gnu: xapian: Fix notmuch test failure.

* gnu/packages/patches/xapian-revert-5489fb2f8.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/search.scm (xapian)[source](patches): Use it.

gnu/local.mk

@@ -1214,6 +1214,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/wpa-supplicant-krack-followups.patch	\
   %D%/packages/patches/wxmaxima-do-not-use-old-gnuplot-parameters.patch	\
   %D%/packages/patches/x265-fix-ppc64le-build.patch		\
+  %D%/packages/patches/xapian-revert-5489fb2f8.patch		\
   %D%/packages/patches/xboing-CVE-2004-0149.patch		\
   %D%/packages/patches/xdotool-fix-makefile.patch               \
   %D%/packages/patches/xf86-video-ark-remove-mibstore.patch	\

gnu/packages/patches/xapian-revert-5489fb2f8.patch

@@ -0,0 +1,23 @@
+Revert this upstream commit which breaks a test case in "notmuch":
+
+https://git.xapian.org/?p=xapian;a=commitdiff;h=5489fb2f838c0f0b0a593b4c17df282a93a1fe5a
+
+See the notmuch FAQ entry:
+
+https://notmuchmail.org/faq/#index12h2
+
+This should be fixed for later releases.
+
+diff --git a/backends/glass/glass_postlist.cc b/xapian-core/backends/glass/glass_postlist.cc
+index 80e578b85..a47f14a68 100644
+--- a/backends/glass/glass_postlist.cc
++++ b/backends/glass/glass_postlist.cc
+@@ -759,7 +759,7 @@ GlassPostList::open_nearby_postlist(const std::string & term_,
+     (void)need_pos;
+     if (term_.empty())
+ 	RETURN(NULL);
+-    if (!this_db.get() || this_db->postlist_table.is_modified())
++    if (!this_db.get() || this_db->postlist_table.is_writable())
+ 	RETURN(NULL);
+     RETURN(new GlassPostList(this_db, term_, cursor->clone()));
+ }

gnu/packages/search.scm

@@ -52,6 +52,7 @@
               (method url-fetch)
               (uri (string-append "https://oligarchy.co.uk/xapian/" version
                                   "/xapian-core-" version ".tar.xz"))
+              (patches (search-patches "xapian-revert-5489fb2f8.patch"))
               (sha256
                (base32 "166qpfq7pvyrj2w2x07v31ypvqg6c2xyvds5sms9h4g2sg0z23hy"))))
     (build-system gnu-build-system)