Re: BUG #7808: unnest doesn't handle nulls in array of composite typescorrectly

Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> writes:
> I did think about that, but the existing code seems to go out of its way
> to build the tuplestore using the tupdesc obtained from the actual
> function result row, rather than the "expected" tupdesc, and it wasn't
> really obvious why that was.

As I noted in a comment, the key hazard would be that heap_form_tuple
copies the tupdesc's type identifier info into the created composite
Datum, thus possibly leading to a mixture of type IDs in the stored
tuples. But tuplestore stores MinimalTuples which omit that data,
so it doesn't matter. I have a feeling that the existing code here
might've been older than the changes to store MinimalTuples rather
than regular tuple datums in tuplestores; or at least, it was written
with the assumption that that was important.

regards, tom lane