Rustfmt duplicates attributes on expressions

[omerbenamram]

Hello!
I'm experiencing this behavior:

using rustfmt on:

pub enum MyEnum {
    Option1,
}

fn main() {
    match MyEnum {
        MyEnum::Option1 if cfg!(target_os = "windows") =>
            #[cfg(target_os = "windows")]{
                1
        }
    }

    ()
}

yields:

pub enum MyEnum {
    Option1,
}

fn main() {
    match MyEnum {
        MyEnum::Option1 if cfg!(target_os = "windows") =>
        #[cfg(target_os = "windows")]
        #[cfg(target_os = "windows")]
        {
            1
        }
    }

    ()
}

I have seen #3410 and #3313, but I'm not sure it's the same problem, since I'm running the latest nightly (rustfmt 1.2.0-nightly (09940a70 2019-03-27)) and it seems to still exist.
I'm also aware that this syntax is considered experimental, so mileage may vary, but still seems like a bug in rustfmt.

Thanks again for the awesome work :)