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Cold Structs #54044

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cramertj opened this issue Sep 7, 2018 · 2 comments · Fixed by #73461
Closed

Cold Structs #54044

cramertj opened this issue Sep 7, 2018 · 2 comments · Fixed by #73461
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A-attributes Area: #[attributes(..)]

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@cramertj
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cramertj commented Sep 7, 2018

#[cold]
struct DonnerParty;

fn main() {
    #[cold] 5;
}

Is it intentional that this work? If so, what is it supposed to do? The reference lists it as a function-only attribute, but I've always known it to work on expressions like loops as well.

@petrochenkov
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A lot of attributes (most of them?) are not validated in any way, neither locations, nor syntax.
So, something like this works as well:

#[cold(foo = 10)]
fn f() {}

This is a known issue, but I'm not sure there's a single issue about the attribute validation problem in general.

@Havvy
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Havvy commented Sep 8, 2018

I'll add a line saying that the attribute is allowed on other places in the reference. That said, it'd be nice to make it a warning in the 2018 edition, error by default in the 2021 edition, and removed completely in the 2024 edition.

@petrochenkov Having an actual list of said attributes would be useful for said documentation purposes.

@cramertj You can't put attributes on expressions, only statements or blocks. Are you saying #[cold] has an effect when placed on loops? If so, that should definitely be documented as well. I did touch that section recently, mainly by removing it and making new sections for the attributes it contains. https://havvy.net/rust-reference/attributes.html#cold-attribute but I only added information about putting the attribute on associated functions.

@Havvy Havvy added the A-attributes Area: #[attributes(..)] label Sep 8, 2018
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this issue Sep 7, 2020
…acement, r=matthewjasper

Validate built-in attribute placement

Closes rust-lang#54584, closes rust-lang#47725, closes rust-lang#54044.

I've changed silently ignoring some incorrectly placed attributes to errors.  I'm not sure what the policy is since this can theoretically break code (should they be warnings instead? does it warrant a crater run?).
@bors bors closed this as completed in dbb73f8 Sep 12, 2020
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3 participants