warning: unexpected `cfg` condition value: `foo`
  --> $DIR/empty-values.rs:7:7
   |
LL | #[cfg(foo = "foo")]
   |       ^^^^^^^^^^^ help: remove the condition
   |
   = note: no expected values for `foo`
   = help: to expect this configuration use `--check-cfg=cfg(foo, values("foo"))`
   = 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: unexpected `cfg` condition value: (none)
  --> $DIR/empty-values.rs:11:7
   |
LL | #[cfg(foo)]
   |       ^^^ help: remove the condition
   |
   = note: no expected values for `foo`
   = help: to expect this configuration use `--check-cfg=cfg(foo)`
   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration

warning: 2 warnings emitted