Postgres 12

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE OR REPLACE FUNCTION f_typetest(smallint)  -- smallint!
  RETURNS bool LANGUAGE sql AS 'SELECT true';

CREATE FUNCTION

-- Working calls
SELECT * FROM f_typetest('1');
SELECT * FROM f_typetest('1'::int2);
SELECT * FROM f_typetest(1::int2);

f_typetest

t

SELECT 1

f_typetest

t

SELECT 1

f_typetest

t

SELECT 1

-- Does NOT work, because the unquoted numeric literal is cast as integer
 SELECT * FROM f_typetest(1)

ERROR:  function f_typetest(integer) does not exist
LINE 2:  SELECT * FROM f_typetest(1)
                       ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.