Function ExecComputeSlotInfo

src/backend/executor/execExpr.c:2768–2860

* Compute additional information for EEOP_*_FETCHSOME ops. * * The goal is to determine whether a slot is 'fixed', that is, every * evaluation of the expression will have the same type of slot, with an * equivalent descriptor. * * Returns true if the deforming step is required, false otherwise. */

 * Returns true if the deforming step is required, false otherwise.
 */
static bool
ExecComputeSlotInfo(ExprState *state, ExprEvalStep *op)
{
	PlanState  *parent = state->parent;
	TupleDesc	desc = NULL;
	const TupleTableSlotOps *tts_ops = NULL;
	bool		isfixed = false;
	ExprEvalOp	opcode = op->opcode;

	Assert(opcode == EEOP_INNER_FETCHSOME ||
		   opcode == EEOP_OUTER_FETCHSOME ||
		   opcode == EEOP_SCAN_FETCHSOME);

	if (op->d.fetch.known_desc != NULL)
	{
		desc = op->d.fetch.known_desc;
		tts_ops = op->d.fetch.kind;
		isfixed = op->d.fetch.kind != NULL;
	}
	else if (!parent)
	{
		isfixed = false;
	}
	else if (opcode == EEOP_INNER_FETCHSOME)
	{
		PlanState  *is = innerPlanState(parent);

		if (parent->inneropsset && !parent->inneropsfixed)
		{
			isfixed = false;
		}
		else if (parent->inneropsset && parent->innerops)
		{
			isfixed = true;
			tts_ops = parent->innerops;
			desc = ExecGetResultType(is);
		}
		else if (is)
		{
			tts_ops = ExecGetResultSlotOps(is, &isfixed);
			desc = ExecGetResultType(is);
		}
	}
	else if (opcode == EEOP_OUTER_FETCHSOME)
	{
		PlanState  *os = outerPlanState(parent);

		if (parent->outeropsset && !parent->outeropsfixed)
		{
			isfixed = false;
		}
		else if (parent->outeropsset && parent->outerops)
		{
			isfixed = true;
			tts_ops = parent->outerops;
			desc = ExecGetResultType(os);
		}
		else if (os)