0c81fd0743
Specify that "option-like" enums must be `#[repr(Rust)]` to be ABI-compatible with their non-1ZST field. Add that the enum must be `#[repr(Rust)]` and not `#[repr(packed)]` or `#[repr(align)]` in order to be ABI-compatible with its null-pointer-optimized field. The specific rules here were decided on here: https://github.com/rust-lang/rust/pull/130628#issuecomment-2402761599 but `repr` was not mentioned. In practice, only `#[repr(Rust)]` (or no `repr` attribute, which is equivalent) works for this, so add that to the docs. ----- Restrict to `#[repr(Rust)]` only, since: * `#[repr(C)]` and the primitive representations (`#[repr(u8)]` etc) definitely disqualify the enum from NPO, since they have defined layouts that store the tag separately to the payload. * `#[repr(transparent)]` enums are covered two bullet points above this (line 1830), and cannot have multiple variants, so would fail the "The enum has exactly two variants" requirement anyway. As for `#[repr(align)]`: my current wording that it is completely disallowed may be too strong: it seems like `#[repr(align(<= alignment of T))] enum Foo { X, Y(T) }` currently does still have the same ABI as `T` in practice, though this may not be something we want to promise. (`#[repr(align(> alignment of T))]` definitely disqualifies the enum from being ABI-compatible with T currently). I added the note about `packed` to match `align`, but `#[repr(packed)]` currently can't be applied to `enum`s at all anyway, so might be unnecessary. ----- I think this needs T-lang approval? cc ``````@workingjubilee`````` |
||
|---|---|---|
| .github | ||
| compiler | ||
| library | ||
| LICENSES | ||
| src | ||
| tests | ||
| .clang-format | ||
| .editorconfig | ||
| .git-blame-ignore-revs | ||
| .gitattributes | ||
| .gitignore | ||
| .gitmodules | ||
| .ignore | ||
| .mailmap | ||
| bootstrap.example.toml | ||
| Cargo.lock | ||
| Cargo.toml | ||
| CODE_OF_CONDUCT.md | ||
| configure | ||
| CONTRIBUTING.md | ||
| COPYRIGHT | ||
| INSTALL.md | ||
| LICENSE-APACHE | ||
| license-metadata.json | ||
| LICENSE-MIT | ||
| README.md | ||
| RELEASES.md | ||
| REUSE.toml | ||
| rust-bors.toml | ||
| rustfmt.toml | ||
| triagebot.toml | ||
| x | ||
| x.ps1 | ||
| x.py | ||
This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.
Why Rust?
-
Performance: Fast and memory-efficient, suitable for critical services, embedded devices, and easily integrated with other languages.
-
Reliability: Our rich type system and ownership model ensure memory and thread safety, reducing bugs at compile-time.
-
Productivity: Comprehensive documentation, a compiler committed to providing great diagnostics, and advanced tooling including package manager and build tool (Cargo), auto-formatter (rustfmt), linter (Clippy) and editor support (rust-analyzer).
Quick Start
Read "Installation" from The Book.
Installing from Source
If you really want to install from source (though this is not recommended), see INSTALL.md.
Getting Help
See https://www.rust-lang.org/community for a list of chat platforms and forums.
Contributing
See CONTRIBUTING.md.
License
Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.
See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.
Trademark
The Rust Foundation owns and protects the Rust and Cargo trademarks and logos (the "Rust Trademarks").
If you want to use these names or brands, please read the Rust language trademark policy.
Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.