Cargo Features

pyo3-macros-backend has no features set by default.

[dependencies]
pyo3-macros-backend = { version = "0.21.2", features = ["experimental-async"] }
experimental-async

pyo3-macros-backend has 1 feature without comment.

Features from optional dependencies

Note: we use default-features = false for proc-macro related crates not to depend on proc-macro itself. See https://github.com/PyO3/pyo3/pull/810 for more.