From 46fc584b00f2ccee5b77d8fc525881def8670a02 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon-Martin=20Schr=C3=B6der?=
 <martin.schroeder@nerdluecht.de>
Date: Mon, 11 Jul 2022 11:14:15 +0200
Subject: [PATCH] gh-87822: Make traceback module robust to exceptions from
 repr() of local values (GH-94691)

---
 Doc/library/traceback.rst                                 | 4 ++++
 Lib/test/test_traceback.py                                | 8 ++++++--
 Lib/traceback.py                                          | 3 ++-
 Misc/ACKS                                                 | 1 +
 .../Library/2022-07-08-17-49-12.gh-issue-87822.F9dzkf.rst | 1 +
 5 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2022-07-08-17-49-12.gh-issue-87822.F9dzkf.rst

diff --git a/Doc/library/traceback.rst b/Doc/library/traceback.rst
index a8412cc93d1..8cb6af9bc84 100644
--- a/Doc/library/traceback.rst
+++ b/Doc/library/traceback.rst
@@ -341,6 +341,10 @@ capture data for later printing in a lightweight fashion.
       local variables in each :class:`FrameSummary` are captured as object
       representations.
 
+      .. versionchanged:: 3.12
+         Exceptions raised from :func:`repr` on a local variable (when
+         *capture_locals* is ``True``) are no longer propagated to the caller.
+
    .. classmethod:: from_list(a_list)
 
       Construct a :class:`StackSummary` object from a supplied list of
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index f4161fbf017..602bd2cae0a 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -2279,6 +2279,9 @@ class TestStack(unittest.TestCase):
             f'  File "{__file__}", line {lno}, in f\n    1/0\n'
         )
 
+class Unrepresentable:
+    def __repr__(self) -> str:
+        raise Exception("Unrepresentable")
 
 class TestTracebackException(unittest.TestCase):
 
@@ -2546,12 +2549,13 @@ class TestTracebackException(unittest.TestCase):
         linecache.updatecache('/foo.py', globals())
         e = Exception("uh oh")
         c = test_code('/foo.py', 'method')
-        f = test_frame(c, globals(), {'something': 1, 'other': 'string'})
+        f = test_frame(c, globals(), {'something': 1, 'other': 'string', 'unrepresentable': Unrepresentable()})
         tb = test_tb(f, 6, None, 0)
         exc = traceback.TracebackException(
             Exception, e, tb, capture_locals=True)
         self.assertEqual(
-            exc.stack[0].locals, {'something': '1', 'other': "'string'"})
+            exc.stack[0].locals,
+            {'something': '1', 'other': "'string'", 'unrepresentable': '<local repr() failed>'})
 
     def test_no_locals(self):
         linecache.updatecache('/foo.py', globals())
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 55f80800440..b1a5fd0a26d 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -279,7 +279,8 @@ class FrameSummary:
         self._line = line
         if lookup_line:
             self.line
-        self.locals = {k: repr(v) for k, v in locals.items()} if locals else None
+        self.locals = {k: _safe_string(v, 'local', func=repr)
+            for k, v in locals.items()} if locals else None
         self.end_lineno = end_lineno
         self.colno = colno
         self.end_colno = end_colno
diff --git a/Misc/ACKS b/Misc/ACKS
index b6340414cf7..32475f874c3 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1590,6 +1590,7 @@ Ed Schouten
 Scott Schram
 Robin Schreiber
 Chad J. Schroeder
+Simon-Martin Schroeder
 Christian Schubert
 Sam Schulenburg
 Andreas Schwab
diff --git a/Misc/NEWS.d/next/Library/2022-07-08-17-49-12.gh-issue-87822.F9dzkf.rst b/Misc/NEWS.d/next/Library/2022-07-08-17-49-12.gh-issue-87822.F9dzkf.rst
new file mode 100644
index 00000000000..7b27f5df45b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-07-08-17-49-12.gh-issue-87822.F9dzkf.rst
@@ -0,0 +1 @@
+When called with ``capture_locals=True``, the :mod:`traceback` module functions swallow exceptions raised from calls to ``repr()`` on local variables of frames. This is in order to prioritize the original exception over rendering errors.  An indication of the failure is printed in place of the missing value.  (Patch by Simon-Martin Schroeder).