bytecheck_derive/lib.rs
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//! Procedural macros for bytecheck.
#![deny(
rust_2018_compatibility,
rust_2018_idioms,
future_incompatible,
nonstandard_style,
unused,
clippy::all
)]
mod attributes;
mod repr;
mod util;
use proc_macro2::TokenStream;
use quote::quote;
use syn::{
parse_macro_input, parse_quote, spanned::Spanned, Data, DeriveInput, Error,
Field, Fields, Ident, Index, Path,
};
use crate::{
attributes::{Attributes, FieldAttributes},
repr::Repr,
util::{iter_fields, strip_raw},
};
/// Derives `CheckBytes` for the labeled type.
///
/// This derive macro automatically adds a type bound `field: CheckBytes<__C>`
/// for each field type. This can cause an overflow while evaluating trait
/// bounds if the structure eventually references its own type, as the
/// implementation of `CheckBytes` for a struct depends on each field type
/// implementing it as well. Adding the attribute `#[check_bytes(omit_bounds)]`
/// to a field will suppress this trait bound and allow recursive structures.
/// This may be too coarse for some types, in which case additional type bounds
/// may be required with `bounds(...)`.
///
/// # Attributes
///
/// Additional arguments can be specified using attributes.
///
/// `#[bytecheck(...)]` accepts the following attributes:
///
/// ## Types only
///
/// - `bounds(...)`: Adds additional bounds to the `CheckBytes` implementation.
/// This can be especially useful when dealing with recursive structures,
/// where bounds may need to be omitted to prevent recursive type definitions.
/// In the context of the added bounds, `__C` is the name of the context
/// generic (e.g. `__C: MyContext`).
/// - `crate = ...`: Chooses an alternative crate path to import bytecheck from.
/// - `verify`: Adds an additional verification step after the validity of each
/// field has been checked. See the `Verify` trait for more information.
///
/// ## Fields only
///
/// - `omit_bounds`: Omits trait bounds for the annotated field in the generated
/// impl.
#[proc_macro_derive(CheckBytes, attributes(bytecheck))]
pub fn check_bytes_derive(
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
match derive_check_bytes(parse_macro_input!(input as DeriveInput)) {
Ok(result) => result.into(),
Err(e) => e.to_compile_error().into(),
}
}
fn derive_check_bytes(mut input: DeriveInput) -> Result<TokenStream, Error> {
let attributes = Attributes::parse(&input)?;
let crate_path = attributes.crate_path();
let name = &input.ident;
let mut trait_generics = input.generics.clone();
// Split type generics for use later
input.generics.make_where_clause();
let (type_impl_generics, type_ty_generics, type_where_clause) =
input.generics.split_for_impl();
let type_where_clause = type_where_clause.unwrap();
// Trait generics are created by modifying the type generics.
// We add a context parameter __C for the CheckBytes type parameter.
trait_generics.params.push(parse_quote! {
__C: #crate_path::rancor::Fallible + ?::core::marker::Sized
});
// We add context error bounds to the where clause for the trait impl.
let trait_where_clause = trait_generics.make_where_clause();
trait_where_clause.predicates.push(match &input.data {
// Structs and unions just propagate any errors from checking their
// fields, so the error type of the context just needs to be `Trace`.
Data::Struct(_) | Data::Union(_) => parse_quote! {
<
__C as #crate_path::rancor::Fallible
>::Error: #crate_path::rancor::Trace
},
// Enums may error while checking the discriminant, so the error type of
// the context needs to implement `Source` so we can create a new error
// from an `InvalidEnumDiscriminantError`.
Data::Enum(_) => parse_quote! {
<
__C as #crate_path::rancor::Fallible
>::Error: #crate_path::rancor::Source
},
});
// If the user specified any aditional bounds, we add them to the where
// clause.
if let Some(ref bounds) = attributes.bounds {
for clause in bounds {
trait_where_clause.predicates.push(clause.clone());
}
}
// If the user specified `verify`, then we need to bound `Self: Verify<__C>`
// so we can call `Verify::verify`.
