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//! This proc macro derives a custom Multihash code table from a list of
//! hashers. It also generates a public type called `Multihash` which
//! corresponds to the specified `alloc_size`.
//!
//! The digests are stack allocated with a fixed size. That size needs to be big
//! enough to hold any of the specified hash digests. This cannot be determined
//! reliably on compile-time, hence it needs to set manually via the
//! `alloc_size` attribute. Also you might want to set it to bigger sizes then
//! necessarily needed for backwards/forward compatibility.
//!
//! If you set `#mh(alloc_size = …)` to a too low value, you will get compiler
//! errors. Please note the the sizes are checked only on a syntactic level and
//! *not* on the type level. This means that digest need to have a size const
//! generic, which is a valid `usize`, for example `32` or `64`.
//!
//! You can disable those compiler errors with setting the
//! `no_alloc_size_errors` attribute. This can be useful if you e.g. have
//! specified type aliases for your hash digests and you are sure you use the
//! correct value for `alloc_size`.
//!
//! # Example
//!
//! ```
//! use sp_multihash::derive::Multihash;
//! use sp_multihash::MultihashDigest;
//!
//! #[derive(Clone, Copy, Debug, Eq, Multihash, PartialEq)]
//! #[mh(alloc_size = 64)]
//! pub enum Code {
//!     #[mh(code = 0x01, hasher = sp_multihash::Sha2_256, digest = sp_multihash::Sha2Digest<32>)]
//!     Foo,
//!     #[mh(code = 0x02, hasher = sp_multihash::Sha2_512, digest = sp_multihash::Sha2Digest<64>)]
//!     Bar,
//! }
//!
//! let hash = Code::Foo.digest(b"hello world!");
//! println!("{:02x?}", hash);
//! ```
extern crate proc_macro;

mod multihash;
mod utils;

use proc_macro::TokenStream;
use proc_macro_error::proc_macro_error;
use synstructure::{
  decl_derive,
  Structure,
};

decl_derive!([Multihash, attributes(mh)] => #[proc_macro_error] multihash);
fn multihash(s: Structure) -> TokenStream { multihash::multihash(s).into() }