alter table add x wrong error position

hi.
Maybe this is a small printout err_position bug.

create table atacc2 ( test int, a int, b int) ;
success tests:
alter table atacc2 add CONSTRAINT x PRIMARY KEY (id, b );
alter table atacc2 add CONSTRAINT x PRIMARY KEY (id, b a);
alter table atacc2 add CONSTRAINT x PRIMARY KEYa (id, b);

tests have problem:
alter table atacc2 add constraints x unique (test, a, b);
ERROR: syntax error at or near "("
LINE 1: alter table atacc2 add constraints x unique (test, a, b);

^
ADD either following with the optional keyword "COLUMN" or
"CONSTRAINT" as the doc.
so I should expect the '^' point at "constraints"?