Crate realia 

Realia provides attribute macros for conditional compilation, analogous to #[cfg(...)] and #[cfg_attr(...)].

Attribute Macros

all

Checks if multiple conditions are met.

any

Checks if at least one of multiple conditions is met.

attr

Applies an attribute when the condition is met. You can also specify const this way.

cmd

Checks whether an executable exists on the PATH.

dep

Checks whether a crate has a certain dependency and optionally if that dependency is a certain version.

dep_before

Checks whether a crate has a certain dependency below a certain version.

dep_from_registry

Checks whether a crate has a certain dependency installed from the registry (as opposed to being a Git dependency or a path dependency). This is useful if you have non-registry dependencies with a registry fallback for publishing.

dep_since

Checks whether a crate has a certain dependency at or above a certain version.

env

Checks whether an environment variable is defined and optionally what value it has.

not

Inverts another condition.