Python: Add support for forward references in unused var query #18921
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Adds two test cases having to do with type annotations. The first one demonstrates that type annotations (even if they are never executed by the Python interpreter) count as uses for the purposes of the unused variable query. The second one demonstrates that this is _not_ the case if all such uses are inside strings (i.e. forward declarations), as we do not currently inspect the content of these strings.
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Fixes the false positive reported in #18910 Adds a new `Annotation` class (subclass of `Expr`) which encompasses all possible kinds of annotations in Python. Using this, we look for string literals which are part of an annotation, and which have the same content as the name of a (potentially) unused global variable, and in that case we do not produce an alert. In future, we may want to support inspecting such string literals more deeply (e.g. to support stuff like "list[unused_var]"), but I think for now this level of support is sufficient.
tausbn
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This way we also get annotations that appear in `Lambda`s
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PR Overview
This PR improves the unused variable query by adding support for forward references, helping to reduce false positives when string literals in annotations match unused global variable names.
- Added test functions for both direct and forward annotations in the test file.
- Updated change notes to document the new behavior concerning forward references.
Reviewed Changes
| File | Description |
|---|---|
| python/ql/test/query-tests/Variables/unused/variables_test.py | Adds tests for both direct and forward annotations to ensure unused globals used only in annotations aren’t flagged. |
| python/ql/src/change-notes/2025-03-04-fix-forward-annotation-fp-in-unused-global-var-query.md | Documents the change that forward reference annotations now prevent false positives in the unused global variable query. |
Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.
Comments suppressed due to low confidence (2)
python/ql/test/query-tests/Variables/unused/variables_test.py:151
- [nitpick] Consider adding explicit assertions within test_direct_annotation to verify that the query behaves as expected regarding unused variables in annotations.
def test_direct_annotation(x: ParamAnnotation) -> ReturnAnnotation:
python/ql/test/query-tests/Variables/unused/variables_test.py:155
- [nitpick] Consider documenting the expected outcome of test_forward_annotation, such as adding inline comments or assertions to clarify that forward-referenced annotations should not be flagged.
def test_forward_annotation(x: "ForwardParamAnnotation") -> "ForwardReturnAnnotation":
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Fixes the false positive reported in #18910
Adds a new
Annotationclass (subclass ofExpr) which encompasses all possible kinds of annotations in Python.Using this, we look for string literals which are part of an annotation, and which have the same content as the name of a (potentially) unused global variable, and in that case we do not produce an alert.
In future, we may want to support inspecting such string literals more deeply (e.g. to support stuff like "list[unused_var]"), but I think for now this level of support is sufficient.