castflip_derive 0.1.15

use proc_macro::TokenStream;
use quote::quote;
use syn::{
    Data, DeriveInput, Field, Fields, Ident,
    punctuated::Punctuated, token::Comma,
};


pub fn proc_tokens(input: TokenStream) -> TokenStream {
    // Parse TokenStream into an Abstract Syntax Tree (AST).
    let ast: DeriveInput = syn::parse(input).unwrap();

    match &ast.data {
        Data::Struct(data_struct) => {
            match &data_struct.fields {
                Fields::Named(fields_named) => {
                    with_bounds(&ast.ident, &fields_named.named)
                },
                Fields::Unnamed(fields_unnamed) => {
                    with_bounds(&ast.ident, &fields_unnamed.unnamed)
                },
                Fields::Unit => {
                    without_bounds(&ast.ident)
                },
            }
        },
        Data::Enum(_data_enum) => {
            panic!("Derive macro `NopFlip` does not support enum.")
        },
        Data::Union(data_union) => {
            with_bounds(&ast.ident, &data_union.fields.named)
        },
    }
}

fn with_bounds(
    ident: &Ident,
    punctuated: &Punctuated<Field, Comma>,
) -> TokenStream {
    let field_type = punctuated.iter().map(|field| &field.ty);

    quote! {
        impl castflip::Flip for #ident
        where
            #( #field_type: castflip::Flip, )*
        {
            fn flip_val_swapped(&self) -> Self {
                unsafe {
                    ::core::ptr::read(self)
                }
            }

            fn flip_var_swapped(&mut self) {}
        }

        impl castflip::NopFlip for #ident {}
    }.into()
}

fn without_bounds(ident: &Ident) -> TokenStream {
    quote! {
        impl castflip::Flip for #ident {
            fn flip_val_swapped(&self) -> Self {
                unsafe {
                    ::core::ptr::read(self)
                }
            }

            fn flip_var_swapped(&mut self) {}
        }

        impl castflip::NopFlip for #ident {}
    }.into()
}