Wire fuzzy prefix matching support through the query stack

Adds `prefix:[true|false]` annotation support to the `fuzzy`
query operator in the YQL and JSON query languages. Fuzzy
prefix matching semantics are wired through to the matcher
implementations for both indexed and streaming search.

Example usage:

  {maxEditDistance:1,prefix:true}fuzzy("foo")

Will match `foo`, `foobar`, `foxtrot`, `zookeeper` and so on.

It can be combined with the existing prefix locking feature:

  {maxEditDistance:1,prefixLength:2,prefix:true}fuzzy("foo")

Which will match `foo`, `foobar`, `foxtrot` etc, but _not_
`zookeeper` since the locked prefix (`fo`) does not match.

Due to the complexities involved with extending the legacy binary
query stack representation, signalling prefix matching for the
fuzzy term is done by pragmatically adding a new, generic "prefix
matching" term-level flag. This is currently ignored for
everything except fuzzy query items.

Modernizing the query stack format to make it more extensible
(i.e. move encoding to Protobuf) is on the backlog...!

1 files changed, 3 insertions, 2 deletions

diff --git a/searchlib/src/vespa/searchlib/query/streaming/queryterm.h b/searchlib/src/vespa/searchlib/query/streaming/queryterm.h
index 05b12804d52..0e0ab98295b 100644
--- a/searchlib/src/vespa/searchlib/query/streaming/queryterm.h
+++ b/searchlib/src/vespa/searchlib/query/streaming/queryterm.h
@@ -100,8 +100,9 @@ public:
     void visitMembers(vespalib::ObjectVisitor &visitor) const override;
     void setIndex(const string & index_) override { _index = index_; }
     const string & getIndex() const override { return _index; }
-    void setFuzzyMaxEditDistance(uint32_t fuzzyMaxEditDistance) { _fuzzyMaxEditDistance = fuzzyMaxEditDistance; }
-    void setFuzzyPrefixLength(uint32_t fuzzyPrefixLength) { _fuzzyPrefixLength = fuzzyPrefixLength; }
+    void set_fuzzy_max_edit_distance(uint32_t fuzzy_max_edit_distance) noexcept { _fuzzy_max_edit_distance = fuzzy_max_edit_distance; }
+    void set_fuzzy_prefix_lock_length(uint32_t fuzzy_prefix_length) noexcept { _fuzzy_prefix_lock_length = fuzzy_prefix_length; }
+    void set_fuzzy_prefix_match(bool prefix_match) noexcept { _fuzzy_prefix_match = prefix_match; }
     virtual NearestNeighborQueryNode* as_nearest_neighbor_query_node() noexcept;
     virtual MultiTerm* as_multi_term() noexcept;
     virtual const MultiTerm* as_multi_term() const noexcept;