[autodoc] add support for singledispatchmethod class methods (#11284)

CHANGES.rst

@@ -93,6 +93,9 @@ Bugs fixed
 * #11474: Fix doctrees caching causing files not be rebuilt in some cases,
   e.g., when :confval:`numfig` is ``True``.
   Patch by Bénédikt Tran.
+* #11278: autodoc: Fix rendering of :class:`functools.singledispatchmethod`
+  combined with :func:`@classmethod <classmethod>`.
+  Patch by Bénédikt Tran.
 
 Testing
 -------

sphinx/ext/autodoc/__init__.py

@@ -2229,7 +2229,8 @@ class MethodDocumenter(DocstringSignatureMixin, ClassLevelDocumenter):  # type:
             self.add_line('   :abstractmethod:', sourcename)
         if inspect.iscoroutinefunction(obj) or inspect.isasyncgenfunction(obj):
             self.add_line('   :async:', sourcename)
-        if inspect.isclassmethod(obj):
+        if (inspect.isclassmethod(obj) or
+                inspect.is_singledispatch_method(obj) and inspect.isclassmethod(obj.func)):
             self.add_line('   :classmethod:', sourcename)
         if inspect.isstaticmethod(obj, cls=self.parent, name=self.object_name):
             self.add_line('   :staticmethod:', sourcename)
@@ -2261,6 +2262,8 @@ class MethodDocumenter(DocstringSignatureMixin, ClassLevelDocumenter):  # type:
                 if typ is object:
                     pass  # default implementation. skipped.
                 else:
+                    if inspect.isclassmethod(func):
+                        func = func.__func__
                     dispatchmeth = self.annotate_to_first_argument(func, typ)
                     if dispatchmeth:
                         documenter = MethodDocumenter(self.directive, '')

tests/roots/test-ext-autodoc/target/singledispatchmethod_classmethod.py

@@ -0,0 +1,31 @@
+from functools import singledispatchmethod
+
+
+class Foo:
+    """docstring"""
+
+    @singledispatchmethod
+    @classmethod
+    def class_meth(cls, arg, kwarg=None):
+        """A class method for general use."""
+        pass
+
+    @class_meth.register(int)
+    @class_meth.register(float)
+    @classmethod
+    def _class_meth_int(cls, arg, kwarg=None):
+        """A class method for numbers."""
+        pass
+
+    @class_meth.register(str)
+    @classmethod
+    def _class_meth_str(cls, arg, kwarg=None):
+        """A class method for str."""
+        pass
+
+    @class_meth.register
+    @classmethod
+    def _class_meth_dict(cls, arg: dict, kwarg=None):
+        """A class method for dict."""
+        # This function tests for specifying type through annotations
+        pass

tests/test_extensions/test_ext_autodoc.py

@@ -2111,6 +2111,55 @@ def test_singledispatchmethod_automethod(app):
     ]
 
 
+@pytest.mark.sphinx('html', testroot='ext-autodoc')
+def test_singledispatchmethod_classmethod(app):
+    options = {"members": None}
+    actual = do_autodoc(app, 'module', 'target.singledispatchmethod_classmethod', options)
+
+    assert list(actual) == [
+        '',
+        '.. py:module:: target.singledispatchmethod_classmethod',
+        '',
+        '',
+        '.. py:class:: Foo()',
+        '   :module: target.singledispatchmethod_classmethod',
+        '',
+        '   docstring',
+        '',
+        '',
+        '   .. py:method:: Foo.class_meth(arg, kwarg=None)',
+        '                  Foo.class_meth(arg: float, kwarg=None)',
+        '                  Foo.class_meth(arg: int, kwarg=None)',
+        '                  Foo.class_meth(arg: str, kwarg=None)',
+        '                  Foo.class_meth(arg: dict, kwarg=None)',
+        '      :module: target.singledispatchmethod_classmethod',
+        '      :classmethod:',
+        '',
+        '      A class method for general use.',
+        '',
+    ]
+
+
+@pytest.mark.sphinx('html', testroot='ext-autodoc')
+def test_singledispatchmethod_classmethod_automethod(app):
+    options = {}
+    actual = do_autodoc(app, 'method', 'target.singledispatchmethod_classmethod.Foo.class_meth', options)
+
+    assert list(actual) == [
+        '',
+        '.. py:method:: Foo.class_meth(arg, kwarg=None)',
+        '               Foo.class_meth(arg: float, kwarg=None)',
+        '               Foo.class_meth(arg: int, kwarg=None)',
+        '               Foo.class_meth(arg: str, kwarg=None)',
+        '               Foo.class_meth(arg: dict, kwarg=None)',
+        '   :module: target.singledispatchmethod_classmethod',
+        '   :classmethod:',
+        '',
+        '   A class method for general use.',
+        '',
+    ]
+
+
 @pytest.mark.skipif(sys.version_info[:2] >= (3, 13),
                     reason='Cython does not support Python 3.13 yet.')
 @pytest.mark.skipif(pyximport is None, reason='cython is not installed')