Cargo Features

[dependencies]
u64-id = { version = "0.1.0", default-features = false, features = ["rand", "serde"] }
default = rand, serde

These default features are set whenever u64-id 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. These features may have been created by mistake, and this functionality may be removed in the future.

rand default
serde default