Remove redundant #[rustc_paren_sugar] feature gate

[mejrs]

It is already gated on rustc_attrs.

Alternatively we could update attribute parsing to optionally require multiple features, but that seems unnecessary.

r? @JonathanBrouwer

[rustbot]

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[JonathanBrouwer]

You seem to have found a mistake in #157195

Before that PR, this attribute was only gated behind unboxed_closures.
I think it's best to return to that state, since it being gated behind two feature gates is weird

View changes since the review

[mejrs]

I feel somewhat uncomfortable about a rustc_ attribute not being gated behind rustc_attrs 🤔, do we have any others that are like that? I think it's an important convention to have.

[JonathanBrouwer]

There's quite a few of them actually, just a random few examples

• rustc_intrinsic is gated behind intrinsics
• rustc_eii_foreign_item is gated behind eii_internals
• rustc_allowed_through_unstable_modules is gated behind staged_api
• rustc_default_body_unstable is gated behind staged_api
• rustc_align is gated behind fn_align (tho this one is intended to stabilize)

This is what I could quickly find, there's a few more of them.

If we do choose rustc_attrs, is the unboxed_closures still useful as a feature then?

[mejrs]

hmm not really, it just defuses this error:

    /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
    /// an error and attempt to build a reasonable structured suggestion.

looks like everything related is behind fn_traits

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rustbot]

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

[mejrs]

Gate changed to unboxed_closures.

@rustbot ready

[JonathanBrouwer]

@bors r+ rollup

View changes since this review

[rust-bors]

📌 Commit 4bd52e9 has been approved by JonathanBrouwer

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 1. This pull request will be tested once the tree is reopened.

Reason for tree closure: spurious CI failures