Cargo Features

codes-un-m49 = { version = "0.1.2", default-features = false, features = ["country_codes", "serde"] }
default = serde

The serde feature is set by default whenever codes-un-m49 is added without default-features = false somewhere in the dependency tree.

country_codes = codes-iso-3166

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.

codes-iso-3166 country_codes?
serde default