All-stopword queries with two or more terms should ignore stopword list

[richard]

Currently, if a single word query is parsed, and that word is a stopword, the stopwording is ignored. However, if a multiple word query is parsed, and all words are stopwords, the stopwording is applied (resulting in an empty query).

If all the words in the query are stopwords, I think it may make sense to ignore the stopwording. However, even if we decide to apply the stopwording in this case, we should be consistent in our behaviour.

Some examples, in python:

import xapian s=xapian.SimpleStopper?() s.add('foo') s.add('bar') qp=xapian.QueryParser?() qp.set_stopper(s) str(qp.parse_query('foo'))

'Xapian::Query(foo:(pos=1))'

str(qp.parse_query('foo foo'))

'Xapian::Query()'

str(qp.parse_query('foo bar'))

'Xapian::Query()'

Either the first parse_query() call should return Xapian::Query(), or the later ones should return non-empty queries.

[olly]

The bug is that all-stopword queries with two or more terms aren't handled specially - the single term case was easy to handle, while the multi-term case seemed trickier for some reason, and I only handled the easy one so far.

There's actually a FIXME comment about this in queryparser.lemony which probably shows where the fix should go:

// FIXME what if E && E->empty() (all terms are stopwords)?

[olly]

Simple approach to fixing this