Fix #9866: autodoc: doccoment for the imported class was ignored

Autodoc tried to scan doccomment on the module where the class defined.
But it failed to get it if the class is imported from other module.

This analyzes the target module to obtain the doccomment.

CHANGES

@@ -19,6 +19,7 @@ Features added
 Bugs fixed
 ----------
 
+* #9866: autodoc: doccoment for the imported class was ignored
 * #9857: Generated RFC links use outdated base url
 
 Testing

sphinx/ext/autodoc/__init__.py

@@ -1743,14 +1743,22 @@ def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
     def get_variable_comment(self) -> Optional[List[str]]:
         try:
             key = ('', '.'.join(self.objpath))
-            analyzer = ModuleAnalyzer.for_module(self.get_real_modname())
+            if self.doc_as_attr:
+                analyzer = ModuleAnalyzer.for_module(self.modname)
+            else:
+                analyzer = ModuleAnalyzer.for_module(self.get_real_modname())
             analyzer.analyze()
-            return list(self.analyzer.attr_docs.get(key, []))
+            return list(analyzer.attr_docs.get(key, []))
         except PycodeError:
             return None
 
     def add_content(self, more_content: Optional[StringList], no_docstring: bool = False
                     ) -> None:
+        if self.doc_as_attr and self.modname != self.get_real_modname():
+            # override analyzer to obtain doccomment around its definition.
+            self.analyzer = ModuleAnalyzer.for_module(self.modname)
+            self.analyzer.analyze()
+
         if self.doc_as_attr and not self.get_variable_comment():
             try:
                 more_content = StringList([_('alias of %s') % restify(self.object)], source='')

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

@@ -37,3 +37,6 @@ class Corge(Quux):
 
 #: docstring
 OtherAlias = Bar
+
+#: docstring
+IntAlias = int

tests/test_ext_autodoc_autoclass.py

@@ -407,6 +407,18 @@ def test_class_alias_having_doccomment(app):
     ]
 
 
+def test_class_alias_for_imported_object_having_doccomment(app):
+    actual = do_autodoc(app, 'class', 'target.classes.IntAlias')
+    assert list(actual) == [
+        '',
+        '.. py:attribute:: IntAlias',
+        '   :module: target.classes',
+        '',
+        '   docstring',
+        '',
+    ]
+
+
 @pytest.mark.sphinx('html', testroot='ext-autodoc')
 def test_coroutine(app):
     options = {"members": None}