#334 Optimization of nested FLWR with order by

[Michael Kay]

When a FLWOR expression with an order by clause is
nested inside another FLWR expression, the expression
defining the sort key may be incorrectly moved outside
the outer FLWR expression, because the optimizer fails
to detect that it is dependent on the range variable of
the inner FLWOR. This results in an attempt to evaluate
an uninitialized variable, which may trigger a number
of failures including a NullPointerException or an
AssertionError.

Source fix: chnage the promote() method (line 77) in
net.sf.saxon.sort.TupleSorter to read:

public Expression promote(PromotionOffer offer)

throws XPathException {
Expression exp = offer.accept(this);
if (exp != null) {
return exp;
} else {
base = base.promote(offer);
if (offer.action !=
PromotionOffer.RANGE_INDEPENDENT) {
for (int i=0; i<sortKeys.length; i++) {

sortKeys[i].setSortKey(sortKeys[i].getSortKey().promote(offer));
}
}
return this;
}
}