problem with notmuch search in recent emacs snapshots

[Eric S Fraga <e.fraga@ucl.ac.uk>]

Hello,

recently, I upgraded my emacs to the latest snapshot (20181111) on
Debian.  Since then, search in gnus does not work.  It always fails.  An
example of the messages that are generated follows:

--8<---------------cut here---------------start------------->8---
Doing notmuch query XXX on mail.misc mail.gemini mail.t3610 mail.pinto...
notmuch args: search --format=text --output=files XXX( path:mail.misc or path:mail.gemini or path:mail.t3610 or path:mail.pinto)
Massaging notmuch output...done
Search produced empty results.
gnus-select-newsgroup: Couldn’t request group nnir:nnir-87lg5rindf.fsf: Search produced empty results.
--8<---------------cut here---------------end--------------->8---

With the exact same gnus and notmuch configuration, everything is fine
with emacs snapshots from a couple of months ago; one of my systems is
running snapshot 20180909.  There is one obvious difference: the notmuch
arguments, for the same search, at the same topic, looks like this:

notmuch args: search --format=text --output=files XXX

I.e. no paths are specified.

I wonder whether the problem is the strange lack of a space between XXX
(my search term) and the opening "(" for the list of paths to check?
Even if only a single group is checked, the latest versions of gnus
append an explicit path.

If I turn nnir-notmuch-filter-group-names-function to nil, I get the old
behaviour back so I can still search but the default does not appear to
work.

Adding a space before "(" on line 1547 of nnir.el might fix this?
Untested.

thanks,
eric
-- 
Eric S Fraga via Emacs 27.0.50 & org 9.1.14 on Debian buster/sid