This provides functionality analogous to query: in the Xapian
QueryParser based parser. Perhaps counterintuitively, the saved
queries currently have to be in the original query syntax (i.e. not
s-expressions).
One subtle aspect is the replacement of _find_prefix with
_notmuch_database_prefix, which understands user headers. Otherwise
the code mainly consists of creating a fake prefix record (since the
user prefixes are not in the prefix table) and error handling.
This is necessary so that programs can take infix syntax queries from
a user and use the sexp query syntax to construct e.g. a refinement of
that query.
At least to the degree that the Xapian QueryParser based parser
also supports them. Support short alias 'rx' as it seems to make more
complex queries nicer to read.
The many tests potentially overkill, but they could catch typos in the
prefixes table. As a simplifying assumption, for now we assume a
single argument to the wildcard operator, as this matches the Xapian
semantics. The name 'starts-with' is chosen to emphasize the supported
case of wildcards in currrent (1.4.x) Xapian.
We use "boolean" to describe fields that should generate terms
literally without stemming or phrase splitting. This terminology
might not be ideal but it is already enshrined in
notmuch-search-terms(7).
Anything that is quoted or not purely word characters is considered a
phrase. Phrases are not stemmed, because the stems do not have
positional information in the database. It is less efficient to scan
the term twice, but it avoids a second pass to add prefixes, so maybe
it balances out. In any case, it seems unlikely query parsing is very
often a bottleneck.
All operations and (Xapian) fields will eventually have an entry in
the prefixes table. The flags field is just a placeholder for now, but
will eventually distinguish between various kinds of prefixes.
There is not much of a parser here yet, but it already does some
useful error reporting. Most functionality sketched in the
documentation is not implemented yet; detailed documentation will
follow with the implementation.
