#[fail(..)] doesn't import correctly in new epoch

[kazcw]

Testing the preview of edition="2018", the fail attribute macro only seems to be recognized when it's inside the lexical block of a #[derive(Fail)] object.

So this works:

use failure::Fail;
#[derive(Fail)]
enum Foo {
    #[fail(display = "foo error: {}", _0)]
    Bad(String),
}

But this doesn't:

use failure::Fail;
#[derive(Fail)]
#[fail(display = "foo error: {}", _0)]
struct Bad(String);
// ^ causes "cannot find attribute macro `fail` in this scope"

I'm not sure what serde would be doing differently but the #[serde(...)] attribute macro still works at either scope.

[kazcw]

Actually, I'm not seeing the error in a test case like the snippet above. I need to pare down my crate to find a minimal case that reproduces the error.

[kazcw]

This turns out to be rust-lang/rust#44925