Function make_op

src/backend/parser/parse_oper.c:671–776

* make_op() * Operator expression construction. * * Transform operator expression ensuring type compatibility. * This is where some type conversion happens. * * last_srf should be a copy of pstate->p_last_srf from just before we * started transforming the operator's arguments; this is used for nested-SRF * detection. If the caller will throw an error anyway for a set-returning * express

 * expression, it's okay to cheat and just pass pstate->p_last_srf.
 */
Expr *
make_op(ParseState *pstate, List *opname, Node *ltree, Node *rtree,
		Node *last_srf, int location)
{
	Oid			ltypeId,
				rtypeId;
	Operator	tup;
	Form_pg_operator opform;
	Oid			actual_arg_types[2];
	Oid			declared_arg_types[2];
	int			nargs;
	List	   *args;
	Oid			rettype;
	OpExpr	   *result;

	/* Check it's not a postfix operator */
	if (rtree == NULL)
		ereport(ERROR,
				(errcode(ERRCODE_SYNTAX_ERROR),
				 errmsg("postfix operators are not supported")));

	/* Select the operator */
	if (ltree == NULL)
	{
		/* prefix operator */
		rtypeId = exprType(rtree);
		ltypeId = InvalidOid;
		tup = left_oper(pstate, opname, rtypeId, false, location);
	}
	else
	{
		/* otherwise, binary operator */
		ltypeId = exprType(ltree);
		rtypeId = exprType(rtree);
		tup = oper(pstate, opname, ltypeId, rtypeId, false, location);
	}

	opform = (Form_pg_operator) GETSTRUCT(tup);

	/* Check it's not a shell */
	if (!RegProcedureIsValid(opform->oprcode))
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_FUNCTION),
				 errmsg("operator is only a shell: %s",
						op_signature_string(opname,
											opform->oprkind,
											opform->oprleft,
											opform->oprright)),
				 parser_errposition(pstate, location)));

	/* Do typecasting and build the expression tree */
	if (ltree == NULL)
	{
		/* prefix operator */
		args = list_make1(rtree);
		actual_arg_types[0] = rtypeId;
		declared_arg_types[0] = opform->oprright;
		nargs = 1;