fix: forward generator return value through the trampoline - #542
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boxed merged 1 commit intoJul 31, 2026
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wrap_in_trampoline's generator branch used a bare "yield from trampoline(...)", so the wrapper generator always finished with an implicit None. A caller doing "result = yield from decorated_gen()" therefore got None instead of the generator's return value, and any test asserting on that value failed under "mutmut run" while passing under plain pytest. Returning the delegation result matches the PEP 380 expansion and mirrors the equivalent fix already applied to the async-generator branch. Adds a returning generator to the trampoline test module plus original and mutated regression tests that consume it with "yield from".
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Closes #540
The generator branch of
wrap_in_trampolineused a bareyield from trampoline(...), so the wrapper generator always ended with an implicitNone. A caller doingresult = yield from decorated_gen()lost the generator's return value, making tests that assert on it fail undermutmut runwhile passing under plain pytest. Returning the delegation result matches the PEP 380 expansion, mirroring the equivalent fix already made for async generators in #525.Added a returning generator plus original/mutated regression tests to
tests/mutation/test_trampoline.py; both fail on the current code and pass with the fix.This change was prepared with AI assistance; the regression test was run locally and fails without the fix.