## Summary
A Query page (TRQL) query that pulls fields out of a run's `output` with
JSON functions (`JSONExtractString`, `JSONExtractInt`, `JSONHas`, and
the rest of the family) failed with "The first argument of function ...
should be a string containing JSON, illegal type: JSON". Those queries
now work.
## Root cause and fix
`output` is a native ClickHouse `JSON` column, but `JSONExtract*`,
`JSONHas`, `JSONLength`, and `JSONType` all expect a String containing
JSON text. The compiler already swaps in the column's String companion
(`output_text`) when a JSON column is selected or compared, but not
inside function-call arguments, so it emitted `JSONExtractInt(output,
'x')` against the native column.
The fix prints the companion column for the first argument of these
functions when it resolves to a bare JSON field, keeping the table alias
when qualified (so it works in JOINs):
JSONExtractInt(output, 'x') -> JSONExtractInt(output_text, 'x')
JSONExtractArrayRaw(assumeNotNull(output), 'y') ->
JSONExtractArrayRaw(assumeNotNull(output_text), 'y')
It also reaches through value-preserving passthrough wrappers like
`assumeNotNull(...)`, while leaving value-changing wrappers like
`toJSONString(output)` on the native column (that argument is already a
String). The swap is also semantically correct, not just a type fix:
`output_text` is the unwrapped data JSON that the TRQL `output` model
already represents, so field paths line up.
Covered by printer unit tests and a ClickHouse integration test that
runs the whole family (plus the wrapped and `toJSONString` cases)
against a real native-JSON column. Both new cases fail with the exact
"illegal type: JSON" error without the fix.
Eric Allam
02cf9c81ad