Fix "Allow use of Gnus search groups as notmuch path: search term"

* lisp/gnus/nnir.el (nnir-notmuch-filter-group-names-function):
  Default to nil -- getting correct behavior requires user
  intervention too often to have this enabled by default.
* lisp/gnus/nnir.el (nnir-run-notmuch): If the user has turned this
  on, then also hardcode `gnus-group-short-name' as a filter -- things
  will never work without it. Also move leading space to before the
  opening parenthesis.
* doc/misc/gnus.texi: Document option.

(Bug#33122)

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/misc/gnus.texi b/doc/misc/gnus.texi
index fb9113f4608..d1c746c2e56 100644
--- a/doc/misc/gnus.texi
+++ b/doc/misc/gnus.texi
@@ -21468,6 +21468,18 @@ The prefix to remove from each file name returned by notmuch in order
 to get a group name (albeit with @samp{/} instead of @samp{.}).  This
 is a regular expression.
 
+@item nnir-notmuch-filter-group-names-function
+A function used to transform the names of groups being searched in,
+for use as a ``path:'' search keyword for notmuch.  If nil, the
+default, ``path:'' keywords are not used.  Otherwise, this should be a
+callable which accepts a single group name and returns a transformed
+name as notmuch expects to see it.  In many mail backends, for
+instance, dots in group names must be converted to forward slashes: to
+achieve this, set this option to
+@example
+(lambda (g) (replace-regexp-in-string "\\." "/" g))
+@end example
+
 @end table