//! Derive macros for [bytemuck](https://docs.rs/bytemuck) traits.
extern crate proc_macro;
mod traits;
use proc_macro2::TokenStream;
use quote::quote;
use syn::{parse_macro_input, DeriveInput, Result};
use crate::traits::{
bytemuck_crate_name, AnyBitPattern, CheckedBitPattern, Contiguous, Derivable,
NoUninit, Pod, TransparentWrapper, Zeroable,
};
/// Derive the `Pod` trait for a struct
///
/// The macro ensures that the struct follows all the the safety requirements
/// for the `Pod` trait.
///
/// The following constraints need to be satisfied for the macro to succeed
///
/// - All fields in the struct must implement `Pod`
/// - The struct must be `#[repr(C)]` or `#[repr(transparent)]`
/// - The struct must not contain any padding bytes
/// - The struct contains no generic parameters, if it is not
/// `#[repr(transparent)]`
///
/// ## Examples
///
/// ```rust
/// # use std::marker::PhantomData;
/// # use bytemuck_derive::{Pod, Zeroable};
/// #[derive(Copy, Clone, Pod, Zeroable)]
/// #[repr(C)]
/// struct Test {
/// a: u16,
/// b: u16,
/// }
///
/// #[derive(Copy, Clone, Pod, Zeroable)]
/// #[repr(transparent)]
/// struct Generic<A, B> {
/// a: A,
/// b: PhantomData<B>,
/// }
/// ```
///
/// If the struct is generic, it must be `#[repr(transparent)]` also.
///
/// ```compile_fail
/// # use bytemuck::{Pod, Zeroable};
/// # use std::marker::PhantomData;
/// #[derive(Copy, Clone, Pod, Zeroable)]
/// #[repr(C)] // must be `#[repr(transparent)]`
/// struct Generic<A> {
/// a: A,
/// }
/// ```
///
/// If the struct is generic and `#[repr(transparent)]`, then it is only `Pod`
/// when all of its generics are `Pod`, not just its fields.
///
/// ```
/// # use bytemuck::{Pod, Zeroable};
/// # use std::marker::PhantomData;
/// #[derive(Copy, Clone, Pod, Zeroable)]
/// #[repr(transparent)]
/// struct Generic<A, B> {
/// a: A,
/// b: PhantomData<B>,
/// }
///
/// let _: u32 = bytemuck::cast(Generic { a: 4u32, b: PhantomData::<u32> });
/// ```
///
/// ```compile_fail
/// # use bytemuck::{Pod, Zeroable};
/// # use std::marker::PhantomData;
/// # #[derive(Copy, Clone, Pod, Zeroable)]
/// # #[repr(transparent)]
/// # struct Generic<A, B> {
/// # a: A,
/// # b: PhantomData<B>,
/// # }
/// struct NotPod;
///
/// let _: u32 = bytemuck::cast(Generic { a: 4u32, b: PhantomData::<NotPod> });
/// ```
#[proc_macro_derive(Pod, attributes(bytemuck))]
pub fn derive_pod(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let expanded =
derive_marker_trait::<Pod>(parse_macro_input!(input as DeriveInput));
proc_macro::TokenStream::from(expanded)
}
/// Derive the `AnyBitPattern` trait for a struct
///
/// The macro ensures that the struct follows all the the safety requirements
/// for the `AnyBitPattern` trait.
///
/// The following constraints need to be satisfied for the macro to succeed
///
/// - All fields in the struct must to implement `AnyBitPattern`
#[proc_macro_derive(AnyBitPattern, attributes(bytemuck))]
pub fn derive_anybitpattern(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let expanded = derive_marker_trait::<AnyBitPattern>(parse_macro_input!(
input as DeriveInput
));
proc_macro::TokenStream::from(expanded)
}
/// Derive the `Zeroable` trait for a struct
///
/// The macro ensures that the struct follows all the the safety requirements
/// for the `Zeroable` trait.
///
/// The following constraints need to be satisfied for the macro to succeed
///
/// - All fields in the struct must to implement `Zeroable`
///
/// ## Example
///
/// ```rust
/// # use bytemuck_derive::{Zeroable};
/// #[derive(Copy, Clone, Zeroable)]
/// #[repr(C)]
/// struct Test {
/// a: u16,
/// b: u16,
/// }
/// ```
///
/// # Custom bounds
///
/// Custom bounds for the derived `Zeroable` impl can be given using the
/// `#[zeroable(bound = "")]` helper attribute.
