[unstable option] inline_attribute_width

[dhardy]

As you can see from this diff, inline-attributes are viable and sometimes even useful (specifically: making diffs align properly, which has been an issue in Rand's lib.rs quite a few times).

-#[cfg(feature="alloc")] use core::slice;
+#[cfg(feature = "alloc")]
+use core::slice;

rustfmt is forcing multi-line attributes everywhere. I would like an option for inline attributes (when small).

[rchaser53]

I also want this feature a bit, so I send the PR.

[soruh]

It appears like this does not work within extern blocks.

i.e.:

extern "C" {
    #[no_mangle]
    fn sprintf(_: *mut c_char, _: *const c_char, ...) -> c_int;
}

should be formatted to this:

extern "C" {
    #[no_mangle] fn sprintf(_: *mut c_char, _: *const c_char, ...) -> c_int;
}

but isn't

versions:

> cargo -V       
cargo 1.43.0-nightly (e02974078 2020-02-18)
> cargo fmt -- -V
rustfmt 1.4.12-nightly (9f53665 2020-02-10)

rustfmt.toml

edition = "2018"
version = "Two"
inline_attribute_width = 100
unstable_features = true

[dhardy]

This also doesn't work within #5538.