Fix #7362: autodoc: does not render correct signatures for built-in functions

CHANGES

@@ -87,6 +87,7 @@ Bugs fixed
   autodoc_typehints='description' mode
 * #7551: autodoc: failed to import nested class
 * #7637: autodoc: system defined TypeVars are shown in Python 3.9
+* #7362: autodoc: does not render correct signatures for built-in functions
 * #7551: autosummary: a nested class is indexed as non-nested class
 * #7535: sphinx-autogen: crashes when custom template uses inheritance
 * #7536: sphinx-autogen: crashes when template uses i18n feature

sphinx/ext/autodoc/__init__.py

@@ -1052,10 +1052,6 @@ class FunctionDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # typ
             kwargs.setdefault('show_annotation', False)
 
         unwrapped = inspect.unwrap(self.object)
-        if ((inspect.isbuiltin(unwrapped) or inspect.ismethoddescriptor(unwrapped)) and
-                not inspect.is_cython_function_or_method(unwrapped)):
-            # cannot introspect arguments of a C function or method
-            return None
         try:
             self.env.app.emit('autodoc-before-process-signature', unwrapped, False)
             sig = inspect.signature(unwrapped)

tests/test_ext_autodoc.py

@@ -1190,6 +1190,32 @@ def test_autofunction_for_method(app):
     ]
 
 
+@pytest.mark.sphinx('html', testroot='ext-autodoc')
+def test_autofunction_for_builtin(app):
+    actual = do_autodoc(app, 'function', 'os.umask')
+    assert list(actual) == [
+        '',
+        '.. py:function:: umask(mask, /)',
+        '   :module: os',
+        '',
+        '   Set the current numeric umask and return the previous umask.',
+        '',
+    ]
+
+
+@pytest.mark.sphinx('html', testroot='ext-autodoc')
+def test_autofunction_for_methoddescriptor(app):
+    actual = do_autodoc(app, 'function', 'builtins.int.__add__')
+    assert list(actual) == [
+        '',
+        '.. py:function:: int.__add__(self, value, /)',
+        '   :module: builtins',
+        '',
+        '   Return self+value.',
+        '',
+    ]
+
+
 def test_abstractmethods(app):
     options = {"members": None,
                "undoc-members": None}