Permit attributes on `use` items

[jhpratt]

Can we permit attributes on use items? I would like the following snippet to be syntactically and semantically valid.

use crate::{alpha, beta, #[cfg(feature = "foo")] gamma};

This would be equivalent to

use crate::{alpha, beta};
#[cfg(feature = "foo")]
use crate::gamma;

This would permit me to use rustfmt's option of one import per module and have it actually be true, rather than one import per module per feature gate. Attributes such as #[allow(unused_imports)] are plausibly useful in this position as well.

Syntactically I see no conflicts in the reference, as # starts any attribute and is unambiguous with the start of an identifier and ::.

---

This feels simple enough to not need a full RFC, which as far as I can tell is what is technically required. I had thought MCPs were for this, but that turns out to be for non-user-facing changes, and ACP deals with T-libs territory. So consider this a lang-MCP, if you will?

cc @rust-lang/lang

[traviscross]

@rustbot labels -I-lang-easy-decision +I-lang-nominated +P-lang-drag-2

Thanks for the question.

(Regarding the label, history has shown that questions of where to allow attributes have never been easy.)

[jhpratt]

Fair enough on the label. It couldn't hurt to try 😅

[caibirdme]

It's a little bit hard to read what crates are included in the current scope. I think your second code is more intuitive:

use crate::{alpha, beta};
#[cfg(feature = "foo")]
use crate::gamma;