Add support for singledispatchmethod class methods in MethodDocumenter

sphinx/ext/autodoc/__init__.py

@@ -2168,7 +2168,8 @@ def add_directive_header(self, sig: str) -> None:
             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)
@@ -2200,6 +2201,8 @@ def format_signature(self, **kwargs: Any) -> str:
                 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 +1,38 @@
+import sys
+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 int."""
+        pass
+
+    @class_meth.register(str)
+    @classmethod
+    def _class_meth_str(cls, arg, kwarg=None):
+        """A class method for str."""
+        pass
+
+    if sys.version_info[:2] >= (3, 9):
+        # registration of a singledispatch'ed classmethod via
+        # type annotation is not supported prior to Python 3.9
+        #
+        # See: https://github.com/python/cpython/issues/83860
+
+        @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_ext_autodoc.py

@@ -2084,6 +2084,102 @@ 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)
+
+    if sys.version_info[:2] >= (3, 9):
+        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.',
+            '',
+        ]
+    else:
+        # Registration of a dispatcher via annotation is not supported
+        # prior to Python 3.9 and the docstring of a singledispatch'ed
+        # classmethod is (as of Sphinx 6.1.3) not extracted properly.
+        import textwrap
+
+        assert list(actual) == [
+            '',
+            '.. py:module:: target.singledispatchmethod_classmethod',
+            '',
+            '',
+            '.. py:class:: Foo()',
+            '   :module: target.singledispatchmethod_classmethod',
+            '',
+            '   docstring',
+            '',
+            '',
+            '   .. py:method:: Foo.class_meth',
+            '                  Foo.class_meth(arg: float, kwarg=None)',
+            '                  Foo.class_meth(arg: int, kwarg=None)',
+            '                  Foo.class_meth(arg: str, kwarg=None)',
+            '      :module: target.singledispatchmethod_classmethod',
+            '      :classmethod:',
+            '',
+            *textwrap.indent(classmethod.__doc__, ' ' * 6).splitlines(),
+            '',
+        ]
+
+
+@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)
+
+    if sys.version_info[:2] >= (3, 9):
+        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.',
+            '',
+        ]
+    else:
+        # Registration of a dispatcher via annotation is not supported
+        # prior to Python 3.9 and the docstring of a singledispatch'ed
+        # classmethod is (as of Sphinx 6.1.3) not extracted properly.
+        import textwrap
+
+        assert list(actual) == [
+            '',
+            '.. py:method:: Foo.class_meth',
+            '               Foo.class_meth(arg: float, kwarg=None)',
+            '               Foo.class_meth(arg: int, kwarg=None)',
+            '               Foo.class_meth(arg: str, kwarg=None)',
+            '   :module: target.singledispatchmethod_classmethod',
+            '   :classmethod:',
+            '',
+            *textwrap.indent(classmethod.__doc__, ' ' * 3).splitlines(),
+            '',
+        ]
+
+
 @pytest.mark.skipif(sys.version_info[:2] >= (3, 11),
                     reason=('cython does not support python-3.11 yet. '
                             'see https://github.com/cython/cython/issues/4365'))