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// Doc Not Optimize
use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use quote::quote;
use syn::{Data, DeriveInput, Field, Fields, Type, parse_macro_input};
/// The located inner field of a `Wrap` struct.
struct InnerInfo {
/// Access the inner value from `self`, e.g. `self.name` or `self.0`.
self_access: TokenStream2,
/// Access the inner value mutably from `self`, e.g. `&mut self.name`.
self_access_mut: TokenStream2,
/// Access the inner value from a bound `wrapper` variable.
wrapper_access: TokenStream2,
/// Expression building `Self` from a bound `inner` variable.
construct: TokenStream2,
/// The inner field's type.
inner_ty: Type,
}
/// Parse the input struct and locate the inner field.
///
/// Rules:
/// - Named struct with a single field → that field is the inner field.
/// - Named struct with multiple fields → exactly one field must be marked `#[wrap]`.
/// - Tuple struct with a single field → that field is the inner field.
fn locate_inner(input: &DeriveInput) -> Result<InnerInfo, TokenStream2> {
let name = &input.ident;
match &input.data {
Data::Struct(data) => match &data.fields {
Fields::Named(fields) => {
let all = &fields.named;
let as_fields: Vec<&Field> = all
.iter()
.filter(|f| f.attrs.iter().any(|a| a.path().is_ident("wrap")))
.collect();
if as_fields.len() > 1 {
let span = as_fields[1].ident.as_ref().unwrap_or(name);
return Err(syn::Error::new_spanned(
span,
"only one field may be marked `#[wrap]`",
)
.to_compile_error());
}
let (inner_field, other_fields): (&Field, Vec<&Field>) = if as_fields.len() == 1 {
let inner = as_fields[0];
let inner_ident = inner.ident.as_ref().unwrap();
let others = all
.iter()
.filter(|f| f.ident.as_ref() != Some(inner_ident))
.collect();
(inner, others)
} else if all.len() == 1 {
(all.first().unwrap(), Vec::new())
} else {
return Err(syn::Error::new_spanned(
name,
"a struct with multiple fields requires exactly one field marked `#[wrap]`",
)
.to_compile_error());
};
let field_ident = inner_field.ident.clone().unwrap();
let mut named = vec![quote! { #field_ident: inner }];
for other in other_fields {
let ident = other.ident.as_ref().unwrap();
named.push(quote! { #ident: ::core::default::Default::default() });
}
Ok(InnerInfo {
self_access: quote! { self.#field_ident },
self_access_mut: quote! { &mut self.#field_ident },
wrapper_access: quote! { wrapper.#field_ident },
construct: quote! { Self { #(#named),* } },
inner_ty: inner_field.ty.clone(),
})
}
Fields::Unnamed(fields) => {
if fields.unnamed.len() == 1 {
Ok(InnerInfo {
self_access: quote! { self.0 },
self_access_mut: quote! { &mut self.0 },
wrapper_access: quote! { wrapper.0 },
construct: quote! { Self(inner) },
inner_ty: fields.unnamed.first().unwrap().ty.clone(),
})
} else {
Err(syn::Error::new_spanned(
name,
"tuple structs with multiple fields are not supported by `Wrap`; \
use a named struct and mark one field with `#[wrap]`",
)
.to_compile_error())
}
}
Fields::Unit => Err(syn::Error::new_spanned(
name,
"unit structs have no inner type; `Wrap` requires a field",
)
.to_compile_error()),
},
Data::Enum(_) | Data::Union(_) => Err(syn::Error::new_spanned(
name,
"`Wrap` can only be derived on structs",
)
.to_compile_error()),
}
}
pub(crate) fn derive_wrap(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = &input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
let info = match locate_inner(&input) {
Ok(info) => info,
Err(err) => return err.into(),
};
let InnerInfo {
self_access,
self_access_mut,
wrapper_access,
construct,
inner_ty,
} = info;
let expanded = quote! {
impl #impl_generics ::core::convert::From<#inner_ty> for #name #ty_generics #where_clause {
fn from(inner: #inner_ty) -> Self {
#construct
}
}
impl #impl_generics ::core::convert::From<#name #ty_generics> for #inner_ty #where_clause {
fn from(wrapper: #name #ty_generics) -> #inner_ty {
#wrapper_access
}
}
impl #impl_generics ::core::ops::Deref for #name #ty_generics #where_clause {
type Target = #inner_ty;
fn deref(&self) -> &Self::Target {
&(#self_access)
}
}
impl #impl_generics ::core::ops::DerefMut for #name #ty_generics #where_clause {
fn deref_mut(&mut self) -> &mut Self::Target {
#self_access_mut
}
}
};
expanded.into()
}
|
