Fixes "exception-escape" false positive with generators (#3128) (#3182)

As reported on #3128, there is a bug when the handler bound object is being used inside a generator causing a false positive. This was due to the way we were identifying if the object was "inside" its handler or not. In the previous implementation we would visit the node parents until we reached the object scope (in the generator case, the scope of the node is the generator, not the handler), while this change continues to go up the parent stack until it reaches its parent handler, or, if it's not inside its handler, it reaches the module's parent (None).

Object is considered inside its handler if it reaches it by going up in the parent chain. It's considered outside its handler if it reaches None.

Signed-off-by: Gabriel R Sezefredo <g@briel.dev>

CONTRIBUTORS.txt

@@ -334,4 +334,8 @@ contributors:
 
 * Rémi Cardona: contributor
 
+* Gabriel R. Sezefredo: contributor
+    - Fixed "exception-escape" false positive with generators
+
 * laike9m: contributor
+

ChangeLog

@@ -11,9 +11,14 @@ Release date: TBA
 
   Close #617
 
+* Fix exception-escape false positive with generators
+
+  Close #3128
+
 * ``inspect.getargvalues`` is no longer marked as deprecated.
 
 
+
 What's New in Pylint 2.4.3?
 ===========================
 

pylint/checkers/python3.py

@@ -1265,16 +1265,11 @@ def visit_attribute(self, node):
     def visit_excepthandler(self, node):
         """Visit an except handler block and check for exception unpacking."""
 
-        def _is_used_in_except_block(node):
-            scope = node.scope()
+        def _is_used_in_except_block(node, block):
             current = node
-            while (
-                current
-                and current != scope
-                and not isinstance(current, astroid.ExceptHandler)
-            ):
+            while current and current is not block:
                 current = current.parent
-            return isinstance(current, astroid.ExceptHandler) and current.type != node
+            return current is not None
 
         if isinstance(node.name, (astroid.Tuple, astroid.List)):
             self.add_message("unpacking-in-except", node=node)
@@ -1292,7 +1287,7 @@ def _is_used_in_except_block(node):
             for scope_name in scope_names
             if scope_name.name == node.name.name
             and scope_name.lineno > node.lineno
-            and not _is_used_in_except_block(scope_name)
+            and not _is_used_in_except_block(scope_name, node)
         ]
         reassignments_for_same_name = {
             assign_name.lineno

tests/unittest_checker_python3.py

@@ -857,6 +857,11 @@ def test_exception_escape(self):
            2/0
         except (ValueError, TypeError): #@
            exc = 2
+        exc #@
+        try:
+           1/0
+        except (ValueError, TypeError) as exc:
+           foo(bar for bar in exc.bar)
         """
         )
         message = testutils.Message("exception-escape", node=module.body[1].value)
@@ -865,6 +870,7 @@ def test_exception_escape(self):
         with self.assertNoMessages():
             self.checker.visit_excepthandler(module.body[2].handlers[0])
             self.checker.visit_excepthandler(module.body[4].handlers[0])
+            self.checker.visit_excepthandler(module.body[6].handlers[0])
 
     def test_bad_sys_attribute(self):
         node = astroid.extract_node(