Re: finish TODOs in to_json_is_immutable, to_jsonb_is_immutable also add tests on it

On Tue, Jan 13, 2026 at 7:12 PM Vaibhav Dalvi
<vaibhav(dot)dalvi(at)enterprisedb(dot)com> wrote:
>
> Hi Jian,
>
> Thanks for working on this. The patch looks good, but I have a few observations:
>
> 1. Index creation fails for range types regardless of the base data type:
>
> postgres=# create type range_int as range(subtype=int);
> CREATE TYPE
> postgres=# create table range_table(r1 range_int);
> CREATE TABLE
> postgres=# create index on range_table(json_array(r1 returning jsonb));
> ERROR: functions in index expression must be marked IMMUTABLE
>
> I believe this is because range_out is a stable function. Consequently, the following
> code snippet in to_jsonb_is_immutable may be redundant, or should simply return
> false without recursing for the sub-type:
>
> + else if (att_typtype == TYPTYPE_RANGE)
> + {
> + to_jsonb_is_immutable(get_range_subtype(typoid), contain_mutable);
> + }
>

yech, your observation is right.

create index on range_table((r1::text));

will fail, because pg_proc.provolatile is 's' for function range_out.

but imagine the function range_out marked as immutable, then we would
need to recurse to the range's subtype.
also, it makes the logic more complite: if the type is container type,
recurse to check its elemental/subtype.

Therefore, I am inclined to leave it unchanged.

> 2. Regarding the function names to_jsonb_is_immutable and to_json_is_immutable:
> since these do not return a boolean value, "is" may no longer be appropriate. Perhaps
> something like to_jsonb_check_mutable would be more accurate?
>

to_jsonb_is_immutable and to_json_is_immutable are marked as extern, so they may
be used by other extensions. Renaming them would require extension authors to
discover and update to the new symbol names. Adding an additional argument makes
the change immediately visible through a signature mismatch.

so I think we should stick to the current name.

--
jian
https://www.enterprisedb.com