Cargo Features

[dependencies]
includedir = { version = "0.6.0", default-features = false, features = ["flate2"] }
default = flate2

The flate2 feature is set by default whenever includedir is added without default-features = false somewhere in the dependency tree.

Features from optional dependencies

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

flate2 default