Python: fix shared CFG exception-handler reachability - #22380
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Pull request overview
Fixes shared Python CFG/SSA regressions affecting exception-handler reachability and module-export phi uses.
Changes:
- Routes exceptional completion through canonical CFG nodes.
- Preserves synthetic normal-exit uses for generic SSA definitions.
- Adds regression tests for both fixes.
| File | Description |
|---|---|
| python/ql/lib/semmle/python/controlflow/internal/AstNodeImpl.qll | Uses canonical CFG-node mapping for exception flow. |
| python/ql/lib/semmle/python/dataflow/new/internal/SsaImpl.qll | Supports phi definitions when resolving uses. |
| python/ql/test/library-tests/ControlFlow/shared-cfg-exceptions/test.py | Adds yield and import exception cases. |
| python/ql/test/library-tests/ControlFlow/shared-cfg-exceptions/ExceptionReachabilityTest.ql | Checks typed-handler reachability. |
| python/ql/test/library-tests/ControlFlow/shared-cfg-exceptions/ExceptionReachabilityTest.expected | Records expected exception results. |
| python/ql/test/library-tests/dataflow-new-ssa/test.py | Adds conditional module-export coverage. |
| python/ql/test/library-tests/dataflow-new-ssa/SsaTest.ql | Checks synthetic exit uses for phi definitions. |
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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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August 20, 2026 06:55
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python/ql/lib/semmle/python/controlflow/internal/AstNodeImpl.qll
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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 860cd56d-31cf-49f4-a947-45e0d72447c6
This was referenced Aug 25, 2026
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LGTM
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Summary
Fixes exception-handler reachability in the shared Python CFG introduced by #21921 and now present on main. Testing the dataflow switch-over in #21925 surfaced the bug.
Leaf expressions that may throw, including bare yield and plain imports, were not always connected to typed exception-handler entries. The fix uses the canonical shared-CFG injects mapping when starting exceptional completion, so these expressions reach the appropriate catch entry.
Tests
Adds focused inline coverage for:
DCA impact
The switch-over DCA in #38556 exposed effects of the missing exception edges in mypy, CPython, and youtube-dl. Restoring these edges recovers the affected catch reachability and downstream flow.
Validation