Cargo Features

waker-fn has no features set by default.

[dependencies]
waker-fn = { version = "1.2.0", features = ["portable-atomic"] }
portable-atomic = portable-atomic-util

Uses portable-atomic polyfill atomics on targets without them

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

portable-atomic-util portable-atomic?