Comment by fl0ki

This isn't the only way a Rust stable update can break your compile. It can also happen simply because they add a symbol to the standard library, and that isn't even protected by language editions.

https://predr.ag/blog/some-rust-breaking-changes-do-not-requ...

"Never add anything" isn't a tenable position, and in practice the breakage hasn't been bad enough to need special treatment yet.