autodoc: make full reference for classes, aliased with "alias of"

We do this here only if class belongs to the different module.

Closes sphinx-doc/sphinx#2437

tests/roots/test-ext-autodoc/autodoc_dummy_bar.py

@@ -0,0 +1,5 @@
+from bug2437.autodoc_dummy_foo import Foo
+
+class Bar(object):
+    """Dummy class Bar with alias."""
+    my_name = Foo

tests/roots/test-ext-autodoc/bug2437/autodoc_dummy_foo.py

@@ -0,0 +1,3 @@
+class Foo(object):
+    """Dummy class Foo."""
+    pass

tests/roots/test-ext-autodoc/conf.py

@@ -10,3 +10,5 @@ source_suffix = '.rst'
 autodoc_mock_imports = [
     'dummy'
 ]
+
+nitpicky = True

tests/roots/test-ext-autodoc/contents.rst

@@ -1,3 +1,9 @@
 
 .. automodule:: autodoc_dummy_module
    :members:
+
+.. automodule:: bug2437.autodoc_dummy_foo
+   :members:
+
+.. automodule:: autodoc_dummy_bar
+   :members:

tests/test_ext_autodoc.py

@@ -22,3 +22,13 @@ def test_autodoc(app, status, warning):
     assert isinstance(content[3], addnodes.desc)
     assert content[3][0].astext() == 'autodoc_dummy_module.test'
     assert content[3][1].astext() == 'Dummy function using dummy.*'
+
+    # issue sphinx-doc/sphinx#2437
+    assert content[11][-1].astext() == """Dummy class Bar with alias.
+
+
+
+my_name
+
+alias of bug2437.autodoc_dummy_foo.Foo"""
+    assert warning.getvalue() == ''