Reproduce error in PG that "should not happen" https://github.com/postgres/postgres/blob/6fa391be4e83139cd134d5ccfc1499809bb8c98c/src/backend/commands/trigger.c#L4027-L4029

reproduce.sql

begin;
  create table a(foo varchar not null primary key);
  create table b(foo varchar not null primary key, constraint qux foreign key (foo) references a deferrable initially deferred);
  create function bar() returns trigger as $$
  begin
    if TG_OP = 'INSERT' then
      insert into b(foo) values(new.foo);
    elsif TG_OP = 'DELETE' then
      delete from b where foo = old.foo;
    end if;
    return new;
  end;
  $$ language plpgsql;

  create trigger bar after insert or delete on a for each row execute procedure bar();
commit;

insert into a values('baz');

begin;
  delete from a where foo = 'baz';
  drop trigger bar on a;
  drop function bar();
  alter table b drop constraint qux;
commit;

$ dropdb pg_test; createdb pg_test && psql -v ON_ERROR_STOP=1 pg_test < testcase.sql
SET
Time: 0.227 ms
BEGIN
Time: 0.064 ms
CREATE TABLE
Time: 4.057 ms
CREATE TABLE
Time: 3.511 ms
CREATE FUNCTION
Time: 2.160 ms
CREATE TRIGGER
Time: 0.342 ms
COMMIT
Time: 3.321 ms
INSERT 0 1
Time: 1.941 ms
BEGIN
Time: 0.077 ms
DELETE 1
Time: 0.929 ms
DROP TRIGGER
Time: 0.584 ms
DROP FUNCTION
Time: 0.173 ms
ALTER TABLE
Time: 0.508 ms
ERROR:  XX000: relation 5022917 has no triggers
LOCATION:  afterTriggerInvokeEvents, trigger.c:3828
Time: 0.178 ms