Cargo Features

tracing-timing = { version = "0.6.0", default-features = false, features = ["layer"] }
default = layer

The layer feature is set by default whenever tracing-timing is added without default-features = false somewhere in the dependency tree.

layer default = tracing-subscriber

Features from optional dependencies

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

tracing-subscriber layer