BUG #15533: error on upsert when used in a fuction and a function parameter has the same name as the column

The following bug has been logged on the website:

Bug reference: 15533
Logged by: Lulzim Bilali
Email address: lulzimbilali(at)gmail(dot)com
PostgreSQL version: 11.1
Operating system: Ubuntu 18.04
Description:

Can't use `ON CONFLICT DO UPDATE` in a function which has a parameter with
the same name as the column where the unique key is.

Here is the error I get.

Query execution failed

Reason:
SQL Error [42702]: ERROR: column reference "id" is ambiguous
Detail: It could refer to either a PL/pgSQL variable or a table
column.
Where: PL/pgSQL function log_tst(integer,text) line 4 at SQL
statement

the test code I'm using:

--DROP TABLE IF EXISTS tst;
CREATE TABLE tst (
id int UNIQUE,
info text
);

--DROP FUNCTION IF EXISTS log_tst;
CREATE OR REPLACE FUNCTION log_tst(id int, info text) RETURNS void AS
$$
BEGIN

INSERT INTO tst (id, info)
VALUES (log_tst.id, log_tst.info)
--ON CONFLICT DO NOTHING
ON CONFLICT (id) DO UPDATE
SET info = log_tst.info
;
END $$
LANGUAGE plpgsql;

SELECT log_tst(1, 'changed');

I would expect it to work since we can't use a parameter to check the
uniqueness even if we want (or can we!?), so PostgreSQL should know to use
the column instead.

Lulzim