Re: json/jsonb cleanup + FmgrInfo caching

Hi Jian,

On Thu, Oct 22, 2026 at 9:12 PM jian he
<jian(dot)universality(at)gmail(dot)com> wrote:
> The attached patch should resolve these issues.

It does. v3 applies cleanly to master and REL_19_STABLE, and make
check passes. Every case from my earlier matrix is now rejected at
CREATE INDEX, as in 18: ADD / RENAME / DROP ATTRIBUTE, the table
rowtype, nested composites, domains over composites, arrays of
composites, JSON_OBJECT, RETURNING json, and the unique, partial,
generated column and partition key forms. Anonymous ROW(), record[]
and JSON_SCALAR are rejected too.

One case still gets through, in the range branch. A range is printed
by range_out, which calls the subtype's output function and never a
cast to json. But when the range has no cast of its own,
json_check_mutability() recurses into the subtype and judges the
subtype's cast to json instead. So an immutable cast on an enum makes
a range over that enum look immutable, while what actually prints it
is enum_out:

CREATE TYPE e AS ENUM ('a', 'b');
CREATE FUNCTION e_json(e) RETURNS json IMMUTABLE LANGUAGE sql
AS $$ SELECT '"x"'::json $$;
CREATE CAST (e AS json) WITH FUNCTION e_json(e);
CREATE TYPE er AS RANGE (subtype = e);
CREATE TABLE t (v er);
INSERT INTO t VALUES (er('a', 'b'));
CREATE INDEX t_i ON t ((json_array(v returning jsonb)));
ALTER TYPE e RENAME VALUE 'a' TO 'z';
SELECT count(*) FROM t
WHERE json_array(v returning jsonb) =
json_array(er('z', 'b') returning jsonb);

The index scan returns 0 and a seq scan returns 1; REINDEX restores 1.
Without the cast on the enum the CREATE INDEX is rejected, and 18
rejects it either way. The multirange behaves the same. Master has
this without v3 as well.

The attached diff, on top of v3, stops looking up casts once the
recursion is below a range or multirange. With it both cases are
rejected, nothing else in my matrix changes (int4range is still
accepted), and make check passes. It's named .txt so it doesn't
disturb the CF bot; feel free to fold it into v4 if you agree.

regards,
Manu