Conditional compilation expressions

Conditional compilation using boolean expression syntax, rather than any(), all(), not().

[dependencies]
efg = "0.1"

Summary

Rust's cfg and cfg_attr conditional compilation attributes use a restrictive domain-specific language for specifying configuration predicates. The syntax is described in the Conditional compilation page of the Rust reference. The reason for this syntax as opposed to ordinary boolean expressions was to accommodate restrictions that old versions of rustc used to have on the grammar of attributes.

However, all restrictions on the attribute grammar were lifted in Rust 1.18.0 by rust-lang/rust#40346. This crate explores implementing conditional compilation using ordinary boolean expressions instead: &&, ||, ! as usual in Rust syntax.

built into rustc	this crate
#[cfg(any(thing1, thing2, …))]	#[efg(thing1 || thing2 || …)]
#[cfg(all(thing1, thing2, …))]	#[efg(thing1 && thing2 && …)]
#[cfg(not(thing))]	#[efg(!thing)]

Examples

A real-world example from the quote crate:

#[efg(feature "proc-macro" && !(target_arch "wasm32" && target_os "unknown"))]
extern crate proc_macro;

and from the proc-macro2 crate:

#[efg(super_unstable || feature "span-locations")]
pub fn start(&self) -> LineColumn {

License

^{Licensed under either of Apache License, Version 2.0 or MIT license at your option.}
_{Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.}