cfg_block 0.2.0

#![no_std]
//! A simple library for applying procedural macros to a block. Simple example:
//!
//! ```
//! use cfg_block::cfg_block;
//!
//! cfg_block! {
//!     if #[cfg(mips)] {
//!         const STR_A: &str = "where did you get this processor";
//!         const STR_B: &str = "mips just makes a good passing doctest";
//!     } else {
//!         const STR_A: &str = "good!";
//!         const STR_B: &str = "better!";
//!     }
//! }
//!
//! assert_eq!(STR_A, "good!");
//! assert_eq!(STR_B, "better!");
//! ```
//!
//! Most of the documentation is contained at [`cfg_block`], please see there
//! for more details.

// Strong clippy config
#![warn(
    clippy::pedantic,
    clippy::cargo,
    clippy::nursery,
    clippy::str_to_string,
    clippy::missing_inline_in_public_items
)]

/// Allow applying inner procedural macros to a `{}` block, which helps a lot
/// with platform-based `const` values.
///
/// # Examples
///
/// Basic example handling differnt
///
/// ```
/// use cfg_block::cfg_block;
///
/// cfg_block! {
///     #[cfg(target_family = "unix")] {
///         const PLATFORM: &str = "posix !";
///         const MY_NUMBER: u8 = 5;
///     }
///     #[cfg(target_family = "windows")] {
///         const PLATFORM: &str = "windows !";
///         const MY_NUMBER: u16 = 20;
///     }
///     #[cfg(target_family = "wasm")] {
///         const PLATFORM: &str = "web !";
///         const MY_NUMBER: i32 = -5;
///     }
/// }
///
///
/// // This is a proof of concept
/// match PLATFORM {
///     "posix !" => assert_eq!(MY_NUMBER as i32, 5),
///     "windows !" => assert_eq!(MY_NUMBER as i32, 20),
///     "web !" => assert_eq!(MY_NUMBER as i32, -5),
///     &_ => panic!(),
/// }
/// ```
///
/// Or, with the if/else syntax (only works for `cfg` macros):
///
/// ```
/// use cfg_block::cfg_block;
///
/// cfg_block! {
///     if #[cfg(mips)] {
///         const STR_A: &str = "where did you get this processor";
///         const STR_B: &str = "mips just makes a good passing doctest";
///     } else {
///         const STR_A: &str = "good!";
///         const STR_B: &str = "better!";
///     }
/// }
///
/// assert_eq!(STR_A, "good!");
/// assert_eq!(STR_B, "better!");
/// ```
///
/// Currently, if/else statements need to be in a separate `cfg_block! {}` from
/// options that do not use if/else.
///
/// It is also possible to put anything that rust considers an `item` inside the
/// block. Note that this does not include `let` bindings.
///
/// ```
/// use cfg_block::cfg_block;
///
/// cfg_block! {
///     if #[cfg(mips)] {
///         const STR_A: &str = "where did you get this processor";
///     } else {
///         const STR_A: &str = "good!";
///     }
///
///     if #[cfg(not(mips))] {
///         assert_eq!(STR_A, "good!");
///     } else {}
/// }
/// ```
#[macro_export]
macro_rules! cfg_block {
    // Note: we might be able to combine the `else` statement using TT munchers

    // Rule for things with an else statement
    // Match e.g.
    // #[cfg(something)] {
    //   item1;
    //   item2;
    // } else {
    //     item3;
    //     item4;
    // }
    //
    // Replace with
    // #[cfg(something)]
    // item1;
    // #[cfg(something)]
    // item2;
    // #[cfg(not(something))]
    // item3;
    // #[cfg(not(something))]
    // item4;
    (
        $(
            if #[cfg($meta:meta)] {
                $($item:item)*
            } else {
                $($item_f:item)*
            }
        )*
    ) => {
        $(
            $(
                #[cfg($meta)]
                $item
            )*
            $(
                #[cfg(not($meta))]
                $item_f
            )*
        )*
    };

    // Rule for things without an else statement
    // Match e.g.
    // #[something] {
    //   item1;
    //   item2;
    // }
    //
    // Replace with
    // #[something]
    // item1;
    // #[something]
    // item2;
    (
        $(
            #[$meta:meta] {
                $( $item:item )*
            }
        )*
    ) => {
        $(
            $(
                #[$meta]
                $item
            )*
        )*
    }
}

#[cfg(test)]
mod tests {
    //! Note: these tests use the (probably correct) assumption that we're not
    //! testing on a mips processor
    use super::*;

    cfg_block! {
        #[cfg(not(mips))] {
            const SINGLE_A: &str = "something a";
            const SINGLE_B: &str = "something b";
        }
    }

    #[test]
    fn single_validation() {
        assert_eq!(SINGLE_A, "something a");
        assert_eq!(SINGLE_B, "something b");
    }

    cfg_block! {
        if #[cfg(mips)] {
            const ELSE_A: &str = "nothing a";
            const ELSE_B: &str = "nothing b";
        } else {
            const ELSE_A: &str = "something a";
            const ELSE_B: &str = "something b";
        }
    }

    #[test]
    fn else_validation() {
        assert_eq!(ELSE_A, "something a");
        assert_eq!(ELSE_B, "something b");
    }

    #[test]
    fn inside_item_validation() {
        cfg_block! {
            if #[cfg(mips)] {
                assert_eq!(ELSE_A, "nothing a");
                assert_eq!(ELSE_B, "nothing b");
            } else {
                assert_eq!(ELSE_A, "something a");
                assert_eq!(ELSE_B, "something b");
            }
        }
    }

    // Currently does not work
    // #[test]
    // fn inside_validation() {
    //     // Test within a function block
    //     cfg_block! {
    //         #[cfg(mips)] {
    //             let inside_a: &str = "nothing a";
    //             let inside_b: &str = "nothing b";
    //         } else {
    //             let inside_a: &str = "something a";
    //             let inside_b: &str = "something b";
    //         }

    //     }
    //     assert_eq!(inside_a, "something a");
    //     assert_eq!(inside_b, "something b");
    // }
}