BUG #18693: Column names not set when using SELECT STRICT INTO with RECORD type

The following bug has been logged on the website:

Bug reference:      18693
Logged by:          Jan Behrens
Email address:      jbe-mlist@magnetkern.de
PostgreSQL version: 16.4
Operating system:   FreeBSD
Description:

I used the following SQL code:

CREATE TABLE tbl (a TEXT, b TEXT);

CREATE FUNCTION "buggy"() RETURNS VOID LANGUAGE plpgsql AS $$
  DECLARE
    t tbl%ROWTYPE;
    r RECORD;
  BEGIN
    SELECT a, b INTO t FROM (SELECT 'A' AS a, 'B' AS b) AS q;
    RAISE NOTICE 'non-strict t = %', t;
    RAISE NOTICE 'non-strict t.a = %', t.a;
    RAISE NOTICE 'non-strict t.b = %', t.b;
    SELECT a, b STRICT INTO t FROM (SELECT 'A' AS a, 'B' AS b) AS q;
    RAISE NOTICE 'STRICT t = %', t;
    RAISE NOTICE 'STRICT t.a = %', t.a;
    RAISE NOTICE 'STRICT t.b = %', t.b;
    SELECT a, b INTO r FROM (SELECT 'A' AS a, 'B' AS b) AS q;
    RAISE NOTICE 'non-strict r = %', r;
    RAISE NOTICE 'non-strict r.a = %', r.a;
    RAISE NOTICE 'non-strict r.b = %', r.b;
    SELECT a, b STRICT INTO r FROM (SELECT 'A' AS a, 'B' AS b) AS q;
    RAISE NOTICE 'STRICT r = %', r;
    RAISE NOTICE 'STRICT r.a = %', r.a;
    RAISE NOTICE 'STRICT r.b = %', r.b;
  END;
$$;

SELECT buggy();

Invoking the buggy() function resulted in:

NOTICE:  non-strict t = (A,B)
NOTICE:  non-strict t.a = A
NOTICE:  non-strict t.b = B
NOTICE:  STRICT t = (A,B)
NOTICE:  STRICT t.a = A
NOTICE:  STRICT t.b = B
NOTICE:  non-strict r = (A,B)
NOTICE:  non-strict r.a = A
NOTICE:  non-strict r.b = B
NOTICE:  STRICT r = (A,B)
NOTICE:  STRICT r.a = A
ERROR:  record "r" has no field "b"
CONTEXT:  SQL expression "r.b"
PL/pgSQL function buggy() line 21 at RAISE

I would expect the last statement to not result in an error but to correctly
access field "b" as in the non-strict case or tbl%ROWTYPE case.