warning: unexpected `cfg` condition value: `bar`
  --> $DIR/values-none.rs:16:7
   |
LL | #[cfg(foo = "bar")]
   |       ^^^^^^^^^^^
   |
   = note: expected values for `foo` are: (none), `too`
   = help: to expect this configuration use `--check-cfg=cfg(foo, values("bar"))`
   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
   = note: `#[warn(unexpected_cfgs)]` on by default

warning: 1 warning emitted