Fix #6887: Sphinx crashes with docutils-0.16b0

7 files changed, 16 insertions, 16 deletions

diff --git a/.travis.yml b/.travis.yml
index b145ceb8a..008f4e442 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -25,7 +25,8 @@ matrix:
         - TOXENV=du15
         - PYTEST_ADDOPTS="--cov ./ --cov-append --cov-config setup.cfg"
     - python: 'nightly'
-      env: TOXENV=py38
+      env:
+        - TOXENV=du16
     - python: '3.6'
       env: TOXENV=docs
     - python: '3.6'
diff --git a/CHANGES b/CHANGES
index 3692108a3..65b8e47c4 100644
--- a/CHANGES
+++ b/CHANGES
@@ -84,6 +84,7 @@ Bugs fixed
 * #6886: LaTeX: xelatex converts straight double quotes into right curly ones
   (shows when :confval:`smartquotes` is ``False``)
 * #6876: LaTeX: multi-line display of authors on title page has ragged edges
+* #6887: Sphinx crashes with docutils-0.16b0
 
 Testing
 --------
diff --git a/sphinx/builders/latex/__init__.py b/sphinx/builders/latex/__init__.py
index c24e87a13..6a0d70e5e 100644
--- a/sphinx/builders/latex/__init__.py
+++ b/sphinx/builders/latex/__init__.py
@@ -234,14 +234,13 @@ class LaTeXBuilder(Builder):
             destination = SphinxFileOutput(destination_path=path.join(self.outdir, targetname),
                                            encoding='utf-8', overwrite_if_changed=True)
             with progress_message(__("processing %s") % targetname):
-                toctrees = self.env.get_doctree(docname).traverse(addnodes.toctree)
-                if toctrees:
-                    if toctrees[0].get('maxdepth') > 0:
-                        tocdepth = toctrees[0].get('maxdepth')
-                    else:
-                        tocdepth = None
+                doctree = self.env.get_doctree(docname)
+                toctree = next(iter(doctree.traverse(addnodes.toctree)), None)
+                if toctree and toctree.get('maxdepth') > 0:
+                    tocdepth = toctree.get('maxdepth')
                 else:
                     tocdepth = None
+
                 doctree = self.assemble_doctree(
                     docname, toctree_only,
                     appendices=((docclass != 'howto') and self.config.latex_appendices or []))
diff --git a/sphinx/domains/std.py b/sphinx/domains/std.py
index 98dda4918..705cf175c 100644
--- a/sphinx/domains/std.py
+++ b/sphinx/domains/std.py
@@ -612,15 +612,13 @@ class StandardDomain(Domain):
                 sectname = self.get_numfig_title(node)
                 if not sectname:
                     continue
-            elif node.traverse(addnodes.toctree):
-                n = node.traverse(addnodes.toctree)[0]
-                if n.get('caption'):
-                    sectname = n['caption']
+            else:
+                toctree = next(iter(node.traverse(addnodes.toctree)), None)
+                if toctree and toctree.get('caption'):
+                    sectname = toctree.get('caption')
                 else:
+                    # anonymous-only labels
                     continue
-            else:
-                # anonymous-only labels
-                continue
             self.labels[name] = docname, labelid, sectname
 
     def add_object(self, objtype: str, name: str, docname: str, labelid: str) -> None:
diff --git a/sphinx/util/nodes.py b/sphinx/util/nodes.py
index 52e43c2e2..53b4d056e 100644
--- a/sphinx/util/nodes.py
+++ b/sphinx/util/nodes.py
@@ -148,7 +148,7 @@ def apply_source_workaround(node: Element) -> None:
         logger.debug('[i18n] PATCH: %r to have rawsource: %s',
                      get_full_module_name(node), repr_domxml(node))
         # strip classifier from rawsource of term
-        for classifier in reversed(node.parent.traverse(nodes.classifier)):
+        for classifier in reversed(list(node.parent.traverse(nodes.classifier))):
             node.rawsource = re.sub(r'\s*:\s*%s' % re.escape(classifier.astext()),
                                     '', node.rawsource)
 
diff --git a/tests/test_directive_code.py b/tests/test_directive_code.py
index ecf5423c2..5d93449f1 100644
--- a/tests/test_directive_code.py
+++ b/tests/test_directive_code.py
@@ -573,7 +573,7 @@ def test_literalinclude_pydecorators(app, status, warning):
 def test_code_block_highlighted(app, status, warning):
     app.builder.build(['highlight'])
     doctree = app.env.get_doctree('highlight')
-    codeblocks = doctree.traverse(nodes.literal_block)
+    codeblocks = list(doctree.traverse(nodes.literal_block))
 
     assert codeblocks[0]['language'] == 'default'
     assert codeblocks[1]['language'] == 'python2'
diff --git a/tox.ini b/tox.ini
index c4ffe33cb..5bc2dec58 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,6 +14,7 @@ deps =
     du13: docutils==0.13.1
     du14: docutils==0.14
     du15: docutils==0.15
+    du16: docutils==0.16b0.dev0
 extras =
     test
 setenv =