Do not serialize mappings with custom __repr__ as dict-s

Fixes #1296

sentry_sdk/serializer.py

@@ -288,7 +288,10 @@ def _serialize_node_impl(
                 else safe_repr(obj)
             )
 
-        elif isinstance(obj, Mapping):
+        elif isinstance(obj, Mapping) and type(obj).__repr__ in (
+            object.__repr__,
+            dict.__repr__,
+        ):
             # Create temporary copy here to avoid calling too much code that
             # might mutate our dictionary while we're still iterating over it.
             obj = dict(iteritems(obj))

tests/test_client.py

@@ -646,7 +646,8 @@ def test_chained_exceptions(sentry_init, capture_events):
 
 
 @pytest.mark.tests_internal_exceptions
-def test_broken_mapping(sentry_init, capture_events):
+@pytest.mark.parametrize("with_custom_repr", [False, True])
+def test_broken_mapping(sentry_init, capture_events, with_custom_repr):
     sentry_init()
     events = capture_events()
 
@@ -660,8 +661,10 @@ def broken(self, *args, **kwargs):
         __iter__ = broken
         __len__ = broken
 
-        def __repr__(self):
-            return "broken"
+        if with_custom_repr:
+
+            def __repr__(self):
+                return "still works"
 
     try:
         a = C()  # noqa
@@ -670,9 +673,13 @@ def __repr__(self):
         capture_exception()
 
     (event,) = events
+    if with_custom_repr:
+        valid_repr = "still works"
+    else:
+        valid_repr = "<failed to serialize, use init(debug=True) to see error logs>"
     assert (
         event["exception"]["values"][0]["stacktrace"]["frames"][0]["vars"]["a"]
-        == "<failed to serialize, use init(debug=True) to see error logs>"
+        == valid_repr
     )
 
 

tests/test_serializer.py

@@ -64,3 +64,12 @@ def test_bytes_serialization_repr(message_normalizer):
 def test_serialize_sets(extra_normalizer):
     result = extra_normalizer({1, 2, 3})
     assert result == [1, 2, 3]
+
+
+def test_serialize_custom_mapping(extra_normalizer):
+    class CustomReprDict(dict):
+        def __repr__(self):
+            return "custom!"
+
+    result = extra_normalizer(CustomReprDict(one=1, two=2))
+    assert result == "custom!"