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extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::{Ident, Span, TokenStream as TokenStream2};
use quote::quote;
use syn::{
parse_macro_input, Data, DataEnum, DataStruct, DeriveInput, Error, Fields,
Meta, NestedMeta,
spanned::Spanned,
};
#[proc_macro_derive(Atom)]
pub fn derive_atom(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
gen_atom_impl(&input)
.unwrap_or_else(|e| e.to_compile_error())
.into()
}
#[proc_macro_derive(AtomLogic)]
pub fn derive_atom_logic(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
gen_marker_trait_impl("AtomLogic", &input)
.unwrap_or_else(|e| e.to_compile_error())
.into()
}
#[proc_macro_derive(AtomInteger)]
pub fn derive_atom_integer(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
gen_marker_trait_impl("AtomInteger", &input)
.unwrap_or_else(|e| e.to_compile_error())
.into()
}
fn gen_marker_trait_impl(trait_name: &str, input: &DeriveInput) -> Result<TokenStream2, Error> {
match input.data {
Data::Struct(_) => {
let type_name = &input.ident;
let trait_name = Ident::new(trait_name, Span::call_site());
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
Ok(quote! {
impl #impl_generics atomig::#trait_name
for #type_name #ty_generics #where_clause {}
})
}
Data::Enum(_) => {
let msg = format!(
"`{}` cannot be derived for enums as this is almost always incorrect to do. \
Please read the documentation of `{}` carefully. If you still think you \
want to implement this trait, you have to do it manually.",
trait_name,
trait_name,
);
Err(Error::new(Span::call_site(), msg))
}
Data::Union(_) => {
let msg = format!("`{}` cannot be derived for unions", trait_name);
Err(Error::new(Span::call_site(), msg))
}
}
}
fn gen_atom_impl(input: &DeriveInput) -> Result<TokenStream2, Error> {
let impl_body = match &input.data {
Data::Struct(s) => atom_impl_for_struct(s),
Data::Enum(e) => atom_impl_for_enum(input, e),
Data::Union(_) => Err(Error::new(Span::call_site(), "unions cannot derive `Atom`")),
}?;
let type_name = &input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
Ok(quote! {
impl #impl_generics atomig::Atom for #type_name #ty_generics #where_clause {
#impl_body
}
})
}
fn atom_impl_for_struct(s: &DataStruct) -> Result<TokenStream2, Error> {
let mut it = s.fields.iter();
let field = it.next().ok_or_else(|| {
let msg = "struct has no fields, but `derive(Atom)` works only for \
structs with exactly one field";
Error::new(s.fields.span(), msg)
})?;
if it.next().is_some() {
let msg = "struct has more than one field, but `derive(Atom)` works only for \
structs with exactly one field";
return Err(Error::new(s.fields.span(), msg));
}
let (field_access, struct_init) = match &field.ident {
Some(name) => (quote! { self.#name }, quote! { Self { #name: src } }),
None => (quote! { self.0 }, quote!{ Self(src) }),
};
let field_type = &field.ty;
Ok(quote! {
type Repr = #field_type;
fn pack(self) -> Self::Repr {
#field_access
}
fn unpack(src: Self::Repr) -> Self {
#struct_init
}
})
}
fn atom_impl_for_enum(input: &DeriveInput, e: &DataEnum) -> Result<TokenStream2, Error> {
let repr_attr = input.attrs.iter()
.filter_map(|attr| attr.parse_meta().ok())
.find(|meta| meta.name() == "repr")
.ok_or_else(|| {
let msg = format!(
"no `repr(_)` attribute on enum '{}', but such an attribute is \
required to automatically derive `Atom`",
input.ident,
);
Error::new(Span::call_site(), msg)
})?;
const INTEGER_NAMES: &[&str] = &[
"u8", "u16", "u32", "u64", "u128", "usize",
"i8", "i16", "i32", "i64", "i128", "isize",
];
let repr_type = match &repr_attr {
Meta::List(list) => {
list.nested.iter()
.find_map(|nested| {
match &nested {
NestedMeta::Meta(Meta::Word(w))
if INTEGER_NAMES.contains(&&*w.to_string()) => Some(w),
_ => None
}
})
.ok_or_else(|| {
let msg = "`repr(_)` attribute does not specify the primitive \
representation (a primitive integer), but this is required \
for `derive(Atom)`";
Error::new(repr_attr.span(), msg)
})?
}
_ => {
let msg = format!(
"`repr` attribute on enum '{}' does not have the form `repr(_)`, but \
it should have for `derive(Atom)`",
input.ident,
);
return Err(Error::new(repr_attr.span(), msg));
}
};
let variant_with_fields = e.variants.iter().find(|variant| {
match variant.fields {
Fields::Unit => false,
_ => true,
}
});
if let Some(v) = variant_with_fields {
let msg = "this variant has fields, but `derive(Atom)` only works \
for C-like enums";
return Err(Error::new(v.span(), msg));
}
let type_name = &input.ident;
let unpack_code = {
let checks: Vec<_> = e.variants.iter().map(|variant| {
let variant_name = &variant.ident;
quote! {
if src == #type_name::#variant_name as #repr_type {
return #type_name::#variant_name;
}
}
}).collect();
let error = format!(
"invalid '{}' value '{{}}' for enum '{}' in `Atom::unpack`",
repr_type,
type_name,
);
quote! {
#(#checks)*
panic!(#error, src);
}
};
Ok(quote! {
type Repr = #repr_type;
fn pack(self) -> Self::Repr {
self as #repr_type
}
fn unpack(src: Self::Repr) -> Self {
#unpack_code
}
})
}