanned, so the parse error that lies past the match is never
raised. Without a path the whole document is read, which is why the
last case above is diagnosed.

Contract, `scripts/fill_help_tables.sql:435`: *"Returns 1 if it does, 0
if not and NULL if any of the arguments are null. An error occurs if
the document or path is not valid, or contains the or * wildcards."*

Affected versions

JSON_CONTAINS was added in 10.2.3 and has stopped at the match
throughout.

Verified on 10.11 only (10.11.19-MariaDB-debug, commit 1dab253482d).
Other branches were not tested.

Note

Found while auditing the JSON functions against their documented
contracts. The suite pins the defect rather than the
contract: func_json_invalid.result:255 records
JSON_CONTAINS('{"a":1,', '1', '$.a') = 1. The missing-comma shapes
are absent.