anchor/lang/derive/space/src/lib.rs

use std::collections::VecDeque;

use proc_macro::TokenStream;
use proc_macro2::{Ident, TokenStream as TokenStream2, TokenTree};
use quote::{quote, quote_spanned, ToTokens};
use syn::{
    parse::ParseStream, parse2, parse_macro_input, Attribute, DeriveInput, Fields, GenericArgument,
    LitInt, PathArguments, Type, TypeArray,
};

/// Implements a [`Space`](./trait.Space.html) trait on the given
/// struct or enum.
///
/// For types that have a variable size like String and Vec, it is necessary to indicate the size by the `max_len` attribute.
/// For nested types, it is necessary to specify a size for each variable type (see example).
///
/// # Example
/// ```ignore
/// #[account]
/// #[derive(InitSpace)]
/// pub struct ExampleAccount {
///     pub data: u64,
///     #[max_len(50)]
///     pub string_one: String,
///     #[max_len(10, 5)]
///     pub nested: Vec<Vec<u8>>,
/// }
///
/// #[derive(Accounts)]
/// pub struct Initialize<'info> {
///    #[account(mut)]
///    pub payer: Signer<'info>,
///    pub system_program: Program<'info, System>,
///    #[account(init, payer = payer, space = 8 + ExampleAccount::INIT_SPACE)]
///    pub data: Account<'info, ExampleAccount>,
/// }
/// ```
#[proc_macro_derive(InitSpace, attributes(max_len))]
pub fn derive_init_space(item: TokenStream) -> TokenStream {
    let input = parse_macro_input!(item as DeriveInput);
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
    let name = input.ident;

    let expanded: TokenStream2 = match input.data {
        syn::Data::Struct(strct) => match strct.fields {
            Fields::Named(named) => {
                let recurse = named.named.into_iter().map(|f| {
                    let mut max_len_args = get_max_len_args(&f.attrs);
                    len_from_type(f.ty, &mut max_len_args)
                });

                quote! {
                    #[automatically_derived]
                    impl #impl_generics anchor_lang::Space for #name #ty_generics #where_clause {
                        const INIT_SPACE: usize = 0 #(+ #recurse)*;
                    }
                }
            }
            _ => panic!("Please use named fields in account structure"),
        },
        syn::Data::Enum(enm) => {
            let variants = enm.variants.into_iter().map(|v| {
                let len = v.fields.into_iter().map(|f| {
                    let mut max_len_args = get_max_len_args(&f.attrs);
                    len_from_type(f.ty, &mut max_len_args)
                });

                quote! {
                    0 #(+ #len)*
                }
            });

            let max = gen_max(variants);

            quote! {
                #[automatically_derived]
                impl anchor_lang::Space for #name {
                    const INIT_SPACE: usize = 1 + #max;
                }
            }
        }
        _ => unimplemented!(),
    };

    TokenStream::from(expanded)
}

fn gen_max<T: Iterator<Item = TokenStream2>>(mut iter: T) -> TokenStream2 {
    if let Some(item) = iter.next() {
        let next_item = gen_max(iter);
        quote!(anchor_lang::__private::max(#item, #next_item))
    } else {
        quote!(0)
    }
}

fn len_from_type(ty: Type, attrs: &mut Option<VecDeque<TokenStream2>>) -> TokenStream2 {
    match ty {
        Type::Array(TypeArray { elem, len, .. }) => {
            let array_len = len.to_token_stream();
            let type_len = len_from_type(*elem, attrs);
            quote!((#array_len * #type_len))
        }
        Type::Path(ty_path) => {
            let path_segment = ty_path.path.segments.last().unwrap();
            let ident = &path_segment.ident;
            let type_name = ident.to_string();
            let first_ty = get_first_ty_arg(&path_segment.arguments);

            match type_name.as_str() {
                "i8" | "u8" | "bool" => quote!(1),
                "i16" | "u16" => quote!(2),
                "i32" | "u32" | "f32" => quote!(4),
                "i64" | "u64" | "f64" => quote!(8),
                "i128" | "u128" => quote!(16),
                "String" => {
                    let max_len = get_next_arg(ident, attrs);
                    quote!((4 + #max_len))
                }
                "Pubkey" => quote!(32),
                "Option" => {
                    if let Some(ty) = first_ty {
                        let type_len = len_from_type(ty, attrs);

                        quote!((1 + #type_len))
                    } else {
                        quote_spanned!(ident.span() => compile_error!("Invalid argument in Vec"))
                    }
                }
                "Vec" => {
                    if let Some(ty) = first_ty {
                        let max_len = get_next_arg(ident, attrs);
                        let type_len = len_from_type(ty, attrs);

                        quote!((4 + #type_len * #max_len))
                    } else {
                        quote_spanned!(ident.span() => compile_error!("Invalid argument in Vec"))
                    }
                }
                _ => {
                    let ty = &ty_path.path;
                    quote!(<#ty as anchor_lang::Space>::INIT_SPACE)
                }
            }
        }
        _ => panic!("Type {ty:?} is not supported"),
    }
}

fn get_first_ty_arg(args: &PathArguments) -> Option<Type> {
    match args {
        PathArguments::AngleBracketed(bracket) => bracket.args.iter().find_map(|el| match el {
            GenericArgument::Type(ty) => Some(ty.to_owned()),
            _ => None,
        }),
        _ => None,
    }
}

fn parse_len_arg(item: ParseStream) -> Result<VecDeque<TokenStream2>, syn::Error> {
    let mut result = VecDeque::new();
    while let Some(token_tree) = item.parse()? {
        match token_tree {
            TokenTree::Ident(ident) => result.push_front(quote!((#ident as usize))),
            TokenTree::Literal(lit) => {
                if let Ok(lit_int) = parse2::<LitInt>(lit.into_token_stream()) {
                    result.push_front(quote!(#lit_int))
                }
            }
            _ => (),
        }
    }

    Ok(result)
}

fn get_max_len_args(attributes: &[Attribute]) -> Option<VecDeque<TokenStream2>> {
    attributes
        .iter()
        .find(|a| a.path.is_ident("max_len"))
        .and_then(|a| a.parse_args_with(parse_len_arg).ok())
}

fn get_next_arg(ident: &Ident, args: &mut Option<VecDeque<TokenStream2>>) -> TokenStream2 {
    if let Some(arg_list) = args {
        if let Some(arg) = arg_list.pop_back() {
            quote!(#arg)
        } else {
            quote_spanned!(ident.span() => compile_error!("The number of lengths are invalid."))
        }
    } else {
        quote_spanned!(ident.span() => compile_error!("Expected max_len attribute."))
    }
}