Cargo Features

failure_ext has no features set by default.

[dependencies]
failure_ext = { version = "0.1.2", features = ["future_ext"] }
future_ext = futures

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.

futures future_ext?

Enables futures ^0.1.28