Function plpgsql_param_fetch

src/pl/plpgsql/src/pl_exec.c:6243–6365

* plpgsql_param_fetch paramFetch callback for dynamic parameter fetch * * We always use the caller's workspace to construct the returned struct. * * Note: this is no longer used during query execution. It is used during * planning (with speculative == true) and when the ParamListInfo we supply * to the executor is copied into a cursor portal or transferred to a * parallel child process.

 * parallel child process.
 */
static ParamExternData *
plpgsql_param_fetch(ParamListInfo params,
					int paramid, bool speculative,
					ParamExternData *prm)
{
	int			dno;
	PLpgSQL_execstate *estate;
	PLpgSQL_expr *expr;
	PLpgSQL_datum *datum;
	bool		ok = true;
	int32		prmtypmod;

	/* paramid's are 1-based, but dnos are 0-based */
	dno = paramid - 1;
	Assert(dno >= 0 && dno < params->numParams);

	/* fetch back the hook data */
	estate = (PLpgSQL_execstate *) params->paramFetchArg;
	expr = (PLpgSQL_expr *) params->parserSetupArg;
	Assert(params->numParams == estate->ndatums);

	/* now we can access the target datum */
	datum = estate->datums[dno];

	/*
	 * Since copyParamList() or SerializeParamList() will try to materialize
	 * every single parameter slot, it's important to return a dummy param
	 * when asked for a datum that's not supposed to be used by this SQL
	 * expression.  Otherwise we risk failures in exec_eval_datum(), or
	 * copying a lot more data than necessary.
	 */
	if (!bms_is_member(dno, expr->paramnos))
		ok = false;

	/*
	 * If the access is speculative, we prefer to return no data rather than
	 * to fail in exec_eval_datum().  Check the likely failure cases.
	 */
	else if (speculative)
	{
		switch (datum->dtype)
		{
			case PLPGSQL_DTYPE_VAR:
			case PLPGSQL_DTYPE_PROMISE:
				/* always safe */
				break;

			case PLPGSQL_DTYPE_ROW:
				/* should be safe in all interesting cases */
				break;

			case PLPGSQL_DTYPE_REC:
				/* always safe (might return NULL, that's fine) */
				break;

			case PLPGSQL_DTYPE_RECFIELD:
				{
					PLpgSQL_recfield *recfield = (PLpgSQL_recfield *) datum;