Fix pylint-dev#4045: Don't assume try ancestors are immediate parents when emitting used-before-assignment

Author: jacobtylerwalls

ChangeLog

@@ -16,6 +16,12 @@ Release date: TBA
 
   Closes #85, #2615
 
+* Fixed false negative for ``used-before-assignment`` when a conditional
+  or context manager intervened before the try statement that suggested
+  it might fail.
+
+  Closes #4045
+
 * Fixed extremely long processing of long lines with comma's.
 
   Closes #5483

doc/whatsnew/2.13.rst

@@ -63,6 +63,12 @@ Other Changes
 
   Closes #85, #2615
 
+* Fixed false negative for ``used-before-assignment`` when a conditional
+  or context manager intervened before the try statement that suggested
+  it might fail.
+
+  Closes #4045
+
 * Fix a false positive for ``assigning-non-slot`` when the slotted class
   defined ``__setattr__``.
 

pylint/checkers/variables.py

@@ -747,7 +747,9 @@ def _uncertain_nodes_in_try_blocks_when_evaluating_except_blocks(
             )
             if other_node_try_ancestor is None:
                 continue
-            if other_node_statement not in other_node_try_ancestor.body:
+            if isinstance(other_node_statement, nodes.ExceptHandler):
+                continue
+            if isinstance(other_node_statement.parent, nodes.ExceptHandler):
                 continue
             if node_statement.parent not in other_node_try_ancestor.handlers:
                 continue

tests/functional/u/use/used_before_assignment_issue2615.py

@@ -4,6 +4,10 @@ def main():
     try:
         res = 1 / 0
         res = 42
+        if main():
+            res = None
+        with open(__file__, encoding="utf-8") as opened_file:
+            res = opened_file.readlines()
     except ZeroDivisionError:
         print(res)  # [used-before-assignment]
     print(res)

tests/functional/u/use/used_before_assignment_issue2615.txt

@@ -1 +1 @@
-used-before-assignment:8:14:8:17:main:Using variable 'res' before assignment:UNDEFINED
+used-before-assignment:12:14:12:17:main:Using variable 'res' before assignment:UNDEFINED