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Tracking Issue for built-in attribute macro #[cfg_eval] #82679

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petrochenkov opened this issue Mar 1, 2021 · 5 comments
Open
1 of 3 tasks

Tracking Issue for built-in attribute macro #[cfg_eval] #82679

petrochenkov opened this issue Mar 1, 2021 · 5 comments
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@petrochenkov
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A-attributes Area: Attributes (`#[…]`, `#![…]`) A-proc-macros Area: Procedural macros C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. 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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petrochenkov commented Mar 1, 2021 •
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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 macros Foo and Bar.

Public API

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

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@petrochenkov petrochenkov added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. labels Mar 1, 2021
@petrochenkov petrochenkov self-assigned this Mar 1, 2021
@jonas-schievink jonas-schievink added A-attributes Area: Attributes (`#[…]`, `#![…]`) A-proc-macros Area: Procedural macros labels Mar 1, 2021
@petrochenkov petrochenkov mentioned this issue Mar 1, 2021
Merged
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this issue Mar 8, 2021
@Dylan-DPC
Rollup merge of rust-lang#82682 - petrochenkov:cfgeval, r=Aaron1011
577ee2f 
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
@Dylan-DPC
Rollup merge of rust-lang#82682 - petrochenkov:cfgeval, r=Aaron1011
de3410e 
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
@Dylan-DPC
Rollup merge of rust-lang#82682 - petrochenkov:cfgeval, r=Aaron1011
0006ea2 
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
@Dylan-DPC
Rollup merge of rust-lang#82682 - petrochenkov:cfgeval, r=Aaron1011
fb90dbf 
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
@Dylan-DPC
Rollup merge of rust-lang#82682 - petrochenkov:cfgeval, r=Aaron1011
9c31057 
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
@Aaron1011
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Aaron1011 commented Mar 14, 2021 •
edited
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It looks like cfg_eval is currently supported as an inner attribute:

#![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?

@petrochenkov
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petrochenkov commented Mar 14, 2021 •
edited
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@Aaron1011
I didn't thought about it, cfg_eval is supposed to be a regular macro attribute, and macro attributes are supported in inner attribute positions in general.
It can be prohibited if it e.g. enables token collection optimizations.

@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.

@petrochenkov petrochenkov mentioned this issue Apr 3, 2021
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@jonasbb jonasbb mentioned this issue Aug 31, 2021
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@petrochenkov petrochenkov mentioned this issue Jan 1, 2022
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@jbr jbr mentioned this issue Apr 18, 2022
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@Sytten Sytten mentioned this issue Jul 16, 2024
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@Piccions
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Piccions commented Aug 7, 2024

Hello!
From my understanding, there hasn't been any major pushback against this feature. Also, in the last year, no issues have been found with the current implementation.
What's next? Is there any roadblock in the way to stable Rust? I offer my help, even though I'm not much of an expert.
Thanks for your hard work.

@petrochenkov
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The previous stabilization attempt - #87221.

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Labels
A-attributes Area: Attributes (`#[…]`, `#![…]`) A-proc-macros Area: Procedural macros C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.
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@Aaron1011 @jonas-schievink @petrochenkov @Piccions