let verify = if attributes.verify.is_some() {
trait_where_clause.predicates.push(parse_quote!(
#name #type_ty_generics: #crate_path::Verify<__C>
));
Some(quote! {
<#name #type_ty_generics as #crate_path::Verify<__C>>::verify(
unsafe { &*value },
context,
)?;
})
} else {
None
};
let mut check_where = trait_where_clause.clone();
for field in iter_fields(&input.data) {
let field_attrs = FieldAttributes::parse(field)?;
if field_attrs.omit_bounds.is_none() {
let ty = &field.ty;
check_where.predicates.push(parse_quote! {
#ty: #crate_path::CheckBytes<__C>
});
}
}
// Split trait generics for use later
let (trait_impl_generics, _, trait_where_clause) =
trait_generics.split_for_impl();
let trait_where_clause = trait_where_clause.unwrap();
// Build CheckBytes impl
let check_bytes_impl = match input.data {
Data::Struct(ref data) => match data.fields {
Fields::Named(ref fields) => {
let field_checks = fields.named.iter().map(|f| {
let field = &f.ident;
let ty = &f.ty;
quote! {
<#ty as #crate_path::CheckBytes<__C>>::check_bytes(
::core::ptr::addr_of!((*value).#field),
context
).map_err(|e| {
<
<
__C as #crate_path::rancor::Fallible
>::Error as #crate_path::rancor::Trace
>::trace(
e,
#crate_path::StructCheckContext {
struct_name: ::core::stringify!(#name),
field_name: ::core::stringify!(#field),
},
)
})?;
}
});
quote! {
#[automatically_derived]
// SAFETY: `check_bytes` only returns `Ok` if all of the
// fields of the struct are valid. If all of the fields are
// valid, then the overall struct is also valid.
unsafe impl #trait_impl_generics
#crate_path::CheckBytes<__C> for #name #type_ty_generics
#check_where
{
unsafe fn check_bytes(
value: *const Self,
context: &mut __C,
) -> ::core::result::Result<
(),
<__C as #crate_path::rancor::Fallible>::Error,
> {
#(#field_checks)*
#verify
::core::result::Result::Ok(())
}
}
}
}
Fields::Unnamed(ref fields) => {
let field_checks =
fields.unnamed.iter().enumerate().map(|(i, f)| {
let ty = &f.ty;
let index = Index::from(i);
quote! {
<
#ty as #crate_path::CheckBytes<__C>
>::check_bytes(
::core::ptr::addr_of!((*value).#index),
context
).map_err(|e| {
<
<
__C as #crate_path::rancor::Fallible
>::Error as #crate_path::rancor::Trace
>::trace(
e,
#crate_path::TupleStructCheckContext {
tuple_struct_name: ::core::stringify!(
#name
),
field_index: #i,
},
)
})?;
}
});
quote! {
#[automatically_derived]
// SAFETY: `check_bytes` only returns `Ok` if all of the
// fields of the struct are valid. If all of the fields are
// valid, then the overall struct is also valid.
unsafe impl #trait_impl_generics
#crate_path::CheckBytes<__C> for #name #type_ty_generics
#check_where
{
unsafe fn check_bytes(
value: *const Self,
context: &mut __C,
) -> ::core::result::Result<
(),
<__C as #crate_path::rancor::Fallible>::Error,
> {
#(#field_checks)*
#verify
::core::result::Result::Ok(())
}
}
}
}
Fields::Unit => {
quote! {
#[automatically_derived]
// SAFETY: Unit structs are always valid since they have a
// size of 0 and no invalid bit patterns.
unsafe impl #trait_impl_generics
#crate_path::CheckBytes<__C> for #name #type_ty_generics
#trait_where_clause
{
unsafe fn check_bytes(
value: *const Self,
context: &mut __C,
) -> ::core::result::Result<
(),
<__C as #crate_path::rancor::Fallible>::Error,
> {
#verify
::core::result::Result::Ok(())
}
}
}
}
},
Data::Enum(ref data) => {
let repr = Repr::from_attrs(&input.attrs)?;
let primitive = match repr {
Repr::Transparent => {
return Err(Error::new_spanned(
name,
"enums cannot be repr(transparent)",
))
}
Repr::Primitive(i) => i,
Repr::C { .. } => {
return Err(Error::new_spanned(
name,
"repr(C) enums are not currently supported",
))
}
Repr::Rust { .. } => {
return Err(Error::new_spanned(
name,
"enums implementing CheckBytes must have an explicit \
repr",
))
}
};
let tag_variant_defs = data.variants.iter().map(|v| {
let variant = &v.ident;
if let Some((_, expr)) = &v.discriminant {
quote! { #variant = #expr }
} else {
quote! { #variant }
}
});
let discriminant_const_defs = data.variants.iter().map(|v| {
let variant = &v.ident;
quote! {
#[allow(non_upper_case_globals)]
