Cargo Features

[dependencies]
messages = { version = "0.3.1", default-features = false, features = ["runtime-tokio", "runtime-async-std"] }
default = runtime-tokio

The runtime-tokio feature is set by default whenever messages is added without default-features = false somewhere in the dependency tree.

runtime-tokio default = once_cell, tokio
runtime-async-std = async-std, once_cell

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.

tokio runtime-tokio

Enables tokio

Runtime section.

async-std runtime-async-std?
once_cell runtime-async-std? runtime-tokio