Cargo Features

libc = { version = "0.2.153", default-features = false, features = ["std", "align", "rustc-dep-of-std", "const-extern-fn", "use_std"] }
default = std

The std feature is set by default whenever libc is added without default-features = false somewhere in the dependency tree.

std default use_std?
align rustc-dep-of-std?
rustc-dep-of-std = align, rustc-std-workspace-core
extra_traits const-extern-fn
use_std = std

use_std is deprecated, use std instead

Features from optional dependencies

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

rustc-std-workspace-core rustc-dep-of-std?