Tracking Issue for built-in attribute macro #[cfg_eval]
#82679
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A-attributes
Area: Attributes (`#[…]`, `#![…]`)
A-proc-macros
Area: Procedural macros
C-tracking-issue
Category: An issue tracking the progress of sth. like the implementation of an RFC
T-libs-api
Relevant to the library API team, which will review and decide on the PR/issue.
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petrochenkov
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Dylan-DPC-zz
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Mar 8, 2021
Implement built-in attribute macro `#[cfg_eval]` + some refactoring This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#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 rust-lang#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: rust-lang#82679
Dylan-DPC-zz
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Mar 8, 2021
Implement built-in attribute macro `#[cfg_eval]` + some refactoring This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#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 rust-lang#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: rust-lang#82679
Dylan-DPC-zz
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Mar 8, 2021
Implement built-in attribute macro `#[cfg_eval]` + some refactoring This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#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 rust-lang#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: rust-lang#82679
Dylan-DPC-zz
pushed a commit
to Dylan-DPC-zz/rust
that referenced
this issue
Mar 8, 2021
Implement built-in attribute macro `#[cfg_eval]` + some refactoring This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#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 rust-lang#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: rust-lang#82679
Dylan-DPC-zz
pushed a commit
to Dylan-DPC-zz/rust
that referenced
this issue
Mar 8, 2021
Implement built-in attribute macro `#[cfg_eval]` + some refactoring This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#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 rust-lang#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: rust-lang#82679
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It looks like #![feature(custom_inner_attributes)]
#![feature(cfg_eval)]
#![feature(stmt_expr_attributes)]
fn main() {
let a = #[cfg_attr(FALSE, rustc_dummy)] {
#![cfg_eval]
};
}Is this intentional? |
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@Aaron1011 |
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I had thought that allowing it as inner attribute would interfere with token collection optimizations, but it turned out to be straightforward to deal with. |
This was referenced Jul 17, 2021
|
Hello! |
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The previous stabilization attempt - #87221. |
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Feature gate:
#![feature(cfg_eval)]This is a tracking issue for built-in attribute macro
#[cfg_eval]that 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 macrosFooandBar.Public API
Steps / History
#[cfg_eval]+ some refactoring #82682Unresolved Questions
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