Fix 'NoneType' object is not iterable on Generics

setup.cfg

@@ -30,7 +30,9 @@ install_requires =
     typing >= 3.5; python_version == "3.4"
 
 [options.extras_require]
-test = pytest >= 3.1.0
+test =
+    pytest >= 3.1.0
+    typing_extensions >= 3.5
 
 [flake8]
 max-line-length = 99

sphinx_autodoc_typehints.py

@@ -5,6 +5,11 @@
 from sphinx.util import logging
 from sphinx.util.inspect import Signature
 
+try:
+    from typing_extensions import Protocol
+except ImportError:
+    Protocol = None
+
 try:
     from inspect import unwrap
 except ImportError:
@@ -47,7 +52,8 @@ def format_annotation(annotation):
         if inspect.isclass(getattr(annotation, '__origin__', None)):
             annotation_cls = annotation.__origin__
             try:
-                if Generic in annotation_cls.mro():
+                mro = annotation_cls.mro()
+                if Generic in mro or (Protocol and Protocol in mro):
                     module = annotation_cls.__module__
             except TypeError:
                 pass  # annotation_cls was either the "type" object or typing.Type
@@ -116,7 +122,8 @@ def format_annotation(annotation):
             annotation_cls = annotation.__origin__
 
         extra = ''
-        if Generic in annotation_cls.mro():
+        mro = annotation_cls.mro()
+        if Generic in mro or (Protocol and Protocol in mro):
             params = (getattr(annotation, '__parameters__', None) or
                       getattr(annotation, '__args__', None))
             if params:

tests/test_sphinx_autodoc_typehints.py

@@ -5,6 +5,8 @@
 from typing import (
     Any, AnyStr, Callable, Dict, Generic, Mapping, Optional, Pattern, Tuple, TypeVar, Union, Type)
 
+from typing_extensions import Protocol
+
 from sphinx_autodoc_typehints import format_annotation, process_docstring
 
 T = TypeVar('T')
@@ -25,6 +27,14 @@ class C(B[str]):
     pass
 
 
+class D(Protocol):
+    pass
+
+
+class E(Protocol[T]):
+    pass
+
+
 class Slotted:
     __slots__ = ()
 
@@ -76,7 +86,10 @@ class Slotted:
     (A,                             ':py:class:`~%s.A`' % __name__),
     (B,                             ':py:class:`~%s.B`\\[\\~T]' % __name__),
     (B[int],                        ':py:class:`~%s.B`\\[:py:class:`int`]' % __name__),
-    (C,                             ':py:class:`~%s.C`' % __name__)
+    (C,                             ':py:class:`~%s.C`' % __name__),
+    (D,                             ':py:class:`~%s.D`' % __name__),
+    (E,                             ':py:class:`~%s.E`\\[\\~T]' % __name__),
+    (E[int],                        ':py:class:`~%s.E`\\[:py:class:`int`]' % __name__)
 ])
 def test_format_annotation(annotation, expected_result):
     result = format_annotation(annotation)