[3.12] gh-123142: Fix too wide source locations in tracebacks of exceptions from broken iterables in comprehensions (GH-123173). (#123210)

(cherry picked from commit ec89620e5e)

Lib/test/test_listcomps.py

@@ -1,8 +1,11 @@
 import doctest
 import textwrap
+import traceback
 import types
 import unittest
 
+from test.support import BrokenIter
+
 
 doctests = """
 ########### Tests borrowed from or inspired by test_genexps.py ############
@@ -706,6 +709,35 @@ class ListComprehensionTest(unittest.TestCase):
         self._check_in_scopes(code, {"x": 2, "y": [3]}, ns={"x": 3}, scopes=["class"])
         self._check_in_scopes(code, {"x": 2, "y": [2]}, ns={"x": 3}, scopes=["function", "module"])
 
+    def test_exception_locations(self):
+        # The location of an exception raised from __init__ or
+        # __next__ should should be the iterator expression
+
+        def init_raises():
+            try:
+                [x for x in BrokenIter(init_raises=True)]
+            except Exception as e:
+                return e
+
+        def next_raises():
+            try:
+                [x for x in BrokenIter(next_raises=True)]
+            except Exception as e:
+                return e
+
+        for func, expected in [(init_raises, "BrokenIter(init_raises=True)"),
+                               (next_raises, "BrokenIter(next_raises=True)"),
+                              ]:
+            with self.subTest(func):
+                exc = func()
+                f = traceback.extract_tb(exc.__traceback__)[0]
+                indent = 16
+                co = func.__code__
+                self.assertEqual(f.lineno, co.co_firstlineno + 2)
+                self.assertEqual(f.end_lineno, co.co_firstlineno + 2)
+                self.assertEqual(f.line[f.colno - indent : f.end_colno - indent],
+                                 expected)
+
 __test__ = {'doctests' : doctests}
 
 def load_tests(loader, tests, pattern):