Postgres 13

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-- helper function I
CREATE OR REPLACE FUNCTION quote_nullable_typed(ANYELEMENT)
  RETURNS text
  LANGUAGE sql PARALLEL SAFE IMMUTABLE AS
$func$
SELECT quote_nullable($1) || '::' || pg_typeof($1);
$func$;

CREATE FUNCTION


-- example
SELECT quote_nullable_typed('2020-01-01'::date);


quote_nullable_typed


'2020-01-01'::date



SELECT 1


-- helper function II
CREATE OR REPLACE FUNCTION f_sql_string_with_params(_sql text, VARIADIC x text[])
  RETURNS text
  LANGUAGE sql PARALLEL SAFE IMMUTABLE AS
$func$
SELECT format(regexp_replace(replace(_sql, '%', '%%'), '(?<=[\s,])\$(\d+)(?=[\s,])', '%\1$s', 'g')
            , x[1],x[2],x[3],x[4],x[5],x[6],x[7],x[8],x[9],x[10])  -- allow more?
$func$;

CREATE FUNCTION


-- example
SELECT f_sql_string_with_params($q$SELECT $1, $2, $3, 'false $1', format('demo: %I', 'xX')$q$
                              , quote_nullable_typed(1)
                              , quote_nullable_typed('2020-01-01'::date)
                              , quote_nullable_typed(NULL::point)
                               );


f_sql_string_with_params


SELECT '1'::integer, '2020-01-01'::date, NULL::point, 'false $1', format('demo: %I', 'xX')



SELECT 1


-- applied to your example
CREATE OR REPLACE FUNCTION fn()
  RETURNS void
  LANGUAGE plpgsql AS
$func$
DECLARE
   _sql text := $q$SELECT $1, $2, $3, 'false $1', format('demo: %I', 'xX')$q$;  -- sql string, extended with potential hazards
   _v1  int  := 1;
   _v2  date := '2020-01-01';
   _v3  date;  -- defaults to NULL
BEGIN
   RAISE NOTICE E'Query string with $-parameters:\n%', _sql;

   RAISE NOTICE E'Query string with typed values:\n%'
              , f_sql_string_with_params(_sql
                                       , quote_nullable_typed(_v1)
                                       , quote_nullable_typed(_v2)
                                       , quote_nullable_typed(_v3)
                                        );
   
   EXECUTE _sql
   USING _v1, _v2, _v3;
END
$func$;

CREATE FUNCTION


SELECT fn();


fn






SELECT 1


-- show notices as output in dbfiddle
CREATE OR REPLACE FUNCTION fn1()
  RETURNS SETOF text
  LANGUAGE plpgsql AS
$func$
DECLARE
   _sql text := $q$SELECT $1, $2, $3, 'false $1', format('demo: %I', 'xX')$q$;  -- sql string, extended with potential hazards
   _v1  int  := 1;
   _v2  date := '2020-01-01';
   _v3  date;  -- defaults to NULL
BEGIN
   RETURN NEXT E'Query string with $-parameters:\n' || _sql;

   RETURN NEXT E'Query string with typed values:\n' || f_sql_string_with_params(_sql, quote_nullable_typed(_v1), quote_nullable_typed(_v2), quote_nullable_typed(_v3));

   EXECUTE _sql
   USING _v1, _v2, _v3;
END
$func$;

CREATE FUNCTION


SELECT * FROM fn1();


fn1


Query string with $-parameters:
SELECT $1, $2, $3, 'false $1', format('demo: %I', 'xX')

Query string with typed values:
SELECT '1'::integer, '2020-01-01'::date, NULL::date, 'false $1', format('demo: %I', 'xX')



SELECT 2