Allow FlattenSentinel in matcher decorator return annotations - #1465
Allow FlattenSentinel in matcher decorator return annotations#1465Sanjays2402 wants to merge 1 commit into
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Annotating a @leave-decorated method with FlattenSentinel raised TypeError: issubclass() arg 1 must be a class, even though returning a FlattenSentinel from leave_<Node> is valid. Two causes: the generated TYPED_FUNCTION_RETURN_MAPPING omitted FlattenSentinel entirely (unlike the leave_ signatures in _typed_visitor.py), and _get_possible_annotated_classes passed the parameterized generic FlattenSentinel[BaseStatement] straight to issubclass(), which only accepts classes. gen_type_mapping now mirrors gen_visitor_functions and emits FlattenSentinel for sequence-valued nodes, and generic aliases are unwrapped to their origin class before the subclass check.
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Closes #1075
Summary
Annotating a
@leave-decorated method withFlattenSentinelraisedTypeError: issubclass() arg 1 must be a class, even though returning aFlattenSentinelfromleave_<Node>is valid.Two causes: the generated
TYPED_FUNCTION_RETURN_MAPPINGomittedFlattenSentinelentirely (unlike theleave_signaturesgen_visitor_functionsemits), and_get_possible_annotated_classespassed the parameterized genericFlattenSentinel[BaseStatement]straight toissubclass(), which only accepts classes.gen_type_mappingnow mirrorsgen_visitor_functionsfor sequence-valued nodes, and generic aliases are unwrapped to their origin class before the subclass check._return_types.pyis regenerated output.Test Plan
Two tests in
libcst/matchers/tests/test_visitors.py(parameterized and bareFlattenSentinel) fail on main with the reportedTypeErrorand pass with the fix.libcst/matchers/tests145 passed / 1 skipped;libcst/codemodunchanged from baseline;ufmt checkclean on the touched files.This change was prepared with AI assistance; the regression tests were run locally and fail without the fix.