///
/// Using this attribute additionally opts-in to "perfect derive" semantics,
/// where instead of adding bounds for each generic type parameter, bounds are
/// added for each field's type.
///
/// ## Examples
///
/// ```rust
/// # use bytemuck::Zeroable;
/// # use std::marker::PhantomData;
/// #[derive(Clone, Zeroable)]
/// #[zeroable(bound = "")]
/// struct AlwaysZeroable<T> {
/// a: PhantomData<T>,
/// }
///
/// AlwaysZeroable::<std::num::NonZeroU8>::zeroed();
/// ```
///
/// ```rust,compile_fail
/// # use bytemuck::Zeroable;
/// # use std::marker::PhantomData;
/// #[derive(Clone, Zeroable)]
/// #[zeroable(bound = "T: Copy")]
/// struct ZeroableWhenTIsCopy<T> {
/// a: PhantomData<T>,
/// }
///
/// ZeroableWhenTIsCopy::<String>::zeroed();
/// ```
///
/// The restriction that all fields must be Zeroable is still applied, and this
/// is enforced using the mentioned "perfect derive" semantics.
///
/// ```rust
/// # use bytemuck::Zeroable;
/// #[derive(Clone, Zeroable)]
/// #[zeroable(bound = "")]
/// struct ZeroableWhenTIsZeroable<T> {
/// a: T,
/// }
/// ZeroableWhenTIsZeroable::<u32>::zeroed();
/// ```
///
/// ```rust,compile_fail
/// # use bytemuck::Zeroable;
/// # #[derive(Clone, Zeroable)]
/// # #[zeroable(bound = "")]
/// # struct ZeroableWhenTIsZeroable<T> {
/// # a: T,
/// # }
/// ZeroableWhenTIsZeroable::<String>::zeroed();
/// ```
#[proc_macro_derive(Zeroable, attributes(bytemuck, zeroable))]
pub fn derive_zeroable(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let expanded =
derive_marker_trait::<Zeroable>(parse_macro_input!(input as DeriveInput));
proc_macro::TokenStream::from(expanded)
}
/// Derive the `NoUninit` trait for a struct or enum
///
/// The macro ensures that the type follows all the the safety requirements
/// for the `NoUninit` trait.
///
/// The following constraints need to be satisfied for the macro to succeed
/// (the rest of the constraints are guaranteed by the `NoUninit` subtrait
/// bounds, i.e. the type must be `Sized + Copy + 'static`):
///
/// If applied to a struct:
/// - All fields in the struct must implement `NoUninit`
/// - The struct must be `#[repr(C)]` or `#[repr(transparent)]`
/// - The struct must not contain any padding bytes
/// - The struct must contain no generic parameters
///
/// If applied to an enum:
/// - The enum must be explicit `#[repr(Int)]`, `#[repr(C)]`, or both
/// - All variants must be fieldless
/// - The enum must contain no generic parameters
#[proc_macro_derive(NoUninit, attributes(bytemuck))]
pub fn derive_no_uninit(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let expanded =
derive_marker_trait::<NoUninit>(parse_macro_input!(input as DeriveInput));
proc_macro::TokenStream::from(expanded)
}
/// Derive the `CheckedBitPattern` trait for a struct or enum.
///
/// The macro ensures that the type follows all the the safety requirements
/// for the `CheckedBitPattern` trait and derives the required `Bits` type
/// definition and `is_valid_bit_pattern` method for the type automatically.
///
/// The following constraints need to be satisfied for the macro to succeed:
///
/// If applied to a struct:
/// - All fields must implement `CheckedBitPattern`
/// - The struct must be `#[repr(C)]` or `#[repr(transparent)]`
/// - The struct must contain no generic parameters
///
/// If applied to an enum:
/// - The enum must be explicit `#[repr(Int)]`
/// - All fields in variants must implement `CheckedBitPattern`
/// - The enum must contain no generic parameters
#[proc_macro_derive(CheckedBitPattern)]
pub fn derive_maybe_pod(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let expanded = derive_marker_trait::<CheckedBitPattern>(parse_macro_input!(
input as DeriveInput
));
proc_macro::TokenStream::from(expanded)
}
/// Derive the `TransparentWrapper` trait for a struct
///
/// The macro ensures that the struct follows all the the safety requirements
/// for the `TransparentWrapper` trait.
