Handle cyclic references in exceptions (#1284)

Author: alexmojaki

logfire/_internal/utils.py

@@ -435,7 +435,7 @@ def platform_is_emscripten() -> bool:
     return platform.system().lower() == 'emscripten'
 
 
-def canonicalize_exception_traceback(exc: BaseException) -> str:
+def canonicalize_exception_traceback(exc: BaseException, seen: set[int] | None = None) -> str:
     """Return a canonical string representation of an exception traceback.
 
     Exceptions with the same representation are considered the same for fingerprinting purposes.
@@ -459,23 +459,28 @@ def canonicalize_exception_traceback(exc: BaseException) -> str:
                 if frame_summary not in visited:  # ignore repeated frames
                     visited.add(frame_summary)
                     parts.append(frame_summary)
-        if isinstance(exc, BaseExceptionGroup):
-            sub_exceptions: tuple[BaseException] = exc.exceptions  # type: ignore
-            parts += [
-                '\n<ExceptionGroup>',
-                *sorted({canonicalize_exception_traceback(nested_exc) for nested_exc in sub_exceptions}),
-                '\n</ExceptionGroup>\n',
-            ]
-        if exc.__cause__ is not None:
-            parts += [
-                '\n__cause__:',
-                canonicalize_exception_traceback(exc.__cause__),
-            ]
-        if exc.__context__ is not None and not exc.__suppress_context__:
-            parts += [
-                '\n__context__:',
-                canonicalize_exception_traceback(exc.__context__),
-            ]
+        seen = seen or set()
+        if id(exc) in seen:
+            parts.append('\n<repeated exception>')
+        else:
+            seen.add(id(exc))
+            if isinstance(exc, BaseExceptionGroup):
+                sub_exceptions: tuple[BaseException] = exc.exceptions  # type: ignore
+                parts += [
+                    '\n<ExceptionGroup>',
+                    *sorted({canonicalize_exception_traceback(nested_exc, seen) for nested_exc in sub_exceptions}),
+                    '\n</ExceptionGroup>\n',
+                ]
+            if exc.__cause__ is not None:
+                parts += [
+                    '\n__cause__:',
+                    canonicalize_exception_traceback(exc.__cause__, seen),
+                ]
+            if exc.__context__ is not None and not exc.__suppress_context__:
+                parts += [
+                    '\n__context__:',
+                    canonicalize_exception_traceback(exc.__context__, seen),
+                ]
         return '\n'.join(parts)
     except Exception:  # pragma: no cover
         log_internal_error()

tests/test_canonicalize_exception.py

@@ -178,3 +178,67 @@ def test_fingerprint_attribute(exporter: TestExporter):
     assert span.attributes[ATTRIBUTES_EXCEPTION_FINGERPRINT_KEY] == snapshot(
         '3ca86c8642e26597ed1f2485859197fd294e17719e31b302b55246dab493ce83'
     )
+
+
+def test_cyclic_exception_cause():
+    try:
+        try:
+            raise ValueError('test')
+        except Exception as e:
+            raise e from e
+    except Exception as e2:
+        assert canonicalize_exception_traceback(e2) == snapshot("""\
+
+builtins.ValueError
+----
+tests.test_canonicalize_exception.test_cyclic_exception_cause
+   raise e from e
+tests.test_canonicalize_exception.test_cyclic_exception_cause
+   raise ValueError('test')
+
+__cause__:
+
+builtins.ValueError
+----
+tests.test_canonicalize_exception.test_cyclic_exception_cause
+   raise e from e
+tests.test_canonicalize_exception.test_cyclic_exception_cause
+   raise ValueError('test')
+
+<repeated exception>\
+""")
+
+
+@pytest.mark.skipif(sys.version_info < (3, 11), reason='ExceptionGroup is not available in Python < 3.11')
+def test_cyclic_exception_group():
+    try:
+        raise ExceptionGroup('group', [ValueError('test')])  # noqa
+    except ExceptionGroup as group:  # noqa
+        try:
+            raise group.exceptions[0]
+        except Exception as e:
+            assert canonicalize_exception_traceback(e) == snapshot("""\
+
+builtins.ValueError
+----
+tests.test_canonicalize_exception.test_cyclic_exception_group
+   raise group.exceptions[0]
+
+__context__:
+
+builtins.ExceptionGroup
+----
+tests.test_canonicalize_exception.test_cyclic_exception_group
+   raise ExceptionGroup('group', [ValueError('test')])  # noqa
+
+<ExceptionGroup>
+
+builtins.ValueError
+----
+tests.test_canonicalize_exception.test_cyclic_exception_group
+   raise group.exceptions[0]
+
+<repeated exception>
+
+</ExceptionGroup>
+""")