Revert addition of new base trait to ReturnThrowable #24975
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The deprecated class NonLocalReturns.ReturnThrowable acquired a new base type `caps.Control` in 3.8. That was a mistake. Later versions of the capture checker reject that inheritance since `ReturnThrowable` is an exception and therefore must be a pure class, whereas inheriting `caps.Control` would automatically add a capture set to that class. It's too late to revert for 3.8, but we should revert for 3.8.1. It's technically a backwards incompatible change, but I would be extremely surprised if anyone has used ReturnThrowable as a caps.Control in the 3.8.0 window.
natsukagami
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Jan 14, 2026
WojciechMazur
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backport:nominated
WojciechMazur
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WojciechMazur
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backport:done
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The deprecated class NonLocalReturns.ReturnThrowable acquired a new base type
caps.Controlin 3.8. That was a mistake. Later versions of the capture checker reject that inheritance sinceReturnThrowableis an exception and therefore must be a pure class, whereas inheritingcaps.Controlwould automatically add a capture set to that class.It's too late to revert for 3.8, but we should revert for 3.8.1. It's technically a backwards incompatible change, but I would be extremely surprised if anyone has used ReturnThrowable as a caps.Control in the 3.8.0 window.