Fix #7331: autodoc: a cython-function is not recognized as a function

CHANGES

@@ -132,6 +132,7 @@ Bugs fixed
 * #7267: autodoc: error message for invalid directive options has wrong location
 * #7329: autodoc: info-field-list is wrongly generated from type hints into the
   class description even if ``autoclass_content='class'`` set
+* #7331: autodoc: a cython-function is not recognized as a function
 * #5637: inheritance_diagram: Incorrect handling of nested class names
 * #7139: ``code-block:: guess`` does not work
 * #7325: html: source_suffix containing dot leads to wrong source link

setup.py

@@ -52,6 +52,7 @@ extras_require = {
         'pytest-cov',
         'html5lib',
         'typed_ast',  # for py35-37
+        'cython',
     ],
 }
 

sphinx/ext/autodoc/__init__.py

@@ -1011,7 +1011,8 @@ class FunctionDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # typ
         if self.env.config.autodoc_typehints in ('none', 'description'):
             kwargs.setdefault('show_annotation', False)
 
-        if inspect.isbuiltin(self.object) or inspect.ismethoddescriptor(self.object):
+        if ((inspect.isbuiltin(self.object) or inspect.ismethoddescriptor(self.object)) and
+                not inspect.is_cython_function_or_method(self.object)):
             # cannot introspect arguments of a C function or method
             return None
         try:

tests/roots/test-ext-autodoc/target/cython.pyx

@@ -0,0 +1,4 @@
+# cython: binding=True
+
+def foo(*args, **kwargs):
+    """Docstring."""

tests/test_autodoc.py

@@ -22,6 +22,13 @@ from sphinx.testing.util import SphinxTestApp, Struct  # NOQA
 from sphinx.util import logging
 from sphinx.util.docutils import LoggingReporter
 
+try:
+    # Enable pyximport to test cython module
+    import pyximport
+    pyximport.install()
+except ImportError:
+    pyximport = None
+
 app = None
 
 
@@ -1609,3 +1616,22 @@ def test_singledispatchmethod():
         '      A method for general use.',
         '',
     ]
+
+
+@pytest.mark.usefixtures('setup_test')
+@pytest.mark.skipif(pyximport is None, reason='cython is not installed')
+def test_cython():
+    options = {"members": None,
+               "undoc-members": None}
+    actual = do_autodoc(app, 'module', 'target.cython', options)
+    assert list(actual) == [
+        '',
+        '.. py:module:: target.cython',
+        '',
+        '',
+        '.. py:function:: foo(*args, **kwargs)',
+        '   :module: target.cython',
+        '',
+        '   Docstring.',
+        '',
+    ]