notmuch @0.31 +emacs: variable rsti_dir is empty

[lafpark]

When building notmuch 0.31 +emacs the following error is reported

:info:build Configuration error:
8509 :info:build There is a programmable error in your configuration file:
8510 :info:build Traceback (most recent call last):
8511 :info:build   File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sphinx/config.py", line 319, in eval_config_file
8512 :info:build     execfile_(filename, namespace)
8513 :info:build   File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sphinx/util/pycompat.py", line 89, in execfile_
8514 :info:build     exec(code, _globals)
8515 :info:build   File "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_mail_notmuch/notmuch/work/notmuch-0.31/doc/conf.py", line 49, in <modu
8516 :info:build     lines.extend(open(rsti_dir+'/'+file))
8517 :info:build FileNotFoundError: [Errno 2] No such file or directory: '/notmuch.rsti'

The error occurs in the file /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_mail_notmuch/notmuch/work/notmuch-0.31/doc/conf.py at line 49.

49         lines.extend(open(rsti_dir+'/'+file)) 

The variable rsti_dir at build time contains an empty string. The variable contents is read from the file

/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_mail_notmuch/notmuch/work/notmuch-0.31/sphinx.config

which contains:

  1 # Generated by configure, run from doc/conf.py
  2 tags.add('WITH_EMACS')
  3 tags.add('WITH_PYTHON')
  4 rsti_dir = ''

showing the problem (the empty string). The above file is generated using

/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_mail_notmuch/notmuch/work/notmuch-0.31/configure

which contains the line

1539     printf "rsti_dir = '%s'\n" $(realpath emacs)

showing that $(realpath emacs) is returning the empty string.