Add regular expression support to streaming search

Introduces an explicit regex query term node (which wraps an
RE2 regex instance internally) and extends the existing
UTF-8 flexible string searcher to use this query node.

Regex matching is optionally case (in)sensitive depending
on the normalization mode used.

Note on `searcher/searcher_test.cpp`: this adds a magic
sentinel `#` char prefix to query term parsing in the test
to let a query term be interpreted as a regex rather than
exact/prefix/suffix/substring match.

1 files changed, 6 insertions, 0 deletions

diff --git a/searchlib/src/vespa/searchlib/query/streaming/queryterm.cpp b/searchlib/src/vespa/searchlib/query/streaming/queryterm.cpp
index 3950a179d67..3e05d381ee2 100644
--- a/searchlib/src/vespa/searchlib/query/streaming/queryterm.cpp
+++ b/searchlib/src/vespa/searchlib/query/streaming/queryterm.cpp
@@ -179,4 +179,10 @@ QueryTerm::as_multi_term() noexcept
     return nullptr;
 }
 
+RegexpTerm*
+QueryTerm::as_regexp_term() noexcept
+{
+    return nullptr;
+}
+
 }