warning: the feature `effects` is incomplete and may not be safe to use and/or cause compiler crashes
  --> $DIR/effect-var.rs:4:12
   |
LL | #![feature(effects)]
   |            ^^^^^^^
   |
   = note: see issue #102090 <https://github.com/rust-lang/rust/issues/102090> for more information
   = note: `#[warn(incomplete_features)]` on by default

warning: 1 warning emitted