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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
//! Custom derives for `ZeroFrom` from the `zerofrom` crate.
// https://github.com/unicode-org/icu4x/blob/main/docs/process/boilerplate.md#library-annotations
#![cfg_attr(
not(test),
deny(
clippy::indexing_slicing,
clippy::unwrap_used,
clippy::expect_used,
clippy::panic,
clippy::exhaustive_structs,
clippy::exhaustive_enums,
missing_debug_implementations,
)
)]
use proc_macro::TokenStream;
use proc_macro2::{Span, TokenStream as TokenStream2};
use quote::quote;
use syn::spanned::Spanned;
use syn::{parse_macro_input, parse_quote, DeriveInput, Ident, Lifetime, Type, WherePredicate};
use synstructure::Structure;
mod visitor;
/// Custom derive for `zerofrom::ZeroFrom`,
///
/// This implements `ZeroFrom<Ty> for Ty` for types
/// without a lifetime parameter, and `ZeroFrom<Ty<'data>> for Ty<'static>`
/// for types with a lifetime parameter.
///
/// Apply the `#[zerofrom(clone)]` attribute to a field if it doesn't implement
/// Copy or ZeroFrom; this data will be cloned when the struct is zero_from'ed.
#[proc_macro_derive(ZeroFrom, attributes(zerofrom))]
pub fn zf_derive(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
TokenStream::from(zf_derive_impl(&input))
}
fn has_clone_attr(attrs: &[syn::Attribute]) -> bool {
attrs.iter().any(|a| {
if let Ok(i) = a.parse_args::<Ident>() {
if i == "clone" {
return true;
}
}
false
})
}
fn zf_derive_impl(input: &DeriveInput) -> TokenStream2 {
let tybounds = input
.generics
.type_params()
.map(|ty| {
// Strip out param defaults, we don't need them in the impl
let mut ty = ty.clone();
ty.eq_token = None;
ty.default = None;
ty
})
.collect::<Vec<_>>();
let typarams = tybounds
.iter()
.map(|ty| ty.ident.clone())
.collect::<Vec<_>>();
let lts = input.generics.lifetimes().count();
let name = &input.ident;
let structure = Structure::new(input);
if lts == 0 {
let has_clone = structure
.variants()
.iter()
.flat_map(|variant| variant.bindings().iter())
.any(|binding| has_clone_attr(&binding.ast().attrs));
let (clone, clone_trait) = if has_clone {
(quote!(this.clone()), quote!(Clone))
} else {
(quote!(*this), quote!(Copy))
};
let bounds: Vec<WherePredicate> = typarams
.iter()
.map(|ty| parse_quote!(#ty: #clone_trait + 'static))
.collect();
quote! {
impl<'zf, #(#tybounds),*> zerofrom::ZeroFrom<'zf, #name<#(#typarams),*>> for #name<#(#typarams),*> where #(#bounds),* {
fn zero_from(this: &'zf Self) -> Self {
#clone
}
}
}
} else {
if lts != 1 {
return syn::Error::new(
input.generics.span(),
"derive(ZeroFrom) cannot have multiple lifetime parameters",
)
.to_compile_error();
}
let generics_env = typarams.iter().cloned().collect();
let mut zf_bounds: Vec<WherePredicate> = vec![];
let body = structure.each_variant(|vi| {
vi.construct(|f, i| {
let binding = format!("__binding_{}", i);
let field = Ident::new(&binding, Span::call_site());
if has_clone_attr(&f.attrs) {
quote! {
#field.clone()
}
} else {
let fty = replace_lifetime(&f.ty, custom_lt("'zf"));
let lifetime_ty = replace_lifetime(&f.ty, custom_lt("'zf_inner"));
let (has_ty, has_lt) = visitor::check_type_for_parameters(&f.ty, &generics_env);
if has_ty {
// For types without type parameters, the compiler can figure out that the field implements
// ZeroFrom on its own. However, if there are type parameters, there may be complex preconditions
// to `FieldTy: ZeroFrom` that need to be satisfied. We get them to be satisfied by requiring
// `FieldTy<'zf>: ZeroFrom<'zf, FieldTy<'zf_inner>>`
if has_lt {
zf_bounds
.push(parse_quote!(#fty: zerofrom::ZeroFrom<'zf, #lifetime_ty>));
} else {
zf_bounds.push(parse_quote!(#fty: zerofrom::ZeroFrom<'zf, #fty>));
}
}
if has_ty || has_lt {
// By doing this we essentially require ZF to be implemented
// on all fields
quote! {
<#fty as zerofrom::ZeroFrom<'zf, #lifetime_ty>>::zero_from(#field)
}
} else {
// No lifetimes, so we can just copy
quote! { *#field }
}
}
})
});
quote! {
impl<'zf, 'zf_inner, #(#tybounds),*> zerofrom::ZeroFrom<'zf, #name<'zf_inner, #(#typarams),*>> for #name<'zf, #(#typarams),*>
where
#(#zf_bounds,)* {
fn zero_from(this: &'zf #name<'zf_inner, #(#typarams),*>) -> Self {
match *this { #body }
}
}
}
}
}
fn custom_lt(s: &str) -> Lifetime {
Lifetime::new(s, Span::call_site())
}
fn replace_lifetime(x: &Type, lt: Lifetime) -> Type {
use syn::fold::Fold;
struct ReplaceLifetime(Lifetime);
impl Fold for ReplaceLifetime {
fn fold_lifetime(&mut self, _: Lifetime) -> Lifetime {
self.0.clone()
}
}
ReplaceLifetime(lt).fold_type(x.clone())
}
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