Function coerce_function_result_tuple

src/pl/plpgsql/src/pl_exec.c:794–897

* Helper for plpgsql_exec_function: coerce composite result to the specified * tuple descriptor, and copy it out to upper executor memory. This is split * out mostly for cosmetic reasons --- the logic would be very deeply nested * otherwise. * * estate->retval is updated in-place. */

 * estate->retval is updated in-place.
 */
static void
coerce_function_result_tuple(PLpgSQL_execstate *estate, TupleDesc tupdesc)
{
	HeapTuple	rettup;
	TupleDesc	retdesc;
	TupleConversionMap *tupmap;

	/* We assume exec_stmt_return verified that result is composite */
	Assert(type_is_rowtype(estate->rettype));

	/* We can special-case expanded records for speed */
	if (VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(estate->retval)))
	{
		ExpandedRecordHeader *erh = (ExpandedRecordHeader *) DatumGetEOHP(estate->retval);

		Assert(erh->er_magic == ER_MAGIC);

		/* Extract record's TupleDesc */
		retdesc = expanded_record_get_tupdesc(erh);

		/* check rowtype compatibility */
		tupmap = convert_tuples_by_position(retdesc,
											tupdesc,
											gettext_noop("returned record type does not match expected record type"));

		/* it might need conversion */
		if (tupmap)
		{
			rettup = expanded_record_get_tuple(erh);
			Assert(rettup);
			rettup = execute_attr_map_tuple(rettup, tupmap);

			/*
			 * Copy tuple to upper executor memory, as a tuple Datum.  Make
			 * sure it is labeled with the caller-supplied tuple type.
			 */
			estate->retval = PointerGetDatum(SPI_returntuple(rettup, tupdesc));
			/* no need to free map, we're about to return anyway */
		}
		else if (!(tupdesc->tdtypeid == erh->er_decltypeid ||
				   (tupdesc->tdtypeid == RECORDOID &&
					!ExpandedRecordIsDomain(erh))))
		{
			/*
			 * The expanded record has the right physical tupdesc, but the
			 * wrong type ID.  (Typically, the expanded record is RECORDOID
			 * but the function is declared to return a named composite type.
			 * As in exec_move_row_from_datum, we don't allow returning a
			 * composite-domain record from a function declared to return
			 * RECORD.)  So we must flatten the record to a tuple datum and
			 * overwrite its type fields with the right thing.  spi.c doesn't
			 * provide any easy way to deal with this case, so we end up
			 * duplicating the guts of datumCopy() :-(
			 */
			Size		resultsize;
			HeapTupleHeader tuphdr;

			resultsize = EOH_get_flat_size(&erh->hdr);