Fix #8105: autodoc: the signature of decorated class is incorrect

In #7651, autodoc stops to undecorate the functions on getting the
signature from the callables.  But some kinds of decorators conceals
the correct signature because they pass through their arguments via
`(*args, **kwargs)`.

This restarts to undecorate the functions again as before #7651.

CHANGES

@@ -7,9 +7,14 @@ Dependencies
 Incompatible changes
 --------------------
 
+* #8105: autodoc: the signature of class constructor will be shown for decorated
+  classes, not a signature of decorator
+
 Deprecated
 ----------
 
+* The ``follow_wrapped`` argument of ``sphinx.util.inspect.signature()``
+
 Features added
 --------------
 
@@ -21,6 +26,8 @@ Bugs fixed
 ----------
 
 * #7613: autodoc: autodoc does not respect __signature__ of the class
+* #8105: autodoc: the signature of class constructor is incorrect if the class
+  is decorated
 
 Testing
 --------

doc/extdev/deprecated.rst

@@ -26,6 +26,12 @@ The following is a list of deprecated interfaces.
      - (will be) Removed
      - Alternatives
 
+
+   * - The ``follow_wrapped`` argument of ``sphinx.util.inspect.signature()``
+     - 3.4
+     - 5.0
+     - N/A
+
    * - ``sphinx.builders.latex.LaTeXBuilder.usepackages``
      - 3.3
      - 5.0

sphinx/ext/autodoc/__init__.py

@@ -1213,7 +1213,7 @@ class FunctionDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # typ
 
         try:
             self.env.app.emit('autodoc-before-process-signature', self.object, False)
-            sig = inspect.signature(self.object, follow_wrapped=True,
+            sig = inspect.signature(self.object,
                                     type_aliases=self.env.config.autodoc_type_aliases)
             args = stringify_signature(sig, **kwargs)
         except TypeError as exc:
@@ -1853,7 +1853,6 @@ class MethodDocumenter(DocstringSignatureMixin, ClassLevelDocumenter):  # type:
                 else:
                     self.env.app.emit('autodoc-before-process-signature', self.object, True)
                     sig = inspect.signature(self.object, bound_method=True,
-                                            follow_wrapped=True,
                                             type_aliases=self.env.config.autodoc_type_aliases)
                 args = stringify_signature(sig, **kwargs)
         except TypeError as exc:

sphinx/util/inspect.py

@@ -439,14 +439,20 @@ def _should_unwrap(subject: Callable) -> bool:
     return False
 
 
-def signature(subject: Callable, bound_method: bool = False, follow_wrapped: bool = False,
+def signature(subject: Callable, bound_method: bool = False, follow_wrapped: bool = None,
               type_aliases: Dict = {}) -> inspect.Signature:
     """Return a Signature object for the given *subject*.
 
     :param bound_method: Specify *subject* is a bound method or not
     :param follow_wrapped: Same as ``inspect.signature()``.
-                           Defaults to ``False`` (get a signature of *subject*).
     """
+
+    if follow_wrapped is None:
+        follow_wrapped = True
+    else:
+        warnings.warn('The follow_wrapped argument of sphinx.util.inspect.signature() is '
+                      'deprecated', RemovedInSphinx50Warning, stacklevel=2)
+
     try:
         try:
             if _should_unwrap(subject):

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

@@ -29,3 +29,25 @@ class Bar:
     @deco1
     def meth(self, name=None, age=None):
         pass
+
+
+class Baz:
+    @deco1
+    def __init__(self, name=None, age=None):
+        pass
+
+
+class Qux:
+    @deco1
+    def __new__(self, name=None, age=None):
+        pass
+
+
+class _Metaclass(type):
+    @deco1
+    def __call__(self, name=None, age=None):
+        pass
+
+
+class Quux(metaclass=_Metaclass):
+    pass

tests/test_ext_autodoc_autoclass.py

@@ -48,3 +48,28 @@ def test_classes(app):
         '',
     ]
 
+
+def test_decorators(app):
+    actual = do_autodoc(app, 'class', 'target.decorator.Baz')
+    assert list(actual) == [
+        '',
+        '.. py:class:: Baz(name=None, age=None)',
+        '   :module: target.decorator',
+        '',
+    ]
+
+    actual = do_autodoc(app, 'class', 'target.decorator.Qux')
+    assert list(actual) == [
+        '',
+        '.. py:class:: Qux(name=None, age=None)',
+        '   :module: target.decorator',
+        '',
+    ]
+
+    actual = do_autodoc(app, 'class', 'target.decorator.Quux')
+    assert list(actual) == [
+        '',
+        '.. py:class:: Quux(name=None, age=None)',
+        '   :module: target.decorator',
+        '',
+    ]

tests/test_util_inspect.py

@@ -100,7 +100,7 @@ def test_signature_methods():
 
     # wrapped bound method
     sig = inspect.signature(wrapped_bound_method)
-    assert stringify_signature(sig) == '(*args, **kwargs)'
+    assert stringify_signature(sig) == '(arg1, **kwargs)'
 
 
 def test_signature_partialmethod():