Alisa Sireneva

> It seems to me that Rust is already mostly unwind safe and making it fully is just a matter of fixing relatively few issues like those with suitable deprecations,...

I'm a bit concerned about this change. Applications and libraries often use crates like `thiserror` to automatically group errors. For example, I often write something like ```rust #[derive(Error)] enum MyError...

> can't we collect all error types used with ? and if all error types inside a block are concrete and the same, then use this type I admit I...

Likely the same bug, but reporting another reproducer for completeness: ```rust m!(impl() { Self {} }); ```

```shell $ cat test.rs m!(impl() { Self {} }); $ rustfmt test.rs 2>&1 | head -10 thread 'main' (547263) panicked at compiler/rustc_parse/src/parser/item.rs:400:32: called `Result::unwrap()` on an `Err` value: Some(DiagInner {...