https://github.com/dtolnay/efg

Conditional compilation using boolean expression syntax, rather than any(), all(), not()
https://github.com/dtolnay/efg

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

• Host: GitHub
• URL: https://github.com/dtolnay/efg
• Owner: dtolnay
• License: apache-2.0
• Archived: true
• Created: 2021-12-05T18:38:04.000Z (almost 3 years ago)
• Default Branch: master
• Last Pushed: 2022-12-18T20:47:04.000Z (almost 2 years ago)
• Last Synced: 2024-05-09T09:38:25.208Z (6 months ago)
• Language: Rust
• Homepage:
• Size: 91.8 KB
• Stars: 295
• Watchers: 3
• Forks: 3
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Funding: .github/FUNDING.yml
  • License: LICENSE-APACHE

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README

        
Conditional compilation expressions

===================================

[](https://github.com/dtolnay/efg)

[](https://crates.io/crates/efg)

[](https://docs.rs/efg)

[](https://github.com/dtolnay/efg/actions?query=branch%3Amaster)

Conditional compilation using boolean expression syntax, rather than *any()*,

*all()*, *not()*.

```toml

[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.

[Conditional compilation]: https://doc.rust-lang.org/1.57.0/reference/conditional-compilation.html

[rust-lang/rust#40346]: https://github.com/rust-lang/rust/pull/40346

built into rustcthis 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:

```rust

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

extern crate proc_macro;

```

and from the `proc-macro2` crate:

```rust

#[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.