Cargo Features

GCC has no features set by default.

[dependencies]
gcc = { version = "0.3.55", features = ["parallel"] }
parallel = rayon

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.

rayon parallel?

Enables rayon ^0.8