Add parsing of nested classes

* Parse nested classes and present them in the class list
* Changes _pep224_docstrings to use Doc.source instead of inspect to keep it
  DRY

pdoc/__init__.py

@@ -225,8 +225,12 @@ def _pep224_docstrings(doc_obj: Union['Module', 'Class'], *,
     if _init_tree:
         tree = _init_tree
     else:
+        source = doc_obj.source
+        if source == "":
+            warn("Couldn't read PEP-224 variable docstrings from {!r}".format(doc_obj))
+            return {}, {}
         try:
-            tree = ast.parse(inspect.getsource(doc_obj.obj))
+            tree = ast.parse(source)
         except (OSError, TypeError, SyntaxError) as exc:
             warn("Couldn't read PEP-224 variable docstrings from {!r}: {}".format(doc_obj, exc))
             return {}, {}
@@ -786,6 +790,17 @@ def classes(self, sort=True):
         """
         return self._filter_doc_objs(Class, sort)
 
+    def all_classes(self, sort=True):
+        """Returns all documented classes in the module even the ones defined
+        in other classes."""
+        stack = self.classes(sort)[::-1]
+        results = []
+        while stack:
+            c = stack.pop()
+            results.append(c)
+            stack.extend(c.classes(sort=sort)[::-1])
+        return results
+
     def functions(self, sort=True):
         """
         Returns all documented module-level functions in the module,
@@ -813,9 +828,9 @@ class Class(Doc):
     """
     Representation of a class' documentation.
     """
-    __slots__ = ('doc', '_super_members')
+    __slots__ = ('doc', 'cls', '_super_members')
 
-    def __init__(self, name, module, obj, *, docstring=None):
+    def __init__(self, name, module, obj, *, docstring=None, cls=None):
         assert inspect.isclass(obj)
 
         if docstring is None:
@@ -826,6 +841,12 @@ def __init__(self, name, module, obj, *, docstring=None):
 
         super().__init__(name, module, obj, docstring=docstring)
 
+        self.cls = cls
+        """
+        The `pdoc.Class` object if this class is defined in a class. If not,
+        this is None.
+        """
+
         self.doc = {}
         """A mapping from identifier name to a `pdoc.Doc` objects."""
 
@@ -845,6 +866,14 @@ def __init__(self, name, module, obj, *, docstring=None):
                 self.doc[name] = Function(
                     name, self.module, obj, cls=self,
                     method=not self._method_type(self.obj, name))
+            elif inspect.isclass(obj):
+                self.doc[name] = Class(
+                    self.name + "." + name,
+                    self.module,
+                    obj,
+                    cls=self,
+                    docstring=inspect.getdoc(obj)
+                )
             else:
                 self.doc[name] = Variable(
                     name, self.module,
@@ -940,6 +969,14 @@ def _filter_doc_objs(self, type: Type[T], include_inherited=True,
                   if (include_inherited or not obj.inherits) and filter_func(obj)]
         return sorted(result) if sort else result
 
+    def classes(self, include_inherited=False, sort=False):
+        """Returns the classes defined in this class."""
+        return self._filter_doc_objs(
+            Class,
+            include_inherited=include_inherited,
+            sort=sort
+        )
+
     def class_variables(self, include_inherited=True, sort=True):
         """
         Returns an optionally-sorted list of `pdoc.Variable` objects that

pdoc/templates/html.mako

@@ -91,7 +91,7 @@
 <%def name="show_module(module)">
   <%
   variables = module.variables(sort=sort_identifiers)
-  classes = module.classes(sort=sort_identifiers)
+  classes = module.all_classes(sort=sort_identifiers)
   functions = module.functions(sort=sort_identifiers)
   submodules = module.submodules()
   %>
@@ -274,7 +274,7 @@
 <%def name="module_index(module)">
   <%
   variables = module.variables(sort=sort_identifiers)
-  classes = module.classes(sort=sort_identifiers)
+  classes = module.all_classes(sort=sort_identifiers)
   functions = module.functions(sort=sort_identifiers)
   submodules = module.submodules()
   supermodule = module.supermodule