Fix #3080: texinfo: multiline rubric is broken

tests/roots/test-markup-rubric/conf.py

@@ -0,0 +1,7 @@
+# -*- coding: utf-8 -*-
+
+master_doc = 'index'
+
+latex_documents = [
+    (master_doc, 'test.tex', 'The basic Sphinx documentation for testing', 'Sphinx', 'report')
+]

tests/roots/test-markup-rubric/index.rst

@@ -0,0 +1,7 @@
+test-markup-rubric
+===================
+
+.. rubric:: This is a rubric
+
+.. rubric:: This is
+   a multiline rubric

tests/test_build_texinfo.py

@@ -72,3 +72,12 @@ def test_texinfo(app, status, warning):
                 assert False, 'makeinfo exited with return code %s' % retcode
     finally:
         os.chdir(cwd)
+
+
+@pytest.mark.sphinx('texinfo', testroot='markup-rubric')
+def test_texinfo_rubric(app, status, warning):
+    app.build()
+
+    output = (app.outdir / 'python.texi').text()
+    assert '@heading This is a rubric' in output
+    assert '@heading This is a multiline rubric' in output