@Override
public final Expr compile(final QueryContext qc, final VarScope scp) throws QueryException {
if (root != null) root = root.compile(qc, scp);
// no steps
if (steps.length == 0) return root == null ? new Context(info) : root;
final Value init = qc.value, cv = initial(qc);
final boolean doc = cv != null && cv.type == NodeType.DOC;
qc.value = cv;
try {
final int sl = steps.length;
for (int s = 0; s < sl; s++) {
Expr e = steps[s];
// axis step: if input is a document, its type is temporarily generalized
final boolean as = e instanceof Step;
if (as && s == 0 && doc) cv.type = NodeType.NOD;
e = e.compile(qc, scp);
if (e.isEmpty()) return optPre(qc);
steps[s] = e;
// no axis step: invalidate context value
if (!as) qc.value = null;
}
} finally {
if (doc) cv.type = NodeType.DOC;
qc.value = init;
}
// optimize path
return optimize(qc, scp);
}
@Override
public Expr optimize(final QueryContext ctx, final VarScope scp) throws QueryException {
if (root instanceof Context) {
ctx.compInfo(OPTREMCTX);
root = null;
}
for (final Expr e : steps) {
// check for empty steps
if (e.isEmpty()) return optPre(null, ctx);
}
return this;
}
@Override
public final Expr optimize(final QueryContext ctx, final VarScope scp) throws QueryException {
// invalidate current context value (will be overwritten by filter)
final Value cv = ctx.value;
try {
// return empty root
if (root.isEmpty()) return optPre(null, ctx);
// convert filters without numeric predicates to axis paths
if (root instanceof AxisPath && !super.has(Flag.FCS))
return ((AxisPath) root.copy(ctx, scp)).addPreds(ctx, scp, preds);
// no predicates.. return root; otherwise, do some advanced compilations
return preds.length == 0 ? root : opt(ctx);
} finally {
ctx.value = cv;
}
}
/**
* Returns true if at least one argument is empty or will yield 0 results.
*
* @return result of check
*/
protected final boolean oneIsEmpty() {
for (final Expr e : exprs) if (e.isEmpty()) return true;
return false;
}