///
/// The following constraints need to be satisfied for the macro to succeed
///
/// - The struct must be `#[repr(transparent)]`
/// - The struct must contain the `Wrapped` type
/// - Any ZST fields must be [`Zeroable`][derive@Zeroable].
///
/// If the struct only contains a single field, the `Wrapped` type will
/// automatically be determined. If there is more then one field in the struct,
/// you need to specify the `Wrapped` type using `#[transparent(T)]`
///
/// ## Examples
///
/// ```rust
/// # use bytemuck_derive::TransparentWrapper;
/// # use std::marker::PhantomData;
/// #[derive(Copy, Clone, TransparentWrapper)]
/// #[repr(transparent)]
/// #[transparent(u16)]
/// struct Test<T> {
/// inner: u16,
/// extra: PhantomData<T>,
/// }
/// ```
///
/// If the struct contains more than one field, the `Wrapped` type must be
/// explicitly specified.
///
/// ```rust,compile_fail
/// # use bytemuck_derive::TransparentWrapper;
/// # use std::marker::PhantomData;
/// #[derive(Copy, Clone, TransparentWrapper)]
/// #[repr(transparent)]
/// // missing `#[transparent(u16)]`
/// struct Test<T> {
/// inner: u16,
/// extra: PhantomData<T>,
/// }
/// ```
///
/// Any ZST fields must be `Zeroable`.
///
/// ```rust,compile_fail
/// # use bytemuck_derive::TransparentWrapper;
/// # use std::marker::PhantomData;
/// struct NonTransparentSafeZST;
///
/// #[derive(TransparentWrapper)]
/// #[repr(transparent)]
/// #[transparent(u16)]
/// struct Test<T> {
/// inner: u16,
/// extra: PhantomData<T>,
/// another_extra: NonTransparentSafeZST, // not `Zeroable`
/// }
/// ```
#[proc_macro_derive(TransparentWrapper, attributes(bytemuck, transparent))]
pub fn derive_transparent(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let expanded = derive_marker_trait::<TransparentWrapper>(parse_macro_input!(
input as DeriveInput
));
proc_macro::TokenStream::from(expanded)
}
/// Derive the `Contiguous` trait for an enum
///
/// The macro ensures that the enum follows all the the safety requirements
/// for the `Contiguous` trait.
///
/// The following constraints need to be satisfied for the macro to succeed
///
/// - The enum must be `#[repr(Int)]`
/// - The enum must be fieldless
/// - The enum discriminants must form a contiguous range
///
/// ## Example
///
/// ```rust
/// # use bytemuck_derive::{Contiguous};
///
/// #[derive(Copy, Clone, Contiguous)]
/// #[repr(u8)]
/// enum Test {
/// A = 0,
/// B = 1,
/// C = 2,
/// }
/// ```
#[proc_macro_derive(Contiguous)]
pub fn derive_contiguous(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let expanded =
derive_marker_trait::<Contiguous>(parse_macro_input!(input as DeriveInput));
proc_macro::TokenStream::from(expanded)
}
/// Derive the `PartialEq` and `Eq` trait for a type
///
/// The macro implements `PartialEq` and `Eq` by casting both sides of the
/// comparison to a byte slice and then compares those.
///
/// ## Warning
///
/// Since this implements a byte wise comparison, the behavior of floating point
/// numbers does not match their usual comparison behavior. Additionally other
/// custom comparison behaviors of the individual fields are also ignored. This
/// also does not implement `StructuralPartialEq` / `StructuralEq` like
/// `PartialEq` / `Eq` would. This means you can't pattern match on the values.
