bpo-35113: Fix inspect.getsource to return correct source for inner classes (#10307)

* Use ast module to find class definition

* Add NEWS entry

* Fix class with multiple children and move decorator code to the method

* Fix PR comments

1. Use node.decorator_list to select decorators
2. Remove unwanted variables in ClassVisitor
3. Simplify stack management as per review

* Add test for nested functions and async calls

* Fix pydoc test since comments are returned now correctly

* Set event loop policy as None to fix environment related change

* Refactor visit_AsyncFunctionDef and tests

* Refactor to use local variables and fix tests

* Add patch attribution

* Use self.addCleanup for asyncio

* Rename ClassVisitor to ClassFinder and fix asyncio cleanup

* Return first class inside conditional in case of multiple definitions. Remove decorator for class source.

* Add docstring to make the test correct

* Modify NEWS entry regarding decorators

* Return decorators too for bpo-15856

* Move ast and the class source code to top. Use proper Exception.

Lib/inspect.py

@@ -32,6 +32,7 @@ __author__ = ('Ka-Ping Yee <ping@lfw.org>',
               'Yury Selivanov <yselivanov@sprymix.com>')
 
 import abc
+import ast
 import dis
 import collections.abc
 import enum
@@ -770,6 +771,42 @@ def getmodule(object, _filename=None):
         if builtinobject is object:
             return builtin
 
+
+class ClassFoundException(Exception):
+    pass
+
+
+class _ClassFinder(ast.NodeVisitor):
+
+    def __init__(self, qualname):
+        self.stack = []
+        self.qualname = qualname
+
+    def visit_FunctionDef(self, node):
+        self.stack.append(node.name)
+        self.stack.append('<locals>')
+        self.generic_visit(node)
+        self.stack.pop()
+        self.stack.pop()
+
+    visit_AsyncFunctionDef = visit_FunctionDef
+
+    def visit_ClassDef(self, node):
+        self.stack.append(node.name)
+        if self.qualname == '.'.join(self.stack):
+            # Return the decorator for the class if present
+            if node.decorator_list:
+                line_number = node.decorator_list[0].lineno
+            else:
+                line_number = node.lineno
+
+            # decrement by one since lines starts with indexing by zero
+            line_number -= 1
+            raise ClassFoundException(line_number)
+        self.generic_visit(node)
+        self.stack.pop()
+
+
 def findsource(object):
     """Return the entire source file and starting line number for an object.
 
@@ -802,25 +839,15 @@ def findsource(object):
         return lines, 0
 
     if isclass(object):
-        name = object.__name__
-        pat = re.compile(r'^(\s*)class\s*' + name + r'\b')
-        # make some effort to find the best matching class definition:
-        # use the one with the least indentation, which is the one
-        # that's most probably not inside a function definition.
-        candidates = []
-        for i in range(len(lines)):
-            match = pat.match(lines[i])
-            if match:
-                # if it's at toplevel, it's already the best one
-                if lines[i][0] == 'c':
-                    return lines, i
-                # else add whitespace to candidate list
-                candidates.append((match.group(1), i))
-        if candidates:
-            # this will sort by whitespace, and by line number,
-            # less whitespace first
-            candidates.sort()
-            return lines, candidates[0][1]
+        qualname = object.__qualname__
+        source = ''.join(lines)
+        tree = ast.parse(source)
+        class_finder = _ClassFinder(qualname)
+        try:
+            class_finder.visit(tree)
+        except ClassFoundException as e:
+            line_number = e.args[0]
+            return lines, line_number
         else:
             raise OSError('could not find class definition')