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Fix traceback circular reference detection to pass test_raise.py #5995

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Fix traceback circular reference detection to pass test_raise.py #5995

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7f33100
Initial plan
Copilot Jul 17, 2025
9f4065c
Add circular reference detection to traceback.tb_next setter
Copilot Jul 17, 2025
ce5fe45
Implement general cycle detection algorithm for traceback.tb_next setter
Copilot Jul 17, 2025
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2 changes: 0 additions & 2 deletions Lib/test/test_raise.py
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Original file line number Diff line number Diff line change
Expand Up @@ -233,8 +233,6 @@ class TestTracebackType(unittest.TestCase):
def raiser(self):
raise ValueError

# TODO: RUSTPYTHON
@unittest.expectedFailure
def test_attrs(self):
try:
self.raiser()
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20 changes: 19 additions & 1 deletion vm/src/builtins/traceback.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
use rustpython_common::lock::PyMutex;
use std::ops::Deref;

use super::{PyType, PyTypeRef};
use crate::{
Expand Down Expand Up @@ -63,8 +64,25 @@ impl PyTraceback {
}

#[pygetset(setter)]
fn set_tb_next(&self, value: Option<PyRef<Self>>) {
fn set_tb_next(&self, value: Option<PyRef<Self>>, vm: &VirtualMachine) -> PyResult<()> {
if let Some(ref new_tb) = value {
// Check for direct loop (tb.tb_next = tb)
if std::ptr::eq(self as *const _, new_tb.deref().deref() as *const _) {
return Err(vm.new_value_error("circular reference in traceback chain".to_owned()));
}

// Check for indirect loops by walking the chain
let mut current = new_tb.tb_next();
while let Some(ref tb) = current {
if std::ptr::eq(self as *const _, tb.deref().deref() as *const _) {
return Err(vm.new_value_error("circular reference in traceback chain".to_owned()));
}
current = tb.tb_next();
}
}
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This is too ad-hoc. You must create a more general logic to detect circular reference in tb_next until the end.

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Implemented a more general cycle detection algorithm using Floyd's cycle detection (tortoise and hare). The new approach simulates the assignment and detects any cycles in the resulting chain rather than only checking for specific patterns. See commit ce5fe45.


*self.next.lock() = value;
Ok(())
}
}

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