Add utils/doclinter.py; a documenter linter for Sphinx

tox.ini

@@ -66,6 +66,15 @@ extras =
 commands =
     python setup.py build_sphinx {posargs}
 
+[testenv:docslint]
+basepython = python3
+description =
+    Lint documentation.
+extras =
+    docs
+commands =
+    python utils/doclinter.py CHANGES CONTRIBUTING.rst README.rst doc/
+
 [testenv:bindep]
 description =
     Install binary dependencies.

utils/doclinter.py

@@ -0,0 +1,59 @@
+"""
+    utils.doclinter
+    ~~~~~~~~~~~~~~~
+
+    A linter for Sphinx docs
+
+    :copyright: Copyright 2007-2019 by the Sphinx team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+
+import os
+import re
+import sys
+from typing import List
+
+
+MAX_LINE_LENGTH = 100
+
+
+def lint(path: str) -> int:
+    with open(path) as f:
+        document = f.readlines()
+
+    errors = 0
+    for i, line in enumerate(document):
+        if line.endswith(' '):
+            print('%s:%d: the line ends with whitespace.' %
+                  (path, i + 1))
+            errors += 1
+
+        if len(line) > MAX_LINE_LENGTH:
+            if re.match(r'^\s*\.\. ', line):
+                # ignore directives and hyperlink targets
+                pass
+            else:
+                print('%s:%d: the line is too long (%d > %d).' %
+                      (path, i + 1, len(line), MAX_LINE_LENGTH))
+                errors += 1
+
+    return errors
+
+
+def main(args: List[str]) -> int:
+    errors = 0
+    for directory in args:
+        for root, dirs, files in os.walk(directory):
+            for filename in files:
+                if filename.endswith('.rst'):
+                    path = os.path.join(root, filename)
+                    errors += lint(path)
+
+    if errors:
+        return 1
+    else:
+        return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv[1:]))