Cargo Features

strum = { version = "0.25.0", default-features = false, features = ["std", "derive", "phf"] }
default = std

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

std default
derive = strum_macros

Features from optional dependencies

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

strum_macros derive?
phf implicit feature

Enables macros and default (std) of phf ^0.10