Make proc-macro bidirectional calls cancellation safe #21410
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rustbot
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ChayimFriedman2
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Jan 9, 2026
| let resp = callback(sr)?; | ||
| let reply = BidirectionalMessage::SubResponse(resp); | ||
| let encoded = C::encode(&reply).map_err(wrap_encode)?; | ||
| let resp = match catch_unwind(AssertUnwindSafe(|| callback(sr))) { |
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I would slightly prefer to have the callback type + UnwindSafe than this AssertUnwindSafe.
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This is tricky because the callback captures &dyn ExpandDatabase (later at implementation), which is not UnwindSafe. Requiring UnwindSafe on the callback would therefore force unwind-safety guarantees on ExpandDatabase.
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Catch panics in subrequest callbacks, reply with Cancel, and propagate cancellation to the proc-macro server