PosgreSQL function error handler that displays comments

function-template.sql

CREATE OR REPLACE FUNCTION dummy_function( col_pk int, col_b my_domain, col_fk text)
AS
$BODY$
declare
  v_msg text;
  v_constraint text;
BEGIN

  INSERT INTO some_table VALUES($1,$2,$3);
  RETURN TRUE;
  
EXCEPTION
   -- this will rewrite the message to be the comment on the constraint and return the original error code
  WHEN check_violation OR unique_violation OR foreign_key_violation THEN
    GET STACKED DIAGNOSTICS v_constraint := CONSTRAINT_NAME;

    SELECT COALESCE(description,SQLERRM) into v_msg
      FROM pg_constraint as c
      JOIN pg_namespace as n ON n.oid = c.connamespace
      LEFT join pg_description as cmt on cmt.objoid = c.oid
      WHERE
        contype IN ('f','p','c','u') AND
        conname = v_constraint;
    RAISE USING ERRCODE = SQLSTATE, MESSAGE=v_msg;
    RETURN FALSE;

END;
$BODY$
LANGUAGE plpgsql;

some_table.sql

drop table if exists some_parent;
drop table if exists some_table;

create table some_parent (
    id int not null primary key
);

create table some_table (
    id serial,
    user_data varchar(200) not null,
    some_fk int,
    
    constraint pk_foo primary key (id),
    constraint fk_bar foreign key (some_fk) references some_parent(id),
    constraint ck_short check (length(user_data) < 2)
);

-- add comments
comment on constraint  pk_foo on some_table is 'Primary key cannot have duplicates.';
comment on constraint  fk_bar on some_table is 'prime numbers are the only ones worth keeping';
comment on constraint  ck_short on some_table is 'for `some business reason` we are only allowing two chars now but might want 200 soon.';

--- add data
insert into some_parent (id)
values (3),(5),(7),(11),(13);

test.psql

\i some_table.sql
\i function-template.sql

-- initialize 
execute dummy_function(1,'aa',3);

-- examples
execute dummy_function(2,'aaa',3);
/*
    Violates the business rule `ck_short` and so displays the 
    message: 
        for `some business reason` we are only allowing two chars now but might want 200 soon.
    instead of the normal check constraint error

*/ 

execute dummy_function(2,'aa',4);
execute dummy_function(1,'aa',3);