packet_derive 0.1.7

Derive implementation for packet_enum
Documentation 
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use proc_macro::TokenStream;
use quote::quote;
use syn::{Data, DeriveInput, Fields, parse_macro_input};

#[proc_macro_derive(PacketEnum)]
pub fn into_packet(input: TokenStream) -> TokenStream {
    // Parse the input tokens into a syntax tree
    let input = parse_macro_input!(input as DeriveInput);

    // Check if the input is an enum
    let variants = if let Data::Enum(data_enum) = input.data {
        data_enum.variants
    } else {
        return quote! { compile_error!("Unsupported structure (enum's only)") }.into();
        // Return empty if not an enum
    };

    // size of the bitflag
    let size = match variants.len() {
        0 => return quote! {}.into(),
        1..=8 => quote! { u8 },
        9..=16 => quote! { u16 },
        17..=32 => quote! { u32 },
        33..=64 => quote! { u64 },
        65..=128 => quote! { u128 },
        _ => return quote! { compile_error!("Enum has too many variants."); }.into(),
    };

    let old_enum_name = input.ident;
    let new_enum_name = quote::format_ident!("{}Kind", old_enum_name);

    // Create the variants for the new enum (copied from the original)
    let flag_arms = variants.iter().enumerate().map(|(i, variant)| {
        let ident = &variant.ident;
        quote! {
            const #ident = 1 << #i;
        }
    });

    let match_arms = variants.iter().map(|variant| {
        let ident = &variant.ident;

        // Handle tuple and struct variants
        match &variant.fields {
            Fields::Unit => {
                quote! {
                    #old_enum_name::#ident => #new_enum_name::#ident,
                }
            }
            Fields::Unnamed(_) => {
                quote! {
                    #old_enum_name::#ident(..) => #new_enum_name::#ident,
                }
            }
            Fields::Named(_) => {
                quote! {
                    #old_enum_name::#ident { .. } => #new_enum_name::#ident,
                }
            }
        }
    });

    let doc_comment = format!("Automatically generated bitflags for [`{old_enum_name}`].",);

    let new_enum = quote! {
        ::bitflags::bitflags! {
            #[doc = #doc_comment]
            #[derive(Clone, Copy, Debug)]
            pub struct #new_enum_name: #size {
                #(#flag_arms)*
            }
        }
    };

    let new_enum_impl = quote! {
        impl AsPacketKind for #new_enum_name {}

        impl AsPacketSend for #old_enum_name {}
        impl<'a> AsPacketRecv<'a, #new_enum_name> for #old_enum_name {
            fn kind(&self) -> #new_enum_name {
                match self {
                    #(#match_arms)*
                }
            }
        }
    };

    // Build the new enum definition
    quote! {
        #new_enum
        #new_enum_impl

    }
    .into()
}