Nightly regression for E0619

[Keats]

This appeared in Travis (stable and beta still work)

$ rustc --version
rustc 1.25.0-nightly (3f92e8d89 2018-01-14)

The error:

error[E0619]: the type of this value must be known in this context
  --> components/content/src/file_info.rs:11:42
   |
11 |         let component = section.as_ref().to_string_lossy();
   |                                          ^^^^^^^^^^^^^^^

Link to Travis: https://travis-ci.org/Keats/gutenberg/builds/328770657?utm_source=github_status&utm_medium=notification

It does compile fine with rustc 1.25.0-nightly (b5392f545 2018-01-08) but I sadly can't download other nightlies atm to pin it down.

[ExpHP]

Probably due to #46985 ?

(section is a Component, and <Component as AsRef<_>> is no longer unique)

[alexcrichton]

The libs team discussed this issue today and concluded that we're going to close this. @Keats if you have difficulty updating though please let us know!

We're hoping we can head off errors like this in the future with #36443