projects / rustc.git / blame
| Commit | Line | Data |
|---|---|---|
| f035d41b XL |
1 | # `rustc_attrs` |
| 2 | ||
| 3 | This feature has no tracking issue, and is therefore internal to | |
| 4 | the compiler, not being intended for general use. | |
| 5 | ||
| 6 | Note: `rustc_attrs` enables many rustc-internal attributes and this page | |
| 7 | only discuss a few of them. | |
| 8 | ||
| 9 | ------------------------ | |
| 10 | ||
| 11 | The `rustc_attrs` feature allows debugging rustc type layouts by using | |
| 12 | `#[rustc_layout(...)]` to debug layout at compile time (it even works | |
| 13 | with `cargo check`) as an alternative to `rustc -Z print-type-sizes` | |
| 14 | that is way more verbose. | |
| 15 | ||
| 1b1a35ee XL |
16 | Options provided by `#[rustc_layout(...)]` are `debug`, `size`, `align`, |
| 17 | `abi`. Note that it only works on sized types without generics. | |
| f035d41b XL |
18 | |
| 19 | ## Examples | |
| 20 | ||
| 21 | ```rust,ignore | |
| 22 | #![feature(rustc_attrs)] | |
| 23 | ||
| 24 | #[rustc_layout(abi, size)] | |
| 25 | pub enum X { | |
| 26 | Y(u8, u8, u8), | |
| 27 | Z(isize), | |
| 28 | } | |
| 29 | ``` | |
| 30 | ||
| 31 | When that is compiled, the compiler will error with something like | |
| 32 | ||
| 33 | ```text | |
| 34 | error: abi: Aggregate { sized: true } | |
| 35 | --> src/lib.rs:4:1 | |
| 36 | | | |
| 37 | 4 | / pub enum T { | |
| 38 | 5 | | Y(u8, u8, u8), | |
| 39 | 6 | | Z(isize), | |
| 40 | 7 | | } | |
| 41 | | |_^ | |
| 42 | ||
| 43 | error: size: Size { raw: 16 } | |
| 44 | --> src/lib.rs:4:1 | |
| 45 | | | |
| 46 | 4 | / pub enum T { | |
| 47 | 5 | | Y(u8, u8, u8), | |
| 48 | 6 | | Z(isize), | |
| 49 | 7 | | } | |
| 50 | | |_^ | |
| 51 | ||
| 52 | error: aborting due to 2 previous errors | |
| 53 | ``` |