Cargo Features

ham = { version = "0.2.0", default-features = false, features = ["hp-sleep"] }
default = hp-sleep

The hp-sleep feature is set by default whenever ham is added without default-features = false somewhere in the dependency tree.

hp-sleep default = spin_sleep

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features.

spin_sleep hp-sleep

Enables spin_sleep ^0.3.7