plpgsql: ambiguous column reference in ON CONFLICT clause

[Torsten Förtsch <tfoertsch123@xxxxxxxxx>]

Is there a way to prevent this from happening? I know I can use the PK constraint name or rename the OUT variable i. The question is can this be resolved while keeping the arbiter inference and the variable name.

CREATE TABLE x.x (
    i INT PRIMARY KEY
);

CREATE OR REPLACE FUNCTION x.ins(p_i INT, OUT i INT)
LANGUAGE plpgsql AS $$
  BEGIN
    INSERT INTO x.x(i)
    SELECT p_i
        ON CONFLICT (i) DO NOTHING;
  END
$$;

postgres=# select * from x.ins(1);
ERROR:  column reference "i" is ambiguous
LINE 3:         ON CONFLICT (i) DO NOTHING
                            ^
DETAIL:  It could refer to either a PL/pgSQL variable or a table column.
QUERY:  INSERT INTO x.x(i)
    SELECT p_i
        ON CONFLICT (i) DO NOTHING
CONTEXT:  PL/pgSQL function x.ins(integer) line 3 at SQL statement

The conflicting variable is the OUT parameter of the function.

Normally, I'd suggest to fully qualify the name but the following or similar is a syntax error:

    INSERT INTO x.x(i) AS t
    SELECT p_i
        ON CONFLICT (t.i) DO NOTHING;

According to the documentation in https://www.postgresql.org/docs/current/plpgsql-implementation.html:

> Query parameters will only be substituted in places where they are syntactically permissible.

and

> Another way to understand this is that variable substitution can only insert data values into an SQL command; it cannot dynamically change which database objects are referenced by the command.

After reading this I am wondering if the current behavior is actually a bug.

Thanks,

Torsten