autodoc: Support Positional-Only Argument separator (PEP-570 compliant)

tests/test_util_inspect.py

@@ -294,6 +294,21 @@ def test_signature_annotations():
     sig = inspect.signature(f7)
     assert stringify_signature(sig, show_return_annotation=False) == '(x: int = None, y: dict = {})'
 
+
+@pytest.mark.skipif(sys.version_info < (3, 8), reason='python 3.8+ is required.')
+@pytest.mark.sphinx(testroot='ext-autodoc')
+def test_signature_annotations_py38(app):
+    from target.pep570 import foo, bar
+
+    # case: separator in the middle
+    sig = inspect.signature(foo)
+    assert stringify_signature(sig) == '(a, b, /, c, d)'
+
+    # case: separator at tail
+    sig = inspect.signature(bar)
+    assert stringify_signature(sig) == '(a, b, /)'
+
+
 def test_safe_getattr_with_default():
     class Foo:
         def __getattr__(self, item):