bors d4f7856569 Auto merge of #155473 - scottmcm:tweak_niche_assignment, r=chenyukang,mati865 ...

Prefer `-1` for `None`



Currently we pick "weird" numbers like `1114112` for `None::<char>`.  While that's not *wrong*, it's kinda *unnatural* -- a human wouldn't make that choice.

This PR instead picks `-1` for thinge like `None::<char>` -- like [clang's `WEOF`](https://github.com/llvm/llvm-project/blob/63ae74b78a11f6c61136dbc445652929389eb9ab/libc/include/llvm-libc-macros/wchar-macros.h#L15) -- and `None::<bool>` and such.

Any enums with more than one niched value (so not `Result` nor `Option`) remain as they were before.  Also we continue to use `0` when that's possible -- `-1` is only preferred when zero *isn't* possible.

---

Inspired when someone in discord posted an example like this <https://rust.godbolt.org/z/W94s9qdYW> and I thought it was odd that we're currently picking `-9223372036854775808` to be the value to store to mark an `Option<Vec<_>>` as `None`.  (Especially since that needs an 8-byte immediate on x64, and writing `-1` is only a 4-byte immediate.)

2026-04-26 17:06:25 +00:00

..

src

Auto merge of #155473 - scottmcm:tweak_niche_assignment, r=chenyukang,mati865

2026-04-26 17:06:25 +00:00

Cargo.toml

Invert dependency between rustc_errors and rustc_abi.

2026-03-30 14:15:36 +11:00