///
/// ## Examples
///
/// ```rust
/// # use bytemuck_derive::{ByteEq, NoUninit};
/// #[derive(Copy, Clone, NoUninit, ByteEq)]
/// #[repr(C)]
/// struct Test {
/// a: u32,
/// b: char,
/// c: f32,
/// }
/// ```
///
/// ```rust
/// # use bytemuck_derive::ByteEq;
/// # use bytemuck::NoUninit;
/// #[derive(Copy, Clone, ByteEq)]
/// #[repr(C)]
/// struct Test<const N: usize> {
/// a: [u32; N],
/// }
/// unsafe impl<const N: usize> NoUninit for Test<N> {}
/// ```
#[proc_macro_derive(ByteEq)]
pub fn derive_byte_eq(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let crate_name = bytemuck_crate_name(&input);
let ident = input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
proc_macro::TokenStream::from(quote! {
impl #impl_generics ::core::cmp::PartialEq for #ident #ty_generics #where_clause {
#[inline]
#[must_use]
fn eq(&self, other: &Self) -> bool {
#crate_name::bytes_of(self) == #crate_name::bytes_of(other)
}
}
impl #impl_generics ::core::cmp::Eq for #ident #ty_generics #where_clause { }
})
}
/// Derive the `Hash` trait for a type
///
/// The macro implements `Hash` by casting the value to a byte slice and hashing
/// that.
///
/// ## Warning
///
/// The hash does not match the standard library's `Hash` derive.
///
/// ## Examples
///
/// ```rust
/// # use bytemuck_derive::{ByteHash, NoUninit};
/// #[derive(Copy, Clone, NoUninit, ByteHash)]
/// #[repr(C)]
/// struct Test {
/// a: u32,
/// b: char,
/// c: f32,
/// }
/// ```
///
/// ```rust
/// # use bytemuck_derive::ByteHash;
/// # use bytemuck::NoUninit;
/// #[derive(Copy, Clone, ByteHash)]
/// #[repr(C)]
/// struct Test<const N: usize> {
/// a: [u32; N],
/// }
/// unsafe impl<const N: usize> NoUninit for Test<N> {}
/// ```
#[proc_macro_derive(ByteHash)]
pub fn derive_byte_hash(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let crate_name = bytemuck_crate_name(&input);
let ident = input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
proc_macro::TokenStream::from(quote! {
impl #impl_generics ::core::hash::Hash for #ident #ty_generics #where_clause {
#[inline]
fn hash<H: ::core::hash::Hasher>(&self, state: &mut H) {
::core::hash::Hash::hash_slice(#crate_name::bytes_of(self), state)
}
#[inline]
fn hash_slice<H: ::core::hash::Hasher>(data: &[Self], state: &mut H) {
::core::hash::Hash::hash_slice(#crate_name::cast_slice::<_, u8>(data), state)
}
}
})
}
/// Basic wrapper for error handling
fn derive_marker_trait<Trait: Derivable>(input: DeriveInput) -> TokenStream {
derive_marker_trait_inner::<Trait>(input)
.unwrap_or_else(|err| err.into_compile_error())
}
/// Find `#[name(key = "value")]` helper attributes on the struct, and return
/// their `"value"`s parsed with `parser`.
///
/// Returns an error if any attributes with the given `name` do not match the
/// expected format. Returns `Ok([])` if no attributes with `name` are found.
fn find_and_parse_helper_attributes<P: syn::parse::Parser + Copy>(
attributes: &[syn::Attribute], name: &str, key: &str, parser: P,
example_value: &str, invalid_value_msg: &str,
) -> Result<Vec<P::Output>> {
let invalid_format_msg =
format!("{name} attribute must be `{name}({key} = \"{example_value}\")`",);
let values_to_check = attributes.iter().filter_map(|attr| match &attr.meta {
// If a `Path` matches our `name`, return an error, else ignore it.
// e.g. `#[zeroable]`
syn::Meta::Path(path) => path
.is_ident(name)
.then(|| Err(syn::Error::new_spanned(path, &invalid_format_msg))),
// If a `NameValue` matches our `name`, return an error, else ignore it.
// e.g. `#[zeroable = "hello"]`
syn::Meta::NameValue(namevalue) => {
namevalue.path.is_ident(name).then(|| {
Err(syn::Error::new_spanned(&namevalue.path, &invalid_format_msg))
})
}
// If a `List` matches our `name`, match its contents to our format, else
// ignore it. If its contents match our format, return the value, else
// return an error.
syn::Meta::List(list) => list.path.is_ident(name).then(|| {
let namevalue: syn::MetaNameValue = syn::parse2(list.tokens.clone())
.map_err(|_| {
syn::Error::new_spanned(&list.tokens, &invalid_format_msg)
})?;
if namevalue.path.is_ident(key) {
match namevalue.value {
syn::Expr::Lit(syn::ExprLit {
lit: syn::Lit::Str(strlit), ..
