Cargo Features

SelfCell has no features set by default.

[dependencies]
self_cell = { version = "1.0.3", features = ["old_rust"] }
old_rust = rustversion

This optional feature lowers the minimum rustc version from 1.51 to 1.36.
However this requires polyfilling std library functionality for older rustc with technically UB versions. Testing does not show older rustc versions (ab)using this. Use at

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.

rustversion old_rust?