4331834003
* Move tests -> testing * Directory restructure * Update Cargo.toml during restructure * Update Makefile during restructure * Fix arbitrary path
127 lines
4.3 KiB
Rust
127 lines
4.3 KiB
Rust
#![recursion_limit = "256"]
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extern crate proc_macro;
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use proc_macro::TokenStream;
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use quote::quote;
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use syn::{parse_macro_input, Attribute, DeriveInput, Meta};
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/// Return a Vec of `syn::Ident` for each named field in the struct, whilst filtering out fields
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/// that should not be hashed.
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///
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/// # Panics
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/// Any unnamed struct field (like in a tuple struct) will raise a panic at compile time.
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fn get_hashable_fields<'a>(struct_data: &'a syn::DataStruct) -> Vec<&'a syn::Ident> {
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get_hashable_fields_and_their_caches(struct_data)
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.into_iter()
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.map(|(ident, _, _)| ident)
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.collect()
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}
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/// Return a Vec of the hashable fields of a struct, and each field's type and optional cache field.
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fn get_hashable_fields_and_their_caches<'a>(
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struct_data: &'a syn::DataStruct,
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) -> Vec<(&'a syn::Ident, syn::Type, Option<syn::Ident>)> {
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struct_data
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.fields
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.iter()
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.filter_map(|f| {
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if should_skip_hashing(&f) {
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None
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} else {
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let ident = f
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.ident
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.as_ref()
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.expect("tree_hash_derive only supports named struct fields");
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let opt_cache_field = get_cache_field_for(&f);
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Some((ident, f.ty.clone(), opt_cache_field))
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}
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})
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.collect()
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}
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/// Parse the cached_tree_hash attribute for a field.
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///
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/// Extract the cache field name from `#[cached_tree_hash(cache_field_name)]`
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///
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/// Return `Some(cache_field_name)` if the field has a cached tree hash attribute,
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/// or `None` otherwise.
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fn get_cache_field_for(field: &syn::Field) -> Option<syn::Ident> {
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use syn::{MetaList, NestedMeta};
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let parsed_attrs = cached_tree_hash_attr_metas(&field.attrs);
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if let [Meta::List(MetaList { nested, .. })] = &parsed_attrs[..] {
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nested.iter().find_map(|x| match x {
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NestedMeta::Meta(Meta::Path(path)) => path.get_ident().cloned(),
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_ => None,
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})
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} else {
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None
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}
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}
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/// Process the `cached_tree_hash` attributes from a list of attributes into structured `Meta`s.
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fn cached_tree_hash_attr_metas(attrs: &[Attribute]) -> Vec<Meta> {
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attrs
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.iter()
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.filter(|attr| attr.path.is_ident("cached_tree_hash"))
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.flat_map(|attr| attr.parse_meta())
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.collect()
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}
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/// Returns true if some field has an attribute declaring it should not be hashed.
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///
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/// The field attribute is: `#[tree_hash(skip_hashing)]`
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fn should_skip_hashing(field: &syn::Field) -> bool {
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field.attrs.iter().any(|attr| {
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attr.path.is_ident("tree_hash")
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&& attr.tokens.to_string().replace(" ", "") == "(skip_hashing)"
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})
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}
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/// Implements `tree_hash::TreeHash` for some `struct`.
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///
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/// Fields are hashed in the order they are defined.
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#[proc_macro_derive(TreeHash, attributes(tree_hash))]
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pub fn tree_hash_derive(input: TokenStream) -> TokenStream {
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let item = parse_macro_input!(input as DeriveInput);
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let name = &item.ident;
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let (impl_generics, ty_generics, where_clause) = &item.generics.split_for_impl();
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let struct_data = match &item.data {
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syn::Data::Struct(s) => s,
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_ => panic!("tree_hash_derive only supports structs."),
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};
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let idents = get_hashable_fields(&struct_data);
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let num_leaves = idents.len();
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let output = quote! {
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impl #impl_generics tree_hash::TreeHash for #name #ty_generics #where_clause {
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fn tree_hash_type() -> tree_hash::TreeHashType {
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tree_hash::TreeHashType::Container
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}
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fn tree_hash_packed_encoding(&self) -> Vec<u8> {
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unreachable!("Struct should never be packed.")
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}
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fn tree_hash_packing_factor() -> usize {
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unreachable!("Struct should never be packed.")
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}
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fn tree_hash_root(&self) -> tree_hash::Hash256 {
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let mut hasher = tree_hash::MerkleHasher::with_leaves(#num_leaves);
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#(
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hasher.write(self.#idents.tree_hash_root().as_bytes())
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.expect("tree hash derive should not apply too many leaves");
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)*
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hasher.finish().expect("tree hash derive should not have a remaining buffer")
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}
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}
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};
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output.into()
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}
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