bitbite_derive 0.1.2

Adds Bitbite derive
Documentation 
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//! # Bitbite derive
//! The Bitbite derive is used to save you a bit of code and make the usage cleaner. \
//! For the cleanest code I recommend using [deref-derive](https://crates.io/crates/deref_derive)
//! # Usage:
//! ```rust
//! use bitbite::*;
//! use bitbite_derive::Bitbite;
//! use deref_derive::*;
//!
//! #[derive(Bitbite, Deref, DerefMut)]
//! struct Header(pub u8);
//!
//! impl Header {
//!     pub const FIRST_NIBBLE_FLAG : Flag<u8> = Flag::new(0b0000_1111);
//! }
//!
//! let h = Header(0b1100_1010);
//! assert_eq!(h.get_flag(&Header::FIRST_NIBBLE_FLAG), 0b1010);
//! ```
//! # Multi fielded structs
//! In case you have more than one field you can use the `bitbite` attribute
//! # Usage:
//! ```rust
//! use bitbite::*;
//! use bitbite_derive::Bitbite;
//! use deref_derive::*;
//!
//! #[derive(Bitbite, Deref, DerefMut)]
//! #[bitbite(u16)]
//! struct Header {
//!     #[deref]
//!     pub field: u16,
//!     pub count:u8
//! }
//!
//! impl Header {
//!     pub const MIDDLE_NIBBLE : Flag<u16> = Flag::new(0b0000_0011_1100_0000);
//! }
//!
//! let h = Header {
//!     field: 0b0010_1010_1000_0110,
//!     count : 0,
//! };
//! assert_eq!(h.get_flag(&Header::MIDDLE_NIBBLE), 0b1010);
//! ```
use proc_macro::TokenStream;
use quote::quote;

const ATTR_NAME: &str = "bitbite";

/// # Bitbite derive
/// The Bitbite derive is used to save you a bit of code and make the usage cleaner. \
/// For the cleanest code I recommend using [deref-derive](https://crates.io/crates/deref_derive)
/// # Usage:
/// ```
/// use bitbite::*;
/// use bitbite_derive::Bitbite;
/// use deref_derive::*;
///
/// #[derive(Bitbite, Deref, DerefMut)]
/// struct Header(pub u8);
///
/// impl Header {
///     pub const FIRST_NIBBLE_FLAG : Flag<u8> = Flag::new(0b0000_1111);
/// }
///
/// let h = Header(0b1100_1010);
/// assert_eq!(h.get_flag(&Header::FIRST_NIBBLE_FLAG), 0b1010);
/// ```
/// # Multi fielded structs
/// In case you have more than one field you can use the `bitbite` attribute
/// # Usage:
/// ```rust
/// use bitbite::*;
/// use bitbite_derive::Bitbite;
/// use deref_derive::*;
///
/// #[derive(Bitbite, Deref, DerefMut)]
/// #[bitbite(u16)]
/// struct Header {
///     #[deref]
///     pub field: u16,
///     pub count:u8
/// }
///
/// impl Header {
///     pub const MIDDLE_NIBBLE : Flag<u16> = Flag::new(0b0000_0011_1100_0000);
/// }
///
/// let h = Header {
///     field: 0b0010_1010_1000_0110,
///     count : 0,
/// };
/// assert_eq!(h.get_flag(&Header::MIDDLE_NIBBLE), 0b1010);
/// ```
#[proc_macro_derive(Bitbite, attributes(bitbite))]
pub fn bitbite_macro_derive(input: TokenStream) -> TokenStream {
    let ast = syn::parse(input).unwrap();
    impl_bitbite_macro(&ast)
}

fn impl_bitbite_macro(ast: &syn::DeriveInput) -> TokenStream {
    let ident = &ast.ident;
    let data = match &ast.data {
        syn::Data::Struct(data_struct) => data_struct,
        _ => panic!("bitbite derive is currently only implemented for structs"),
    };

    let field_type = match &data.fields.len() {
        1 => {
            let field_type: Vec<_> = data.fields.iter().map(|f| f.ty.clone()).collect();
            field_type.first().unwrap().clone()
        }
        _ => {
            let attr = ast
                .attrs
                .iter()
                .find(|attr| attr.path().is_ident(ATTR_NAME))
                .expect("bitbite attribute is missing, consider adding it");
            attr.parse_args::<syn::Type>().unwrap()
        }
    };

    let expanded = quote! {
        impl Bitbite for #ident {
            type Unit = #field_type;
        }
    };

    TokenStream::from(expanded)
}