Fix #4969: autodoc: constructor method should not have return annotation

CHANGES

@@ -27,6 +27,7 @@ Bugs fixed
   (escaped) line breaks are present.
 * C++, properly use ``desc_addname`` nodes for prefixes of names.
 * #4915, #4916: links on search page are broken when using dirhtml builder
+* #4969: autodoc: constructor method should not have return annotation
 
 Testing
 --------

sphinx/ext/autodoc/__init__.py

@@ -1035,9 +1035,11 @@ class FunctionDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # typ
             # typing) we try to use the constructor signature as function
             # signature without the first argument.
             try:
-                args = Signature(self.object.__new__, bound_method=True).format_args()
+                sig = Signature(self.object.__new__, bound_method=True, has_retval=False)
+                args = sig.format_args()
             except TypeError:
-                args = Signature(self.object.__init__, bound_method=True).format_args()
+                sig = Signature(self.object.__init__, bound_method=True, has_retval=False)
+                args = sig.format_args()
 
         # escape backslashes for reST
         args = args.replace('\\', '\\\\')
@@ -1090,7 +1092,7 @@ class ClassDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # type:
                 not(inspect.ismethod(initmeth) or inspect.isfunction(initmeth)):
             return None
         try:
-            return Signature(initmeth, bound_method=True).format_args()
+            return Signature(initmeth, bound_method=True, has_retval=False).format_args()
         except TypeError:
             # still not possible: happens e.g. for old-style classes
             # with __init__ in C

sphinx/util/inspect.py

@@ -298,8 +298,8 @@ class Signature(object):
     its return annotation.
     """
 
-    def __init__(self, subject, bound_method=False):
-        # type: (Callable, bool) -> None
+    def __init__(self, subject, bound_method=False, has_retval=True):
+        # type: (Callable, bool, bool) -> None
         # check subject is not a built-in class (ex. int, str)
         if (isinstance(subject, type) and
                 is_builtin_class_method(subject, "__new__") and
@@ -307,6 +307,7 @@ class Signature(object):
             raise TypeError("can't compute signature for built-in type {}".format(subject))
 
         self.subject = subject
+        self.has_retval = has_retval
         self.partialmethod_with_noargs = False
 
         if PY3:
@@ -375,7 +376,10 @@ class Signature(object):
     def return_annotation(self):
         # type: () -> Any
         if PY3 and self.signature:
-            return self.signature.return_annotation
+            if self.has_retval:
+                return self.signature.return_annotation
+            else:
+                return inspect.Parameter.empty
         else:
             return None
 

tests/test_util_inspect.py

@@ -280,6 +280,10 @@ def test_Signature_annotations():
     sig = inspect.Signature(f11).format_args()
     assert sig == '(x: CustomAnnotation, y: 123) -> None'
 
+    # has_retval=False
+    sig = inspect.Signature(f11, has_retval=False).format_args()
+    assert sig == '(x: CustomAnnotation, y: 123)'
+
 
 def test_safe_getattr_with_default():
     class Foo(object):