[PATCH] doc: add support for adding configure options as Sphinx tags

[Jani Nikula <jani@nikula.org>]

Add the configure options specified in $(TAGS) that equal 1 as tags on
the Sphinx command line using the -t option. The tags may be used to
conditionally include documentation using the Sphinx "only" directive
[1].

As an example, indicate in the documentation whether the Xapian field
processor is likely to be available (assuming the notmuch binary was
built in the same environment as the documentation).

[1] http://www.sphinx-doc.org/en/stable/markup/misc.html#including-content-based-on-tags

---

This is something I wrote two years ago, ISTR David asking about
something like this on IRC, but I've already forgotten what it was
about...
---
 doc/Makefile.local                | 7 ++++++-
 doc/man7/notmuch-search-terms.rst | 8 ++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/doc/Makefile.local b/doc/Makefile.local
index bab3d0d286ce..95df9ae82b4f 100644
--- a/doc/Makefile.local
+++ b/doc/Makefile.local
@@ -7,8 +7,13 @@ SPHINXOPTS    := -q
 SPHINXBUILD   = sphinx-build
 DOCBUILDDIR      := $(dir)/_build
 
+# Configure options to be added as Sphinx tags.
+# Add "-t <tag>" for each make variable in TAGS that equals 1.
+TAGS := HAVE_XAPIAN_FIELD_PROCESSOR HAVE_XAPIAN_COMPACT
+TAGOPTS := $(patsubst %=1,-t %,$(filter %=1,$(foreach tag,$(TAGS),$(tag)=$(value $(tag)))))
+
 # Internal variables.
-ALLSPHINXOPTS   := -d $(DOCBUILDDIR)/doctrees $(SPHINXOPTS) $(srcdir)/$(dir)
+ALLSPHINXOPTS   := -d $(DOCBUILDDIR)/doctrees $(SPHINXOPTS) $(TAGOPTS) $(srcdir)/$(dir)
 APIMAN		:= $(DOCBUILDDIR)/man/man3/notmuch.3
 DOXYFILE	:= $(srcdir)/$(dir)/doxygen.cfg
 
diff --git a/doc/man7/notmuch-search-terms.rst b/doc/man7/notmuch-search-terms.rst
index f7a39ceb9df4..4840f03743aa 100644
--- a/doc/man7/notmuch-search-terms.rst
+++ b/doc/man7/notmuch-search-terms.rst
@@ -451,6 +451,14 @@ notmuch was built against a sufficiently recent version of Xapian by running
 
   % notmuch config get built_with.field_processor
 
+.. only:: HAVE_XAPIAN_FIELD_PROCESSOR
+
+   The documentation was built on a host with field processor support.
+
+.. only:: not HAVE_XAPIAN_FIELD_PROCESSOR
+
+   The documentation was built on a host without field processor support.
+
 Currently the following features require field processor support:
 
 - non-range date queries, e.g. "date:today"
-- 
2.20.1