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Fix traceback circular reference detection to pass test_raise.py#5995
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Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>
@unittest.expectedFailure from test_raise.py 's TestTracebackType.test_attrs. Run the test and fix the errors by editingtraceback.rsvm/src/builtins/traceback.rs Outdated
| 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 commitce5fe45.
Replace ad-hoc circular reference checking with Floyd's cycle detection algorithm for more comprehensive cycle detection.Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>
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Fixes the traceback
tb_nextsetter to properly detect and prevent circular references, enablingtest_raise.py::TestTracebackType.test_attrsto pass.Problem
The test
TestTracebackType.test_attrsintest_raise.pywas marked with@unittest.expectedFailurebecause the traceback implementation was missing circular reference detection. The test expects:But the current implementation allowed these assignments without validation.
Solution
Added circular reference detection to the
set_tb_nextmethod invm/src/builtins/traceback.rs:selfselfdoesn't appear anywhere in the chainstd::ptr::eqwith correct dereferencing to compare the underlyingPyTracebackobjectsThe implementation raises
ValueError("circular reference in traceback chain")when a circular reference is detected, matching CPython's behavior.Changes
@unittest.expectedFailuredecorator fromTestTracebackType.test_attrsPyTraceback::set_tb_next()std::ops::Derefimport for proper object dereferencingTesting
TestTracebackType.test_attrsnow passestest_raise.pycontinue to passThe fix is minimal and surgical, only adding the necessary validation without changing any existing working functionality.
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