Cargo Features

[dependencies]
compact_u64 = { version = "0.1.0", default-features = false, features = ["dev", "std"] }
default = std

The std feature is set by default whenever compact_u64 is added without default-features = false somewhere in the dependency tree.

dev = arbitrary, std
std default dev?

Provide functionality that relies on the std library. Enabled by default.

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.

arbitrary dev?