rust/compiler/rustc_builtin_macros
Dylan DPC 9c310571a8
Rollup merge of #82682 - petrochenkov:cfgeval, r=Aaron1011
Implement built-in attribute macro `#[cfg_eval]` + some refactoring

This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in https://github.com/rust-lang/rust/pull/79078 to avoid `#[derive()]` without arguments being abused as a way to configure input for other attributes.

The macro is used for eagerly expanding all `#[cfg]` and `#[cfg_attr]` attributes in its input ("fully configuring" the input).
The effect is identical to effect of `#[derive(Foo, Bar)]` which also fully configures its input before passing it to macros `Foo` and `Bar`, but unlike `#[derive]` `#[cfg_eval]` can be applied to any syntax nodes supporting macro attributes, not only certain items.

`cfg_eval` was the first name suggested in https://github.com/rust-lang/rust/pull/79078, but other alternatives are also possible, e.g. `cfg_expand`.

```rust
#[cfg_eval]
#[my_attr] // Receives `struct S {}` as input, the field is configured away by `#[cfg_eval]`
struct S {
    #[cfg(FALSE)]
    field: u8,
}
```

Tracking issue: https://github.com/rust-lang/rust/issues/82679
2021-03-08 13:13:23 +01:00
..
src Rollup merge of #82682 - petrochenkov:cfgeval, r=Aaron1011 2021-03-08 13:13:23 +01:00
Cargo.toml bumped smallvec deps 2021-02-14 18:03:11 +03:00