const #variant: #primitive = Tag::#variant as #primitive;
}
});
let tag_variant_values = data.variants.iter().map(|v| {
let name = &v.ident;
quote! { Discriminant::#name }
});
let variant_structs = data.variants.iter().map(|v| {
let variant = &v.ident;
let variant_name = Ident::new(
&format!("Variant{}", strip_raw(variant)),
v.span(),
);
match v.fields {
Fields::Named(ref fields) => {
let fields = fields.named.iter().map(|f| {
let name = &f.ident;
let ty = &f.ty;
quote! { #name: #ty }
});
quote! {
#[repr(C)]
struct #variant_name #type_impl_generics
#type_where_clause
{
__tag: Tag,
#(#fields,)*
__phantom: ::core::marker::PhantomData<
#name #type_ty_generics
>,
}
}
}
Fields::Unnamed(ref fields) => {
let fields = fields.unnamed.iter().map(|f| {
let ty = &f.ty;
quote! { #ty }
});
quote! {
#[repr(C)]
struct #variant_name #type_impl_generics (
Tag,
#(#fields,)*
::core::marker::PhantomData<
#name #type_ty_generics
>
) #type_where_clause;
}
}
Fields::Unit => quote! {},
}
});
let check_arms = data.variants.iter().map(|v| {
let variant = &v.ident;
let variant_name = Ident::new(
&format!("Variant{}", strip_raw(variant)),
v.span(),
);
match v.fields {
Fields::Named(ref fields) => {
let checks = fields.named.iter().map(|f| {
check_arm_named_field(f, &crate_path, name, variant)
});
quote! { {
let value =
value.cast::<#variant_name #type_ty_generics>();
#(#checks)*
} }
}
Fields::Unnamed(ref fields) => {
let checks =
fields.unnamed.iter().enumerate().map(|(i, f)| {
check_arm_unnamed_field(
i,
f,
&crate_path,
name,
variant,
)
});
quote! { {
let value =
value.cast::<#variant_name #type_ty_generics>();
#(#checks)*
} }
}
Fields::Unit => quote! { (), },
}
});
let no_matching_tag_arm = quote! {
return ::core::result::Result::Err(
<
<
__C as #crate_path::rancor::Fallible
>::Error as #crate_path::rancor::Source
>::new(
#crate_path::InvalidEnumDiscriminantError {
enum_name: ::core::stringify!(#name),
invalid_discriminant: tag,
}
)
)
};
quote! {
const _: () = {
#[repr(#primitive)]
enum Tag {
#(#tag_variant_defs,)*
}
struct Discriminant;
#[automatically_derived]
impl Discriminant {
#(#discriminant_const_defs)*
}
#(#variant_structs)*
#[automatically_derived]
// SAFETY: `check_bytes` only returns `Ok` if:
// - The discriminant is valid for some variant of the enum,
// and
// - Each field of the variant struct is valid.
// If the discriminant is valid and the fields of the
// indicated variant struct are valid, then the overall enum
// is valid.
unsafe impl #trait_impl_generics
#crate_path::CheckBytes<__C> for #name #type_ty_generics
#check_where
{
unsafe fn check_bytes(
value: *const Self,
context: &mut __C,
) -> ::core::result::Result<
(),
<__C as #crate_path::rancor::Fallible>::Error,
> {
let tag = *value.cast::<#primitive>();
match tag {
#(#tag_variant_values => #check_arms)*
_ => #no_matching_tag_arm,
}
#verify
::core::result::Result::Ok(())
}
}
};
}
}
Data::Union(_) => {
return Err(Error::new(
input.span(),
"CheckBytes cannot be derived for unions",
));
}
};
Ok(check_bytes_impl)
}
fn check_arm_named_field(
f: &Field,
crate_path: &Path,
name: &Ident,
variant: &Ident,
) -> TokenStream {
let field_name = &f.ident;
let ty = &f.ty;
quote! {
<#ty as #crate_path::CheckBytes<__C>>::check_bytes(
::core::ptr::addr_of!((*value).#field_name),
context
).map_err(|e| {
<
<
__C as #crate_path::rancor::Fallible
>::Error as #crate_path::rancor::Trace
>::trace(
e,
#crate_path::NamedEnumVariantCheckContext {
enum_name: ::core::stringify!(#name),
variant_name: ::core::stringify!(#variant),
field_name: ::core::stringify!(#field_name),
},
)
})?;
}
}
fn check_arm_unnamed_field(
i: usize,
f: &Field,
crate_path: &Path,
name: &Ident,
variant: &Ident,
) -> TokenStream {
let ty = &f.ty;
let index = Index::from(i + 1);
quote! {
<#ty as #crate_path::CheckBytes<__C>>::check_bytes(
::core::ptr::addr_of!((*value).#index),
context
).map_err(|e| {
<
<
__C as #crate_path::rancor::Fallible
>::Error as #crate_path::rancor::Trace
>::trace(
e,
#crate_path::UnnamedEnumVariantCheckContext {
enum_name: ::core::stringify!(#name),
variant_name: ::core::stringify!(#variant),
field_index: #index,
},
)
})?;
}
}