add UnwindSafe impl for AsDynError

[cosmicexplorer]

Hello!! I love this crate :))

Problem

thiserror::Error is not able to convert a Box<dyn Error + Send + Sync + UnwindSafe + 'static> into a dyn Error with the #[source] annotation, which caused it to be unsuitable for the purposes of the Signal client: see signalapp/libsignal#296 (comment). Signal uses UnwindSafe (I just learned about this trait) to convert errors into a format suitable for its ffi/jni/node.js bindings.

Solution

@jrose-signal pointed me to #41, which enabled wrapping a Box<dyn Error + Send + 'static> with #[source], and I was able to figure out how to extend it for the purposes of boxed UnwindSafe errors as well.

Result

Using this change allowed me to remove the boilerplate error manipulation code in the signal client, and this commit (cosmicexplorer/libsignal@9d82971) passed tests locally.

Please let me know if there are test cases I should add -- it looks like the test_boxed_source() method is already intended to apply to all the types of boxed errors thiserror supports, and I tried to create a test wrapping e.g. ParseIntError which is UnwindSafe using std::panic::catch_unwind, but was having difficulty and was thinking it might be better to leave the tests simple as they are. Let me know if I should investigate more on that.

[dtolnay]

Thanks!

[dtolnay]

Published in 1.0.30.

[cosmicexplorer]

Amazing!! Thanks so much!!