Python: Handle loop constructs outside of loops #18703
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Observed on some test files in Nuitka/Nuitka, having `break` and `continue` outside of loops in Python is (to Python) a syntax error, but our parser happily accepted this broken syntax. This then caused issues further downstream in the control-flow construction, as it broke some invariants. To fix this we now skip the code that would previously fail when the invariants are broken. Co-authored-by: yoff <yoff@github.com>
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PR Overview
This pull request addresses the handling of Python’s "break" and "continue" statements that appear outside of valid loop constructs. Previously, such occurrences were accepted as syntactically valid, which caused downstream failures in control-flow construction. Now, the parser code checks for loop context before adding flow information, preventing these failures.
- Adds a test file demonstrating "break" and "continue" usage outside a loop.
- Updates a change note to reflect this fix.
- Updates the flow analysis code to skip the invalid "break" or "continue" when they appear outside a loop context.
Changes
| File | Description |
|---|---|
| python/ql/test/extractor-tests/syntax_error/without_loop.py | Adds a test file with intentionally invalid Python code (break/continue outside loops). |
| python/ql/lib/change-notes/2025-02-06-robustly-handle-loop-constructs.md | Documents the fix affecting "break" and "continue" statements in invalid contexts. |
| python/extractor/semmle/python/passes/flow.py | Updates flow analysis to gracefully handle out-of-loop "break" and "continue" statements. |
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Observed on some test files in Nuitka/Nuitka, having
breakandcontinueoutside of loops in Python is (to Python) a syntax error, but our parser happily accepted this broken syntax.This then caused issues further downstream in the control-flow construction, as it broke some invariants.
To fix this we now skip the code that would previously fail when the invariants are broken.