}) => Ok(strlit),
_ => {
Err(syn::Error::new_spanned(&namevalue.path, &invalid_format_msg))
}
}
} else {
Err(syn::Error::new_spanned(&namevalue.path, &invalid_format_msg))
}
}),
});
// Parse each value found with the given parser, and return them if no errors
// occur.
values_to_check
.map(|lit| {
let lit = lit?;
lit.parse_with(parser).map_err(|err| {
syn::Error::new_spanned(&lit, format!("{invalid_value_msg}: {err}"))
})
})
.collect()
}
fn derive_marker_trait_inner<Trait: Derivable>(
mut input: DeriveInput,
) -> Result<TokenStream> {
let crate_name = bytemuck_crate_name(&input);
let trait_ = Trait::ident(&input, &crate_name)?;
// If this trait allows explicit bounds, and any explicit bounds were given,
// then use those explicit bounds. Else, apply the default bounds (bound
// each generic type on this trait).
if let Some(name) = Trait::explicit_bounds_attribute_name() {
// See if any explicit bounds were given in attributes.
let explicit_bounds = find_and_parse_helper_attributes(
&input.attrs,
name,
"bound",
<syn::punctuated::Punctuated<syn::WherePredicate, syn::Token![,]>>::parse_terminated,
"Type: Trait",
"invalid where predicate",
)?;
if !explicit_bounds.is_empty() {
// Explicit bounds were given.
// Enforce explicitly given bounds, and emit "perfect derive" (i.e. add
// bounds for each field's type).
let explicit_bounds = explicit_bounds
.into_iter()
.flatten()
.collect::<Vec<syn::WherePredicate>>();
let predicates = &mut input.generics.make_where_clause().predicates;
predicates.extend(explicit_bounds);
let fields = match &input.data {
syn::Data::Struct(syn::DataStruct { fields, .. }) => fields.clone(),
syn::Data::Union(_) => {
return Err(syn::Error::new_spanned(
trait_,
&"perfect derive is not supported for unions",
));
}
syn::Data::Enum(_) => {
return Err(syn::Error::new_spanned(
trait_,
&"perfect derive is not supported for enums",
));
}
};
for field in fields {
let ty = field.ty;
predicates.push(syn::parse_quote!(
#ty: #trait_
));
}
} else {
// No explicit bounds were given.
// Enforce trait bound on all type generics.
add_trait_marker(&mut input.generics, &trait_);
}
} else {
// This trait does not allow explicit bounds.
// Enforce trait bound on all type generics.
add_trait_marker(&mut input.generics, &trait_);
}
let name = &input.ident;
let (impl_generics, ty_generics, where_clause) =
input.generics.split_for_impl();
Trait::check_attributes(&input.data, &input.attrs)?;
let asserts = Trait::asserts(&input, &crate_name)?;
let (trait_impl_extras, trait_impl) = Trait::trait_impl(&input, &crate_name)?;
let implies_trait = if let Some(implies_trait) =
Trait::implies_trait(&crate_name)
{
quote!(unsafe impl #impl_generics #implies_trait for #name #ty_generics #where_clause {})
} else {
quote!()
};
let where_clause =
if Trait::requires_where_clause() { where_clause } else { None };
Ok(quote! {
#asserts
#trait_impl_extras
unsafe impl #impl_generics #trait_ for #name #ty_generics #where_clause {
#trait_impl
}
#implies_trait
})
}
/// Add a trait marker to the generics if it is not already present
fn add_trait_marker(generics: &mut syn::Generics, trait_name: &syn::Path) {
// Get each generic type parameter.
let type_params = generics
.type_params()
.map(|param| ¶m.ident)
.map(|param| {
syn::parse_quote!(
#param: #trait_name
)
})
.collect::<Vec<syn::WherePredicate>>();
generics.make_where_clause().predicates.extend(type_params);
}
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