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|
use crate::utils::{
add_where_clauses_for_new_ident, AttrParams, DeriveType, MultiFieldData, State,
};
use proc_macro2::{Span, TokenStream};
use quote::{quote, ToTokens};
use std::collections::HashMap;
use syn::{parse::Result, DeriveInput, Ident, Index};
/// Provides the hook to expand `#[derive(From)]` into an implementation of `From`
pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
let state = State::with_attr_params(
input,
trait_name,
quote!(::core::convert),
trait_name.to_lowercase(),
AttrParams {
enum_: vec!["forward", "ignore"],
variant: vec!["forward", "ignore"],
struct_: vec!["forward"],
field: vec!["forward"],
},
)?;
if state.derive_type == DeriveType::Enum {
Ok(enum_from(input, state))
} else {
Ok(struct_from(input, &state))
}
}
pub fn struct_from(input: &DeriveInput, state: &State) -> TokenStream {
let multi_field_data = state.enabled_fields_data();
let MultiFieldData {
fields,
infos,
input_type,
trait_path,
..
} = multi_field_data.clone();
let mut new_generics = input.generics.clone();
let sub_items: Vec<_> = infos
.iter()
.zip(fields.iter())
.enumerate()
.map(|(i, (info, field))| {
let field_type = &field.ty;
let variable = if fields.len() == 1 {
quote!(original)
} else {
let tuple_index = Index::from(i);
quote!(original.#tuple_index)
};
if info.forward {
let type_param =
&Ident::new(&format!("__FromT{}", i), Span::call_site());
let sub_trait_path = quote!(#trait_path<#type_param>);
let type_where_clauses = quote! {
where #field_type: #sub_trait_path
};
new_generics = add_where_clauses_for_new_ident(
&input.generics,
&[field],
type_param,
type_where_clauses,
true,
);
let casted_trait = quote!(<#field_type as #sub_trait_path>);
(quote!(#casted_trait::from(#variable)), quote!(#type_param))
} else {
(variable, quote!(#field_type))
}
})
.collect();
let initializers: Vec<_> = sub_items.iter().map(|i| &i.0).collect();
let from_types: Vec<_> = sub_items.iter().map(|i| &i.1).collect();
let body = multi_field_data.initializer(&initializers);
let (impl_generics, _, where_clause) = new_generics.split_for_impl();
let (_, ty_generics, _) = input.generics.split_for_impl();
quote! {
impl#impl_generics #trait_path<(#(#from_types),*)> for
#input_type#ty_generics #where_clause {
#[allow(unused_variables)]
#[inline]
fn from(original: (#(#from_types),*)) -> #input_type#ty_generics {
#body
}
}
}
}
fn enum_from(input: &DeriveInput, state: State) -> TokenStream {
let mut tokens = TokenStream::new();
let mut variants_per_types = HashMap::new();
for variant_state in state.enabled_variant_data().variant_states {
let multi_field_data = variant_state.enabled_fields_data();
let MultiFieldData { field_types, .. } = multi_field_data.clone();
variants_per_types
.entry(field_types.clone())
.or_insert_with(Vec::new)
.push(variant_state);
}
for (ref field_types, ref variant_states) in variants_per_types {
for variant_state in variant_states {
let multi_field_data = variant_state.enabled_fields_data();
let MultiFieldData {
variant_info,
infos,
..
} = multi_field_data.clone();
// If there would be a conflict on a empty tuple derive, ignore the
// variants that are not explicitely enabled or have explicitely enabled
// or disabled fields
if field_types.is_empty()
&& variant_states.len() > 1
&& !std::iter::once(variant_info)
.chain(infos)
.any(|info| info.info.enabled.is_some())
{
continue;
}
struct_from(input, variant_state).to_tokens(&mut tokens);
}
}
tokens
}
|
